47
ARTICLE Stress-induced microvascular reactivity in normal-weight and obese individuals Chun-Jung Huang, Robert L. Franco, Ronald K. Evans, David C. Mari, and Edmund O. Acevedo
Abstract: Obesity has been shown to have profound effects on hemodynamics and neurological states in humans. Previous studies have demonstrated that obese individuals are highly susceptible to increases in tension, anxiety, and depression. However, the relationship between mental stressors and vascular fluidity in obese humans is not well understood. Thus, the purpose of this study was to investigate mental-stress-induced microvascular reactivity (excess blood flow (EBF)) in normalweight and obese individuals. In addition, the relationships between potential vascular response modulators (heart rate (HR) and norepinephrine (NE)) and EBF were examined. Twenty-two male subjects were classified as obese (n = 12) or normal-weight (n = 10), and each subject completed a 20 min bout of acute mental stress. Our analyses demonstrate significant elevations in forearm blood flow (FBF) and EBF immediately after mental stress in both normal-weight and obese groups. HR was only correlated with EBF immediately poststress in the normal-weight group. Furthermore, stress-induced plasma NE was not associated with FBF or EBF in either group, although in the obese group, stress-induced plasma NE was associated with body mass index and percent body fat. These results suggest that microvascular reactivity after mental stress is not directly related to plasma NE in normal-weight or obese individuals. The novel results presented in this study provide a foundation for additional examination of the mechanisms involved in the effects of mental stress on microvascular reactivity. Key words: mental stress, obesity, forearm blood flow, excess blood flow, norepinephrine. Résumé : Les répercussions importantes de l’obésité sur les fonctions hémodynamiques et neurologiques des humains sont bien connues. D’après des études antérieures, les personnes obèses sont particulièrement vulnérables a` des augmentations de tension et d’anxiété et a` la dépression. Toutefois, on ne connait pas bien la relation entre les agents de tension mentale et la fluidité vasculaire chez les personnes obèses. Par conséquent, cette étude se propose d’examiner la réactivité microvasculaire (surplus de débit sanguin (« EBF »)) suscitée par la tension mentale chez des personnes obèses et de poids normal. En outre, cette étude analyse la relation entre les modulateurs potentiels des réponses vasculaires (rythme cardiaque (« HR ») et norépinéphrine (« NE »)) et l’EBF. On classe 22 hommes dans deux groupes, l’un obèse (n = 12) et l’autre de poids normal (n = 10); les deux groupes participent a` une séance de tension mentale. Nos analyses révèlent une augmentation significative du débit sanguin dans l’avant-bras (« FBF ») et de l’EBF immédiatement après la séance de tension mentale dans les deux groupes. Dans le groupe de poids normal, le HR est corrélé seulement a` l’EBF immédiatement après la séance de tension mentale. De plus, la présence de NE plasmatique suscitée par la tension mentale n’est pas associée aux FBF et EBF dans l’un et l’autre des groupes; toutefois, la présence de NE plasmatique suscitée par la tension mentale dans le groupe obèse est associée a` l’IMC et au pourcentage de gras corporel. D’après les résultats de cette étude, la réactivité microvasculaire consécutive a` la tension mentale n’est pas directement associée a` la concentration plasmatique de NE chez des personnes obèses et de poids normal. Les résultats originaux de cette étude procurent une assise pour d’autres expérimentations sur les mécanismes impliqués dans les effets de la tension mentale sur la réactivité microvasculaire. [Traduit par la Rédaction] Mots-clés : tension mentale, obésité, débit sanguin dans l’avant-bras, surplus de débit sanguin, norépinéphrine.
Introduction The epidemic of obesity and overweight continues to grow in the United States, with recent reports indicating that more than 64.1% of American women and 72.3% of American men are categorized as having a body mass index (BMI) ≥25 kg·m−2 (Flega et al. 2010). Obesity-attributable illnesses, such as cardiovascular disease (CVD), account for approximately 300 000 deaths annually in the United States (Manson and Bassuk 2003). Interestingly, obese individuals are more susceptible to job-associated stress (tension and anxiety) and depression. These stress-related disorders have been found to lead to an increased risk of CVD and mortality (Nishitani and Sakakibara 2006; Valtonen et al. 2012). Conse-
quently, acute stress-induced physiological responses have been used in the prediction of cardiovascular events (Steptoe et al. 2007). The link between obesity and psychological stress could help determine the pathophysiologic mechanisms of CVD development. In rats, psychological stress has been associated with changes in catecholamine (such as norepinephrine (NE)) uptake pathways in vascular walls that modulate sympathetic activation (Bouzinova et al. 2012). In addition, the elevated catecholamines offset the direct vasoconstrictor effects through vasodilatory mechanisms in human vascularity (Halliwill et al. 1997; Harris et al. 2000). More specifically, Halliwill et al. (1997) found that under normal physiological conditions, different mechanisms related to mental stress, such as the
Received 5 March 2013. Accepted 4 June 2013. C.-J. Huang and D.C. Mari. Department of Exercise Science and Health Promotion, Florida Atlantic University, Boca Raton, FL 33431, USA. R.L. Franco, R.K. Evans, and E.O. Acevedo. Department of Health and Human Performance, Virginia Commonwealth University, Richmond, VA 23284, USA. Corresponding author: Chun-Jung Huang (e-mail: [email protected]). Appl. Physiol. Nutr. Metab. 39: 47–52 (2014) dx.doi.org/10.1139/apnm-2013-0094
Published at www.nrcresearchpress.com/apnm on 26 June 2013.
48
release of nitric oxide, NE-induced sympathetic withdrawal (a reduction in NE), and beta-adrenergic vasodilation resulting from elevated epinephrine, can increase forearm blood flow (FBF). These findings suggest that catecholamine response to mental stress, specifically NE, could play a role in human vascular hemodynamics. Because catecholamine release (Agapitov et al. 2008), reuptake (Gando et al. 1993; Burgdorf et al. 2006; Coppack et al. 1998), and responsiveness (Limberg et al. 2012; Agapitov et al. 2008) can be altered with obesity, the question remains whether obesity can modify the effects of NE on vascular flow after mental stress. Possible alterations in both catecholamine release and reuptake can be identified by examining differences in catecholamine plasma expression between obese and normal-weight individuals. Therefore, the purpose of this study was to examine the effect of mental stress on microvascular reactivity (excess blood flow (EBF)) in normal-weight and obese subjects. Previous research has demonstrated that NE-modulated sympathetic activation is strongly associated with increased CVD risk (Schroeder and Jordan 2012; Rahn et al. 1999). Although epinephrine contributes to partial stress-induced forearm vasodilation (Lindqvist et al. 1996), NE transporter-deficient mice have been shown to exhibit excessive tachycardia and elevated blood pressure (Keller et al. 2004). These studies suggest that NE is an important mediator of blood flow, with varying levels affecting CVD risk in an individual. Because stress increases NE and because obese individuals are more susceptible to stress effects, this study also investigated the relationships between potential vascular response modulators (heart rate (HR) and NE) and EBF in response to mental stress in normalweight and obese subjects. It was hypothesized that stressinduced NE release would be positively related to BMI and body fat percentage, resulting in blunted EBF in obesity. A greater understanding of the reactive neurovascular response to mental stress in obese humans might provide insight into the mechanisms that explain the relationship between obesity, mental stress, and CVD.
Materials and methods Subjects Twenty-two healthy male subjects (12 obese and 10 normalweight) were recruited to participate in the study. Participant characteristics are reported in Table 1. Subjects with a BMI above 30 kg·m−2 who had more than 30% body fat comprised the obese group; those with a BMI below 25 kg·m−2 and who had less than 25% body fat comprised the normal-weight group (Vincent et al. 2004). Only male subjects were investigated to control variability of the dependent measures of interest; women could have attenuated cardiovascular responses to mental stress (Ceresini et al. 2000). Percent body fat was determined with dual-energy x-ray absorptiometry (GE iDXA, Milwaukee, Wis., USA). All subjects provided informed consent and completed a medical history questionnaire prior to data collection. Experimental procedures were approved by the institutional review board. Subjects were excluded from the study if they had known or suspected cardiovascular, metabolic, rheumatologic, or other inflammatory diseases or conditions. Subjects were also excluded if they were taking medication, used tobacco products (cigarettes, cigars, chewing tobacco), or consumed an average of more than 10 alcoholic beverages per week. Additionally, subjects who had a history of psychological disorders and (or) chronic illnesses or who experienced a major life event within 30 days of enrollment (e.g., death in family, divorce, or wedding) were excluded. Prior to each testing session, subjects were asked to fast overnight for at least 8 h, to abstain from alcohol and caffeine intake for at least 24 h, and to abstain from physical activity for at least 48 h. Recent studies have demonstrated reduced activity of the autonomic nervous system (e.g., lower heart rate) (Acevedo et al. 2006) and vascular reactivity (DeSouza et al. 2000; Olive et al. 2002) related to acute psychological stress in physically active individuals. Thus,
Appl. Physiol. Nutr. Metab. Vol. 39, 2014
Table 1. Descriptive characteristics of the participants. Variable
Normal-weight (n = 10)
Obese (n = 12)
Age (y) Height (cm) Body weight (kg) Body mass index (kg·m−2) Body fat (%)
23.8±1.0 173.8±2.4 64.6±2.9 21.3±0.6 16.1±1.5
26.6±2.1 179.4±2.1 125.3±5.2* 39.0±1.6* 40.4±1.7*
Note: Data are presented as means ± SE. *p < 0.05 for normal-weight vs. obese groups before stress (baseline).
