Scandinavian Journal of Clinical & Laboratory Investigation, 2014; 74: 555–559
TECHNICAL NOTE
Measuring systolic ankle and toe pressure using the strain gauge technique – a comparison study between mercury and indium-gallium strain gauges
Scand J Clin Lab Invest Downloaded from informahealthcare.com by Nyu Medical Center on 06/21/15 For personal use only.
RIKKE BROHOLM, NIELS WIINBERG & LENE SIMONSEN Department of Clinical Physiology and Nuclear Medicine, Bispebjerg and Frederiksberg Hospital, University of Copenhagen, Denmark Abstract Background. Measurement of the ankle and toe pressures are often performed using a plethysmograph, compression cuffs and a strain gauge. Usually, the strain gauge contains mercury but other alternatives exist. From 2014, the mercurycontaining strain gauge will no longer be available in the European Union. The aim of this study was to compare an indium-gallium strain gauge to the established mercury-containing strain gauge. Methods. Consecutive patients referred to the Department of Clinical Physiology and Nuclear Medicine at Bispebjerg and Frederiksberg Hospitals for measurements of systolic ankle and toe pressures volunteered for the study. Ankle and toe pressures were measured twice with the mercury and the indium-gallium strain gauge in random order. Comparison of the correlation between the mean pressure using the mercury and the indium-gallium device and the difference between the two devices was performed for both toe and ankle level. Results. A total of 53 patients were included (36 male). Mean age was 69 (range, 45–92 years). Mean pressures at toe and ankle level with the mercury and the indium-gallium strain gauges were 77 (range, 0–180) mm Hg and 113 (range, 15–190) mm Hg, respectively. Comparison between the mercury and the indium-gallium strain gauge showed a difference in toe blood pressure values of ⫺ 0.7 mm Hg (SD: 7.0). At the ankle level, a difference of 2.0 mm Hg (SD: 8.6) was found. Conclusion. The two different devices agree sufficiently in the measurements of systolic ankle and toe pressure for the indium-gallium strain gauge to replace the mercury strain gauge. Key Words: Claudication, ischemia, peripheral arterial disease
Introduction Measuring systolic ankle pressure is a standard procedure in the initial evaluation of patients with suspected peripheral artery disease (PAD) [1–3]. Usually, a pneumatic cuff is placed around the ankle and a hand-held Doppler instrument is used to measure the systolic pressure of the dorsalis pedis and posterior tibial arteries. The pressures are normalised to the brachial pressure to form the ankle-brachial index (ABI) using the higher of the two arm blood pressures. A reduced ABI may together with proximal auscultation or Doppler verification confirm the diagnosis of PAD in symptomatic patients, can detect significant PAD in asymptomatic patients, and can be used in the differential diagnosis of leg symptoms [4]. Furthermore, it can be used in the follow-up of
individual patients and provide surveillance after vascular interventions [4]. In some groups of patients, i.e. patients with diabetes or renal insufficiency, the vessels become incompressible because of media sclerosis [5]. This may lead to a falsely elevated ankle pressure and in these patients other non-invasive diagnostic tests can be performed to evaluate whether PAD is present or not. One alternative includes measurements of the systolic toe pressure as the digital arteries of the toes tend to be relatively less affected by media sclerosis [6]. A small occlusion cuff is placed around the first or second toe and a strain gauge is placed distally to the cuff. Usually, a strain gauge with mercury is the standard choice [7]. Both cuff and strain gauge are connected to a plethysmograph that detects and records changes in limb volume. The main limitation
Correspondence: Rikke Broholm, Department of Clinical Physiology and Nuclear Medicine, Bispebjerg Hospital, Bispebjerg Bakke 23, DK- 2400 Copenhagen NV, Denmark. Tel: ⫹ 45 31 35 27 94. Fax: ⫹ 45 35 31 39 54. E-mail: [email protected] (Received 1 November 2013 ; accepted 1 March 2014 ) ISSN 0036-5513 print/ISSN 1502-7686 online © 2014 Informa Healthcare DOI: 10.3109/00365513.2014.903431
Scand J Clin Lab Invest Downloaded from informahealthcare.com by Nyu Medical Center on 06/21/15 For personal use only.
