Ventilatory inefficiency increases ventilatory demand; corresponds to an abnormal increase in the ratio of minute ventilation (V̇E) to CO2 production (V̇CO2); represents increased dead space, deregulation of respiratory control, and early lactic threshold; and is associated with expiratory flow limitation that enhances dynamic hyperinflation and may limit exercise capacity.
OBJECTIVE:
To evaluate the influence of ventilatory inefficiency over exercise capacity in COPD patients.
METHODS:
Prospective study of 35 COPD subjects with different levels of severity, in whom cardiopulmonary stress test was performed. Ventilatory inefficiency was represented by the V̇E/V̇CO2 relation. Its influence over maximal oxygen consumption (V̇O2max), power (W), and ventilatory threshold was evaluated. Surrogate parameters of cardiac function, like oxygen pulse (V̇O2/heart rate) and circulatory power (%V̇O2max × peak systolic pressure), were also evaluated.
RESULTS:
Cardiopulmonary stress test was stopped due to dyspnea with elevated V̇E and marked reduction of breathing reserve. A severe increase in V̇E/V̇CO2 (mean ± SD 35.9 ± 5.6), a decrease of V̇O2max (mean ± SD 75.2 ± 20%), and a decrease of W (mean ± SD 68.6 ± 23.3%) were demonstrated. Twenty-eight patients presented dynamic hyperinflation. Linear regression showed a reduction of 2.04% on V̇O2max (P < .001), 2.6% on W (P < .001), 1% on V̇O2/heart rate (P = .049), and 322.7 units on circulatory power (P = .02) per each unit of increment in V̇E/V̇CO2, respectively.
CONCLUSIONS:
Ventilatory inefficiency correlates with a reduction in exercise capacity in COPD patients. Including this parameter in the evaluation of exercise limitation in this patient population may mean a contribution toward the understanding of its pathophysiology.
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