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Hypoxic respiratory response during acute stable hypocapnia
Stephen Corne1, Kim Webster, Magdy Younes
1Department of Respiratory Medicine, University of Manitoba, Winnipeg, Manitoba, Canada. scorne@hsc.mb.ca
American Journal of Respiratory and Critical Care Medicine
|April 26, 2003
Summary
Hypocapnia significantly reduces the hypoxic ventilatory response. This blunts the body's reaction to low oxygen, increasing the risk of dangerous hypoxemia during apnea when carbon dioxide levels are low.
Area of Science:
- Physiology
- Respiratory Control
Background:
- The hypoxic ventilatory response (HVR) is crucial for maintaining oxygen levels.
- Previous studies on HVR during hypocapnia yielded conflicting results.
Purpose of the Study:
- To investigate the effect of stable hypocapnia on the HVR in spontaneously breathing individuals.
- To quantify changes in respiratory muscle pressure output and respiratory rate during hypoxia under varying levels of hypocapnia.
Main Methods:
- Utilized volume-cycled ventilation in healthy subjects.
- Assessed HVR at eucapnia and two levels of hypocapnia (mild and moderate) defined by end-tidal partial carbon dioxide pressure (PETCO2).
- Measured changes in muscle pressure output (Pmus) and respiratory rate in response to hypoxia.
Main Results:
- The HVR, measured by Pmus, was significantly attenuated during mild hypocapnia and negligible during moderate hypocapnia compared to eucapnia.
- Respiratory rate response to hypoxia also decreased significantly with increasing hypocapnia.
- At moderate hypocapnia, the HVR was not statistically different from zero.
Conclusions:
- Stable hypocapnia markedly diminishes the hypoxic ventilatory response.
- Individuals with low central carbon dioxide levels are at increased risk of severe hypoxemia due to a lack of HVR during apnea.