Ventilatory response to exercise in diabetic subjects with autonomic neuropathy

Distinct effects of type 2 diabetes and obesity on cardiopulmonary performance

AIM

Effort intolerance is frequent in patients with overweight/obesity and/or type 2 diabetes (T2D) free from cardiac and respiratory disease. We sought to quantify the independent effects of T2D and body mass index (BMI) on cardiopulmonary capacity and gain insights on the possible pathophysiology by case-control and regression analyses.

METHODS

Patients at high/moderate cardiovascular risk, with or without T2D, underwent spirometry and combined echocardiography-cardiopulmonary exercise test as part of their clinical workup. Subjects with evidence of cardiopulmonary disease were excluded. The effects of T2D and obesity were estimated by multivariable models accounting for known/potential confounders and the major pathophysiological determinants of oxygen uptake at peak exercise (VO2peak ) normalized for fat-free mass (FFM).

RESULTS

In total, 109 patients with T2D and 97 controls were included in the analysis. The two groups had similar demographic and anthropometric characteristics except for higher BMI in T2D (28.6 ± 4.6 vs. 26.3 ± 4.4 kg/m2 , p = .0003) but comparable FFM. Patients with T2D achieved lower VO2peak than controls (18.5 ± 4.4 vs. 21.7 ± 8.3 ml/min/kg, p = .0006). Subclinical cardiovascular dysfunctions were observed in T2D: concentric left ventricular remodelling, autonomic dysfunction, systolic dysfunction and reduced systolic reserve. After accounting for confounders and major determinants of VO2peakFFM , T2D still displayed reduced VO2peak by 1.0 (-1.7/-0.3) ml/min/kgFFM , p = .0089, while the effect of BMI [-0.2 (-0.3/0.1) ml/min/kgFFM , p = .06 per unit increase], was largely explained by a combination of chronotropic incompetence, reduced peripheral oxygen extraction, impaired systolic reserve and ventilatory (in)efficiency.

CONCLUSIONS

T2D is an independent negative determinant of VO2peak whose effect is additive to other pathophysiological determinants of oxygen uptake, including BMI.

Exercise training affects hemodynamics and exercise capacity in cases of heart failure with preserved ejection fraction: a non-randomized controlled trial in individuals aged 65-80 years

Introduction

Exercise training is an established intervention method for improving exercise capacity and survival rates in patients with heart failure with preserved ejection fraction (HFpEF). However, most reports have focused on European and American patients, with limited data regarding the effects of exercise training on cardiac function, hemodynamics, and exercise capacity in East Asian patients. This study investigated the effects of exercise training on cardiac function, hemodynamics, and exercise capacity in Japanese patients aged 65-80 years with HFpEF.

Methods

This single-center, open-label, non-randomized, controlled trial prospectively enrolled 99 outpatients. Eligibility criteria for HFpEF patients were an HFA score ≥5 in addition to clinical symptoms of heart failure and left ventricular diastolic dysfunction. Exercise training in the intervention group consisted of aerobic exercise and strength training thrice weekly for 5 months. Patients in the control group continued the usual treatment for 5 months. Resting cardiac function was evaluated using echocardiography. Peak oxygen uptake (peakVO2), ventilatory equivalent (VE) vs. carbon dioxide output (VCO2) slope, peak cardiac output index, and arteriovenous oxygen difference were calculated using cardiopulmonary exercise testing combined with impedance cardiography.

Results

After 5 months of exercise training, remarkable interactions were observed, with peakVO2 as the primary outcome. Additionally, significant interactions were observed between hemodynamic indices and some echocardiographic parameters. The mean percentage change in peakVO2 from baseline was 8.3% in the intervention group. Fifteen study participants (30.1%) in the intervention group achieved a clinically meaningful change of 3.0 ml/min/kg (10% improvement) in peakVO2 from baseline. The group with 3.0 ml/min/kg or 10% improvement in peakVO2 from baseline had a considerably lower prevalence of diabetes mellitus and VE vs. VCO2 slope and considerably higher left atrial-global longitudinal strain values than the group without any notable improvements.

