Gas exchange during exercise in diabetic children

Youth with type 1 diabetes mellitus are more inactive and sedentary than apparently healthy peers: a systematic review and meta-analysis

AIMS

To conduct a meta-analysis of differences in physical activity, sedentary behaviour, and physical fitness between children and adolescents with type 1 diabetes and their healthy peers.

METHODS

The databases EMBASE, PubMed and SportsDiscus were searched for studies. Pooled effects were calculated using random effects inverse-variance models with the Hartung-Knapp-Sidik-Jonkman adjustment.

RESULTS

Thirty-five studies were included, comprising a total of 4,751 youths (53% girls) of which 2,452 with type 1 diabetes. Youth with type 1 diabetes were less physically active (Coheńs d=-0.23, 95%CI -0.42 to -0.04), more sedentary (Coheńs d=0.33, 95%CI 0.06 to 0.61), and had lower cardiorespiratory fitness (Coheńs d=-0.52, 95%CI -0.73 to -0.31) than their healthy peers. This corresponds to -12.72 min/day of moderate-to-vigorous physical activity, 63.3 min/day of sedentary time (accelerometry) and -4.07 ml/kg/min of maximum/peak oxygen consumption. In addition, young people with type 1 diabetes were less likely to meet the international physical activity recommendations than their healthy peers (odds ratio=0.44, 95%CI 0.31 to 0.62).

CONCLUSIONS

Keeping in mind the heterogeneity between studies in the design, population and assessment, our findings show that children and adolescents with type 1 diabetes seem to be less active, more sedentary, and have lower cardiorespiratory fitness levels than their healthy peers.

Respiratory function in uncomplicated type 1 diabetes: Blunted during exercise even though normal at rest!

AIMS

Type 1 diabetes is associated with a substantially increased risk of impaired lung function, which may impair aerobic fitness. We therefore aimed to examine the ventilatory response during maximal exercise and the pulmonary diffusion capacity function at rest in individuals with uncomplicated type 1 diabetes.

METHODS

In all, 17 adults with type 1 diabetes free from micro-macrovascular complications (glycated haemoglobin: 8.0 ± 1.3%), and 17 non-diabetic adults, carefully matched to the type 1 diabetes group according to gender, age, level of physical activity and body composition, participated in our study. Lung function was assessed by spirometry and measurements of the combined diffusing capacity for nitric oxide (DLNO) and carbon monoxide (DLCO) at rest. Subjects performed a maximal exercise test during which the respiratory parameters were measured.

RESULTS

At rest, DLCO (30.4 ± 6.1 ml min^-1  mmHg^-1 vs. 31.4 ± 5.7 ml min^-1 mmHg^-1 , respectively, p = 0.2), its determinants Dm (membrane diffusion capacity) and Vc (pulmonary capillary volume) were comparable among type 1 diabetes and control groups, respectively. Nevertheless, spirometry parameters (forced vital capacity = 4.9 ± 1.0 L vs. 5.5 ± 1.0 L, p < 0.05; forced expiratory volume 1 = 4.0 ± 0.7 L vs. 4.3 ± 0.7 L, p < 0.05) were lower in individuals with type 1 diabetes, although in the predicted normal range. During exercise, ventilatory response to exercise was different between the two groups: tidal volume was lower in type 1 diabetes vs. individuals without diabetes (p < 0.05). Type 1 diabetes showed a reduced VO_2max (34.7 ± 6.8 vs. 37.9 ± 6.3, respectively, p = 0.04) in comparison to healthy subjects.

CONCLUSIONS

Individuals with uncomplicated type 1 diabetes display normal alveolar-capillary diffusion capacity and at rest, while their forced vital capacity, tidal volumes and VO₂ are reduced during maximal exercise.

