Repeated Ischemic Preconditioning Effects on Physiological Responses to Hypoxic Exercise

Introduction Repeated ischemic preconditioning (IPC) can improve muscle and pulmonary oxygen on-kinetics, blood flow and exercise efficiency but these effects have not been investigated severe hypoxia. The aim of the current study was to evaluate the effects of 7 d of IPC on resting and exercising muscle and cardio-pulmonary responses to severe hypoxia. Methods Fourteen subjects received either: 1) 7 d of repeated lower-limb occlusion (4 x 5 min, 217±30 mm Hg) at limb occlusive pressure (IPC) or SHAM (4 x 5 min, 20 mm Hg). Subjects were tested for resting limb blood flow (72), relative microvascular deoxyhemoglobin concentration ([HHB]) and pulmonary oxygen (V ̇O2p) responses to steady state and incremental exercise to exhaustion in hypoxia (fractional inspired O2 = 0.103), which was followed by 7 d of IPC or SHAM, and retesting 72 h post intervention. Results There were no effects of IPC on maximal oxygen consumption, time to exhaustion during the incremental test or minute ventilation and arterial oxygen saturation. However, the IPC group had higher delta efficiency based on pooled results and lower steady state delta[HHB] (IPC ~24% vs. SHAM ~6% pre-to-post), as well as slowing the [HHB] time constant (IPC ~26% vs. SHAM ~3% pre-to-post) and reducing the overshoot in [HHB]:V ̇O2 ratio during exercise onset. Conclusions Collectively, these results demonstrate that muscle O2 efficiency and microvascular O2 distribution can be improved by repeated IPC but there are no effects on maximal exercise capacity in a severe hypoxia.