Conclusions

Although exercise training can help improve exercise intolerance in Japanese patients aged 65-80 years with HFpEF, its benefits are limited. Our results suggest that HFpEF, complicated by diabetes mellitus and decreased ventilatory efficiency during exercise, may require reconsideration of intervention strategies. This trial was registered with the University Hospital Medical Information Network, a trial registry in Japan (registration number: UMIN000045474).

Effects of comorbid type II diabetes mellitus and heart failure on rat hindlimb and respiratory muscle blood flow during treadmill exercise

In rats with type II diabetes mellitus (T2DM) compared with nondiabetic healthy controls, muscle blood flow (Q̇m) to primarily glycolytic hindlimb muscles and the diaphragm muscle are elevated during submaximal treadmill running consequent to lower skeletal muscle mass, a finding that held even when muscle mass was normalized to body mass. In rats with heart failure with reduced ejection fraction (HF-rEF) compared with healthy controls, hindlimb Q̇m was lower, whereas diaphragm Q̇m is elevated during submaximal treadmill running. Importantly, T2DM is the most common comorbidity present in patients with HF-rEF, but the effect of concurrent T2DM and HF-rEF on limb and respiratory Q̇m during exercise is unknown. We hypothesized that during treadmill running (20 m·min-1; 10% incline), hindlimb and diaphragm Q̇m would be higher in T2DM Goto-Kakizaki rats with HF-rEF (i.e., HF-rEF + T2DM) compared with nondiabetic Wistar rats with HF-rEF. Ejection fractions were not different between groups (HF-rEF: 30 ± 5; HF-rEF + T2DM: 28 ± 8%; P = 0.617), whereas blood glucose was higher in HF-rEF + T2DM (209 ± 150 mg/dL) compared with HF-rEF rats (113 ± 28 mg/dL; P = 0.040). Hindlimb muscle mass normalized to body mass was lower in rats with HF-rEF + T2DM (36.3 ± 1.6 mg/g) than in nondiabetic HF-rEF counterparts (40.3 ± 2.7 mg/g; P < 0.001). During exercise, Q̇m was elevated in rats with HF-rEF + T2DM compared with nondiabetic counterparts to the hindlimb (HF-rEF: 100 ± 28; HF-rEF + T2DM: 139 ± 23 mL·min-1·100 g-1; P < 0.001) and diaphragm (HF-rEF: 177 ± 66; HF-rEF + T2DM: 215 ± 93 mL·min-1·100g-1; P = 0.035). These data suggest that the pathophysiological consequences of T2DM on hindlimb and diaphragm Q̇m during treadmill running in the GK rat persist even in the presence of HF-rEF.NEW & NOTEWORTHY Herein, we demonstrate that rats comorbid with heart failure with reduced ejection fraction (HF-rEF) and type II diabetes mellitus (T2DM) have a higher hindlimb and respiratory muscle blood flow during submaximal treadmill running (20 m·min-1; 10% incline) compared with nondiabetic HF-rEF counterparts. These data may carry important clinical implications for roughly half of all patients with HF-rEF who present with T2DM.

Differential control of respiratory frequency and tidal volume during exercise

The lack of a testable model explaining how ventilation is regulated in different exercise conditions has been repeatedly acknowledged in the field of exercise physiology. Yet, this issue contrasts with the abundance of insightful findings produced over the last century and calls for the adoption of new integrative perspectives. In this review, we provide a methodological approach supporting the importance of producing a set of evidence by evaluating different studies together-especially those conducted in 'real' exercise conditions-instead of single studies separately. We show how the collective assessment of findings from three domains and three levels of observation support the development of a simple model of ventilatory control which proves to be effective in different exercise protocols, populations and experimental interventions. The main feature of the model is the differential control of respiratory frequency (f_R) and tidal volume (V_T); f_R is primarily modulated by central command (especially during high-intensity exercise) and muscle afferent feedback (especially during moderate exercise) whereas V_T by metabolic inputs. Furthermore, V_T appears to be fine-tuned based on f_R levels to match alveolar ventilation with metabolic requirements in different intensity domains, and even at a breath-by-breath level. This model reconciles the classical neuro-humoral theory with apparently contrasting findings by leveraging on the emerging control properties of the behavioural (i.e. f_R) and metabolic (i.e. V_T) components of minute ventilation. The integrative approach presented is expected to help in the design and interpretation of future studies on the control of f_R and V_T during exercise.