Association of HbA1c with VO2max in Individuals with Type 1 Diabetes: A Systematic Review and Meta-Analysis

The aim of this systematic review and meta-analysis was to evaluate the association between glycemic control (HbA1c) and functional capacity (VO2max) in individuals with type 1 diabetes (T1DM). A systematic literature search was conducted in EMBASE, PubMed, Cochrane Central Register of Controlled Trials, and ISI Web of Knowledge for publications from January 1950 until July 2020. Randomized and observational controlled trials with a minimum number of three participants were included if cardio-pulmonary exercise tests to determine VO2max and HbA1c measurement has been performed. Pooled mean values were estimated for VO2max and HbA1c and weighted Pearson correlation and meta-regression were performed to assess the association between these parameters. We included 187 studies with a total of 3278 individuals with T1DM. The pooled mean HbA1c value was 8.1% (95%CI; 7.9−8.3%), and relative VO2max was 38.5 mL/min/kg (37.3−39.6). The pooled mean VO2max was significantly lower (36.9 vs. 40.7, p = 0.001) in studies reporting a mean HbA1c > 7.5% compared to studies with a mean HbA1c ≤ 7.5%. Weighted Pearson correlation coefficient was r = −0.19 (p < 0.001) between VO2max and HbA1c. Meta-regression adjusted for age and sex showed a significant decrease of −0.94 mL/min/kg in VO2max per HbA1c increase of 1% (p = 0.024). In conclusion, we were able to determine a statistically significant correlation between HbA1c and VO2max in individuals with T1DM. However, as the correlation was only weak, the association of HbA1c and VO2max might not be of clinical relevance in individuals with T1DM.

Effects of gas exchange on acid-base balance

This paper describes the interactions between ventilation and acid-base balance under a variety of conditions including rest, exercise, altitude, pregnancy, and various muscle, respiratory, cardiac, and renal pathologies. We introduce the physicochemical approach to assessing acid-base status and demonstrate how this approach can be used to quantify the origins of acid-base disorders using examples from the literature. The relationships between chemoreceptor and metaboreceptor control of ventilation and acid-base balance summarized here for adults, youth, and in various pathological conditions. There is a dynamic interplay between disturbances in acid-base balance, that is, exercise, that affect ventilation as well as imposed or pathological disturbances of ventilation that affect acid-base balance. Interactions between ventilation and acid-base balance are highlighted for moderate- to high-intensity exercise, altitude, induced acidosis and alkalosis, pregnancy, obesity, and some pathological conditions. In many situations, complete acid-base data are lacking, indicating a need for further research aimed at elucidating mechanistic bases for relationships between alterations in acid-base state and the ventilatory responses.

Exercise and type 1 diabetes (T1DM)

Physical exercise is firmly incorporated in the management of type 1 diabetes (T1DM), due to multiple recognized beneficial health effects (cardiovascular disease prevention being preeminent). When glycemic values are not excessively low or high at the time of exercise, few absolute contraindications exist; practical guidelines regarding amount, type, and duration of age-appropriate exercise are regularly updated by entities such as the American Diabetes Association and the International Society for Pediatric and Adolescent Diabetes. Practical implementation of exercise regimens, however, may at times be problematic. In the poorly controlled patient, specific structural changes may occur within skeletal muscle fiber, which is considered by some to be a disease-specific myopathy. Further, even in well-controlled patients, several homeostatic mechanisms regulating carbohydrate metabolism often become impaired, causing hypo- or hyperglycemia during and/or after exercise. Some altered responses may be related to inappropriate exogenous insulin administration, but are often also partly caused by the "metabolic memory" of prior glycemic events. In this context, prior hyperglycemia correlates with increased inflammatory and oxidative stress responses, possibly modulating key exercise-associated cardio-protective pathways. Similarly, prior hypoglycemia correlates with impaired glucose counterregulation, resulting in greater likelihood of further hypoglycemia to develop. Additional exercise responses that may be altered in T1DM include growth factor release, which may be especially important in children and adolescents. These multiple alterations in the exercise response should not discourage physical activity in patients with T1DM, but rather should stimulate the quest for the identification of the exercise formats that maximize beneficial health effects.

Diastolic function is reduced in adolescents with type 1 diabetes in response to exercise

OBJECTIVE

To determine whether adolescents with type 1 diabetes have left ventricular functional changes at rest and during acute exercise and whether these changes are affected by metabolic control and diabetes duration.

