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Reduced arterial O2 saturation during supine exercise in highly trained cyclists
P K Pedersen1, H Mandøe, K Jensen
1Department of Sports Science, Odense University, Denmark.
Acta Physiologica Scandinavica
|December 1, 1996
Summary
Intense exercise in athletes reduces oxygen saturation (SaO2) and partial pressure of oxygen (PaO2). Changing from upright to supine positions did not alter this arterial oxygen desaturation during maximal exercise.
Area of Science:
- Exercise Physiology
- Respiratory Physiology
- Sports Medicine
Background:
- Elite athletes often experience reduced arterial oxygen saturation (SaO2) and partial pressure of oxygen (PaO2) during intense dynamic exercise.
- The impact of body position on these physiological responses during maximal exertion is not fully understood.
Purpose of the Study:
- To investigate whether supine exercise, compared to upright exercise, results in a smaller reduction in SaO2 in elite athletes.
- To examine the influence of body position on maximal oxygen uptake (VO2max), ventilation, and arterial blood gases during exhaustive exercise.
Main Methods:
- Eight elite bicyclists performed incremental cycle ergometry to exhaustion in both upright and supine positions.
- Measurements included ventilatory data, arterial blood gases (PaO2, SaO2, PCO2), and pH.
- Maximal oxygen uptake (VO2max) was determined for each condition.
Main Results:
- VO2max was significantly lower (10.6%) during supine cycling compared to upright cycling.
- Maximal pulmonary and alveolar ventilation were reduced in the supine position, primarily due to a lower tidal volume.
- Despite these differences, arterial oxygen saturation (SaO2) and partial pressure of oxygen (PaO2) decreased similarly from rest to exhaustion in both positions.
- The alveolar-arterial oxygen difference increased significantly in both postures, indicating impaired gas exchange.
Conclusions:
- Altering body position from upright to supine does not prevent or reduce arterial oxygen desaturation during intense exercise in elite athletes.
- The hypothesis that supine exercise would lead to a smaller SaO2 reduction due to lower VO2max or improved ventilation-perfusion distribution was not supported.
- Gas exchange impairment, evidenced by the increased alveolar-arterial oxygen difference, occurs similarly in both upright and supine positions during maximal exertion.