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.

Impaired Ventilatory Efficiency, Dyspnea and Exercise Intolerance in Chronic Obstructive Pulmonary Disease: Results from the CanCOLD Study

RATIONALE

Impaired exercise ventilatory efficiency (high ventilatory requirements for CO2 [V̇E/V̇CO2]) provides an indication of pulmonary gas exchange abnormalities in chronic obstructive pulmonary disease (COPD).

OBJECTIVES

To determine: 1) the association between high V̇E/V̇CO2 and clinical outcomes (dyspnea and exercise capacity) and its relationship to lung function and structural radiographic abnormalities; and 2) its prevalence in a large population-based cohort.

METHODS

Participants were recruited randomly from the population and underwent clinical evaluation, pulmonary function, cardiopulmonary exercise testing and chest computed tomography (CT). Impaired exercise ventilatory efficiency was defined by a nadir V̇E/V̇CO2 above the upper limit of normal (V̇E/V̇CO2>ULN), using population-based normative values.

MEASUREMENTS AND MAIN RESULTS

Participants included 445 never-smokers, 381 ever-smokers without airflow obstruction, 224 with GOLD 1 COPD, and 200 with GOLD 2-4 COPD. Participants with V̇E/V̇CO2>ULN were more likely to have activity-related dyspnea (Medical Research Council dyspnea scale≥2, odds ratio=1.77[1.31-2.39]) and abnormally low peak oxygen uptake (V̇O2peak<LLN, odds ratio=4.58[3.06-6.86]). The carbon monoxide transfer coefficient (KCO) had a stronger correlation with nadir V̇E/V̇CO2 (r=-0.38, p<0.001) than other relevant lung function and CT metrics. The prevalence of V̇E/V̇CO2>ULN was 24% in COPD (similar in GOLD 1 and 2-4), which was greater than in never-smokers (13%) and ever-smokers (12%).

CONCLUSIONS

V̇E/V̇CO2>ULN was associated with greater dyspnea and low VO2peak and was present in 24% of all participants with COPD, regardless of GOLD stage. The results show the importance of recognizing impaired exercise ventilatory efficiency as a potential contributor to dyspnea and exercise limitation, even in mild COPD.

Type 2 diabetes and reduced exercise tolerance: a review of the literature through an integrated physiology approach

The association between type 2 diabetes mellitus (T2DM) and heart failure (HF) is well established. Early in the course of the diabetic disease, some degree of impaired exercise capacity (a powerful marker of health status with prognostic value) can be frequently highlighted in otherwise asymptomatic T2DM subjects. However, the literature is quite heterogeneous, and the underlying pathophysiologic mechanisms are far from clear. Imaging-cardiopulmonary exercise testing (CPET) is a non-invasive, provocative test providing a multi-variable assessment of pulmonary, cardiovascular, muscular, and cellular oxidative systems during exercise, capable of offering unique integrated pathophysiological information. With this review we aimed at defying the cardiorespiratory alterations revealed through imaging-CPET that appear specific of T2DM subjects without overt cardiovascular or pulmonary disease. In synthesis, there is compelling evidence indicating a reduction of peak workload, peak oxygen assumption, oxygen pulse, as well as ventilatory efficiency. On the contrary, evidence remains inconclusive about reduced peripheral oxygen extraction, impaired heart rate adjustment, and lower anaerobic threshold, compared to non-diabetic subjects. Based on the multiparametric evaluation provided by imaging-CPET, a dissection and a hierarchy of the underlying mechanisms can be obtained. Here we propose four possible integrated pathophysiological mechanisms, namely myocardiogenic, myogenic, vasculogenic and neurogenic. While each hypothesis alone can potentially explain the majority of the CPET alterations observed, seemingly different combinations exist in any given subject. Finally, a discussion on the effects -and on the physiological mechanisms-of physical activity and exercise training on oxygen uptake in T2DM subjects is also offered. The understanding of the early alterations in the cardiopulmonary response that are specific of T2DM would allow the early identification of those at a higher risk of developing HF and possibly help to understand the pathophysiological link between T2DM and HF.