Fig. 1. Time progression of the experimental protocol (in min). The assessments were taken in the following order: heart rate (HR), blood sample (BS), forearm blood flow (FBF), and State Anxiety Inventory (SAI) prior to and after stress. PSS, Perceived Stress Scale.
to limit the effect of fitness on physiological response to mental stress, all subjects completed the Seven-Day Physical Activity Recall questionnaire (Blair et al. 1985); those who reported more than 150 min of moderate- or high-intensity physical activity per week were excluded from participation. Testing procedures Subjects attended 2 laboratory sessions. On the first laboratory visit, subjects completed the informed consent form and medical history questionnaire, and had their height and weight assessed. They also participated in a 2-min mental stress task (Stroop ColorWord Task and a mental arithmetic task) to familiarize themselves with the mental stress. On the second laboratory visit, subjects arrived at 0630 h. After 45 min of rest, subjects were exposed to 20 min of acute stress (5 cycles of the computer-based color-word task (2 min) and the mental arithmetic task (2 min)) while they sat in a semirecumbent position (see experimental protocol in Fig. 1). Cardiovascular responses to color-word and mental arithmetic tasks are highly correlated with responses to real-life stressors (Kamarck et al. 2003). HR was collected with a polar heart rate monitor (Polar Co., Port Washington, N.Y., USA) prior to stress, every 4 min during the 20 min of acute psychological stress (at 4, 8, 12, 16, and 20 min), and 1 h after stress. FBF and blood samples were collected prior to stress, immediately poststress, and 1 h after stress. Blood sampling was performed by a certified phlebotomy technician using standard aseptic techniques. An intravenous catheter (BD, 20 g, 25 mm) was inserted into an antecubital vein on the left arm, and a positive pressure adaptor (CLC2000, ICU Medical, San Clemente, Calif., USA) was attached. During each blood draw, the first 1 mL of blood (with saline from the extension set) was collected in a syringe and discarded. Immediately thereafter, appropriate sample volumes were collected in specific collection tubes for subsequent analysis. Stress and anxiety measures To measure the perceptions of stress during the 30 days prior to testing, the Perceived Stress Scale (Cohen et al. 1983) was used. The Perceived Stress Scale has an alpha (Cronbach’s ␣) reliability coefficient of 0.78. Cohen and colleagues (1983) demonstrated the Published by NRC Research Press
Huang et al.
49
Table 2. Assessments of heart rate (HR), norepinephrine (NE), State Anxiety Inventory (SAI) scores, forearm blood flow (FBF), and excess blood flow (EBF). Variable
Group
Prestress (0 min)
HR (beats·min−1)
Normal-weight Obese Normal-weight Obese Normal-weight Obese Normal-weight Obese Normal-weight Obese Normal-weight Obese
65.3±2.8 69.2±2.8 423.1±20.3 394.5±34.4 19.4±1.4 15.0±1.1 216.6±22.5* 330.1±24.4 347.9±44.1* 604.3±55.1 147.8±22.5* 295.3±40.3
NE (pg·mL−1) SAI score FBF at baseline (mL per 100 mL per min × s) FBF during RH (mL per 100 mL per min × s) EBF (mL per 100 mL per min × s)
4 min
8 min
12 min
16 min
81.9±4.2 79.8±3.9
80.9±3.6 81.6±3.5
79.2±3.1 81.1±3.4
80.6±3.7 79.4±3.5
Poststress (20 min)
Recovery (1 h poststress)
79.4±3.6 80.1±3.0 678.3±36.5 718.7±40.4 23.3±1.3 22.5±1.8 233.0±18.7 416.1±31.4 399.8±60.1 758.3±84.3 205.2±38.0 349.3±55.5
66.4±2.7 68.3±2.7 475.9±27.3 502.8±19.3
214.6±20.5 346.2±33.7 355.7±51.5 633.0±58.1 151.0±33.9 277.2±41.4
Effect Time Time Time Time Time Time Time Time Time Time Time Time
Note: Data are presented as means ± SE. There was a significant change over time for all variables in both normal-weight and obese groups. RH, reactive hyperemia. *p < 0.05 for normal-weight vs. obese groups before stress (baseline).
validity of this measure in the assessment of chronic perceived stress. In addition, the State Anxiety Inventory (SAI) (Devito and Kubis 1983) was administered to assess each subject’s anxiety prior to and immediately poststress. The SAI version used in this study was the alternative form “A”, which has an alpha (Cronbach’s ␣) reliability coefficient of 0.80. Assessment of microvascular reactivity Noninvasive FBF measures using reactive hyperemia (RH) have been shown to be a useful alternative in the assessment of microvascular reactivity (Higashi et al. 2001). To evaluate vascular function, Irace et al. (2001) demonstrated a strong correlation between vascular function, strain-gauge plethysmography, and brachial artery ultrasound techniques in both normal-weight and obese individuals. In this study, FBF was assessed using mercury-inrubber strain-gauge plethysmography (Model AI6, D.E. Hokanson, Inc., Bellevue, Wash., USA). With this method, depth of blood flow measurement was maintained (Ardilouze et al. 2004). Thus, the same microvascular territory for each subject was measured in this study. Blood pressure cuffs were positioned around each subject’s upper right arm and right wrist, and a mercury-in-rubber strain gauge was placed around the forearm approximately 10 cm distal to the olecranon process (Alomari et al. 2004). During each trial, the wrist cuff was inflated to a pressure of 240 mm Hg prior to each measurement to occlude hand circulation. Baseline FBF was determined by rapidly inflating the upper cuff to 40 mm Hg for 10 s to occlude venous flow during a 20-s cycle (Bousquet-Santos et al. 2005). Nine measurements were recorded to determine the average rate of volume change during venous occlusion (mL per 100 mL of forearm tissue volume per min). Subsequently, the upper arm cuff was inflated to 240 mm Hg to induce forearm ischemia for a period of 5 min. After 5 min of occlusion, the cuff was released and FBF, as described above, was determined during a 3-min period of RH. FBF before and during RH was assessed as an area under the curve, calculated as a flow-time index (BousquetSantos et al. 2005). Total EBF above baseline was calculated as FBF during RH minus FBF at baseline. Measures of plasma NE During each blood draw, a 3 mL blood sample was collected in a tube containing EDTA for NE analysis, and centrifuged for 15 min at 2000g at 4 °C. All samples were stored at −80 °C for further analyses. The plasma NE was assayed in duplicate with enzymelinked immunosorbent assays (ELISA, Labor Diagnostika Nord, Nordhorn, Germany), in accordance with the manufacturer’s recommended protocol. Typically, the resting levels for plasma NE are less than 600 pg·mL−1. Inter- and intra-assay coefficients of variation for NE were 8.5% and 9.8%, respectively.
Statistical analyses Data analyses were performed with the Statistical Package for the Social Sciences (SPSS version 18.0). Independent t tests were conducted to compare resting levels on all variables, percent change (pre- to poststress) in NE, FBF at baseline (preocclusion) and during RH, and EBF between normal-weight and obese groups. A 2-group (normal-weight and obese) × 7 timepoint (0 (prestress), 4, 8, 12, 16, 20 min (immediately poststress), and 1 h poststress), and a 2-group (normal-weight and obese) × 2-timepoint (0 and 20 min) repeated-measures analyses of variance (ANOVA) were used to examine changes in HR and SAI scores in response to mental stress, respectively. Significant effects were further analyzed with Bonferroni post hoc comparisons. In addition, a 2-group (normalweight and obese) × 3-timepoint (0 min, 20 min, and 1 h poststress) repeated-measures ANOVA was used to evaluate the effect of mental stress on the release of NE and changes in FBF, at baseline and during RH, and EBF. Greenhouse–Geisser corrections for repeated measures were used to verify repeated-measures ANOVA results. The ANOVA results were reported as follows: F score [betweengroups degrees of freedom (df), within-groups df] = F statistic, p value. Finally, Pearson’s product–moment correlations were used to examine the relationships between the percent change in HR and NE and changes in FBF and EBF after a mental challenge. Statistical significance was set at p ≤ 0.05.
Results Changes in SAI scores To quantify mental stress, self-reported state anxiety (SAI) was administered to each subject prior to and immediately after an acute mental stress event. SAI was significantly elevated immediately after mental stress (F[1,20] = 26.63, p < 0.001) (see Table 2). However, no significant difference was observed between the normal-weight and obese groups. This finding demonstrates a similar perception of stress in both groups. Assessments of HR and NE At baseline there were no significant differences in HR or NE between the normal-weight and obese groups. Although no significant differences existed between the 2 groups, all HR values measured during mental stress were significantly higher than at baseline, and returned to baseline at 1 h poststress in both groups (F[2.30,46.04] = 56.23, p < 0.001) (see Table 2). Also, NE immediately poststress was significantly higher than at baseline (F[1.712,34.243] = 82.611, p < 0.001), but no significant difference was found between normal-weight and obese groups. Published by NRC Research Press
50
Appl. Physiol. Nutr. Metab. Vol. 39, 2014
Fig. 2. Immediately after the mental challenge. (A) Correlation in percent change between heart rate (HR) and excess blood flow (EBF) in normal-weight and obese groups; (B, C) relationships of percent change in norepinephrine (NE) with body mass index (BMI) and percent body fat in normal-weight and obese groups.
