Effects of Mild Hypobaric Hypoxia on Oxygen Saturation During Sleep
Condition: Sleep-related Respiratory Disturbance
MeSH terms: Hypoxia
Study type: Interventional

Summary: 
      Ascent to altitude lowers oxygen saturation. In addition, sleep lowers oxygen saturation at
      any altitude. In a prior study, we observed that sleep at 8000 feet resulted in pronounced
      reduction in oxygen saturation, but did not result in reduced post sleep neurobehavioral
      performance or impaired sleep quality or quantity. We plan to do a more sophisticated
      physiological evaluation of the respiratory mechanisms responsible for the reduced oxygen
      saturation and determine if there are any adverse consequences to this level of intermittent
      hypoxia. We anticipate that central respiratory apnea is the physiologic mechanism, and that
      there will not be persistent changes in autonomic nervous activity measured by heart rate
      variability.
    

Detailed description: 
      This study has 6 primary objectives/hypotheses:

        1. Replicate findings of earlier study in which no effects of altitude were observed on
           post sleep neurobehavioral performance, sleep quantity or quality.

        2. Determine if sleep at 6000 feet has effects similar to sleep at 8000 feet.

        3. Identify if central or obstructive apnea is responsible for the reduction in oxygen
           saturation observed during sleep at 8000 feet.

        4. Determine if respiratory abnormalities observed at 6000 feet are similar but less severe
           than at 8000 feet.

        5. Determine if there are individual differences in respiratory physiology at sea level
           that enable prediction of pronounced respiratory disturbances during sleep at altitude.

        6. Determine if changes in autonomic nervous activity, measured by heart rate variability,
           occur, and if so, do they persist for 8 hours.

      Twenty healthy males between 30 and 60 years of age whose baseline apnea-hypopnea index is
      less than 15/hour will be recruited from the general population surrounding Burnaby, British
      Columbia, Canada. Women are excluded because of the changes in sleep structure associated
      with the menstrual cycle.

      Participants will be involved in the blinded crossover study for a 14 day period during which
      time they will monitor their sleep by actigraphy and sleep diaries, will spend 2 nights an
      altitude chamber at Simon Fraser University at ambient barometric pressure to become adapted
      to sleeping in that environment, then spend 3 study nights, each followed by 2 rest nights,
      sleeping at barometric pressures equivalent to sea level, 6000 feet, and 8000 feet. The order
      of exposures will be randomly balanced.

      Pre study physiologic measures will include hypoxic ventilatory response, hypercapnic
      ventilatory response, and during one of the adaptation nights, apnea hypoxia index. Study
      sessions will consist of a 4 hour presleep period, a 6 hour sleep period, and a 1 hour post
      sleep period at the study barometric pressure. During the study sessions, heart rate, SpO2,
      polysomnographic measures, nasal air flow rates, and chest motion will be monitored and
      recorded. Psychomotor Vigilance Task response time will be measured before and after the
      sleep period. Heart rate will be recorded by ambulatory recording equipment for 8 hours
      following return to ambient barometric pressure conditions. This will be analyzed to
      determine if changes in heart rate variability are persistent.

      Outcomes of primary interest will include total sleep time, duration of sleep stages, oxygen
      saturation, heart rate and heart rate variability, respiratory rates, air flow, and chest
      motion to assess if central or obstructive apnea is temporally related to reductions in
      oxygen saturation.
    

Intervention name(s): Reduced barometric pressure; Sea level equivalent barometric pressure; Reduced barometric pressure
Intervention type(s): Other; Other; Other
Intervention description(s): Sleep in reduced barometric pressure environment.; Sleep in barometric pressure equivalent to sea level.; Sleep in reduced barometric pressure environment.
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Double (Participant, Investigator)
Primary purpose: Basic Science
Keywords: environmental; hypobaric hypoxia; sleep; respiratory-disturbance; neurobehavioral performance; Effect of altitude on sleep-related respiratory disturbance