556
R. Broholm et al.
of this technique is that it can be impossible to measure toe pressure in patients with ulceration or tissue loss and very low pressure may be a limitation as well. Ankle pressure can also be recorded using this technique placing the cuff around the ankle and the strain gauge at the toe or forefoot. Other pressure measuring methods include laser Doppler, transcutaneous oxygen measurements, and photoplethysmography. However, from January 2014 strain gauges containing mercury are not allowed in the European Union because of its environmental toxicity [8]. One alternative to the mercury-containing strain gauge is a strain gauge containing indium-gallium. However, no studies comparing the two different devices have been published. The primary aim of this study was to evaluate measurements of systolic ankle and toe pressures performed with a mercury strain gauge and compare them to measurements of systolic ankle and toe pressures performed with an indium-gallium strain gauge.
Ethical approval The national Ethics Committee for the Capital Region of Denmark considered the study (journal number: H-3-2013-FSP12) as a quality assurance project. Informed consent was obtained from all patients.
patient (Figure 1). Both types of strain gauges were stretched approximately 10% as recommended by the manufacturer. All measurements were performed twice by the same person and with occlusion cuffs at the ankle and toe, respectively (Medimatic® Plethysmograph, Hellerup, Denmark). Standard cuffs (12 ⫻ 35 cm) were used at the ankle level and cuff size at the toe varied according to toe size. Simultaneously, the brachial pressure of either arm was measured in triplicate using an automated device (the mean of the three pressures was used) (WatchBP® office, Microlife, Widnau, Switzerland) to calculate the ABI (using the arm blood pressure with the highest systolic pressure). A physician specialized in Clinical Physiology and Nuclear Medicine visually assessed the resulting pulse volume recordings blinded to the results of the primary readings (no marks were allowed in the original curve recordings). The blood pressure values were assessed to the nearest 5 mm Hg. The indium-gallium strain gauge is useable to a temperature down to 10.7oC where the gauge freezes. The electric resistance of the indium-gallium strain gauge is 1/3, and the sensitivity is about 1/3 of mercury, with the same dimensions. Statistics Average toe- and ankle-blood pressure values with both the mercury and the indium-gallium device were calculated.
Methods Consecutive patients referred to the Department of Clinical Physiology and Nuclear Medicine at Bispebjerg and Frederiksberg Hospital for measurements of systolic ankle and toe pressure were invited to participate in the study. Patients were included in the period from July to September 2013 and were referred because of lack of palpable foot pulses or because of symptoms of PAD (i.e. intermittent claudication, rest pain or non-healing foot ulcerations/ gangrene). A specially trained nurse or technician performed all examinations. Measurements were performed with patients in the supine position. Before the measurements, the patient rested in the supine position for at least 5 minutes. Skin temperature of the foot was registered before performing the examination (ETI Thermometers®, UK) and in cases with a skin temperature less than 30°C the foot was warmed using a ‘dry’ footbath (feet in a plastic bag). Skin temperature was controlled after warming the feet. Systolic ankle and toe pressures were measured using the strain gauge technique; first using the mercury-containing strain gauge (Medimatic®, Hellerup, Denmark) and then the indium-galliumcontaining strain gauge (Hokanson®, Bellevúe WA 98005, USA); and then vice versa for the following
Figure 1. The indium-gallium- (left) and mercury- (right) containing strain gauges.
Strain gauge – mercury vs indium-gallium A comparison of the correlation between the mean pressure using the mercury and the indiumgallium device and the difference between the two devices [9] were performed for both toe and ankle level. Patients were described using mean, standard deviation (SD) and range. A Bland-Altman plot was performed to visualize a possible relation between the difference between two measurements and their mean value [9].
Scand J Clin Lab Invest Downloaded from informahealthcare.com by Nyu Medical Center on 06/21/15 For personal use only.