Vascular responses (FBF and EBF) Before mental stress, obese subjects had significantly higher FBF, both before and during RH, and EBF. As shown in Table 2, immediately after mental stress, FBF, both before and during RH, demonstrated no significant group × time interaction. However, there was a significant change across time, with an increase in FBF, before and during RH, immediately poststress (F[1.78,35.56] = 4.38, p = 0.02; F[1.92,38.37] = 4.78, p = 0.01, respectively). In addition, the repeated-measures ANOVA for EBF demonstrated a significant elevation immediately poststress in both groups (F[1.94,38.89] = 4.15, p = 0.02) (see Table 2). It was found that the percent change (pre- to poststress) in EBF did not differ between the 2 groups (see Table 2). Correlation analyses The immediate poststress percent change in HR was only significantly correlated with immediate poststress percent change in EBF in the normal-weight group (r = 0.783, p = 0.007) (see Fig. 2A). Furthermore, the percent change in NE (pre- to poststress) was correlated with BMI and percent body fat in the obese group (r = 0.733, p = 0.010; r = 0.614, p = 0.044, respectively) (see Figs. 2B and 2C) and collectively in all 22 subjects in the groups combined (r = 0.518, p = 0.019; r = 0.433, p = 0.050, respectively).
Discussion This study sought to examine mental-stress-induced microvascular reactivity in normal-weight and obese individuals. Our results demonstrate a significant elevation in FBF and EBF immediately poststress in both groups, with higher resting FBF and EBF observed in obese subjects. In addition, the stress-induced change in NE was correlated to BMI and percent body fat, but was not related to FBF and EBF reactivity. Future studies are warranted with more sensitive measurements to examine whether there is a
microvascular change in NE related to stress in obese individuals. To conclude, this study found that mental stress results in increased microvascular reactivity, microvascular reactivity in response to mental stress is not altered with obesity, and microvascular reactivity is not correlated to plasma NE in either normal-weight or obese individuals. The results of this study demonstrate that, at rest, obese individuals have significantly higher FBF and EBF. Although equivocal data exist from studies evaluating FBF in obese individuals, resting FBF has predominantly been shown to be higher in overweight and obese individuals (Hamer et al. 2007; Raison et al. 1998). Elevated FBF at rest in obese individuals might be partially due to a greater absolute forearm area than in normal-weight individuals (Blaak et al. 1994). However, the measurement used to establish FBF was normalized to forearm size (mL per min × 100 mL) in this study. Importantly, although obese individuals have a greater relative quantity of adipose tissue than normal-weight individuals, adipose tissue blood flow does not contribute to elevated total FBF at rest (Blaak et al. 1994). It is possible that obese individuals have greater FBF and EBF at rest because of higher whole-body vibrations from each subject’s excessive mass. Sañudo et al. (2013) found that whole-body vibration training improves blood flow to the legs, and that significant correlations exist between changes in percent body fat and blood flow. The SAI scores increased in response to acute mental stress, but there was not a difference in SAI scores between the normalweight and obese groups. This demonstrates a similar perception of stress between normal-weight and obese individuals. This effectiveness of the stressor is further supported by similar elevations in HR and plasma NE in both normal-weight and obese subjects. Published by NRC Research Press
Huang et al.
Previous research has shown that the elevations in HR and systolic blood pressure are associated with forearm vasodilation in response to acute stress in healthy adults (Pike et al. 2009). Kuniyoshi et al. (2003) found that elevated HR and blood pressure were similar in normal-weight and obese individuals after an acute mental stress event. In this study, the percent change in HR was only significantly correlated with the percent change in EBF immediately poststress in normal-weight individuals. This finding could be due to the physical activity difference between the 2 groups. Recently, Stebbings and colleagues (2013) found resting arterial diameter and blood flow changes with resistance training and detraining. Also, studies have demonstrated changes in the autonomic nervous system (e.g., lower heart rate) (Acevedo et al. 2006) and a reduction in vascular reactivity (Olive et al. 2002) to acute psychological stress in physically active individuals. Taken together, it is plausible that the greater muscularity and (or) cardiovascular fitness usually seen in normal-weight individuals could affect blood flow in response to acute psychological stress. In regard to the significant increase in plasma NE immediately after mental stress, our results demonstrate that NE is not associated with FBF or EBF in either group, although the stress-induced change in NE was correlated with both BMI and percent body fat. The lack of a significant relationship between NE and FBF and EBF suggests that NE does not have a direct effect on vascular flow reactivity in response to mental stress. However, the measure of circulating catecholamines (such as NE) does not elucidate whether central, peripheral, or local mechanisms are responsible, directly or indirectly, for the change in forearm vasodilation (Hamer et al. 2002). Limitations in the methodology of this study must be considered when interpreting these results. These include the fact that blood pressure was not measured because of the catheter insertion in one arm and the FBF and EBF assessment in the other arm, the fact that venous NE as a sole measure of sympathetic activation does not fully describe sympathetic activity, and the fact that there are other more sensitive methods of measuring NE that could allude to NE’s role in microvascular reactivity after mental stress (but the question remains on feasibility in real-world practice). In summary, the results of this study suggest that in normal-weight and obese individuals, microvascular reactivity after mental stress can be mediated by hemodynamic changes unrelated directly to systematic sympathetic activation, based on plasma NE and HR measures. The novel results from this study provide a foundation for additional examination of the mechanisms involved in the effects of mental stress on microvascular reactivity.
Acknowledgements The authors would like to thank undergraduate students May Cheung and Kristine Clinton for their assistance with the data collection.
References Acevedo, E.O., Webb, H.E., Weldy, M.L., Fabianke, E.C., Orndorff, G.R., and Starks, M.A. 2006. Cardiorespiratory Responses of hi fit and low fit subjects to mental challenge during exercise. Int. J. Sports Med. 27(12): 1013–1022. doi: 10.1055/s-2006-923902. PMID:16612743. Agapitov, A.V., Correia, M.L., Sinkey, C.A., and Haynes, W.G. 2008. Dissociation between sympathetic nerve traffic and sympathetically mediated vascular tone in normotensive human obesity. Hypertension, 52(4): 687–695. doi:10. 1161/HYPERTENSIONAHA.107.109603. PMID:18695151. Alomari, M.A., Solomito, A., Reyes, R., Khalil, S.M., Wood, R.H., and Welsch, M.A. 2004. Measurements of vascular function using strain-gauge plethysmography: technical considerations, standardization, and physiological findings. Am. J. Physiol. Heart Circ. Physiol. 286(1): H99–H107. doi:10.1152/ajpheart. 00529.2003. PMID:14512279. Ardilouze, J.-L., Karpe, F., Currie, J.M., Frayn, K.N., and Fielding, B.A. 2004. Subcutaneous adipose tissue blood flow varies between superior and inferior levels of the anterior abdominal wall. Int. J. Obes. 28(2): 228–233. doi:10.1038/ sj.ijo.0802541. PMID:14647178. Blaak, E.E., van Baak, M.A., Kemerink, G.J., Pakbiers, M.T., Heidendal, G.A., and
51
