Cardiopulmonary Responses, Brain And Muscle Oxygenation During Incremental Exercise On Acute Hypoxia And Hyperoxia

Abstract

Changes in inspired oxygen concentration will be affect the peak oxygen uptake compared with normoxia. These underlying mechanism are not fully understood, but peripheral and central mechanisms have been proposed. PURPOSE: Our study focuses on the effect of acute moderate hypoxia and hyperoxia on cardiopulmonary responses, brain and muscle oxygenation during exercise. METHODS: Seven healthy male subjects performed on incremental maximal exercise test under normoxia (Norm: 20.9 FIO2), hypoxia (Hypo: 14.5% FIO2) and hyperoxia (Hyper: 28.5% FIO2) conditions. We measured cardiopulmonary measurements (VE, VO2, HR and Q) and blood gas (PO2 and PCO2) on incremental exercise. Near-infrared spectroscopy (NIRS) was also 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 and used as index of change in regional blood volume. Repeated-measures ANOVA were performed across treatments. RESULTS: VO2 peak decreased in Hypo (38.5±3.1 ml/kg/min, p<0.05) and no difference in Hyper (42.6±3.4 ml/kg/min) compered with Norm (42.2±3.9 ml/kg/min). But blood PO2 at rest and moderate exercise was low in Hypo (57.7±3.1 and 52.2±5.4 mmHg, p<0.05) and high in Hyper (98.6±8.8 and 105.3±9.3 mmHg, p<0.05) compared with Norm (79.3±12.6 and 84.3±4.7 mmHg). Muscle oxygenation dropped progressively during Hypo, and also changes in muscle oxygenation during Hyper were similar to Norm. 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 Hypo 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 related with oxygen uptake in hyperoxia, despite a similar difference absolute PO2 in inspired oxygen and blood from hypoxia and/or hyperoxia to normoxia.