Cardiorespiratory Responses to Voluntary Hyperventilation During Normobaric Hypoxia

Alexander Haddon, Joel Kanhai, Onalenna Nako, Thomas G Smith, Peter D Hodkinson, Ross D Pollock

Research output: Contribution to journalArticlepeer-review


BACKGROUND: Unexplained physiological events (PE), possibly related to hypoxia and hyperventilation, are a concern for some air forces. Physiological monitoring could aid research into PEs, with measurement of arterial oxygen saturation (S po 2) often suggested despite potential limitations in its use. Given similar physiological responses to hypoxia and hyperventilation, the present study characterized the cardiovascular and respiratory responses to each. METHODS: T en healthy subjects were exposed to 55 mins of normobaric hypoxia simulating altitudes of 0, 8000, and 12,000 ft (0, 2438, and 3658 m) while breathing normally and voluntarily hyperventilating (doubling minute ventilation). Respiratory gas analysis and spirometry measured end-tidal gases (P ETo 2 and P ETo 2) and minute ventilation. S po 2 was assessed using finger pulse oximetry. Mean arterial, systolic, and diastolic blood pressure were measured noninvasively. Cognitive impairment was assessed using the Stroop test. RESULTS: Voluntary hyperventilation resulted in a doubling of minute ventilation and lowered P ETo 2, while altitude had no effect on these. PET o2 and S po 2 declined with increasing altitude. However, despite a significant drop in PET o2 of 15.2 mmHg from 8000 to 12,000 ft, S po 2 was similar when hyperventilating (94.7 ± 2.3% vs. 93.4 ± 4.3%, respectively). The only cardiovascular response was an increase in heart rate while hyperventilating. Altitude had no effect on cognitive impairment, but hyperventilation did. DISCUSSION: For many cardiovascular and respiratory variables, there is minimal difference in responses to hypoxia and hyperventilation, making these challenging to differentiate.

Original languageEnglish
Pages (from-to)59-65
Number of pages7
JournalAerospace medicine and human performance
Issue number2
Publication statusPublished - 1 Feb 2023


  • Humans
  • Carbon Dioxide
  • Hyperventilation
  • Hypoxia
  • Oximetry
  • Altitude


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