Oxygen Transport in Normobaric vs. Hypobaric Hypoxia

The specific objective of the study is to identify physiological differences between acute exposure to normobaric and hypobaric hypoxia.

The majority of well controlled research investigating the physiological effects of altitude have been conducted in chambers that create a hypoxic environment by reducing the fraction of oxygen in the environment (normobaric hypoxia). With actual altitude exposure, the fraction of oxygen remains constant but the barometric pressure providing the driving force for the binding of oxygen to hemoglobin is reduced (hypobaric hypoxia). Both circumstances should in theory lead to the same partial pressure of oxygen. Recent research has called the normobaric hypoxia model for altitude exposure into question and demonstrates that normobaric and hypobaric hypoxia may lead to differential physiological responses. Indeed, research from our lab has shown a higher heart rate and lower arterial oxygen saturation with hypobaric hypoxia compared to normobaric hypoxia. Others have also documented a further decrease in physical performance lower ventilatory response and pH, and higher oxidative stress in hypobaric hypoxia compared to normobaric hypoxia. The ability to interchange these methods of achieving a hypoxic environment is not without controversy. our lab has recently investigated the skeletal muscle transcriptional response after exposure to both normobaric and hypobaric hypoxia. The investigators found only limited differences in the muscle transcriptional response between the two forms of hypoxia despite differences in arterial oxygen saturation and heart rate. Clearly, more work is needed to determine the physiological aspects that may be differentially affected by normobaric and hypobaric hypoxia. This project will fill the knowledge gap of differences between forms of hypoxia in the resting and exercise response. Specifically, we will non-invasively determine the muscle oxygenation (NIRS) response that may help explain the lack of difference between the forms of hypoxia on the muscle transcriptional response. Furthermore, while heart rate has been shown to be differentially affected, no data currently exists on the variability of heart rate. It will determine the effects on heart rate variability (a marker of autonomic nervous system function and strong predictor of mortality). The addition of this data to the body of literature will have an impact on the physiological understanding of the effects of hypoxia and have major implications to the interpretation of previous research based on the experimental model used.