No abstract

Both continuous and interval exercise training program improves exercise capacity in CHF patients. However, continuous rather than interval exercise training improves early HRR1, a marker of parasympathetic activity, suggesting a greater contribution to the autonomic nervous system.

Background: Patients who suffer from obstructive sleep apnea (OSA) have a decreased exercise capacity and abnormal autonomic nervous function. However, the kinetics of early oxygen (O 2 ) and heart rate recovery (HRR) have not been described. Materials and Methods:We evaluated 21 men with moderate to severe OSA (mean age: 48 ± 11 yrs, mean apnea-hypopnea index [AHI]: 55 ± 13) and without known heart disease and 10 healthy men matched for age and body mass index (BMI; controls). Men with OSA underwent overnight polysomnography, and both groups underwent symptom-limited incremental cardiopulmonary exercise testing (CPET). We recorded the CPET parameters including peak O 2 uptake (VO 2 p), kinetics of early O 2 recovery by the first degree slope of VO 2 during the first minute (VO 2 /t slope), the time required for a 50% decline of VO 2 p during recovery (T 1/2 ), and early heart rate recovery (HRR = HR at maximal exercise − HR at 1 min of recovery), as well as the chronotropic reserve to exercise ([CR] = [peak HR − resting HR/220 − age − resting HR] × 100). Patients with OSA had a lower VO 2 p (28.7 ± 4.0 vs 34.7 ± 6.2 mL/kg/min), VO 2 /t slope (1.04 ± 0.3 vs 1.4 ± 0.17 mL/kg/min 2 ), and T 1/2 (74 ± 10 vs 56 ± 6 sec) compared to controls (all P < 0.001). In addition, both HRR and CR were lower in the OSA group (22.0 ± 7.0 vs 31.0 ± 6.0 bpm,P:0.003, and 79.0% ± 15% vs 99.0% ± 13.0%, P:0.01, respectively). Conclusions: Patients with OSA demonstrate reduced exercise capacity, delayed oxygen kinetics, and reduced HRR. These data point to abnormal oxygen delivery and/or oxidative function of the peripheral muscles and impaired autonomic nervous activity in OSA patients.

Background: Patients with chronic heart failure (CHF) present with exercise-induced hyperpnea, but its pathophysiological mechanism has not been thoroughly investigated. We aimed to determine the relationship between exercise-induced hyperpnea, resting haemodynamic measurements and the validity of ventilatory response (V E /V CO 2 slope) as a mortality predictor in CHF patients. Methods: Ninety-eight CHF patients (90M/8F) underwent a symptom-limited treadmill cardiopulmonary exercise test (CPET). Right heart catheterization and radionuclide ventriculography were performed within 72 h of CPET. Results: Twenty-seven patients died from cardiac causes during 20 T 6 months follow-up. Non-survivors had a lower peak oxygen consumption (V O 2 p), (16.5 T 4.9 vs. 20.2 T 6.1, ml/kg/min, p = 0.003), a steeper V E /V CO 2 slope (34.8 T 8.3 vs. 28.9 T 4.8, p < 0.001) and a higher pulmonary capillary wedge pressure (PCWP) (19.5 T 8.6 vs. 11.7 T 6.5 mm Hg, p = 0.008) than survivors. By multivariate survival analysis, the V E /V CO 2 slope as a continuous variable was an independent prognostic factor (v 2 : 8.5, relative risk: 1.1, 95% CI: 1.03 -1.18, p = 0.004). Overall mortality was 52% in patients with V E /V CO 2 slope ! 34 and 18% in those with V E /V CO 2 slope < 34 (log rank: 18.5, p < 0.001). In a subgroup of patients (V O 2 p: 10 -18 ml/kg/min), V E /V CO 2 slope was a significant predictor of mortality (relative risk: 6.2, 95% CI: 1.7 -22.2, p = 0.002). Patients with high V E /V CO 2 slope had higher resting PCWP (19.9 T 9.1 vs. 11.3 T 5.7 mmHg, p < 0.001) and V E /V CO 2 slope correlated significantly with PCWP (r: 0.57, p < 0.001). Conclusions:The V E /V CO 2 slope, as an index of ventilatory response to exercise, improves the risk stratification of CHF patients. Interstitial pulmonary oedema may be a pathophysiological mechanism of inefficient ventilation during exercise in these patients. Abbreviations: AT, oxygen consumption at the anaerobic threshold exercise level; BMI, body mass index; BR, breathing reserve; CI, cardiac index; CHF, congestive heart failure; DL CO , carbon monoxide lung diffusing capacity; ECG, electrocardiogram; FEV 1 , forced expired volume in 1 s; FVC, forced vital capacity; LVEF, left ventricular ejection fraction; NYHA, New York Heart Association; PAP, mean pulmonary artery pressure; PCWP, pulmonary capillary wedge pressure; RAP, right atrial pressure; V CO 2 , carbon dioxide output; V E , expired minute ventilation; V Ep , peak minute ventilation over the last 20 s of exercise; V E /V CO 2 , regression slope relating V E and V CO 2 from exercise onset to anaerobic threshold; V O 2 , oxygen uptake; V O 2 p, average oxygen consumption over the last 20 s of exercise; AUC, area under curve; ROC, receiver operator characteristic.

Both continuous and interval exercise training program improves exercise capacity in CHF patients. However, continuous rather than interval exercise training improves early HRR1, a marker of parasympathetic activity, suggesting a greater contribution to the autonomic nervous system.