Results A total of 53 consecutive patients were included in the study. Baseline characteristics of the included patients can be seen in Table I. Mean systolic pressures at toe and ankle level with the mercury and the indium-gallium strain gauges were 77 (range, 0–180) mm Hg and 113 (range, 15–190) mm Hg, respectively. A total of 106 comparisons were made at toe level and 100 at the ankle level. Excluded measurements were due to severe sclerosis in ankle arteries resulting in noncompressible arteries. Non-compressible arteries were defined from the resulting pulse volume recordings and from an ABI ⬎ 1.3. In the 106 legs in the study, a comparison between the mercury and the indium-gallium strain gauge showed a difference in systolic toe blood pressure values of ⫺ 0.7 mm Hg (SD: 7.0), meaning that the mercury strain gauge measured 0.7 mm Hg lower than the indium-gallium. At the ankle level, a difference of 2.0 mm Hg (SD: 8.6) was found. The results are presented in a Bland-Altman plot for systolic pressures at the toe and at the ankle level, respectively (Figure 2A and 2B).
Table I. Patient characteristics. Characteristics Patients Males Females Age (years) Systolic arm blood pressure (SD) (mmHg) Diabetes (%) Smokers (%) Mean systolic toe pressure Hg (SD) (mmHg) Mean systolic toe pressure In-G (SD) (mmHg) Mean systolic ankle pressure Hg (SD) (mmHg) Mean systolic ankle pressure In-G (SD) (mmHg) Ankle-brachial index (ABI) (SD) Peripheral arterial disease (PAD) (ABI ⬍ 0.9) (%)
Number 53 36 17 69 (range, 45–92) 136.0 (16.5) 27 (51) 20 (38) 76.6 (39.7) 77.3 (38.3) 113.2 (38.4) 112.2 (36.0) 0.85 (0.3) 39 (74)
557
Further analyses separating the patients in diabetics and non-diabetics did not show a systematic difference between the two groups (data not shown).
Discussion In this study we found a maximum difference of 2.0 mm Hg between the mercury and indiumgallium strain gauges and we conclude that the two different devices can be used equally. The study reflects measurements in a wide range of pressures, from 0–190 mm Hg and includes patients both with and without diabetes. The observed variation may in part be due to the fact that measurements with the two devices were not performed at the same time and that alteration in the systolic pressure therefore has been observed between the measurements. However, it was not possible to perform the measurements at the same time, as the sensitivity must be raised using the indium-gallium device. Measurements of systolic ankle and toe pressures with the strain gauge technique have been described to have low inter-observer variability [7,10]. In this study, we found a similar small difference between two different strain gauge devices with mercury and indium-gallium, respectively. Accurate and precise measurement devices are required when measuring the systolic ankle and toe pressure. In 1987, the American Association for the Advancement of Medical Instrumentation (AAMI) published a standard for assessing electronic and automated sphygmomanometers [11]. A revised standard was published in 1992 and a summary of the guidelines was published in 1993 [12]. The standard requires that the pressures measured by the devices achieve a mean difference of ⫾ 5 mm Hg and standard deviation of 8 mm Hg against a reference standard. However, no standards for measurements of systolic ankle and toe pressures exist. In our study, we found a mean difference of maximum 2 mm Hg and standard deviation of 8.6 mm Hg in accordance with the abovementioned standard for measurement of blood pressures. Some may argue that a standard deviation of 8.6 mm Hg is quite large and it may be of importance when diagnosing patients with pressures near the ‘critical limits’; i.e. pressures near 50 mm Hg for the ankle level. A patient with ankle pressures near 50 mm Hg is diagnosed as having critical limb ischemia with a pressure of 45 mmHg. However, when pressure is 8.6 mm Hg higher, this changes the diagnosis. The purpose of this study was to compare measurements of systolic ankle and toe pressure performed with the new indium-gallium strain gauge with the established method using mercury.
558
R. Broholm et al. (A)
Toe pressure 30
20 +2sd
Hg-In (mmHg)
0 0
20
40
60
80
100
120
140
160
180
–10 –2sd –20
–30 Mean Hg, In (mmHg)
(B)
Ankle pressure 30
20
+2sd
10 Hg-In (mmHg)
Scand J Clin Lab Invest Downloaded from informahealthcare.com by Nyu Medical Center on 06/21/15 For personal use only.