Type II diabetes accentuates diaphragm blood flow increases during submaximal exercise in the rat

We investigated the effect of type 2 diabetes mellitus (T2DM) on respiratory muscle blood flow (BF) during exercise. Using the Goto-Kakizaki (GK) rat model of T2DM, we hypothesized that diaphragm, intercostal and transverse abdominis BFs (radiolabeled microspheres) would be higher in male GK rats (n = 10) compared to healthy male Wistar controls (CON; n = 8) during submaximal exercise (20 m/min, 10 % grade). Blood glucose was significantly higher in GK (246 ± 29 mg/dL) compared to CON (103 ± 4 mg/dL; P < 0.01). Respiratory muscle BFs were not different at rest (P> 0.50). From rest to submaximal exercise, respiratory muscle BFs increased in both groups to all muscles (P < 0.01). During submaximal exercise GK rats had higher diaphragm BFs (GK: 189 ± 13; CON: 138 ± 14 mL/min/100 g, P < 0.01), and vascular conductance (GK: 1.4 ± 0.1; CON: 1.0 ± 0.1 mL/min/mmHg/100 g; P < 0.01) compared to CON. There were no differences in intercostal or transverse abdominis BF or VC during exercise (P> 0.15). These findings suggest that submaximal exercise requires a higher diaphragm BF and VC in T2DM compared to healthy counterparts.

Pulmonary Function and Sleep Breathing: Two New Targets for Type 2 Diabetes Care

Population-based studies showing the negative impact of type 2 diabetes (T2D) on lung function are overviewed. Among the well-recognized pathophysiological mechanisms, the metabolic pathways related to insulin resistance (IR), low-grade chronic inflammation, leptin resistance, microvascular damage, and autonomic neuropathy are emphasized. Histopathological changes are exposed, and findings reported from experimental models are clearly differentiated from those described in humans. The accelerated decline in pulmonary function that appears in patients with cystic fibrosis (CF) with related abnormalities of glucose tolerance and diabetes is considered as an example to further investigate the relationship between T2D and the lung. Furthermore, a possible causal link between antihyperglycemic therapies and pulmonary function is examined. T2D similarly affects breathing during sleep, becoming an independent risk factor for higher rates of sleep apnea, leading to nocturnal hypoxemia and daytime sleepiness. Therefore, the impact of T2D on sleep breathing and its influence on sleep architecture is analyzed. Finally, the effect of improving some pathophysiological mechanisms, primarily IR and inflammation, as well as the optimization of blood glucose control on sleep breathing is evaluated. In summary, the lung should be considered by those providing care for people with diabetes and raise the central issue of whether the normalization of glucose levels can improve pulmonary function and ameliorate sleep-disordered breathing. Therefore, patients with T2D should be considered a vulnerable group for pulmonary dysfunction. However, further research aimed at elucidating how to screen for the lung impairment in the population with diabetes in a cost-effective manner is needed.

Differential Patterns of Impaired Cardiorespiratory Fitness and Cardiac Autonomic Dysfunction in Recently Diagnosed Type 1 and Type 2 Diabetes

OBJECTIVE

Both impaired cardiorespiratory fitness (CRF) and heart rate variability (HRV) are predictors of mortality, but their relative roles in recent-onset diabetes are unknown. We determined to which extent CRF and HRV are reduced and interrelated in recent-onset diabetes.

