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

Abstract

PurposeEvaluation 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.MethodsTen 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 % O2) and under various normobaric hypoxic conditions (16.5 % O2, 14.5 % O2, 12.8 % O2, and 11.2 % O2) 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.ResultsThe 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 % O2 and below compared with 20.9 and 16.5 % O2 during exercise and recovery.ConclusionA decrease in the oxygen partial pressure to 14.5 % O2 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.

Effects of an Acute Pilates Program under Hypoxic Conditions on Vascular Endothelial Function in Pilates Participants: A Randomized Crossover Trial

“…Corroborating the results of Moon et al [31], we observed no significant difference in VO 2 between hypoxic and normoxic conditions during submaximal exercise; this is likely because the exercise intensity was fixed at a constant level across simulated environment conditions, resulting in the expenditure of same amount of energy. In addition, Hill et al [35] and Mazzeo [36] reported that the lack of difference in VO 2 during submaximal exercise between both environmental conditions is due to an increase in VE, HR, and CO because of acute hypoxic conditions.…”

“…Hypoxic conditions reduce arterial oxygen saturation, which is more affected during exercise due to increased pulmonary blood flow, which limits gas exchange at the alveoli [30]. Exercise under hypoxic conditions results in higher VE and HR than similar workloads performed under normoxic conditions; this finding might be attributed to the need to maintain O 2 perfusion [31]. However, these physiological adjustments are limited by the decrease in VO 2 max at high altitudes [32].…”

“…Replacement of the oxidation substrate from fatty acids to glucose at constant load exercise helps to maintain energy supply under hypoxic conditions because of greater energy yield per liter of O 2 consumed (carbohydrate = 5.05 kcal, fatty acid = 4.69 kcal) when glucose is fully oxidized compared to complete oxidation of fatty acids [34]. This shift in fuel selection indicates a higher relative exercise intensity under hypoxic conditions than that under normoxic conditions when the same absolute workload is performed [31,32]. Therefore, acute exercise under hypoxic conditions elicits an additional metabolic stress that the body must overcome to maintain energy supply within exercising muscles [29].…”

“…However, no significant difference between the values of VO 2 , SV, CO, EDV, ESV, and EF were observed during the Pilates program performed under hypoxic conditions and normoxic conditions. Moon et al [31] evaluated the effects of various acute hypoxic conditions (F i O 2 = 16.5%, 14,5%, 12.8%, and 11.2%) vs. normoxic conditions (F i O 2 = 20.9%) on metabolic parameters and cardiac function during constant load (116.7 ± 20.1 W and 60 rpm, 70% HRmax under normoxic conditions) submaximal bicycle exercise. They reported that acute exercise under hypoxic conditions (F i O 2 = 14.5% and below) might be associated with decreases in EDV and ESV and increases in blood lactate level, VE, HR, EF, and CO during submaximal exercise.…”

“…With respect to the cardiac function, EDV and ESV are major determinants of SV, and an increase in EDV and decrease in ESV result in an increase in ventricular contractility and SV [40]. Moon et al [31] reported that there was no significant difference between EDV values under the hypoxic and normoxic conditions and that ESV decreased to a greater degree under severe hypoxic conditions (FiO 2 = 12.8% and FiO 2 = 11.2%) than under normoxic conditions. They showed that these results were probably because of the activation of the sympathetic nervous system and alteration in the catecholamine level of the blood, which was triggered by increased levels of calcium ions in cardiac muscle cells during exercise under severe hypoxic conditions [41].…”