10
0 0
20
40
60
80
100
120
140
160
180
200
–10
–2sd –20
–30
Mean Hg, In (mmHg) Figure 2. (A) Bland-Altman plot illustrating toe pressures with the mean (mmHg) on the X-axis and the difference (Hg-In) between mercury (Hg) and indium-gallium (In) strain gauge on the Y-axis (mmHg). (B) Bland-Altman plot illustrating ankle pressures with the mean (mmHg) on the X-axis and the difference (Hg-In) between the mercury (Hg) and indium-gallium (In) strain gauges on the Y-axis (mmHg).
As the mercury strain gauge will no longer be available from 2014, it was necessary to compare the two different devices to see whether they agreed sufficiently
for the new to replace the old. In this exact setting, the indium-gallium strain gauge shows potential to replace the mercury strain gauge.
Strain gauge – mercury vs indium-gallium Acknowledgements The authors thank the nurses and technicians at the Department of Clinical Physiology and Nuclear Medicine, Bispebjerg and Frederiksberg Hospitals, for performing the measurements.
[5]
[6]
Declaration of interest: The authors have no conflicts of interest. The authors alone are responsible for the content and writing of the paper. [7]
Scand J Clin Lab Invest Downloaded from informahealthcare.com by Nyu Medical Center on 06/21/15 For personal use only.
References [1] McDermott MM, Greenland P, Liu K, Guralnik JM, Celic L, Criqui MH, Chan C, Martin GJ, Schneider J, Pearce WH, Taylor LM, Clark E. The ankle brachial index is associated with leg function and physical activity: the Walking and Leg Circulation Study. Ann Intern Med 2002;136:873–83. [2] Mohler ER, III. Peripheral arterial disease: identification and implications. Arch Intern Med 2003;163:2306–14. [3] Rutherford RB, Baker JD, Ernst C, Johnston KW, Porter JM, Ahn S, Jones DN. Recommended standards for reports dealing with lower extremity ischemia: revised version. J Vasc Surg 1997;26:517–38. [4] Norgren L, Hiatt WR, Dormandy JA, Nehler MR, Harris KA, Fowkes FG, Bell K, Caporusso J, DurandZaleski I, Komori K, Lammer J, Liapis C, Novo S, Razavi M, Robbs J, Schaper N, Shigematsu H, Sapoval M, White C, White J, Clement D, Creager M, Jaff M, Mohler E, III, Rutherford RB, Sheehan P, Sillesen H, Rosenfield K. Inter-Society Consensus for the Management of Peripheral
[8]
[9]
[10]
[11]
[12]
559
Arterial Disease (TASC II). Eur J Vasc Endovasc Surg 2007; 33(Suppl. 1):S1–75. Neubauer B, Christensen NJ, Christensen T, Gundersen HJ, Jorgensen J. Diabetic macroangiopathy. Medial calcifications, narrowing, rugosities, stiffness, norepinephrine depletion and reduced blood flow capacity in the leg arteries. Acta Med Scand Suppl 1984;687:37–45. Orchard TJ, Strandness DE, Jr. Assessment of peripheral vascular disease in diabetes. Report and recommendations of an international workshop sponsored by the American Diabetes Association and the American Heart Association September 18–20, 1992 New Orleans, Louisiana. Circulation 1993;88:819–28. Arveschoug AK, Revsbech P, Brochner-Mortensen J. Sources of variation in the determination of distal blood pressure measured using the strain gauge technique. Clin Physiol 1998;18:361–8. Official Journal of the European Union. 2013. http://eur-lex. europa.eu/LexUriServ/LexUriServ.do?uri ⫽ OJ:L:2012:253: 0001:0004:EN:PDF. Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986;1:307–10. Hoyer C, Pavar S, Pedersen BH, Biurrun Manresa JA, Petersen LJ. Reliability of mercury-in-silastic strain gauge plethysmography curve reading: influence of clinical clues and observer variation. Scand J Clin Lab Invest 2013; 73:380–6. Association for the Advancement of Medical Instrumentation (AAMI), Arlington Va. American National Standard for Electronic or Automated Sphygmomanometers. 1987. Ref Type: Generic White WB, Berson AS, Robbins C, Jamieson MJ, Prisant LM, Roccella E, Sheps SG. National standard for measurement of resting and ambulatory blood pressures with automated sphygmomanometers. Hypertension 1993;21:504–9.