RESEARCH DESIGN AND METHODS

The study evaluated 53 adolescents with type 1 diabetes and 22 control adolescents. Baseline data included peak exercise capacity and body composition by dual-energy X-ray absorptiometry. Left ventricular functional parameters were obtained at rest and during acute exercise using magnetic resonance imaging.

RESULTS

Compared with nondiabetic control subjects, adolescents with type 1 diabetes had lower exercise capacity (44.7 ± 09 vs. 48.5 ± 1.4 mL/kg fat-free mass [FFM]/min; P < 0.05). Stroke volume was reduced in the diabetes group at rest (1.86 ± 0.04 vs. 2.05 ± 0.07 mL/kg FFM; P = 0.02) and during acute exercise (1.89 ± 0.04 vs. 2.17 ± 0.06 mL/kg FFM; P = 0.01). Diabetic adolescents also had reduced end-diastolic volume at rest (2.94 ± 0.06 vs. 3.26 ± 0.09 mL/kg FFM; P = 0.01) and during acute exercise (2.78 ± 0.05 vs. 3.09 ± 0.08 mL/kg FFM; P = 0.01). End-systolic volume was lower in the diabetic group at rest (1.08 ± 0.03 vs. 1.21 ± 0.04 mL/kg FFM; P = 0.01) but not during acute exercise. Exercise capacity and resting and exercise stroke volumes were correlated with glycemic control but not with diabetes duration.

CONCLUSIONS

Adolescents with type 1 diabetes have reduced exercise capacity and display alterations in cardiac function compared with nondiabetic control subjects, associated with reduced stroke volume during exercise.

Mitochondrial superoxide and coenzyme Q in insulin-deficient rats: increased electron leak

Mitochondrial superoxide is important in the pathogeneses of diabetes and its complications. However, there is uncertainty regarding the intrinsic propensity of mitochondria to generate this radical. Studies to date suggest that superoxide production by mitochondria of insulin-sensitive target tissues of insulin-deficient rodents is reduced or unchanged. Moreover, little is known of the role of the Coenzyme Q (CoQ), whose semiquinone form reacts with molecular oxygen to generate superoxide. We measured reactive oxygen species (ROS) production, respiratory parameters, and CoQ content in mitochondria from gastrocnemius muscle of control and streptozotocin (STZ)-diabetic rats. CoQ content did not differ between mitochondria isolated from vehicle- or STZ-treated animals. CoQ also was unaffected by weight loss in the absence of diabetes (induced by caloric restriction). Under state 4 or state 3 conditions, both respiration and ROS release were reduced in diabetic mitochondria fueled with succinate, glutamate plus malate, or with all three substrates (continuous TCA cycle). However, H(2)O(2) and directly measured superoxide production were substantially increased in gastrocnemius mitochondria of diabetic rats when expressed per unit oxygen consumed. On the basis of substrate and inhibitor effects, the mechanism involved multiple electron transport sites. More limited results using heart mitochondria were similar. ROS per unit respiration was greater in muscle mitochondria from diabetic compared with control rats during state 3, as well as state 4, while the reduction in ROS per unit respiration on transition to state 3 was less for diabetic mitochondria. In summary, ROS production is, in fact, increased in mitochondria from insulin-deficient muscle when considered relative to electron transport. This is evident on multiple energy substrates and in different respiratory states. CoQ is not reduced in diabetic mitochondria or with weight loss due to food restriction. The implications of these findings are discussed.

Aerobic exercise capacity and pulmonary function in athletes with and without type 1 diabetes

OBJECTIVE

To compare the aerobic exercise capacity and pulmonary function between athletes with and without type 1 diabetes.

RESEARCH DESIGN AND METHODS

Fifty-one adult age-matched individuals were assessed in random order to the maximum volume of O(2) consumption (Vo(2 peak max)) (ml/kg/min), anaerobic threshold (ml/kg/min), peak pulmonary ventilation (Ve), heart rate (beats per min), time to exhaustion (min), forced vital capacity (FEV) (%), forced expiratory volume in the first second (FEV1) (%), total lung capacity (TLC) (%), and lung diffusion capacity for carbon monoxide (DL(CO)) (%). Individuals were 27 with type 1 diabetes: 15 athletes (ADM) and 12 nonathletes (NADM); and 24 healthy individuals: 12 ADM and 12 NADM. Duration of diabetes was 14.6 ± 6.2 and 15.2 ± 6.7 years in ADM and NADM, respectively.