Saris, W.H. 1994. Total forearm blood flow as an indicator of skeletal muscle blood flow: effect of subcutaneous adipose tissue blood flow. Clin. Sci. (Lond.), 87(5): 559–566. doi:10.1042/cs0870559. PMID:7874845. Blair, S.N., Haskell, W.L., Ho, P., Paffenbarger, R.S., Vranizan, K.M., Farquhar, J.W., and Wood, P.D. 1985. Assessment of habitual physical activity by a seven-day recall in a community survey and controlled experiments. Am. J. Epidemiol. 122(5): 794–804. PMID:3876763. Bousquet-Santos, K., Soares, P.P., and Nobrega, A.C. 2005. Subacute effects of a maximal exercise bout on endothelium-mediated vasodilation in healthy subjects. Braz. J. Med. Biol. Res. 38(4): 621–627. doi:10.1590/S0100879X2005000400017. PMID:15962189. Bouzinova, E.V., Møller-Nielsen, N., Boedtkjer, D.B., Broegger, T., Wiborg, O., Aalkjaer, C., and Matchkov, V.V. 2012. Chronic mild stress-induced depressionlike symptoms in rats and abnormalities in catecholamine uptake in small arteries. Psychosom. Med. 74(3): 278–287. doi:10.1097/PSY.0b013e31824c40a9. PMID:22408132. Burgdorf, C., Richardt, G., Schütte, F., Dendorfer, A., and Kurz, T. 2006. Impairment of presynaptic alpha2-adrenoceptor-regulated norepinephrine overflow in failing hearts from Zucker diabetic fatty rats. J. Cardiovasc. Pharmacol. 47(2): 256–262. doi:10.1097/01.fjc.0000202560.61667.3e. PMID: 16495764. Ceresini, G., Freddi, M., Morganti, S., Rebecchi, I., Modena, A.B., Rinaldi, M., et al. 2000. The effects of transdermal estradiol on the response to mental stress in postmenopausal women: a randomized trial. Am. J. Med. 109(6): 463–468. doi:10.1016/S0002-9343(00)00523-4. PMID:11042235. Cohen, S., Kamarck, T., and Mermelstein, R. 1983. A global measure of perceived stress. J. Health Soc. Behav. 24(4): 385–396. doi:10.2307/2136404. PMID: 6668417. Coppack, S.W., Horowitz, J.F., Paramore, D.S., Cryer, P.E., Royal, H.D, and Klein, S. 1998. Whole body, adipose tissue, and forearm norepinephrine kinetics in lean and obese women. Am. J. Physiol. 275(5): E830–E834. PMID: 9815003. DeSouza, C.A., Shapiro, L.F., Clevenger, C.M., Dinenno, F.A., Monahan, K.D., Tanaka, H., and Seals, D.R. 2000. Regular aerobic exercise prevents and restores age-related declines in endothelium-dependent vasodilation in healthy men. Circulation, 102(12): 1351–1357. doi:10.1161/01.CIR.102.12.1351. PMID:10993851. Devito, A.J., and Kubis, J.F. 1983. Alternate forms of the state-strait anxiety inventory. Educ. Psychol. Meas. 43(3): 729–734. doi:10.1177/001316448304300306. Flega, K.M., Carroll, M.D., Ogden, C.L., and Curtin, L.R. 2010. Prevalence and trends in obesity among US adults, 1999-2008. JAMA, 303(3): 235–241. doi:10.1001/jama.2009.2014. PMID:20071471. Gando, S., Hattori, Y., and Kanno, M. 1993. Altered cardiac adrenergic neurotransmission in streptozotocin-induced diabetic rats. Br. J. Pharmacol. 109(4): 1276–1281. doi:10.1111/j.1476-5381.1993.tb13761.x. PMID:8401939. Halliwill, J.R., Lawler, L.A., Eickhoff, T.J., Dietz, N.M., Nauss, L.A., and Joyner, M.J. 1997. Forearm sympathetic withdrawal and vasodilatation during mental stress in humans. J. Physiol. 504(1): 211–220. doi:10.1111/j.1469-7793.1997. 211bf.x. PMID:9350631. Hamer, M., Boutcher, Y., and Boutcher, S.H. 2002. Cardiovascular and renal responses to mental challenge in highly and moderately active male with a family history of hypertension. J. Hum. Hypertens. 16(5): 319–326. doi:10.1038/ sj.jhh.1001396. PMID:12082492. Hamer, M., Boutcher., Y.N., and Boutcher, S.H. 2007. Fatness is related to blunted vascular stress responsivity, independent of cadiorespiratory fitness in normal and overweight men. Int. J. Psychophysiol. 63(3): 251–257. doi:10.1016/j. ijpsycho.2006.11.002. PMID:17196278. Harris, C.W., Edwards, J.L., Baruch, A., Riley, W.A., Pusser, B.E., Rejeski, W.J., and Herrington, D.M. 2000. Effect of mental stress on brachial artery flowmediated vasodilation in healthy normal individuals. Am. Heart J. 139(3): 405–411. doi:10.1016/S0002-8703(00)90083-8. PMID:10689254. Higashi, Y., Sasaki, S., Nakagawa, K., Matsuura, H., Kajiyama, G., and Oshima, T. 2001. A noninvasive measurement of reactive hyperemia that can be used to assess resistance artery endothelial function in humans. Am. J. Cardiol. 87(1): 121–125. doi:10.1016/S0002-9149(00)01288-1. PMID:11137850. Irace, C., Ceravolo, R., Notarangelo, L., Crescenzo, A., Ventura, G., Tamburrini, O., et al. 2001. Comparison of endothelial function evaluated by strain gauge plethysmography and brachial artery ultrasound. Atherosclerosis, 158(1): 53–59. doi:10.1016/S0021-9150(01)00406-3. PMID:11500174. Kamarck, T.W., Schwartz, J.E., Janicki, D.L., Shiffman, S., and Raynor, DA . 2003. Correspondence between laboratory and ambulatory measures of cardiovascular reactivity: a multilevel modeling approach. Psychophysiology, 40(5): 675–683. doi:10.1111/1469-8986.00069. PMID:14696722. Keller, N.R., Diedrich, A., Appalsamy, M., Tuntrakool, S., Lonce, S., Finney, C., et al. 2004. Norepinephrine transporter-deficient mice exhibit excessive tachycardia and elevated blood pressure with wakefulness and activity. Circulation, 110(10): 1191–1196. doi:10.1161/01.CIR.0000141804.90845.E6. PMID: 15337696. Kuniyoshi, F.H., Trombetta, I.C., Batalha, L.T., Rondon, M.U., Laterza, M.C., Gowdak, M.M., et al. 2003. Abnormal neurovascular control during sympathoxcitation in obesity. Obes. Res. 11(11): 1411–1419. doi:10.1038/oby.2003.190. PMID:14627763. Limberg, J.K., Evans, T.D., Blain, G.M., Pegelow, D.F., Danielson, J.R., Published by NRC Research Press
52
Eldridge, M.W., et al. 2012. Effect of obesity and metabolic syndrome on hypoxic vasodilation. Eur. J. Appl. Physiol. 112(2): 699–709. doi:10.1007/s00421011-2025-x. PMID:21656228. Lindqvist, M., Kahan, T., Melcher, A., Bie, P., and Hjemdahl, P. 1996. Forearm vasodilator mechanisms during mental stress: possible roles for epinephrine and ANP. Am. J. Physiol. 270(3): E393–E399. PMID:8638683. Manson, J.E., and Bassuk, S.S. 2003. Obesity in the United States: a fresh look at its high toll. JAMA, 289(2): 229–230. doi:10.1001/jama.289.2.229. PMID: 12517236. Nishitani, N., and Sakakibara, H. 2006. Relationship of obesity to job stress and eating behavior in male Japanese workers. Int. J. Obes. 30(3): 528–533. doi: 10.1038/sj.ijo.0803153. PMID:16247505. Olive, J.L., DeVan, A.E., and McCully, K.K. 2002. The effects of aging and activity on muscle blood flow. Dyn. Med. 1: 2. doi:10.1186/1476-5918-1-2. PMID:12605712. Pike, T.L., Elvebak, R.L., Jegede, M., Gleich, S.J., and Eisenach, J.H. 2009. Forearm vascular conductance during mental stress is related to the heart rate response. Clin. Auton. Res. 19(3): 183–187. doi:10.1007/s10286-009-0005-6. PMID: 19280245. Rahn, K.H., Barenbrock, M., and Hausberg, M. 1999. The sympathetic nervous system in the pathogenesis of hypertension. J. Hypertens. Suppl. 17(3): S11– S14. PMID:10489093. Raison, J.M., Safar, M.E., Cambien, F.A., and London, G.M. 1998. Forearm haemo-
Appl. Physiol. Nutr. Metab. Vol. 39, 2014
dynamics in obese normotensive and hypertensive subjects. J. Hypertens. 6(4): 299–303. doi:10.1097/00004872-198804000-00006. PMID:2967861. Sañudo, B., Alfonso-Rosa, R., Del Pozo-Cruz, B., Del Pozo-Cruz, J., Galiano, D., and Figueroa, A. 2013. Whole body vibration training improves leg blood flow and adiposity in patients with type 2 diabetes mellitus. Eur. J. Appl. Physiol. In press. doi:10.1007/s00421-013-2654-3. PMID:23657766. Schroeder, C., and Jordan, J. 2012. Norepinephrine transporter function and human cardiovascular disease. Am. J. Physiol. Heart Circ. Physiol. 303(11): H1273–H1282. doi:10.1152/ajpheart.00492.2012. PMID:23023867. Stebbings, G.K., Morse, C.I., McMahon, G.E., and Onambele, G.L. 2013. Resting arterial diameter and blood flow changes with resistance training and detraining in healthy young individuals. J. Athl. Train. 48(2): 209–219. doi:10. 4085/1062-6050-48.1.17. PMID:23672385. Steptoe, A., Hamer, M., and Chida, Y. 2007. The effects of acute psychological stress on circulating inflammatory factors in humans: A review and metaanalysis. Brain Behav. Immun. 21(7): 901–912. doi:10.1016/j.bbi.2007.03.011. PMID:17475444. Valtonen, M.K., Laaksonen, D.E., Laukkanen, J.A., Tolmunen, T., Viinamäki, H., Lakka, H.M., et al. 2012. Low-grade inflammation and depressive symptoms as predictors of abdominal obesity. Scand. J. Public Health, 40(7): 674–680. doi: 10.1177/1403494812461730. PMID:23042459. Vincent, H.K., Morgan, J.W., and Vincent, K.R. 2004. Obesity exacerbates oxidative stress levels after acute exercise. Med. Sci. Sports Exerc. 36(5): 772–779. doi:10.1249/01.MSS.0000126576.53038.E9. PMID:15126709.
