Pediatric Pulmonology 13:15&160 (1992)

Gas Exchange During Exercise in Diabetic Children Eugenio Baraldi, MD, Carla Monciotti, MD, Marco Filippone, MD, Pierantonio Santuz, MD, Giampiero Magagnin, MD, Stefania Zanconato, MD, and Franco Zacchello, MD Summary. The purpose of this study was to evaluate the cardiorespiratory and metabolic response to exercise in 33 children, aged 9 to 15 years, affected by type I diabetes mellitus, in comparison with 47 age-, sex-, weight-, and height-matchedhealthy children. All diabetic children were on a mixed split-dose insulin regimen, consisting of both regular and long-acting insulin in the morning and evening. The last insulin injection was administered on average 6 hours before the test. The mean duration of diabetes mellitus was 5.0 2 3.1 years. The metabolic control was evaluated on the basis of HbAl levels (mean, 8.9 2 1.8Yo). Pulmonary function tests and progressive exercisetests on the treadmill were performed. Gas exchange, ventilation, and heart rate (HR) were monitored during the tests. The 0, pulse (VdHR) was calculated. There was no difference in the baseline oxygen uptake (V0J between the diabetic children and the control group. ,V peak was significantly lower (P < 0.01) in the diabetic adolescents (41.2 5 5.9 mUminlkg) compared to control subjects (46.3r 9.6 mUminlkg) and it was achieved at an earlier (P < 0.01) time of run (7.5 5 1.8 vs. 9.1 k 2.8 min). Anaerobic threshold and minute ventilation were similar in the two groups. The 0, pulse throughout the test was significantlylower (ANOVA, P < 0.001) in the diabetic group compared to the controls. No differences were found in resting and post-exercise spirometric values. In conclusion, our study shows that well-controlleddiabetic adolescents have a reduced working capacity. The lower 0, pulse reflects a reduced peripheral oxygen utilization that might suggest early microvascular disease. Pediatr Pulmonol. 1992; 13:155-160. 8 1992 wiley-Liss. Inc.

Key words: Progressive treadmill exercise; maximum O2uptake to heart rate ratio; working capacity.

INTRODUCTION

For both healthy children and those with chronic diseases like diabetes, the ability to engage in play, exercise, and other physical activities is an essential component of daily life. Precise assessment of cardiorespiratory and metabolic responses to exercise is an invaluable tool in diagnosing disease, assessing its impact, and making recommendations of specific programs of physical activity.I4 In the control of juvenile diabetes, physical activity is of the utmost importance. Thoren recommended exercise .~ testing in diabetic children as a matter of r o ~ t i n eStarting in 1962, when Larsson et al. published the first work assessing physical fitness and pulmonary function in diabetic children,6 several authors studied the response to exercise in subjects with insulin-dependent diabetes mellitus (IDDM).’-I5 However, little is known about gas exchange dynamics during exercise in these children. We evaluated the adaptation to physical activity in diabetic children by measuring gas exchange at the mouth during acute incremental exercise. By determining gas and heart rate (HR) responses exchange, ventilation (0,) to exercise-inducedincreases in metabolism, the relationship between respiration at the cellular level and respiration of the whole organism can be evaluated. l6 0 1992 Wiley-Liss, Inc.

The purpose of this study was: 1) to compare the cardiovascular and metabolic response to exercise between children with IDDM and healthy controls; and 2) to evaluate if increased metabolic demands can reveal latent abnormalities, in cardiocirculatory, respiratory, or metabolic functions, not noticeable at rest. MATERIALS AND METHODS Population The study comprised 33 insulin-dependent diabetic subjects (17 boys, 16 girls) aged 9.2-15.7 years (mean, 13.2 k 1.7 SD years), recruited among patients regularly attending the outpatient clinic at the Department of PediFrom the Department of Pediatrics, Lung Function Laboratory, University of Padova, Italy. Received December 5 , 199 I; (revision) accepted for publication March 9. 1992. Presented at the IX Meeting of the European Pediatric Respiratory Society, June 27-29, 1991, Rome, Italy. Address correspondence and reprint requests to Dr. E. Baraldi, Department of Pediatrics, University of Padova, Via Giustiniani 3, 35128 Padova. Italy.

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Baraldi et al.