RESULTS

Vo(2 peak) (max) was higher in ADM than in NADM (P < 0.001). The anaerobic threshold was lower in subjects with type 1 diabetes than in control subjects (P < 0.001). FEV1 was lower in ADM than in other groups (NADM, athletes control, and nonathletes control, P < 0.001).

CONCLUSIONS

Aerobic capacity in subjects with type 1 diabetes with programmed exercise is similar to the capacity of normal athletes despite lower anaerobic threshold and FEV1.

Impaired growth and force production in skeletal muscles of young partially pancreatectomized rats: a model of adolescent type 1 diabetic myopathy?

This present study investigated the temporal effects of type 1 diabetes mellitus (T1DM) on adolescent skeletal muscle growth, morphology and contractile properties using a 90% partial pancreatecomy (Px) model of the disease. Four week-old male Sprague-Dawley rats were randomly assigned to Px (n = 25) or Sham (n = 24) surgery groups and euthanized at 4 or 8 weeks following an in situ assessment of muscle force production. Compared to Shams, Px were hyperglycemic (>15 mM) and displayed attenuated body mass gains by days 2 and 4, respectively (both P<0.05). Absolute maximal force production of the gastrocnemius plantaris soleus complex (GPS) was 30% and 50% lower in Px vs. Shams at 4 and 8 weeks, respectively (P<0.01). GP mass was 35% lower in Px vs Shams at 4 weeks (1.24±0.06 g vs. 1.93±0.03 g, P<0.05) and 45% lower at 8 weeks (1.57±0.12 vs. 2.80±0.06, P<0.05). GP fiber area was 15–20% lower in Px vs. Shams at 4 weeks in all fiber types. At 8 weeks, GP type I and II fiber areas were ∼25% and 40% less, respectively, in Px vs. Shams (group by fiber type interactions, P<0.05). Phosphorylation states of 4E-BP1 and S6K1 following leucine gavage increased 2.0- and 3.5-fold, respectively, in Shams but not in Px. Px rats also had impaired rates of muscle protein synthesis in the basal state and in response to gavage. Taken together, these data indicate that exposure of growing skeletal muscle to uncontrolled T1DM significantly impairs muscle growth and function largely as a result of impaired protein synthesis in type II fibers.

Lung function changes related to diabetes mellitus

Diabetic microangiopathy targets the lung as it does other organs. Even though respiratory dysfunction in most patients with diabetes is subclinical and rarely the presenting complaint, there are several reasons why pulmonary assessment is important: (1) Pulmonary function testing noninvasively quantifies physiological reserves in a large microvascular bed that is not clinically devastated by diabetes. (2) Subclinical loss of pulmonary reserves becomes overtly debilitating under conditions of stress, such as with aging, chronic hypoxia due to lung disease or high altitude exposure, or volume overload secondary to cardiac and renal failure. (3) Unlike myocardial or skeletal muscle function, pulmonary indices are largely independent of physical fitness. (4) Interpretation of pulmonary function indices is not complicated by secondary sequelae of diabetic end-organ failure or prior therapy. Lung function could provide useful measures of the progression of systemic microangiopathy. (5) Chronic use of inhaled insulin may affect long-term pulmonary function, while preexisting pulmonary dysfunction may alter the absorption and bioavailability of inhaled insulin. This review will discuss the changes in lung function observed in diabetes, their underlying mechanisms, and their physiological and clinical implications.

Physical activity, sport, and pediatric diabetes

The benefits derived from regular physical activity include improved cardiovascular fitness, increased lean mass, improved blood lipid profile, enhanced psychosocial well-being, and decreased body adiposity. The benefits for children with diabetes may also include blood glucose control and enhanced insulin sensitivity. However, for these children, engagement in vigorous physical activity and sport must be properly controlled through modifications in insulin therapy and nutritional intake so that the benefits of exercise outweigh the risks. The following review describes the various physiological and metabolic factors which occur both during exercise and during sport while describing specific recommendations to control glucose excursions by proper insulin management and diet.

