Repeated Ischemic Preconditioning Effects on Physiological Responses to Hypoxic Exercise

Abstract

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 in severe hypoxia. The aim of the current study was toevaluate the effects of 7 d of IPC on resting and exercising muscle and cardio-pulmonary responses to severe hypoxia.METHODS: A total of 14 subjects received either: 1) 7 d of repeated lower-limb occlusion (4 × 5 min, 217 ± 30 mmHg) at limbocclusive pressure (IPC) or SHAM (4 × 5 min, 20 mmHg). Subjects were tested for resting limb blood flow, relativemicrovascular deoxyhemoglobin concentration ([HHB]), and pulmonary oxygen (V·o2p) responses to steady state andincremental exercise to exhaustion in hypoxia (fractional inspired O2 = 0.103), which was followed by 7 d of IPC or SHAMand retesting 72 h post-intervention.RESULTS: T here were no effects of IPC on maximal oxygen consumption, time to exhaustion during the incremental test, orminute ventilation and arterial oxygen saturation. However, the IPC group had higher delta efficiency based on pooledresults and lower steady state Δ[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: C ollectively, these results demonstrate that muscle O2efficiency and microvascular O2 distribution can be improved byrepeated IPC, but there are no effects on maximal exercise capacity in severe hypoxia