RESEARCH DESIGN AND METHODS

Participants from the German Diabetes Study with type 1 (n = 163) or type 2 (n = 188) diabetes with known diabetes duration <1 year and two age-matched glucose-tolerant control groups (n = 40 each) underwent spiroergometry and HRV assessment during a hyperinsulinemic-euglycemic clamp.

RESULTS

Compared with control subjects, patients with type 2 diabetes showed reduced VO_2max (median [1st-3rd quartiles] 19.3 [16.5-22.9] vs. 25.6 [20.7-29.9] mL/kg body weight/min; P < 0.05), diminished VCO_2max (23.0 [19.1-26.8] vs. 30.9 [24.5-34.4] mL/kg body weight/min; P < 0.05), blunted heart rate recovery after 2 min (-29.0 [-35.0 to -23.0] vs. -36.0 [-42.8 to -28.0] beats/min; P < 0.05), and reduced HRV in four of nine indices, whereas patients with type 1 diabetes had unaltered CRF but reduced HRV in three of nine indices (P < 0.05), indicating diminished vagal and sympathetic HRV modulation. HRV measures correlated with VO_2max in patients with type 1 diabetes (r >0.34; P < 0.05) but not in those with type 2 diabetes.

CONCLUSIONS

CRF is reduced in recently diagnosed type 2 diabetes but preserved in type 1 diabetes, whereas cardiac autonomic function is reduced in both diabetes types but is strongly associated with CRF only in type 1 diabetes. These results support the therapeutic concept of promoting physical fitness in the early course of diabetes.

Cardiorespiratory fitness, pulmonary function and C-reactive protein levels in nonsmoking individuals with diabetes

The objective of this study was to evaluate cardiorespiratory fitness and pulmonary function and the relationship with metabolic variables and C-reactive protein (CRP) plasma levels in individuals with diabetes mellitus (DM). Nineteen men with diabetes and 19 age- and gender-matched control subjects were studied. All individuals were given incremental cardiopulmonary exercise and pulmonary function tests. In the exercise test, maximal workload (158.3±22.3 vs 135.1±25.2, P=0.005), peak heart rate (HR_peak: 149±12 vs 139±10, P=0.009), peak oxygen uptake (VO_2peak: 24.2±3.2 vs 18.9±2.8, P<0.001), and anaerobic threshold (VO_2VT: 14.1±3.4 vs 12.2±2.2, P=0.04) were significantly lower in individuals with diabetes than in control subjects. Pulmonary function test parameters, blood pressure, lipid profile (triglycerides, HDL, LDL, and total cholesterol), and CRP plasma levels were not different in control subjects and individuals with DM. No correlations were observed between hemoglobin A1C (HbA1c), CRP and pulmonary function test and cardiopulmonary exercise test performance. In conclusion, the results demonstrate that nonsmoking individuals with DM have decreased cardiorespiratory fitness that is not correlated with resting pulmonary function parameters, HbA1c, and CRP plasma levels.

Impact of Obstructive Sleep Apnoea on Type 2 Diabetes and Vice Versa

Type 2 diabetes and obstructive sleep apnoea (OSA) are diseases with high prevalence and major public health impact. There is evidence that OSA is independently associated with alterations in glucose metabolism. Furthermore, OSA is a significant risk factor for the development of type 2 diabetes. Possible causes might be intermittent hypoxaemia and sleep fragmentation with increased oxidative stress and sympathetic activity, which are typical features of OSA. OSA might also be a reason for ineffective treatment of type 2 diabetes. There is further evidence that the treatment of OSA by continuous positive airway pressure (CPAP) therapy might improve glucose metabolism. On the other hand, there are also hints in the literature that type 2 diabetes might induce sleep apnoea, especially in patients with autonomic neuropathy, but that OSA also facilitates the development of neuropathy in terms of mutual interactions between OSA, type 2 diabetes and diabetic neuropathy. Based on the current scientific data, clinicians have to be aware of the relations between OSA and type 2 diabetes, both from the sleep medical and the diabetological point of view.