Normal physical working capacity in prepubertal children with type 1 diabetes compared with healthy controls

BACKGROUND

Exercise testing has become a valuable help for the physician to examine the influence of recommended exercise training on physical fitness. However, the question as to how diabetic prepubertal children differ from their non-diabetic peers in their performance capacity has only partial and sometimes conflicting answers in the literature.

AIM AND METHODS

The aim of the current study was thus to evaluate aerobic fitness during an incremental submaximal test (measure of the Physical Working Capacity 170 (PWC170)) in 17 well-controlled prepubertal insulin-dependent diabetic boys aged 8.5-13 y. Eighteen healthy prepubertal boys matched for age, body size and physical activity served as controls. Part of the method was to check capillary blood glucose level in the diabetic patients and in nine of the healthy subjects throughout the exercise.

RESULTS

From this experiment it appeared that the level of physical fitness was similar in diabetic and healthy boys (PWC170 2.28+/-0.09 vs 2.37+/-0.13 W x kg(-1)). While glucose homeostasis was well maintained in the healthy group, diabetic children showed a marked fall in blood glucose during the exercise. In addition, the PWC170 level correlated significantly with the estimate of energy expenditure attributed to vigorous activities in the diabetic boys.

CONCLUSION

By studying the responses to incremental exercise there is growing evidence that normal physical fitness is preserved in diabetic prepubertal boys given appropriate involvement in physical activity.

Aerobic exercise capacity in normal adolescents and those with type 1 diabetes mellitus

OBJECTIVE

To compare the aerobic exercise capacity between normal adolescents and those with type 1 diabetes mellitus (T1DM).

METHODS

An experimental group with 72 individuals diagnosed with T1DM aged 9--20, time from diagnosis 4.9 +/- 3.6 yr, without clinical cardiopulmonary disease or anemia and a control group (C) with 46 healthy individuals aged 10--18, matched by age, weight, height, body mass index, and lean and fat mass (kg), underwent an incremental aerobic exercising test on a motorized treadmill, where gas exchange variables - peak pulmonary ventilation (VE), peak oxygen consumption (VO(2)), and carbon dioxide production (CO(2)) - as well as their heart rate (HR) and time to exhaustion were recorded.

RESULTS

Body mass composition had no significant difference between experimental and control groups, and male and female subjects had similar exercising performances. The mean of hemoglobin A1c in the control group was 5.2+/- 0.9% and in the diabetic group 8.1+/- 2.2%; p=0.000. The patients with T1DM showed lower levels of aerobic capacity than the control group. Their respective values for each variable were as follows: (i) maximal VO(2) (T1DM: 41.57+/-7.68 vs. C: 51.12+/- 9.94 mL/kg/min; p< 0.001) and (ii) maximal VE (T1DM: 76.39+/-19.93 vs. C: 96.90 +/- 25.72 mL/kg/min; p< 0.001). Patients with T1DM also had an earlier time to exhaustion (T1DM: 8.75+/-1.60 vs. 10.82+/-1.44 min).

CONCLUSIONS

Adolescent patients with T1DM showed a reduced aerobic exercising capacity when compared to healthy peers matched to anthropometric conditions. This potential condition should be taken into consideration by the time of evaluation of the aerobic performance of these patients with glycemic control level.

Altered Exercise Gas Exchange as Related to Microalbuminuria in Type 2 Diabetic Patients

STUDY OBJECTIVE

Microalbuminuria in diabetes mellitus is a risk factor for cardiovascular disease. We hypothesized that microalbuminuria in type 2 diabetic patients is related to impaired cardiopulmonary function during exercise, and that the severity of impairment is correlated with the degree of microalbuminuria.

