Influence of mild hypoxia on cardiorespiratory responses and muscle oxygenation during incremental exercise

pressure of arterial oxygen and has an influence on ventilatory, circulatory and metabolic processes during exercise; measuring the gas exchange has been used to study cardiorespiratory response under hypoxic conditions. Recently, muscle metabolism and oxygenation, as well as arterial oxygenation and cardiorespiratory action, are seen as being limited in healthy subjects under hypoxic conditions, and also under conditions of pulmonary patient induced hypoxemia. To assess muscle metabolism, muscle biopsy during resting and phosphorus magnetic resonance spectroscopy during exercise are often used and to assess muscle Introduction oxygenation; using arterial and venous blood sampling. However, this requires invasive techniques, which limits its application to physiological and clinical measurements. Recently, measurements using near infrared spectroscopy (NIRS) have made it possible to noninvasively measure in vivo changes in tissue of both oxygenated and deoxygenated hemoglobin and myoglobin. Although several incremental exercise experiments in hypoxic conditions have been reported5-7, 9, 10, 13, 15-17) , few investigations have been done in respect to the relationship between cardiorespiratory responses and oxygenation in exercising muscle during mild hypoxia. The purpose of this study was to determine the relationships among gas exchange responses, blood lactate concentrations, and NIRS responses during Influence of mild hypoxia on cardiorespiratory responses and muscle oxygenation during incremental exercise