Published by NRC Research Press
Copyright of Applied Physiology, Nutrition & Metabolism is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
ARTICLE Stress-induced microvascular reactivity in normal-weight and obese individuals Chun-Jung Huang, Robert L. Franco, Ronald K. Evans, David C. Mari, and Edmund O. Acevedo
Abstract: Obesity has been shown to have profound effects on hemodynamics and neurological states in humans. Previous studies have demonstrated that obese individuals are highly susceptible to increases in tension, anxiety, and depression. However, the relationship between mental stressors and vascular fluidity in obese humans is not well understood. Thus, the purpose of this study was to investigate mental-stress-induced microvascular reactivity (excess blood flow (EBF)) in normalweight and obese individuals. In addition, the relationships between potential vascular response modulators (heart rate (HR) and norepinephrine (NE)) and EBF were examined. Twenty-two male subjects were classified as obese (n = 12) or normal-weight (n = 10), and each subject completed a 20 min bout of acute mental stress. Our analyses demonstrate significant elevations in forearm blood flow (FBF) and EBF immediately after mental stress in both normal-weight and obese groups. HR was only correlated with EBF immediately poststress in the normal-weight group. Furthermore, stress-induced plasma NE was not associated with FBF or EBF in either group, although in the obese group, stress-induced plasma NE was associated with body mass index and percent body fat. These results suggest that microvascular reactivity after mental stress is not directly related to plasma NE in normal-weight or obese individuals. The novel results presented in this study provide a foundation for additional examination of the mechanisms involved in the effects of mental stress on microvascular reactivity. Key words: mental stress, obesity, forearm blood flow, excess blood flow, norepinephrine. Résumé : Les répercussions importantes de l’obésité sur les fonctions hémodynamiques et neurologiques des humains sont bien connues. D’après des études antérieures, les personnes obèses sont particulièrement vulnérables a` des augmentations de tension et d’anxiété et a` la dépression. Toutefois, on ne connait pas bien la relation entre les agents de tension mentale et la fluidité vasculaire chez les personnes obèses. Par conséquent, cette étude se propose d’examiner la réactivité microvasculaire (surplus de débit sanguin (« EBF »)) suscitée par la tension mentale chez des personnes obèses et de poids normal. En outre, cette étude analyse la relation entre les modulateurs potentiels des réponses vasculaires (rythme cardiaque (« HR ») et norépinéphrine (« NE »)) et l’EBF. On classe 22 hommes dans deux groupes, l’un obèse (n = 12) et l’autre de poids normal (n = 10); les deux groupes participent a` une séance de tension mentale. Nos analyses révèlent une augmentation significative du débit sanguin dans l’avant-bras (« FBF ») et de l’EBF immédiatement après la séance de tension mentale dans les deux groupes. Dans le groupe de poids normal, le HR est corrélé seulement a` l’EBF immédiatement après la séance de tension mentale. De plus, la présence de NE plasmatique suscitée par la tension mentale n’est pas associée aux FBF et EBF dans l’un et l’autre des groupes; toutefois, la présence de NE plasmatique suscitée par la tension mentale dans le groupe obèse est associée a` l’IMC et au pourcentage de gras corporel. D’après les résultats de cette étude, la réactivité microvasculaire consécutive a` la tension mentale n’est pas directement associée a` la concentration plasmatique de NE chez des personnes obèses et de poids normal. Les résultats originaux de cette étude procurent une assise pour d’autres expérimentations sur les mécanismes impliqués dans les effets de la tension mentale sur la réactivité microvasculaire. [Traduit par la Rédaction] Mots-clés : tension mentale, obésité, débit sanguin dans l’avant-bras, surplus de débit sanguin, norépinéphrine.
Introduction The epidemic of obesity and overweight continues to grow in the United States, with recent reports indicating that more than 64.1% of American women and 72.3% of American men are categorized as having a body mass index (BMI) ≥25 kg·m−2 (Flega et al. 2010). Obesity-attributable illnesses, such as cardiovascular disease (CVD), account for approximately 300 000 deaths annually in the United States (Manson and Bassuk 2003). Interestingly, obese individuals are more susceptible to job-associated stress (tension and anxiety) and depression. These stress-related disorders have been found to lead to an increased risk of CVD and mortality (Nishitani and Sakakibara 2006; Valtonen et al. 2012). Conse-
quently, acute stress-induced physiological responses have been used in the prediction of cardiovascular events (Steptoe et al. 2007). The link between obesity and psychological stress could help determine the pathophysiologic mechanisms of CVD development. In rats, psychological stress has been associated with changes in catecholamine (such as norepinephrine (NE)) uptake pathways in vascular walls that modulate sympathetic activation (Bouzinova et al. 2012). In addition, the elevated catecholamines offset the direct vasoconstrictor effects through vasodilatory mechanisms in human vascularity (Halliwill et al. 1997; Harris et al. 2000). More specifically, Halliwill et al. (1997) found that under normal physiological conditions, different mechanisms related to mental stress, such as the
Received 5 March 2013. Accepted 4 June 2013. C.-J. Huang and D.C. Mari. Department of Exercise Science and Health Promotion, Florida Atlantic University, Boca Raton, FL 33431, USA. R.L. Franco, R.K. Evans, and E.O. Acevedo. Department of Health and Human Performance, Virginia Commonwealth University, Richmond, VA 23284, USA. Corresponding author: Chun-Jung Huang (e-mail: [email protected]). Appl. Physiol. Nutr. Metab. 39: 47–52 (2014) dx.doi.org/10.1139/apnm-2013-0094
Published at www.nrcresearchpress.com/apnm on 26 June 2013.
48
release of nitric oxide, NE-induced sympathetic withdrawal (a reduction in NE), and beta-adrenergic vasodilation resulting from elevated epinephrine, can increase forearm blood flow (FBF). These findings suggest that catecholamine response to mental stress, specifically NE, could play a role in human vascular hemodynamics. Because catecholamine release (Agapitov et al. 2008), reuptake (Gando et al. 1993; Burgdorf et al. 2006; Coppack et al. 1998), and responsiveness (Limberg et al. 2012; Agapitov et al. 2008) can be altered with obesity, the question remains whether obesity can modify the effects of NE on vascular flow after mental stress. Possible alterations in both catecholamine release and reuptake can be identified by examining differences in catecholamine plasma expression between obese and normal-weight individuals. Therefore, the purpose of this study was to examine the effect of mental stress on microvascular reactivity (excess blood flow (EBF)) in normal-weight and obese subjects. Previous research has demonstrated that NE-modulated sympathetic activation is strongly associated with increased CVD risk (Schroeder and Jordan 2012; Rahn et al. 1999). Although epinephrine contributes to partial stress-induced forearm vasodilation (Lindqvist et al. 1996), NE transporter-deficient mice have been shown to exhibit excessive tachycardia and elevated blood pressure (Keller et al. 2004). These studies suggest that NE is an important mediator of blood flow, with varying levels affecting CVD risk in an individual. Because stress increases NE and because obese individuals are more susceptible to stress effects, this study also investigated the relationships between potential vascular response modulators (heart rate (HR) and NE) and EBF in response to mental stress in normalweight and obese subjects. It was hypothesized that stressinduced NE release would be positively related to BMI and body fat percentage, resulting in blunted EBF in obesity. A greater understanding of the reactive neurovascular response to mental stress in obese humans might provide insight into the mechanisms that explain the relationship between obesity, mental stress, and CVD.
Materials and methods Subjects Twenty-two healthy male subjects (12 obese and 10 normalweight) were recruited to participate in the study. Participant characteristics are reported in Table 1. Subjects with a BMI above 30 kg·m−2 who had more than 30% body fat comprised the obese group; those with a BMI below 25 kg·m−2 and who had less than 25% body fat comprised the normal-weight group (Vincent et al. 2004). Only male subjects were investigated to control variability of the dependent measures of interest; women could have attenuated cardiovascular responses to mental stress (Ceresini et al. 2000). Percent body fat was determined with dual-energy x-ray absorptiometry (GE iDXA, Milwaukee, Wis., USA). All subjects provided informed consent and completed a medical history questionnaire prior to data collection. Experimental procedures were approved by the institutional review board. Subjects were excluded from the study if they had known or suspected cardiovascular, metabolic, rheumatologic, or other inflammatory diseases or conditions. Subjects were also excluded if they were taking medication, used tobacco products (cigarettes, cigars, chewing tobacco), or consumed an average of more than 10 alcoholic beverages per week. Additionally, subjects who had a history of psychological disorders and (or) chronic illnesses or who experienced a major life event within 30 days of enrollment (e.g., death in family, divorce, or wedding) were excluded. Prior to each testing session, subjects were asked to fast overnight for at least 8 h, to abstain from alcohol and caffeine intake for at least 24 h, and to abstain from physical activity for at least 48 h. Recent studies have demonstrated reduced activity of the autonomic nervous system (e.g., lower heart rate) (Acevedo et al. 2006) and vascular reactivity (DeSouza et al. 2000; Olive et al. 2002) related to acute psychological stress in physically active individuals. Thus,
Appl. Physiol. Nutr. Metab. Vol. 39, 2014
Table 1. Descriptive characteristics of the participants. Variable
Normal-weight (n = 10)
Obese (n = 12)
Age (y) Height (cm) Body weight (kg) Body mass index (kg·m−2) Body fat (%)
23.8±1.0 173.8±2.4 64.6±2.9 21.3±0.6 16.1±1.5
26.6±2.1 179.4±2.1 125.3±5.2* 39.0±1.6* 40.4±1.7*
Note: Data are presented as means ± SE. *p < 0.05 for normal-weight vs. obese groups before stress (baseline).