Alveolar gas exchange and tissue deoxygenation during exercise in type 1 diabetes patients and healthy controls

We used near-infrared spectroscopy to investigate whether leg and arm skeletal muscle and cerebral deoxygenation differ during incremental cycling exercise in men with type 1 diabetes (T1D, n=10, mean±SD age 33±7 years) and healthy control men (matched by age, anthrometry, and self-reported physical activity, CON, n=10, 32±7 years) to seek an explanation for lower aerobic capacity (˙VO2peak) often reported in T1D. T1D had lower ˙VO2peak (35±4mlkg(-1)min(-1) vs. 43±8mlkg(-1)min(-1), P<0.01) and peak work rate (219±33W vs. 290±44W, P<0.001) than CON. Leg muscle deoxygenation (↑ [deoxyhemoglobin]; ↓ tissue saturation index) was greater in T1D than CON at a given absolute submaximal work rate, but not at peak exercise, while arm muscle and cerebral deoxygenation were similar. Thus, in T1D compared with CON, faster leg muscle deoxygenation suggests limited circulatory ability to increase O(2) delivery as a plausible explanation for lower ˙VO2peak and earlier fatigue in T1D.

Obstructive sleep apnea and type 2 diabetes

Type 2 diabetes and obstructive sleep apnea (OSA) are diseases with high prevalence and major public health impact. There is evidence that regular snoring and OSA are independently associated with alterations in glucose metabolism. Thus, OSA might be a risk factor for the development of type 2 diabetes. Possible causes might be intermittent hypoxia and sleep fragmentation, which are typical features of OSA. OSA might also be a reason of ineffective treatment of type 2 diabetes. There is further evidence that the treatment of OSA by continuous positive airway pressure (CPAP) therapy might correct metabolic abnormalities in glucose metabolism. It is assumed that this depends on therapy compliance to CPAP. On the other hand, there are also hints in the literature that type 2 diabetes per se might induce sleep apnea, especially in patients with autonomic neuropathy. Pathophysiological considerations open up new insights into that problem. Based on the current scientific data, clinicians have to be aware of the relations between the two diseases, both from the sleep medical and the diabetological point of view. The paper summarizes the most important issues concerning the different associations of OSA and type 2 diabetes.

Effects of beta-blockers on ventilation efficiency in heart failure

BACKGROUND

Hyperventilation and consequent reduction of ventilation (VE) efficiency are frequently observed during exercise in heart failure (HF) patients, resulting in an increased slope of VE/carbon dioxide (VE/Vco(2)) relationship. The latter is an independent predictor of HF prognosis. beta-Blockers improve the prognosis of HF patients. We evaluated the effect on the efficiency of VE of a beta(1)-beta(2) unselective (carvedilol) versus a beta(1) selective (bisoprolol) beta-blocker.

METHODS

We analyzed consecutive maximal cardiopulmonary exercise tests performed on 572 clinically stable HF patients (New York Heart Association class I-III, left ventricle ejection fraction < or =50%) categorized in 3 groups: 81 were not treated with beta-blocker, 304 were treated with carvedilol, and 187 were treated with bisoprolol. Clinical conditions were similar.

RESULTS

The VE/Vco(2) slope was lower in carvedilol- compared with bisoprolol-treated patients (29.7 +/- 0.4 vs 31.6 +/- 0.5, P = .023, peak oxygen consumption adjusted) and with patients not receiving beta-blockers (31.6 +/- 0.7, P = .036). Maximum end-tidal CO(2) pressure during the isocapnic buffering period was higher in patients treated with carvedilol (39.0 +/- 0.3 mm Hg) than with bisoprolol (37.2 +/- 0.4 mm Hg, P < .001) and in patients not receiving beta-blockers (37.2 +/- 0.5 mm Hg, P = .001).

CONCLUSIONS

Reduction of hyperventilation, with improvement of VE efficiency during exercise (reduction of VE/Vco(2) slope and increase of maximum end-tidal CO(2) pressure), is specific to carvedilol (beta(1)-beta(2) unselective blocker) and not to bisoprolol (beta(1)-selective blocker).

