Oxygen Transport in Normobaric vs. Hypobaric Hypoxia
Condition: Hypoxia, Altitude; Exercise
MeSH terms: Altitude Sickness; Hypoxia
Study type: Interventional

Summary: 
      1) Oxygen Transport in Normobaric versus Hypobaric Hypoxia. 2) The purpose of this study is
      to examine acute responses in arterial and muscle tissue oxygenation during incremental
      exercise in normobaric versus hypobaric hypoxia. 3) The participants in this study will
      consist of 12 recreationally active males and females between the ages of 19 and
      45.Recreationally active is defined as participating in moderate to vigorous physical
      activity for 30 minutes at least 3 days per week.4) Subjects will complete an incremental
      cycle test to volitional fatigue in three conditions in a randomized counter-balanced order,
      normobaric normoxia (20.9% O2, 730 mmHg), normobaric hypoxia (14.3% O2, 730 mmHg) and
      hypobaric hypoxia (20.9% O2, 530mmHg). Two of the three trials will be conducted in an
      environmental chamber to simulate normobaric normoxia at 350 m (elevation of Omaha, NE) and
      normobaric hypoxia at 3094 m (elevation of Leadville, CO). The hypobaric hypoxia trial will
      be conducted in Leadville, Colorado at 3094 m. Trials will be separated by at least two days.
      Rating of perceived exertion, heart rate, blood oxygenation, respiration rate, muscle tissue
      oxygenation, and whole body gases will be analyzed during the trials. 5) There is no
      follow-up as a part of this study.
    

Detailed description: 
      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.
    

Intervention name(s): Hypoxia; Exercise
Intervention type(s): Other; Other
Intervention description(s): Participants will be exposed to hypoxia by reducing barometric pressure or by reducing oxygen concentration; Graded cycling exercise to volitional fatigue
Allocation: Randomized
Intervention model: Crossover Assignment
Intervention model description: Randomized,Counter Balanced, Repeated Measures, Crossover
Masking: None (Open Label)
Primary purpose: Basic Science