Fig. 1. Time progression of the experimental protocol (in min). The assessments were taken in the following order: heart rate (HR), blood sample (BS), forearm blood flow (FBF), and State Anxiety Inventory (SAI) prior to and after stress. PSS, Perceived Stress Scale.
to limit the effect of fitness on physiological response to mental stress, all subjects completed the Seven-Day Physical Activity Recall questionnaire (Blair et al. 1985); those who reported more than 150 min of moderate- or high-intensity physical activity per week were excluded from participation. Testing procedures Subjects attended 2 laboratory sessions. On the first laboratory visit, subjects completed the informed consent form and medical history questionnaire, and had their height and weight assessed. They also participated in a 2-min mental stress task (Stroop ColorWord Task and a mental arithmetic task) to familiarize themselves with the mental stress. On the second laboratory visit, subjects arrived at 0630 h. After 45 min of rest, subjects were exposed to 20 min of acute stress (5 cycles of the computer-based color-word task (2 min) and the mental arithmetic task (2 min)) while they sat in a semirecumbent position (see experimental protocol in Fig. 1). Cardiovascular responses to color-word and mental arithmetic tasks are highly correlated with responses to real-life stressors (Kamarck et al. 2003). HR was collected with a polar heart rate monitor (Polar Co., Port Washington, N.Y., USA) prior to stress, every 4 min during the 20 min of acute psychological stress (at 4, 8, 12, 16, and 20 min), and 1 h after stress. FBF and blood samples were collected prior to stress, immediately poststress, and 1 h after stress. Blood sampling was performed by a certified phlebotomy technician using standard aseptic techniques. An intravenous catheter (BD, 20 g, 25 mm) was inserted into an antecubital vein on the left arm, and a positive pressure adaptor (CLC2000, ICU Medical, San Clemente, Calif., USA) was attached. During each blood draw, the first 1 mL of blood (with saline from the extension set) was collected in a syringe and discarded. Immediately thereafter, appropriate sample volumes were collected in specific collection tubes for subsequent analysis. Stress and anxiety measures To measure the perceptions of stress during the 30 days prior to testing, the Perceived Stress Scale (Cohen et al. 1983) was used. The Perceived Stress Scale has an alpha (Cronbach’s ␣) reliability coefficient of 0.78. Cohen and colleagues (1983) demonstrated the Published by NRC Research Press
Huang et al.
49
Table 2. Assessments of heart rate (HR), norepinephrine (NE), State Anxiety Inventory (SAI) scores, forearm blood flow (FBF), and excess blood flow (EBF). Variable
Group
Prestress (0 min)
HR (beats·min−1)
Normal-weight Obese Normal-weight Obese Normal-weight Obese Normal-weight Obese Normal-weight Obese Normal-weight Obese
65.3±2.8 69.2±2.8 423.1±20.3 394.5±34.4 19.4±1.4 15.0±1.1 216.6±22.5* 330.1±24.4 347.9±44.1* 604.3±55.1 147.8±22.5* 295.3±40.3
NE (pg·mL−1) SAI score FBF at baseline (mL per 100 mL per min × s) FBF during RH (mL per 100 mL per min × s) EBF (mL per 100 mL per min × s)
4 min
8 min
12 min
16 min
81.9±4.2 79.8±3.9
80.9±3.6 81.6±3.5
79.2±3.1 81.1±3.4
80.6±3.7 79.4±3.5
Poststress (20 min)
Recovery (1 h poststress)
79.4±3.6 80.1±3.0 678.3±36.5 718.7±40.4 23.3±1.3 22.5±1.8 233.0±18.7 416.1±31.4 399.8±60.1 758.3±84.3 205.2±38.0 349.3±55.5
66.4±2.7 68.3±2.7 475.9±27.3 502.8±19.3
214.6±20.5 346.2±33.7 355.7±51.5 633.0±58.1 151.0±33.9 277.2±41.4
Effect Time Time Time Time Time Time Time Time Time Time Time Time
Note: Data are presented as means ± SE. There was a significant change over time for all variables in both normal-weight and obese groups. RH, reactive hyperemia. *p < 0.05 for normal-weight vs. obese groups before stress (baseline).
validity of this measure in the assessment of chronic perceived stress. In addition, the State Anxiety Inventory (SAI) (Devito and Kubis 1983) was administered to assess each subject’s anxiety prior to and immediately poststress. The SAI version used in this study was the alternative form “A”, which has an alpha (Cronbach’s ␣) reliability coefficient of 0.80. Assessment of microvascular reactivity Noninvasive FBF measures using reactive hyperemia (RH) have been shown to be a useful alternative in the assessment of microvascular reactivity (Higashi et al. 2001). To evaluate vascular function, Irace et al. (2001) demonstrated a strong correlation between vascular function, strain-gauge plethysmography, and brachial artery ultrasound techniques in both normal-weight and obese individuals. In this study, FBF was assessed using mercury-inrubber strain-gauge plethysmography (Model AI6, D.E. Hokanson, Inc., Bellevue, Wash., USA). With this method, depth of blood flow measurement was maintained (Ardilouze et al. 2004). Thus, the same microvascular territory for each subject was measured in this study. Blood pressure cuffs were positioned around each subject’s upper right arm and right wrist, and a mercury-in-rubber strain gauge was placed around the forearm approximately 10 cm distal to the olecranon process (Alomari et al. 2004). During each trial, the wrist cuff was inflated to a pressure of 240 mm Hg prior to each measurement to occlude hand circulation. Baseline FBF was determined by rapidly inflating the upper cuff to 40 mm Hg for 10 s to occlude venous flow during a 20-s cycle (Bousquet-Santos et al. 2005). Nine measurements were recorded to determine the average rate of volume change during venous occlusion (mL per 100 mL of forearm tissue volume per min). Subsequently, the upper arm cuff was inflated to 240 mm Hg to induce forearm ischemia for a period of 5 min. After 5 min of occlusion, the cuff was released and FBF, as described above, was determined during a 3-min period of RH. FBF before and during RH was assessed as an area under the curve, calculated as a flow-time index (BousquetSantos et al. 2005). Total EBF above baseline was calculated as FBF during RH minus FBF at baseline. Measures of plasma NE During each blood draw, a 3 mL blood sample was collected in a tube containing EDTA for NE analysis, and centrifuged for 15 min at 2000g at 4 °C. All samples were stored at −80 °C for further analyses. The plasma NE was assayed in duplicate with enzymelinked immunosorbent assays (ELISA, Labor Diagnostika Nord, Nordhorn, Germany), in accordance with the manufacturer’s recommended protocol. Typically, the resting levels for plasma NE are less than 600 pg·mL−1. Inter- and intra-assay coefficients of variation for NE were 8.5% and 9.8%, respectively.
Statistical analyses Data analyses were performed with the Statistical Package for the Social Sciences (SPSS version 18.0). Independent t tests were conducted to compare resting levels on all variables, percent change (pre- to poststress) in NE, FBF at baseline (preocclusion) and during RH, and EBF between normal-weight and obese groups. A 2-group (normal-weight and obese) × 7 timepoint (0 (prestress), 4, 8, 12, 16, 20 min (immediately poststress), and 1 h poststress), and a 2-group (normal-weight and obese) × 2-timepoint (0 and 20 min) repeated-measures analyses of variance (ANOVA) were used to examine changes in HR and SAI scores in response to mental stress, respectively. Significant effects were further analyzed with Bonferroni post hoc comparisons. In addition, a 2-group (normalweight and obese) × 3-timepoint (0 min, 20 min, and 1 h poststress) repeated-measures ANOVA was used to evaluate the effect of mental stress on the release of NE and changes in FBF, at baseline and during RH, and EBF. Greenhouse–Geisser corrections for repeated measures were used to verify repeated-measures ANOVA results. The ANOVA results were reported as follows: F score [betweengroups degrees of freedom (df), within-groups df] = F statistic, p value. Finally, Pearson’s product–moment correlations were used to examine the relationships between the percent change in HR and NE and changes in FBF and EBF after a mental challenge. Statistical significance was set at p ≤ 0.05.
Results Changes in SAI scores To quantify mental stress, self-reported state anxiety (SAI) was administered to each subject prior to and immediately after an acute mental stress event. SAI was significantly elevated immediately after mental stress (F[1,20] = 26.63, p < 0.001) (see Table 2). However, no significant difference was observed between the normal-weight and obese groups. This finding demonstrates a similar perception of stress in both groups. Assessments of HR and NE At baseline there were no significant differences in HR or NE between the normal-weight and obese groups. Although no significant differences existed between the 2 groups, all HR values measured during mental stress were significantly higher than at baseline, and returned to baseline at 1 h poststress in both groups (F[2.30,46.04] = 56.23, p < 0.001) (see Table 2). Also, NE immediately poststress was significantly higher than at baseline (F[1.712,34.243] = 82.611, p < 0.001), but no significant difference was found between normal-weight and obese groups. Published by NRC Research Press
50
Appl. Physiol. Nutr. Metab. Vol. 39, 2014
Fig. 2. Immediately after the mental challenge. (A) Correlation in percent change between heart rate (HR) and excess blood flow (EBF) in normal-weight and obese groups; (B, C) relationships of percent change in norepinephrine (NE) with body mass index (BMI) and percent body fat in normal-weight and obese groups.