TECHNICAL NOTE
Measuring systolic ankle and toe pressure using the strain gauge technique – a comparison study between mercury and indium-gallium strain gauges
Scand J Clin Lab Invest Downloaded from informahealthcare.com by Nyu Medical Center on 06/21/15 For personal use only.
RIKKE BROHOLM, NIELS WIINBERG & LENE SIMONSEN Department of Clinical Physiology and Nuclear Medicine, Bispebjerg and Frederiksberg Hospital, University of Copenhagen, Denmark Abstract Background. Measurement of the ankle and toe pressures are often performed using a plethysmograph, compression cuffs and a strain gauge. Usually, the strain gauge contains mercury but other alternatives exist. From 2014, the mercurycontaining strain gauge will no longer be available in the European Union. The aim of this study was to compare an indium-gallium strain gauge to the established mercury-containing strain gauge. Methods. Consecutive patients referred to the Department of Clinical Physiology and Nuclear Medicine at Bispebjerg and Frederiksberg Hospitals for measurements of systolic ankle and toe pressures volunteered for the study. Ankle and toe pressures were measured twice with the mercury and the indium-gallium strain gauge in random order. Comparison of the correlation between the mean pressure using the mercury and the indium-gallium device and the difference between the two devices was performed for both toe and ankle level. Results. A total of 53 patients were included (36 male). Mean age was 69 (range, 45–92 years). Mean pressures at toe and ankle level with the mercury and the indium-gallium strain gauges were 77 (range, 0–180) mm Hg and 113 (range, 15–190) mm Hg, respectively. Comparison between the mercury and the indium-gallium strain gauge showed a difference in toe blood pressure values of ⫺ 0.7 mm Hg (SD: 7.0). At the ankle level, a difference of 2.0 mm Hg (SD: 8.6) was found. Conclusion. The two different devices agree sufficiently in the measurements of systolic ankle and toe pressure for the indium-gallium strain gauge to replace the mercury strain gauge. Key Words: Claudication, ischemia, peripheral arterial disease
Introduction Measuring systolic ankle pressure is a standard procedure in the initial evaluation of patients with suspected peripheral artery disease (PAD) [1–3]. Usually, a pneumatic cuff is placed around the ankle and a hand-held Doppler instrument is used to measure the systolic pressure of the dorsalis pedis and posterior tibial arteries. The pressures are normalised to the brachial pressure to form the ankle-brachial index (ABI) using the higher of the two arm blood pressures. A reduced ABI may together with proximal auscultation or Doppler verification confirm the diagnosis of PAD in symptomatic patients, can detect significant PAD in asymptomatic patients, and can be used in the differential diagnosis of leg symptoms [4]. Furthermore, it can be used in the follow-up of
individual patients and provide surveillance after vascular interventions [4]. In some groups of patients, i.e. patients with diabetes or renal insufficiency, the vessels become incompressible because of media sclerosis [5]. This may lead to a falsely elevated ankle pressure and in these patients other non-invasive diagnostic tests can be performed to evaluate whether PAD is present or not. One alternative includes measurements of the systolic toe pressure as the digital arteries of the toes tend to be relatively less affected by media sclerosis [6]. A small occlusion cuff is placed around the first or second toe and a strain gauge is placed distally to the cuff. Usually, a strain gauge with mercury is the standard choice [7]. Both cuff and strain gauge are connected to a plethysmograph that detects and records changes in limb volume. The main limitation
Correspondence: Rikke Broholm, Department of Clinical Physiology and Nuclear Medicine, Bispebjerg Hospital, Bispebjerg Bakke 23, DK- 2400 Copenhagen NV, Denmark. Tel: ⫹ 45 31 35 27 94. Fax: ⫹ 45 35 31 39 54. E-mail: [email protected] (Received 1 November 2013 ; accepted 1 March 2014 ) ISSN 0036-5513 print/ISSN 1502-7686 online © 2014 Informa Healthcare DOI: 10.3109/00365513.2014.903431
Scand J Clin Lab Invest Downloaded from informahealthcare.com by Nyu Medical Center on 06/21/15 For personal use only.