Pulmonary complications in diabetes mellitus

Clear decrements in lung function have been reported in patients with diabetes over the past two decades, and many reports have suggested plausible pathophysiological mechanisms. However, there are no reports of functional limitations of activities of daily living ascribable to pulmonary disease in patients with diabetes. This review attempts to summarize the available information from the present literature, to describe the nature of the lung dysfunction in diabetes and the emerging clinical implications of such dysfunction.

Decline of neuroadrenergic bronchial innervation and respiratory function in type 1 diabetes mellitus: a longitudinal study

BACKGROUND AND AIM

Type 1 diabetes mellitus complicated by autonomic neuropathy (AN) is characterized by depressed cholinergic bronchomotor tone and neuroadrenergic denervation of the lung. We explored the effects of AN on the rate of decline of pulmonary sympathetic innervation and respiratory function during a 5-year follow-up.

METHODS

Twenty diabetic patients, 11 with AN, were enrolled in 1998 and then followed-up until 2003. During follow-up, glycosylated haemoglobin (HbA1c) was measured every 3 months. In 1998 and 2003 the patients underwent respiratory function tests and a ventilatory scintigraphic study of neuroadrenergic bronchial innervation using 123I-MIBG.

RESULTS

During follow-up 4 patients, all with AN, were lost, and 1 developed AN. Forced vital capacity (FVC), and diffusing capacity of the lung for carbon monoxide (DLCO) showed comparable rates of decrease in patients with and without AN. The yearly decline of forced expiratory volume in 1 s (FEV1) was about double the physiologic rate, in both AN and AN-free patients. The MIBG clearance significantly increased both in patients with AN (T1/2: 118.88 +/- 30.14 min at baseline and 92.10 +/- 24.52 min at the end of follow-up) and without AN (135.14 +/- 17.09 min and 92.68 +/- 13.52 min, respectively), indicating a rapidly progressive neuroadrenergic denervation. The rate of the neuroadrenergic denervation was inversely related to the severity of autonomic dysfunction at baseline (Spearman's rho - 0.62, p = 0.017). Neither respiratory function indexes nor MIBG clearance changes correlated with the overall HbA1c values.

CONCLUSIONS

Neuroadrenergic denervation of the lung parallels the decline of respiratory function indexes in diabetic patients both with and without AN and seems to be independent from the quality of glycemic control.

Use of heart rate reserve and rating of perceived exertion to prescribe exercise intensity in diabetic autonomic neuropathy

OBJECTIVE

Individuals with diabetic autonomic neuropathy (DAN) exhibit an increased resting heart rate but depressed maximal heart rate. Thus, the purpose of this study was to examine the validity of using either percent of heart rate reserve (HRR) or a rating of perceived exertion (RPE) scale to prescribe exercise intensity in diabetic individuals both with and without DAN.

RESEARCH DESIGN AND METHODS

The subjects consisted of 23 individuals with type 2 diabetes, ages 45-75 years, with (DAN; n = 13) or without (No DAN; n = 10) clinical signs of DAN, as assessed by heart rate variability using the expiration-to-inspiration ratio of the R-R interval. Peak aerobic capacity was determined using a graded protocol on a cycle ergometer, with RPE, heart rate, and VO(2) values recorded at each stage.

RESULTS

The subjects were similar with the exception of depressed autonomic function in DAN subjects. Peak respiratory exchange ratio values were significantly higher (P < 0.05) in the DAN group (1.08 +/- 0.02 vs. 1.02 +/- 0.01 in No DAN subjects), although DAN subjects exhibited a significantly lower (P < 0.05) peak exercise heart rate. A similarly highly linear relationship between %HRR and percent VO(2) reserve (VO(2)R) existed for both groups (r = 0.98). A similar slightly weaker relationship (r = 0.94) was found between RPE and %VO(2)R.

CONCLUSIONS

In conclusion, in diabetic individuals, %HRR provides an accurate prediction of %VO(2)R and can be used to prescribe and monitor exercise intensity, regardless of the presence of DAN. The RPE scale is also a valid, albeit slightly less accurate, method to monitor exercise intensity in diabetic individuals.

