Effects of Acute Hypoxia and Hyperoxia on Oxygen Uptake, Brain and Muscle Oxygenation during Incremental Exercise

Abstract

Changes in inspired oxygen concentration will be affect the peak oxygen uptake compared with normoxia. These underlying mechanism are not fully understood, but central and peripheral mechanisms have been proposed. PURPOSE: Our study focuses on the effect of acute hypoxia and hyperoxia on oxygen uptake, brain and muscle oxygenation during exercise. METHODS: Eight healthy male subjects performed on incremental maximal exercise test (15W/min step) under normoxia (Norm: 20.9 FIO2), acute hypoxia (Hypox: 14.5% FIO2) and acute hyperoxia (Hyper: 28.0% FIO2) conditions. The order of each condition was randomized and trials were spaced by 5 days. We measured oxygen uptake (VO2 peak) on incremental exercise. Near-infrared spectroscopy (NIRS) was used to monitor concentration (μM) changes of oxy- and deoxyhemoglobin ([INCREMENT][O2Hb], [INCREMENT][HHb]) in left frontal cortex region of the forehead and ipsilateral vastus lateralis muscle. Changes in total Hb and StO2 were calculated ([INCREMENT][THb] = [INCREMENT][O2Hb] + [INCREMENT][HHb], [INCREMENT][StO2]) and used as index of change in regional blood volume. Repeated-measures ANOVA were performed across treatments. RESULTS: VO2 peak decreased in Hypox (38.6±4.0ml/kg/min, p>0.05) and slightly increased in Hyper (45.2±7.5ml/kg/min) compered with Norm (43.3±5.9ml/kg/min). Muscle oxygenation dropped progressively during Hypox (decrease [INCREMENT][O2Hb]; −1.79±0.61μM and [INCREMENT]StO2; −19.55±3.86%, increase [INCREMENT][HHb]; 3.37±0.96μM at 100% Powerpeak), and also changes in muscle oxygenation during Hyper (decrease [INCREMENT][O2Hb]; −1.26±0.76μM and [INCREMENT]StO2; −16.30±5.13%, increase [INCREMENT][HHb]; 2.96±1.06μM at 100% Powerpeak) were similar to Norm (decrease [INCREMENT][O2Hb]; −1.35±0.76μM and [INCREMENT]StO2; −16.17±5.30%, increase [INCREMENT][HHb]; 3.01±1.35μM at 100% Powerpeak). Interestingly, Brain oxygenation ([INCREMENT][O2Hb]) was slightly increased and deoxygenation ([INCREMENT][HHb]) was increased during exercise under each three conditions, respectively. Furthermore, changes brain and muscle oxygenation was also greater in Hypox compared with Norm and Hyper (p>0.05). CONCLUSIONS: Acute hypoxia decrease oxygen uptake with decreased muscle oxygenation and slightly increased brain oxygenation. But it is unlikely that changes in brain and muscle oxygenation was relate with oxygen uptake in hyperoxia, despite a similar change absolute PO2 from hypoxia and/or hyperoxia to normoxia.