Bronchodilator effect on ventilatory, pulmonary gas exchange, and heart rate kinetics during high-intensity exercise in COPD

Abstract

Respiratory mechanical abnormalities in patients with chronic obstructive pulmonary disease (COPD) may impair cardiodynamic responses and convective oxygen delivery during exercise, resulting in slower ventilatory, pulmonary gas exchange (PGE), and heart rate (HR) kinetics compared with normal. We reasoned that bronchodilators and the attendant reduction of operating lung volumes should accelerate ventilatory, PGE, and HR kinetics in the transition from rest to high-intensity exercise. Twelve clinically stable COPD patients undertook constant-work rate cycle testing at 75% of each individual's maximum work capacity after receiving either combined nebulized bronchodilators (BD) or placebo (PL), randomly. Mean response time (MRT) and amplitude of slow component for oxygen uptake (V'O(2)), carbon dioxide production (V'CO(2)), ventilation (V'(E)), and HR together with operating dynamic end-expiratory lung volume (EELV) were measured. Resting and exercise EELV decreased significantly by 0.38 L after BD compared with PL. After BD, V'O(2), V'CO(2), V'(E), and HR MRT accelerated (p < 0.05) by an average of 12, 22, 27, and 22 s, respectively (i.e., 15, 18, 22 and 27%, respectively). The slow component for V'O(2) declined by an average of 55 ml/min compared with PL. Speeded MRT for V'O(2) correlated with indices of reduced lung hyperinflation, such as resting EELV (r = -0.64, p = 0.025) and EELV at isotime (r = -0.77, p = 0.0032). The results confirm an important interaction between abnormal dynamic respiratory mechanics and indices of cardio-circulatory function in the rest-to-exercise transition in COPD patients.