DESIGN

Twenty of each of the following categories of subjects performed symptom-limited cardiopulmonary exercise testing on a cycle ergometer: (1) type 2 diabetic patients with normoalbuminuria (daily urinary albumin excretion [UAE] < 30 mg/d); (2) type 2 diabetic patients with microalbuminuria (daily UAE, 30 to 300 mg/d); and (3) normal control subjects.

MEASUREMENTS AND RESULTS

Oxygen consumption (VO(2)) of patients with microalbuminuria was lower than that of control subjects at anaerobic threshold (AT) [p < 0.001], and was lower than both control subjects (p < 0.001) and patients with normoalbuminuria (p = 0.015) at peak exercise. There was a progressive worsening in gas exchange efficiency at the lungs, as measured by minute ventilation (VE)/carbon dioxide production (VCO(2)) at AT or DeltaVE/DeltaVCO(2) slope, (p = 0.006 and p = 0.019, respectively) going from control subjects to patients with normoalbuminuria and then to patients with microalbuminuria. Left ventricular ejection fractions and BP were similar in patients with normoalbuminuria and microalbuminuria. More patients with microalbuminuria (n = 9) than with normoalbuminuria (n = 2) demonstrated diastolic dysfunction (p = 0.013). These 11 patients had lower peak VO(2) values (p = 0.001) and higher daily UAE (p = 0.028). An inverse linear relationship was found between peak VO(2) and log(10) daily UAE (r = - 0.57, r(2) = 0.29, p < 0.001).

CONCLUSIONS

Abnormalities reflecting reduced oxygen transport and impaired gas exchange efficiency were found during exercise, and were especially profound in patients with microalbuminuria. These changes could be secondary to pulmonary microangiopathy and myocardial interstitial changes. Increases in capillary permeability to proteins may take place in the myocardium as they do in the kidneys, and contribute to impaired myocardial distensibility and hence diastolic dysfunction.

Clinical and demographic predictors of exercise capacity in end-stage renal disease

Patients on maintenance hemodialysis therapy for end-stage renal disease have reduced exercise tolerance. Multiple processes related to uremia and hemodialysis have been implicated in the pathophysiology of this impairment. However, limited data are available to identify the separate and combined effects of clinical factors on the degree of impairment for individuals within this population. For this purpose, data from 193 patients who had undergone exercise testing for two clinical trials were retrospectively analyzed. Univariate and multiple linear regression analyses were used to identify demographic and clinical correlates of peak exercise oxygen uptake (VO2). Peak VO2 averaged 18.5 +/- 6.4 mL/min/kg. On univariate analysis, peak VO2 correlated positively with male sex and hemoglobin, serum albumin, and serum creatinine concentrations and correlated negatively with dialytic age and diagnosis of diabetes or chronic heart failure. In a multiple linear regression model, sex, hemoglobin concentration, age, and diagnosis of diabetes each remained statistically significant. Together, factors included in the model accounted for 41% of the variability in peak VO2 (P = 0.0001). Among factors not correlating significantly with peak VO2 were resting blood pressure, serum carnitine level, and urea clearance assessed by Kt/V. Findings show the range of exercise impairment among clinically stable ambulatory hemodialysis patients, which may be sufficient to interfere with normal daily activities for many of these patients. Although this impairment may be broadly attributable to physiological consequences of uremia, the degree of impairment for individual patients is predicted by demographic factors, coexistent disease, and factors potentially modified by medical therapeutics.

Glycemic control and cardiopulmonary function in patients with insulin-dependent diabetes mellitus

BACKGROUND

We studied cardiopulmonary function during exercise in young subjects with long-standing insulin-dependent diabetes mellitus (IDDM) who have no clinical cardiopulmonary disease to determine the relationships of aerobic capacity, gas exchange, ventilatory power requirement, and cardiac output to chronic glycemic control.

METHODS

Eighteen subjects with IDDM and 14 normal control subjects were studied. Nine diabetic subjects received twice daily insulin injections and had chronically elevated levels of glycosylated hemoglobin (hyperglycemic group); 9 other diabetic subjects received insulin via continuous infusion pumps and maintained chronic near-normal levels of glycosylated hemoglobin (normoglycemic group). At the end of at least 7 years of regular follow-up, aerobic capacity was determined by cycle ergometry. Lung volume, diffusing capacity, and cardiac output during exercise were measured by a rebreathing technique. Ventilatory power was measured by the esophageal balloon technique.

