Effects of Mild Hypobaric Hypoxia on Oxygen Saturation During Sleep

The Effects of Mild Hypobaric Hypoxia on Oxygen Saturation During Sleep: An Investigation of the Physiologic Mechanisms and Significance

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.

Study Overview

• Status: Completed
• Conditions: Sleep-related Respiratory Disturbance
• Intervention / Treatment: Other: Sea level equivalent barometric pressure; Other: Reduced barometric pressure

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.

• Study Type: Interventional
• Enrollment (Actual): 16
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Canada
  • British Columbia
    • Burnaby, British Columbia, Canada, V5A 1S6
      • Environmental Physiology Unit, School of Kinesiology, Simon Fraser University

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 30 years to 60 years (Adult)
• Accepts Healthy Volunteers: No
• Genders Eligible for Study: Male

Description

Inclusion Criteria:

• Male
• Between 30 and 60 years of age.
• Healthy, able to pass FAA Class III examination
• Body mass index less than 30
• Height less than 75 inches
• Ability to read and speak English

Exclusion Criteria:

• Prolonged residence above 5000 feet
• Recent travel to altitudes above 5000 feet
• Use of drugs or medications that affect sleep
• History of mood or psychiatric disorders that affect sleep.
• History of medical conditions that increase risk of adverse effects of hypoxia.
• Apnea hypopnea index greater than 15/hr at ground level.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: Double

Number of Arms

3

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Active Comparator: 1; Barometric pressure equivalent to sea level (760 mm Hg).	Other: Sea level equivalent barometric pressure; Sleep in barometric pressure equivalent to sea level.
Experimental: 2; Barometric pressure equivalent to 6000 feet (609 mm Hg)	Other: Reduced barometric pressure; Sleep in reduced barometric pressure environment.
Experimental: 3; Barometric pressure equivalent to 8000 feet (565 mm Hg).	Other: Reduced barometric pressure; Sleep in reduced barometric pressure environment.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Time Frame
SpO2	Continuous during sleep
Respiratory Disturbance	Continuous during sleep
Sleep architecture	Continuous during sleep

Secondary Outcome Measures

Outcome Measure	Time Frame
Heart rate variability	Continuous during sleep and 8 hr following exposure

Collaborators and Investigators

• Sponsor: The Boeing Company
• Collaborators: Simon Fraser University; Massey University
• Investigators: Principal Investigator: James M Muhm, MD, MPH, The Boeing Company

Study record dates

Study Major Dates

• Study Start: May 1, 2008
• Primary Completion (Actual): March 1, 2009
• Study Completion (Actual): March 1, 2009

Study Registration Dates

• First Submitted: April 14, 2008
• First Submitted That Met QC Criteria: April 15, 2008
• First Posted (Estimate): April 16, 2008

Study Record Updates

• Last Update Posted (Estimate): August 15, 2012
• Last Update Submitted That Met QC Criteria: August 14, 2012
• Last Verified: February 1, 2010

More Information

Terms related to this study

• Keywords: sleep; environmental; hypobaric hypoxia; respiratory-disturbance; neurobehavioral performance; Effect of altitude on sleep-related respiratory disturbance
• Additional Relevant MeSH Terms: Signs and Symptoms, Respiratory; Hypoxia
• Other Study ID Numbers: Boeing-003