Magnitude of Ventilatory Reserve at Exhaustion

Abstract

The purpose of this study was to determine the maximal level of ventilation that could be obtained in normal individuals exercising with dead space and to determine whether this level of ventilation is best predicted by a short-term or a sustained measurement of maximum voluntary ventilation (MVV) or by spirometry. Four maximal incremental (50 W/min) cycle exercise tests were performed by each of seven subjects (FEV1/FVC = 82%), in a randomized single blind fashion, with measurement of the volume of expired gas and end-tidal PCO2 (PETCO2, mm Hg). Testing was performed at baseline (BL), and with 1L, 2L, and 3L of added dead space (DS) in order to load the respiratory system. Actual ventilatory reserve was defined as the difference between the maximum exercise ventilation (e) at BL and the greatest ventilation at exhaustion elicited with DS loading (eDS-eBL). Each subject also performed a “sprint” 10 second MVV (MVVlOs) and a “sustained” 4 minute MVV (MVV 4m). The actual mean ventilatory reserve for the group was 38 ± 27 L. The mean maximal ventilation during exercise with dead space (eDS = 165 L/min) was closest to the FEV1 ± 35 (160 L/min) while the MVV 10s overestimated (198 L/min) and the MVV 4m (140 L/min) underestimated the eDS. However, when linear regression analysis using the eDS as the dependent variable was performed, the eDS was more closely correlated with the MVV 10s (r = 0.88, S.E.E. = 11.4) than it was with the MVV 4m (r = 0.67, S.E.E. = 17.9) or the FEV1 (r = 0.68, S.E.E. = 17.8). From this study the authors conclude that a sprint MVV maneuver is a better predictor of actual ventilatory capacity at exhaustion than is a sustained MVV maneuver or spirometry.