Vascular responses (FBF and EBF) Before mental stress, obese subjects had significantly higher FBF, both before and during RH, and EBF. As shown in Table 2, immediately after mental stress, FBF, both before and during RH, demonstrated no significant group × time interaction. However, there was a significant change across time, with an increase in FBF, before and during RH, immediately poststress (F[1.78,35.56] = 4.38, p = 0.02; F[1.92,38.37] = 4.78, p = 0.01, respectively). In addition, the repeated-measures ANOVA for EBF demonstrated a significant elevation immediately poststress in both groups (F[1.94,38.89] = 4.15, p = 0.02) (see Table 2). It was found that the percent change (pre- to poststress) in EBF did not differ between the 2 groups (see Table 2). Correlation analyses The immediate poststress percent change in HR was only significantly correlated with immediate poststress percent change in EBF in the normal-weight group (r = 0.783, p = 0.007) (see Fig. 2A). Furthermore, the percent change in NE (pre- to poststress) was correlated with BMI and percent body fat in the obese group (r = 0.733, p = 0.010; r = 0.614, p = 0.044, respectively) (see Figs. 2B and 2C) and collectively in all 22 subjects in the groups combined (r = 0.518, p = 0.019; r = 0.433, p = 0.050, respectively).
Discussion This study sought to examine mental-stress-induced microvascular reactivity in normal-weight and obese individuals. Our results demonstrate a significant elevation in FBF and EBF immediately poststress in both groups, with higher resting FBF and EBF observed in obese subjects. In addition, the stress-induced change in NE was correlated to BMI and percent body fat, but was not related to FBF and EBF reactivity. Future studies are warranted with more sensitive measurements to examine whether there is a
microvascular change in NE related to stress in obese individuals. To conclude, this study found that mental stress results in increased microvascular reactivity, microvascular reactivity in response to mental stress is not altered with obesity, and microvascular reactivity is not correlated to plasma NE in either normal-weight or obese individuals. The results of this study demonstrate that, at rest, obese individuals have significantly higher FBF and EBF. Although equivocal data exist from studies evaluating FBF in obese individuals, resting FBF has predominantly been shown to be higher in overweight and obese individuals (Hamer et al. 2007; Raison et al. 1998). Elevated FBF at rest in obese individuals might be partially due to a greater absolute forearm area than in normal-weight individuals (Blaak et al. 1994). However, the measurement used to establish FBF was normalized to forearm size (mL per min × 100 mL) in this study. Importantly, although obese individuals have a greater relative quantity of adipose tissue than normal-weight individuals, adipose tissue blood flow does not contribute to elevated total FBF at rest (Blaak et al. 1994). It is possible that obese individuals have greater FBF and EBF at rest because of higher whole-body vibrations from each subject’s excessive mass. Sañudo et al. (2013) found that whole-body vibration training improves blood flow to the legs, and that significant correlations exist between changes in percent body fat and blood flow. The SAI scores increased in response to acute mental stress, but there was not a difference in SAI scores between the normalweight and obese groups. This demonstrates a similar perception of stress between normal-weight and obese individuals. This effectiveness of the stressor is further supported by similar elevations in HR and plasma NE in both normal-weight and obese subjects. Published by NRC Research Press
Huang et al.
Previous research has shown that the elevations in HR and systolic blood pressure are associated with forearm vasodilation in response to acute stress in healthy adults (Pike et al. 2009). Kuniyoshi et al. (2003) found that elevated HR and blood pressure were similar in normal-weight and obese individuals after an acute mental stress event. In this study, the percent change in HR was only significantly correlated with the percent change in EBF immediately poststress in normal-weight individuals. This finding could be due to the physical activity difference between the 2 groups. Recently, Stebbings and colleagues (2013) found resting arterial diameter and blood flow changes with resistance training and detraining. Also, studies have demonstrated changes in the autonomic nervous system (e.g., lower heart rate) (Acevedo et al. 2006) and a reduction in vascular reactivity (Olive et al. 2002) to acute psychological stress in physically active individuals. Taken together, it is plausible that the greater muscularity and (or) cardiovascular fitness usually seen in normal-weight individuals could affect blood flow in response to acute psychological stress. In regard to the significant increase in plasma NE immediately after mental stress, our results demonstrate that NE is not associated with FBF or EBF in either group, although the stress-induced change in NE was correlated with both BMI and percent body fat. The lack of a significant relationship between NE and FBF and EBF suggests that NE does not have a direct effect on vascular flow reactivity in response to mental stress. However, the measure of circulating catecholamines (such as NE) does not elucidate whether central, peripheral, or local mechanisms are responsible, directly or indirectly, for the change in forearm vasodilation (Hamer et al. 2002). Limitations in the methodology of this study must be considered when interpreting these results. These include the fact that blood pressure was not measured because of the catheter insertion in one arm and the FBF and EBF assessment in the other arm, the fact that venous NE as a sole measure of sympathetic activation does not fully describe sympathetic activity, and the fact that there are other more sensitive methods of measuring NE that could allude to NE’s role in microvascular reactivity after mental stress (but the question remains on feasibility in real-world practice). In summary, the results of this study suggest that in normal-weight and obese individuals, microvascular reactivity after mental stress can be mediated by hemodynamic changes unrelated directly to systematic sympathetic activation, based on plasma NE and HR measures. The novel results from this study provide a foundation for additional examination of the mechanisms involved in the effects of mental stress on microvascular reactivity.
Acknowledgements The authors would like to thank undergraduate students May Cheung and Kristine Clinton for their assistance with the data collection.
References Acevedo, E.O., Webb, H.E., Weldy, M.L., Fabianke, E.C., Orndorff, G.R., and Starks, M.A. 2006. Cardiorespiratory Responses of hi fit and low fit subjects to mental challenge during exercise. Int. J. Sports Med. 27(12): 1013–1022. doi: 10.1055/s-2006-923902. PMID:16612743. Agapitov, A.V., Correia, M.L., Sinkey, C.A., and Haynes, W.G. 2008. Dissociation between sympathetic nerve traffic and sympathetically mediated vascular tone in normotensive human obesity. Hypertension, 52(4): 687–695. doi:10. 1161/HYPERTENSIONAHA.107.109603. PMID:18695151. Alomari, M.A., Solomito, A., Reyes, R., Khalil, S.M., Wood, R.H., and Welsch, M.A. 2004. Measurements of vascular function using strain-gauge plethysmography: technical considerations, standardization, and physiological findings. Am. J. Physiol. Heart Circ. Physiol. 286(1): H99–H107. doi:10.1152/ajpheart. 00529.2003. PMID:14512279. Ardilouze, J.-L., Karpe, F., Currie, J.M., Frayn, K.N., and Fielding, B.A. 2004. Subcutaneous adipose tissue blood flow varies between superior and inferior levels of the anterior abdominal wall. Int. J. Obes. 28(2): 228–233. doi:10.1038/ sj.ijo.0802541. PMID:14647178. Blaak, E.E., van Baak, M.A., Kemerink, G.J., Pakbiers, M.T., Heidendal, G.A., and
51
