Effects of various acute hypoxic conditions on metabolic parameters and cardiac function during exercise and recovery

Purpose: Evaluation of metabolic parameters and cardiac function is important to determine the decrease in aerobic exercise capacity under hypoxic conditions. However, the variations in metabolic parameters and cardiac function and the reasons for the decrease in aerobic exercise capacity under hypoxic conditions have not been clearly explained. The purpose of this study was to compare the responses between sea level and various acute normobaric hypoxic conditions on metabolic parameters and cardiac function during exercise and recovery in order to evaluate aerobic exercise capacity. Methods: Ten healthy male participants (21.3 +/- 3.06 y) performed submaximal bicycle exercise (116.7 +/- 20.1 W and 60 rpm) at sea level (20.9 % O-2) and under various normobaric hypoxic conditions (16.5 % O-2, 14.5 % O-2, 12.8 % O-2, and 11.2 % O-2) in a random order. Metabolic parameters (arterial oxygen saturation; SPO2, oxygen consumption; VO2, blood lactate level) and cardiac function (heart rate; HR, stroke volume; SV, end-systolic volume; ESV, end-diastolic volume; EDV, ejection fraction; EF, cardiac output; CO) were measured at rest, during exercise (30 min), and recovery (30 min). We compared the responses on metabolic parameters and cardiac function between the different oxygen partial pressure conditions during exercise and recovery. Results: The various acute normobaric hypoxic conditions did not affect VO2 and SV during exercise and recovery. SPO2 decreased (p < .05) and blood lactate level increased (p < .05) as the oxygen partial pressure decreased. HR, EF, CO increased (p < .05) and EDV, ESV decreased (p < .05) at oxygen partial pressures of 14.5 % O-2 and below compared with 20.9 and 16.5 % O-2 during exercise and recovery. Conclusion: A decrease in the oxygen partial pressure to 14.5 % O-2 and below might be associated with significant changes in metabolic parameters and cardiac function during exercise and recovery. These changes are an acute compensation response to reduced aerobic exercise capacity by decreased oxygen delivering and utilizing capacities under hypoxic conditions.