556
R. Broholm et al.
of this technique is that it can be impossible to measure toe pressure in patients with ulceration or tissue loss and very low pressure may be a limitation as well. Ankle pressure can also be recorded using this technique placing the cuff around the ankle and the strain gauge at the toe or forefoot. Other pressure measuring methods include laser Doppler, transcutaneous oxygen measurements, and photoplethysmography. However, from January 2014 strain gauges containing mercury are not allowed in the European Union because of its environmental toxicity [8]. One alternative to the mercury-containing strain gauge is a strain gauge containing indium-gallium. However, no studies comparing the two different devices have been published. The primary aim of this study was to evaluate measurements of systolic ankle and toe pressures performed with a mercury strain gauge and compare them to measurements of systolic ankle and toe pressures performed with an indium-gallium strain gauge.
Ethical approval The national Ethics Committee for the Capital Region of Denmark considered the study (journal number: H-3-2013-FSP12) as a quality assurance project. Informed consent was obtained from all patients.
patient (Figure 1). Both types of strain gauges were stretched approximately 10% as recommended by the manufacturer. All measurements were performed twice by the same person and with occlusion cuffs at the ankle and toe, respectively (Medimatic® Plethysmograph, Hellerup, Denmark). Standard cuffs (12 ⫻ 35 cm) were used at the ankle level and cuff size at the toe varied according to toe size. Simultaneously, the brachial pressure of either arm was measured in triplicate using an automated device (the mean of the three pressures was used) (WatchBP® office, Microlife, Widnau, Switzerland) to calculate the ABI (using the arm blood pressure with the highest systolic pressure). A physician specialized in Clinical Physiology and Nuclear Medicine visually assessed the resulting pulse volume recordings blinded to the results of the primary readings (no marks were allowed in the original curve recordings). The blood pressure values were assessed to the nearest 5 mm Hg. The indium-gallium strain gauge is useable to a temperature down to 10.7oC where the gauge freezes. The electric resistance of the indium-gallium strain gauge is 1/3, and the sensitivity is about 1/3 of mercury, with the same dimensions. Statistics Average toe- and ankle-blood pressure values with both the mercury and the indium-gallium device were calculated.
Methods Consecutive patients referred to the Department of Clinical Physiology and Nuclear Medicine at Bispebjerg and Frederiksberg Hospital for measurements of systolic ankle and toe pressure were invited to participate in the study. Patients were included in the period from July to September 2013 and were referred because of lack of palpable foot pulses or because of symptoms of PAD (i.e. intermittent claudication, rest pain or non-healing foot ulcerations/ gangrene). A specially trained nurse or technician performed all examinations. Measurements were performed with patients in the supine position. Before the measurements, the patient rested in the supine position for at least 5 minutes. Skin temperature of the foot was registered before performing the examination (ETI Thermometers®, UK) and in cases with a skin temperature less than 30°C the foot was warmed using a ‘dry’ footbath (feet in a plastic bag). Skin temperature was controlled after warming the feet. Systolic ankle and toe pressures were measured using the strain gauge technique; first using the mercury-containing strain gauge (Medimatic®, Hellerup, Denmark) and then the indium-galliumcontaining strain gauge (Hokanson®, Bellevúe WA 98005, USA); and then vice versa for the following
Figure 1. The indium-gallium- (left) and mercury- (right) containing strain gauges.
Strain gauge – mercury vs indium-gallium A comparison of the correlation between the mean pressure using the mercury and the indiumgallium device and the difference between the two devices [9] were performed for both toe and ankle level. Patients were described using mean, standard deviation (SD) and range. A Bland-Altman plot was performed to visualize a possible relation between the difference between two measurements and their mean value [9].
Scand J Clin Lab Invest Downloaded from informahealthcare.com by Nyu Medical Center on 06/21/15 For personal use only.
