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A Model to Simulate Clinically Relevant Hypoxia in Humans
Published on: December 22, 2016
Aggravated hypoxia during breath-holds after prolonged exercise
Peter Lindholm1, Mikael Gennser
1Section of Environmental Physiology, Department of Physiology and Pharmacology, Karolinska Institutet, Berzelius väg 13, 17177 Stockholm, Sweden. peter.lindholm@fyfa.ki.se
European Journal of Applied Physiology
|March 22, 2005
Summary
Prolonged exercise before breath-hold diving, by increasing lipid metabolism, lowers carbon dioxide production. This leads to breath-holds ending sooner at lower oxygen levels, increasing blackout risk during swimming and diving.
Area of Science:
- Physiology
- Sports Science
- Diving Medicine
Background:
- Hyperventilation before breath-hold diving is known to increase syncope risk due to hypoxia.
- Near-drowning incidents involving swimmers who did not hyperventilate but engaged in prolonged exercise prior to breath-holding have been observed.
- Prolonged exercise shifts metabolism towards lipids, reducing carbon dioxide (CO2) production per oxygen (O2) consumed.
Purpose of the Study:
- To test the hypothesis that exercise-induced lipid metabolism and reduced CO2 production cause breath-holds to terminate at lower partial pressure of oxygen (PO2), increasing hypoxia-induced syncope risk.
- To investigate the impact of prolonged sub-maximal exercise on breath-hold duration and physiological parameters.
Main Methods:
- Eight experienced breath-hold divers participated in two conditions: control (rest) and post-prolonged exercise (PPE).
- Breath-holds were performed at rest and during dynamic apnoea (DA) with intermittent ergometer exercise.
- Subjects consumed a carbohydrate-free diet for 18 hours before PPE to deplete glycogen. Respiratory exchange ratio (RER), end-tidal CO2 (PCO2), PO2, and oxygen saturation (SaO2) were measured.
Main Results:
- The RER was significantly lower after PPE (0.70) compared to control (0.83), indicating increased lipid metabolism.
- Breath-hold duration during dynamic apnoea was similar in both conditions (96 seconds).
- However, PO2 and PCO2 were significantly lower at the end of breath-holds after PPE compared to control conditions (PO2: 6.2 vs 6.9 kPa; PCO2: 6.7 vs 7.8 kPa).
Conclusions:
- Breath-holding under conditions of low RER following prolonged exercise is terminated at a lower PO2 and PCO2.
- Elevated lipid metabolism due to prolonged exercise may be a risk factor for syncope during breath-holding activities like swimming and diving.
- These findings highlight a potential danger in breath-hold diving scenarios following strenuous physical activity.
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