Acute and daily effects of repeated voluntary hyperpnea on pulmonary function in healthy adults.

PURPOSE: Hyperpnea training has been used as a method for both improving exercise performance in healthy persons and improving ventilatory capacity in patients with pulmonary disease. However, voluntary hyperpnea causes acute declines in pulmonary function, but the effects of repeated days of hyperpnea on airway function are not known. The purpose of this study was to determine the effects of repeated normocapnic hyperpnea on daily and post-hyperpnea pulmonary function in healthy adults. METHODS: Ten healthy adults (21 years; 170 cm; 66 kg) completed ten hyperpnea training sessions within 17-days (TR). Training sessions consisted of 20-minutes of normocapnic hyperpnea with gradually increased minute ventilation over the 10 days. Spirometry was assessed at baseline and serially following hyperpnea during each experimental day. A control group (24 years; 171 cm; 66 kg) completed 10 days of spirometry with no hyperpnea training (CON). RESULTS: In both CON and TR subjects, baseline pulmonary function was unchanged during the 10 days. In TR subjects, pulmonary function was decreased at 5 mins after hyperpnea but thereafter increased to pre-hyperpnea values by 30 mins. Furthermore, these changes in pulmonary function were consistent during the 10 training days. In TR subjects, maximal voluntary ventilation decreased by 10.4 ± 8.9% (168-150 L min-1) over the 10 days (P < 0.05), whereas it was unchanged in CON subjects. CONCLUSIONS: These findings demonstrate that voluntary hyperpnea acutely decreases airway function in healthy subjects. However, there does not appear to be a cumulative effect of repeated hyperpnea, as daily pulmonary function was unchanged.

No effect of elevated operating lung volumes on airway function during variable workrate exercise in asthmatic humans.

In asthmatic adults, airway caliber fluctuates during variable intensity exercise such that bronchodilation (BD) occurs with increased workrate whereas bronchoconstriction (BC) occurs with decreased workrate. We hypothesized that increased lung mechanical stretch would prevent BC during such variable workrate exercise. Ten asthmatic and ten nonasthmatic subjects completed two exercise trials on a cycle ergometer. Both trials included a 28-min exercise bout consisting of alternating four min periods at workloads equal to 40 % (Low) and 70% (High) peak power output. During one trial, subjects breathed spontaneously throughout exercise (SVT), such that tidal volume (VT) and end-inspiratory lung volume (EILV) were increased by 0.5 and 0.6 liters during the high compared with the low workload in nonasthmatic and asthmatic subjects, respectively. During the second trial (MVT), VT and EILV were maintained constant when transitioning from the high to the low workload. Forced exhalations from total lung capacity were performed during each exercise workload. In asthmatic subjects, forced expiratory volume 1.0 s (FEV1.0) increased and decreased with the increases and decreases in workrate during both SVT (Low, 3.3 ± 0.3 liters; High, 3.6 ± 0.2 liters; P < 0.05) and MVT (Low, 3.3 ± 0.3 liters; High, 3.5 ± 0.2 liters; P < 0.05). Thus increased lung stretch during MVT did not prevent decreases in airway caliber when workload was reduced. We conclude that neural factors controlling airway smooth muscle (ASM) contractile activity during whole body exercise are more robust determinants of airway caliber than the ability of lung stretch to alter ASM actin-myosin binding and contraction.