Results A total of 53 consecutive patients were included in the study. Baseline characteristics of the included patients can be seen in Table I. Mean systolic pressures at toe and ankle level with the mercury and the indium-gallium strain gauges were 77 (range, 0–180) mm Hg and 113 (range, 15–190) mm Hg, respectively. A total of 106 comparisons were made at toe level and 100 at the ankle level. Excluded measurements were due to severe sclerosis in ankle arteries resulting in noncompressible arteries. Non-compressible arteries were defined from the resulting pulse volume recordings and from an ABI ⬎ 1.3. In the 106 legs in the study, a comparison between the mercury and the indium-gallium strain gauge showed a difference in systolic toe blood pressure values of ⫺ 0.7 mm Hg (SD: 7.0), meaning that the mercury strain gauge measured 0.7 mm Hg lower than the indium-gallium. At the ankle level, a difference of 2.0 mm Hg (SD: 8.6) was found. The results are presented in a Bland-Altman plot for systolic pressures at the toe and at the ankle level, respectively (Figure 2A and 2B).
Table I. Patient characteristics. Characteristics Patients Males Females Age (years) Systolic arm blood pressure (SD) (mmHg) Diabetes (%) Smokers (%) Mean systolic toe pressure Hg (SD) (mmHg) Mean systolic toe pressure In-G (SD) (mmHg) Mean systolic ankle pressure Hg (SD) (mmHg) Mean systolic ankle pressure In-G (SD) (mmHg) Ankle-brachial index (ABI) (SD) Peripheral arterial disease (PAD) (ABI ⬍ 0.9) (%)
Number 53 36 17 69 (range, 45–92) 136.0 (16.5) 27 (51) 20 (38) 76.6 (39.7) 77.3 (38.3) 113.2 (38.4) 112.2 (36.0) 0.85 (0.3) 39 (74)
557
Further analyses separating the patients in diabetics and non-diabetics did not show a systematic difference between the two groups (data not shown).
Discussion In this study we found a maximum difference of 2.0 mm Hg between the mercury and indiumgallium strain gauges and we conclude that the two different devices can be used equally. The study reflects measurements in a wide range of pressures, from 0–190 mm Hg and includes patients both with and without diabetes. The observed variation may in part be due to the fact that measurements with the two devices were not performed at the same time and that alteration in the systolic pressure therefore has been observed between the measurements. However, it was not possible to perform the measurements at the same time, as the sensitivity must be raised using the indium-gallium device. Measurements of systolic ankle and toe pressures with the strain gauge technique have been described to have low inter-observer variability [7,10]. In this study, we found a similar small difference between two different strain gauge devices with mercury and indium-gallium, respectively. Accurate and precise measurement devices are required when measuring the systolic ankle and toe pressure. In 1987, the American Association for the Advancement of Medical Instrumentation (AAMI) published a standard for assessing electronic and automated sphygmomanometers [11]. A revised standard was published in 1992 and a summary of the guidelines was published in 1993 [12]. The standard requires that the pressures measured by the devices achieve a mean difference of ⫾ 5 mm Hg and standard deviation of 8 mm Hg against a reference standard. However, no standards for measurements of systolic ankle and toe pressures exist. In our study, we found a mean difference of maximum 2 mm Hg and standard deviation of 8.6 mm Hg in accordance with the abovementioned standard for measurement of blood pressures. Some may argue that a standard deviation of 8.6 mm Hg is quite large and it may be of importance when diagnosing patients with pressures near the ‘critical limits’; i.e. pressures near 50 mm Hg for the ankle level. A patient with ankle pressures near 50 mm Hg is diagnosed as having critical limb ischemia with a pressure of 45 mmHg. However, when pressure is 8.6 mm Hg higher, this changes the diagnosis. The purpose of this study was to compare measurements of systolic ankle and toe pressure performed with the new indium-gallium strain gauge with the established method using mercury.
558
R. Broholm et al. (A)
Toe pressure 30
20 +2sd
Hg-In (mmHg)
0 0
20
40
60
80
100
120
140
160
180
–10 –2sd –20
–30 Mean Hg, In (mmHg)
(B)
Ankle pressure 30
20
+2sd
10 Hg-In (mmHg)
Scand J Clin Lab Invest Downloaded from informahealthcare.com by Nyu Medical Center on 06/21/15 For personal use only.