RESULTS

Maximal work load and oxygen uptake were markedly impaired in chronically hyperglycemic diabetic patients associated with significant restrictions of lung volume, lung diffusing capacity, and stroke index during exercise. Membrane diffusing capacity was significantly reduced at a given cardiac index. The normoglycemic patients consistently showed less impairment than the hyperglycemic patients.

CONCLUSION

Physiologically significant cardiopulmonary dysfunction develops in asymptomatic patients with long-standing IDDM. Chronic maintenance of near-normoglycemia is associated with improved cardiopulmonary function.

Effect of disodium cromoglycate on ventilation and gas exchange during exercise in asthmatic children with a postexertion FEV1 fall less than 15 percent

The purpose of this study is to evaluate the effect of disodium cromoglycate (DSCG) on gas exchange and ventilation during incremental exercise in asthmatic children with an FEV1 fall less than 15 percent from the baseline after the exercise. Seventeen children (aged 8 to 14 years) with a history of mild to moderate asthma but no clinical and spirometric evidence of exercise-induced asthma (EIA) underwent two maximal exercise tests in a randomized order: test A without premidication and test B after inhalation of DSCG, 40 mg. To evaluate the effect of DSCG on normal airways, nine healthy children performed the same exercise protocol. Pulmonary function was normal at rest and after treadmill exercise test (the mean postexercise fall in FEV1 was 5.9 percent in test A and 1.5 percent in test B). Gas exchange, minute ventilation (VE) and heart rate (HR) were monitored during running in both tests. In the asthmatic subjects, there were no differences in oxygen uptake (VO2), carbon dioxide output (VCO2), and VE at rest between the two tests. During exercise, VE, VO2, VCO2, and energy cost (EC[O2 ml.kg-1.m-1]) of running in the asthmatic subjects were significantly lower in test B than in test A (analysis of variance, p < 0.01) for comparable work rates. Maximal minute ventilation (VEmax) was significantly higher in test A (46.9 +/- 14.6[+/- SD]L.min-1) than in test B (43.2 +/- 14 L. min-1; p < 0.05). We found no significant effect of DSCG on gas exchange and ventilation during exercise in the healthy children (VEmax 47.8 +/- 25 and 48.4 +/- 25 L.min-1 in test A and B, respectively). In conclusion, premedication with DSCG appears to decrease the ventilatory cost of exercise in asthmatic children who do not present a substantial fall in FEV1 after an exercise test without pretreatment.

Voluntary exercise improves glycemia in non-obese diabetic (NOD) mice

The non-obese diabetic (NOD) mouse was used to investigate the effects of voluntary wheel running exercise on blood glucose levels, glycosylated hemoglobin, and longevity in Type 1 diabetes mellitus. In Experiment 1, diabetic and normoglycemic mice exercised 5 h/day, 5 days/week for 3 weeks matched with non-exercising controls. In diabetic animals a positive correlation was found between blood glucose and the number of revolutions performed (P < or = 0.02). Exercise also significantly lowered blood glucose between baseline and post-exercise in both diabetic and normoglycemic animals. In Experiment 2, mice exercised 2 h/day, 5 days/week. For the diabetic animals, glycosylated hemoglobin was lower than that of matched non-exercising diabetic animals at week 3 (11.1 +/- 0.6% vs. 15.0 +/- 1.6%, P < 0.001). Diabetic runners were able to train and significantly increased running in the first 4 weeks (P < 0.05). At the end of 9 weeks all 5 diabetic runners were alive, compared with 3 of 5 non-running diabetic animals. We conclude: (i) the NOD mouse is a useful model for the study of exercise in Type 1 diabetes, (ii) running exercise is associated with a drop in blood glucose, (iii) the amount of voluntary exercise performed correlates with blood glucose in diabetic animals, and (iv) diabetic mice will increase running distance in the first few weeks after diagnosis.