Interaction of hypoxia and vascular occlusion on cardiorespiratory responses during exercise

BackgroundThe interaction of group III/IV afferents and chemoreflex during exercise is critical in healthy adults during high altitude exercise or in clinical populations who experience hypoxia. PurposeInvestigate the cardiorespiratory response to simultaneous vascular occlusion (to activate group III/IV afferents) and hypoxia (to activate chemoreflex) during cycling exercise. Methods18 adults (9 women, 25 5 years) attended two sessions. Session 1: maximal cycle ergometry test. Session 2: two 26-minute bouts (randomized between hypoxia, 12.5% FiO(2) and normoxia, 21% FiO(2)). Participants cycled at 30% of peak workload for 3 minutes (control, CTL) followed by alternating 2 minute periods of bilateral vascular occlusion of the proximal thigh at pressures of 20, 40, 60, 80, 100 mm Hg in a randomized sequence. ResultsVentilation (V-E) increased from CTL to 100 mm Hg during hypoxia (39 +/- 9 to 51 +/- 16 L/min) and normoxia (31 +/- 7 to 39 +/- 9 L/min, P < 0.01). Respiratory rate increased with vascular occlusion (P < 0.05) but not hypoxia (P = 0.10). Tidal volume was greater during hypoxia (P < 0.05), with no influence of vascular occlusion (P = 0.40). Mean arterial pressure and heart rate increased more with hypoxia compared with normoxia (P < 0.05). ConclusionsOur findings suggest that vascular occlusion and hypoxia both increase V-E, albeit via different mechanisms. While hypoxia increased tidal volume, vascular occlusion increased respiratory rate.