10
0 0
20
40
60
80
100
120
140
160
180
200
–10
–2sd –20
–30
Mean Hg, In (mmHg) Figure 2. (A) Bland-Altman plot illustrating toe pressures with the mean (mmHg) on the X-axis and the difference (Hg-In) between mercury (Hg) and indium-gallium (In) strain gauge on the Y-axis (mmHg). (B) Bland-Altman plot illustrating ankle pressures with the mean (mmHg) on the X-axis and the difference (Hg-In) between the mercury (Hg) and indium-gallium (In) strain gauges on the Y-axis (mmHg).
As the mercury strain gauge will no longer be available from 2014, it was necessary to compare the two different devices to see whether they agreed sufficiently
for the new to replace the old. In this exact setting, the indium-gallium strain gauge shows potential to replace the mercury strain gauge.
Strain gauge – mercury vs indium-gallium Acknowledgements The authors thank the nurses and technicians at the Department of Clinical Physiology and Nuclear Medicine, Bispebjerg and Frederiksberg Hospitals, for performing the measurements.
[5]
[6]
Declaration of interest: The authors have no conflicts of interest. The authors alone are responsible for the content and writing of the paper. [7]
Scand J Clin Lab Invest Downloaded from informahealthcare.com by Nyu Medical Center on 06/21/15 For personal use only.
References [1] McDermott MM, Greenland P, Liu K, Guralnik JM, Celic L, Criqui MH, Chan C, Martin GJ, Schneider J, Pearce WH, Taylor LM, Clark E. The ankle brachial index is associated with leg function and physical activity: the Walking and Leg Circulation Study. Ann Intern Med 2002;136:873–83. [2] Mohler ER, III. Peripheral arterial disease: identification and implications. Arch Intern Med 2003;163:2306–14. [3] Rutherford RB, Baker JD, Ernst C, Johnston KW, Porter JM, Ahn S, Jones DN. Recommended standards for reports dealing with lower extremity ischemia: revised version. J Vasc Surg 1997;26:517–38. [4] Norgren L, Hiatt WR, Dormandy JA, Nehler MR, Harris KA, Fowkes FG, Bell K, Caporusso J, DurandZaleski I, Komori K, Lammer J, Liapis C, Novo S, Razavi M, Robbs J, Schaper N, Shigematsu H, Sapoval M, White C, White J, Clement D, Creager M, Jaff M, Mohler E, III, Rutherford RB, Sheehan P, Sillesen H, Rosenfield K. Inter-Society Consensus for the Management of Peripheral
[8]
[9]
[10]
[11]
[12]
559
Arterial Disease (TASC II). Eur J Vasc Endovasc Surg 2007; 33(Suppl. 1):S1–75. Neubauer B, Christensen NJ, Christensen T, Gundersen HJ, Jorgensen J. Diabetic macroangiopathy. Medial calcifications, narrowing, rugosities, stiffness, norepinephrine depletion and reduced blood flow capacity in the leg arteries. Acta Med Scand Suppl 1984;687:37–45. Orchard TJ, Strandness DE, Jr. Assessment of peripheral vascular disease in diabetes. Report and recommendations of an international workshop sponsored by the American Diabetes Association and the American Heart Association September 18–20, 1992 New Orleans, Louisiana. Circulation 1993;88:819–28. Arveschoug AK, Revsbech P, Brochner-Mortensen J. Sources of variation in the determination of distal blood pressure measured using the strain gauge technique. Clin Physiol 1998;18:361–8. Official Journal of the European Union. 2013. http://eur-lex. europa.eu/LexUriServ/LexUriServ.do?uri ⫽ OJ:L:2012:253: 0001:0004:EN:PDF. Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986;1:307–10. Hoyer C, Pavar S, Pedersen BH, Biurrun Manresa JA, Petersen LJ. Reliability of mercury-in-silastic strain gauge plethysmography curve reading: influence of clinical clues and observer variation. Scand J Clin Lab Invest 2013; 73:380–6. Association for the Advancement of Medical Instrumentation (AAMI), Arlington Va. American National Standard for Electronic or Automated Sphygmomanometers. 1987. Ref Type: Generic White WB, Berson AS, Robbins C, Jamieson MJ, Prisant LM, Roccella E, Sheps SG. National standard for measurement of resting and ambulatory blood pressures with automated sphygmomanometers. Hypertension 1993;21:504–9.