Respiratory muscle function and hypoxic ventilatory control in patients with type I diabetes

STUDY OBJECTIVES

The interaction among pulmonary mechanics, respiratory muscle performance, and ventilatory control in subjects with insulin-dependent diabetes mellitus has so far received little attention. We therefore decided to assess the role of central factors and peripheral factors on the ventilatory response to a hypoxic stimulus in type I diabetic patients.

SUBJECTS

Eight patients in stable condition aged 19 to 48 years old, with insulin-dependent diabetes mellitus (duration of the disease, 36 to 240 months) and no history of smoking, cardiopulmonary involvement, or autonomic neuropathy; and an age- and gender-matched control group.

MEASUREMENTS

In each patient, we measured the following: pulmonary volumes; diffusing capacity of the lung for carbon monoxide (D(LCO)); time and volume components of ventilation (tidal volume [V(T)] and respiratory frequency); static compliance (Clstat) and dynamic compliance (Cldyn); swings in pleural pressure (Pes) and gastric pressure (Pg); and transdiaphragmatic pressure (Pdi), obtained by subtracting Pes from Pg. Maximal inspiratory Pes and Pdi during a maximal sniff maneuver were also measured. Swings in Pes and Pdi during V(T) as a percentage of Pes and Pdi during the maximal sniff maneuver [Pessw(%Pessn) and Pdisw(%Pdisn), respectively] were both considered as a measure of central respiratory output, and the Pessw(%Pessn)/V(T) ratio was considered as an index of neuroventilatory dissociation (NVD) of the inspiratory pump. Subjects were studied at baseline and during hypoxic rebreathing.

RESULTS

Pulmonary volumes and D(LCO) were normal or slightly reduced. A lower Cldyn, higher central respiratory output, and NVD were found. During hypoxic rebreathing, patients had lower V(T), similar central respiratory output, and greater NVD per unit change in arterial oxygen saturation compared with values in control subjects. An increase in dynamic elastance, computed as 1/Cldyn, during hypoxia was found in patients, but not in normal subjects, and was directly related to concurrent changes in NVD.

CONCLUSIONS

We have shown that the assessment of a normal Clstat and normal routine parameters of airway obstruction does not permit the definite exclusion of the role of peripheral airway involvement in insulin-dependent diabetes mellitus. Peripheral airway involvement is likely to influence indices of hypoxic ventilator) drive by modulating a normal central motor output into a rapid and shallow pattern of ventilatory response.

Ventilatory control during exercise in normal children

We investigated the relation between age and respiratory control during exercise in 80 children aged 6.4-17.6 y (42 male, age, 11.6 +/- 3.3 y; body weight, 41.3 +/- 14.7 kg; and 38 female, age, 12.6 +/- 2.7 y; body weight, 42.5 +/- 9.3 kg). Exercise tests were performed on a treadmill after a standard symptom-limited Bruce protocol. Data were analyzed separately for boys and girls. At rest and at peak exercise, the ratio of minute ventilation to carbon dioxide production (VE/VCO2), the ratio of effective alveolar ventilation to carbon dioxide production (VA/VCO2), the ratio of pulmonary dead space to tidal volume (Vd/Vt), and arterial PCO2 (PaCO2) were not correlated with age. At the exercise intensity of ventilatory anaerobic threshold, the PaCO2 increased, and the VA/VCO2 decreased, significantly with age, whereas the Vd/Vt was not related to age. Linear regression analysis demonstrated that the slope of the relationship between VE and VCO2 (deltaVE/deltaVCO2) and the slope of the relationship between VA and VCO2 (deltaVA/deltaVCO2) decreased with age. There were no gender differences in the regression slopes and the intercepts of the relationships. Results show that younger children breathe more during exercise to eliminate a given amount of CO2 to keep PaCO2 set point slightly but significantly lower than older children. This age dependence must be considered in investigating ventilatory control during exercise in children.