TABLE 1-Characteristics of Subiects Diabetics (n = 33) Age (YB) Height (cm) Weight (kg) Duration of diabetes (yrs) HbAl (g%)

13.2 2 157 ? 49.7 2 5.0 2

1.7 10.2 10.2 3. I

8.9 2 1.8

Controls (fl = 47)

*

12.7 1.5 154 2 9 47.3 k 8.8 -

-

'f

NS NS NS

treadmill speed was set at 6.5 km/h and the inclination of the belt was increased by 2% steps every minute, until exhaustion. Periodically the children were actively encouraged throughout the test. Gas Exchange Measurements

The children, connected by a pediatric mask to an Area 1 System (Biomedin, Padova, Italy), breathed through a low-resistance valve (dead space, 40 mL). Ventilation (VE) was measured by a bell spirometer (Biomedin) without counterweight. 0,and CO, concentrationswere measured by a polarimetric and infrared analyzer. VE (BTPS), 0, uptakes (Vo2) (STPD), and CO, output (Vco2)(STPD) were computed on-line as previously described. I 8 HR was determined by a cardiofrequency meter (Sport Tester 3000, Polar Kempele, Finland). Peak VO2was taken as the largest Vo2achieved during the test. The anaerobic threshold (AT) was identified as the point where hyperventilation with respect to Vo2occurred with an increase in the ventilatory equivalent for 0, (VE/Vo,) without concomitant increase in the ventilatory equivalent for CO, (VE/VC02).19

atrics, University of Padova. For healthy controls we selected 47 age-, sex-, height-, and weight-matched children (24 boys, 23 girls) aged 9.8-15.5 years (mean, 12.7 ? 1.5 years) from local schools; they were within the normal range for height and weight, according to reference tables.17 None of the children in the diabetic and control group suffered from asthma or other lung diseases. Subjects' characteristics are reported in Table 1. The patients had been diagnosed as having IDDM for at least 1 year before the study (the mean duration of diabetes was 5 ? 3.1 years). All diabetic children were on a mixed split-dose insulin regimen consisting of both regular and long-acting insulin in the morning and evening. They were in good nutritional balance and ingested a Analysis of Vo2-HR Relationship (0, Pulse) weight-maintaining diet that consisted of approximately At rest and during exercise 0, pulse was calculated by 60% carbohydrate, 30% fat, and 10%protein. When the dividing the oxygen uptake by heart rate. Oxygen pulse is study was performed, they were considered in stable metthe volume of 0, extracted by the peripheral tissues and abolic control (hemoglobin A1 values, 8.9 ? 1.8 g%). can be shown to be equal to the product of stroke volume None of them had any clinical or laboratory evidence of and the arterial mixed venous 0, difference. l9 nephropathy, hypertension, retinopathy and cardiac disease, or other problems that would contraindicate their participation in exercise testing. A normal electrocardio- Data Analysis gram was a prerequisite for participation in the study. To compare exercise responses of different-sized subWritten informed consent was obtained from the parents jects, VO?,0, pulse, and work rate data were divided by of each child. body weight for each subject. Statistical analysis included unpaired and paired Student's t-test and analysis Protocol of variance (repeated measures, ANOVA). Statistical All studies were performed in the afternoon, at an significance was considered for P values less than 0.05. average of 6 hours after the last insulin injection and at Data are expressed as mean & SD. least 2 hours after the last meal. Spirometric values [forced vital capacity (FVC), forced expiratory volume in 1 second (FEV,), forced RESULTS expiratory flow between 25-75% of vital capacity Population (FEF25-75%)]were measured at rest and 5 minutes after None of the patients experienced serious symptoms the exercise. Each child made at least three forced expira(hypoglycemia, dyspnea) during or after exercise. tions from full inspiration, in the standing position. The percent post-exercise change in FEV, and FEF25-,5% with respect to the baseline values was calculated. Arte- Pulmonary Function Tests In the diabetic children, the resting FEV, , FVC, and rial blood pressure (BP) was measured by auscultation prior to and immediately after exercise. Simultaneously, FEF25-75% values, expressed as percent of predicted,," glucose concentration was measured in whole blood by were 97 f 9%, 100 f 9%,and 113 2 20%, respectively. In the control group the mean resting FEV,, FVC, and the glucose oxidase reaction. Exercise tests were performed on a treadmill (PK Mor- FEF2s-7s4, values were 97 ? 9%, 98 ? 9%, and 1 I I 2 gan Ltd, Gillingham, England). After a warming-up pe- 18%, respectively. No difference was found between preriod of 5 minutes and a 3 minutes resting evaluation, the and post-exercise spirometric values in the diabetic

Exercise Testing in Diabetic Children TABLE 2-Exercise Testing Results 6o

Time run (min) VO2max(mL/min/kg) VFmn(Wmin) HRmax (beatslmin) Maximal work (W/kg) VAT (mLO,/kg/min)

Diabetics (n = 33)

Controls (n = 47)

7.5 2 1.8 41.2 f 5.9 56.8 2 14.6 196 f 7 2.6 ? 0.7 31.4 2 5.3

9.1 f 2.8 46.3 f 9.6 58.4 2 13.9 198 f 7 3.1 0.9 32.5 f 5.6

1

P