Saris, W.H. 1994. Total forearm blood flow as an indicator of skeletal muscle blood flow: effect of subcutaneous adipose tissue blood flow. Clin. Sci. (Lond.), 87(5): 559–566. doi:10.1042/cs0870559. PMID:7874845. Blair, S.N., Haskell, W.L., Ho, P., Paffenbarger, R.S., Vranizan, K.M., Farquhar, J.W., and Wood, P.D. 1985. Assessment of habitual physical activity by a seven-day recall in a community survey and controlled experiments. Am. J. Epidemiol. 122(5): 794–804. PMID:3876763. Bousquet-Santos, K., Soares, P.P., and Nobrega, A.C. 2005. Subacute effects of a maximal exercise bout on endothelium-mediated vasodilation in healthy subjects. Braz. J. Med. Biol. Res. 38(4): 621–627. doi:10.1590/S0100879X2005000400017. PMID:15962189. Bouzinova, E.V., Møller-Nielsen, N., Boedtkjer, D.B., Broegger, T., Wiborg, O., Aalkjaer, C., and Matchkov, V.V. 2012. Chronic mild stress-induced depressionlike symptoms in rats and abnormalities in catecholamine uptake in small arteries. Psychosom. Med. 74(3): 278–287. doi:10.1097/PSY.0b013e31824c40a9. PMID:22408132. Burgdorf, C., Richardt, G., Schütte, F., Dendorfer, A., and Kurz, T. 2006. Impairment of presynaptic alpha2-adrenoceptor-regulated norepinephrine overflow in failing hearts from Zucker diabetic fatty rats. J. Cardiovasc. Pharmacol. 47(2): 256–262. doi:10.1097/01.fjc.0000202560.61667.3e. PMID: 16495764. Ceresini, G., Freddi, M., Morganti, S., Rebecchi, I., Modena, A.B., Rinaldi, M., et al. 2000. The effects of transdermal estradiol on the response to mental stress in postmenopausal women: a randomized trial. Am. J. Med. 109(6): 463–468. doi:10.1016/S0002-9343(00)00523-4. PMID:11042235. Cohen, S., Kamarck, T., and Mermelstein, R. 1983. A global measure of perceived stress. J. Health Soc. Behav. 24(4): 385–396. doi:10.2307/2136404. PMID: 6668417. Coppack, S.W., Horowitz, J.F., Paramore, D.S., Cryer, P.E., Royal, H.D, and Klein, S. 1998. Whole body, adipose tissue, and forearm norepinephrine kinetics in lean and obese women. Am. J. Physiol. 275(5): E830–E834. PMID: 9815003. DeSouza, C.A., Shapiro, L.F., Clevenger, C.M., Dinenno, F.A., Monahan, K.D., Tanaka, H., and Seals, D.R. 2000. Regular aerobic exercise prevents and restores age-related declines in endothelium-dependent vasodilation in healthy men. Circulation, 102(12): 1351–1357. doi:10.1161/01.CIR.102.12.1351. PMID:10993851. Devito, A.J., and Kubis, J.F. 1983. Alternate forms of the state-strait anxiety inventory. Educ. Psychol. Meas. 43(3): 729–734. doi:10.1177/001316448304300306. Flega, K.M., Carroll, M.D., Ogden, C.L., and Curtin, L.R. 2010. Prevalence and trends in obesity among US adults, 1999-2008. JAMA, 303(3): 235–241. doi:10.1001/jama.2009.2014. PMID:20071471. Gando, S., Hattori, Y., and Kanno, M. 1993. Altered cardiac adrenergic neurotransmission in streptozotocin-induced diabetic rats. Br. J. Pharmacol. 109(4): 1276–1281. doi:10.1111/j.1476-5381.1993.tb13761.x. PMID:8401939. Halliwill, J.R., Lawler, L.A., Eickhoff, T.J., Dietz, N.M., Nauss, L.A., and Joyner, M.J. 1997. Forearm sympathetic withdrawal and vasodilatation during mental stress in humans. J. Physiol. 504(1): 211–220. doi:10.1111/j.1469-7793.1997. 211bf.x. PMID:9350631. Hamer, M., Boutcher, Y., and Boutcher, S.H. 2002. Cardiovascular and renal responses to mental challenge in highly and moderately active male with a family history of hypertension. J. Hum. Hypertens. 16(5): 319–326. doi:10.1038/ sj.jhh.1001396. PMID:12082492. Hamer, M., Boutcher., Y.N., and Boutcher, S.H. 2007. Fatness is related to blunted vascular stress responsivity, independent of cadiorespiratory fitness in normal and overweight men. Int. J. Psychophysiol. 63(3): 251–257. doi:10.1016/j. ijpsycho.2006.11.002. PMID:17196278. Harris, C.W., Edwards, J.L., Baruch, A., Riley, W.A., Pusser, B.E., Rejeski, W.J., and Herrington, D.M. 2000. Effect of mental stress on brachial artery flowmediated vasodilation in healthy normal individuals. Am. Heart J. 139(3): 405–411. doi:10.1016/S0002-8703(00)90083-8. PMID:10689254. Higashi, Y., Sasaki, S., Nakagawa, K., Matsuura, H., Kajiyama, G., and Oshima, T. 2001. A noninvasive measurement of reactive hyperemia that can be used to assess resistance artery endothelial function in humans. Am. J. Cardiol. 87(1): 121–125. doi:10.1016/S0002-9149(00)01288-1. PMID:11137850. Irace, C., Ceravolo, R., Notarangelo, L., Crescenzo, A., Ventura, G., Tamburrini, O., et al. 2001. Comparison of endothelial function evaluated by strain gauge plethysmography and brachial artery ultrasound. Atherosclerosis, 158(1): 53–59. doi:10.1016/S0021-9150(01)00406-3. PMID:11500174. Kamarck, T.W., Schwartz, J.E., Janicki, D.L., Shiffman, S., and Raynor, DA . 2003. Correspondence between laboratory and ambulatory measures of cardiovascular reactivity: a multilevel modeling approach. Psychophysiology, 40(5): 675–683. doi:10.1111/1469-8986.00069. PMID:14696722. Keller, N.R., Diedrich, A., Appalsamy, M., Tuntrakool, S., Lonce, S., Finney, C., et al. 2004. Norepinephrine transporter-deficient mice exhibit excessive tachycardia and elevated blood pressure with wakefulness and activity. Circulation, 110(10): 1191–1196. doi:10.1161/01.CIR.0000141804.90845.E6. PMID: 15337696. Kuniyoshi, F.H., Trombetta, I.C., Batalha, L.T., Rondon, M.U., Laterza, M.C., Gowdak, M.M., et al. 2003. Abnormal neurovascular control during sympathoxcitation in obesity. Obes. Res. 11(11): 1411–1419. doi:10.1038/oby.2003.190. PMID:14627763. Limberg, J.K., Evans, T.D., Blain, G.M., Pegelow, D.F., Danielson, J.R., Published by NRC Research Press
52
Eldridge, M.W., et al. 2012. Effect of obesity and metabolic syndrome on hypoxic vasodilation. Eur. J. Appl. Physiol. 112(2): 699–709. doi:10.1007/s00421011-2025-x. PMID:21656228. Lindqvist, M., Kahan, T., Melcher, A., Bie, P., and Hjemdahl, P. 1996. Forearm vasodilator mechanisms during mental stress: possible roles for epinephrine and ANP. Am. J. Physiol. 270(3): E393–E399. PMID:8638683. Manson, J.E., and Bassuk, S.S. 2003. Obesity in the United States: a fresh look at its high toll. JAMA, 289(2): 229–230. doi:10.1001/jama.289.2.229. PMID: 12517236. Nishitani, N., and Sakakibara, H. 2006. Relationship of obesity to job stress and eating behavior in male Japanese workers. Int. J. Obes. 30(3): 528–533. doi: 10.1038/sj.ijo.0803153. PMID:16247505. Olive, J.L., DeVan, A.E., and McCully, K.K. 2002. The effects of aging and activity on muscle blood flow. Dyn. Med. 1: 2. doi:10.1186/1476-5918-1-2. PMID:12605712. Pike, T.L., Elvebak, R.L., Jegede, M., Gleich, S.J., and Eisenach, J.H. 2009. Forearm vascular conductance during mental stress is related to the heart rate response. Clin. Auton. Res. 19(3): 183–187. doi:10.1007/s10286-009-0005-6. PMID: 19280245. Rahn, K.H., Barenbrock, M., and Hausberg, M. 1999. The sympathetic nervous system in the pathogenesis of hypertension. J. Hypertens. Suppl. 17(3): S11– S14. PMID:10489093. Raison, J.M., Safar, M.E., Cambien, F.A., and London, G.M. 1998. Forearm haemo-
Appl. Physiol. Nutr. Metab. Vol. 39, 2014
dynamics in obese normotensive and hypertensive subjects. J. Hypertens. 6(4): 299–303. doi:10.1097/00004872-198804000-00006. PMID:2967861. Sañudo, B., Alfonso-Rosa, R., Del Pozo-Cruz, B., Del Pozo-Cruz, J., Galiano, D., and Figueroa, A. 2013. Whole body vibration training improves leg blood flow and adiposity in patients with type 2 diabetes mellitus. Eur. J. Appl. Physiol. In press. doi:10.1007/s00421-013-2654-3. PMID:23657766. Schroeder, C., and Jordan, J. 2012. Norepinephrine transporter function and human cardiovascular disease. Am. J. Physiol. Heart Circ. Physiol. 303(11): H1273–H1282. doi:10.1152/ajpheart.00492.2012. PMID:23023867. Stebbings, G.K., Morse, C.I., McMahon, G.E., and Onambele, G.L. 2013. Resting arterial diameter and blood flow changes with resistance training and detraining in healthy young individuals. J. Athl. Train. 48(2): 209–219. doi:10. 4085/1062-6050-48.1.17. PMID:23672385. Steptoe, A., Hamer, M., and Chida, Y. 2007. The effects of acute psychological stress on circulating inflammatory factors in humans: A review and metaanalysis. Brain Behav. Immun. 21(7): 901–912. doi:10.1016/j.bbi.2007.03.011. PMID:17475444. Valtonen, M.K., Laaksonen, D.E., Laukkanen, J.A., Tolmunen, T., Viinamäki, H., Lakka, H.M., et al. 2012. Low-grade inflammation and depressive symptoms as predictors of abdominal obesity. Scand. J. Public Health, 40(7): 674–680. doi: 10.1177/1403494812461730. PMID:23042459. Vincent, H.K., Morgan, J.W., and Vincent, K.R. 2004. Obesity exacerbates oxidative stress levels after acute exercise. Med. Sci. Sports Exerc. 36(5): 772–779. doi:10.1249/01.MSS.0000126576.53038.E9. PMID:15126709.
Published by NRC Research Press
Copyright of Applied Physiology, Nutrition & Metabolism is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
