Alveolar CO₂ during breath holding and exercise

¹ Department of Physiology, University of Rochester School of Medicine and Dentistry, Rochester, New York

When 12 healthy adult male subjects held their breath after breathing 100% O₂, the Pa_COCO2, at the breaking point was higher when they exercised than when they were at rest. Attention was not a factor, and passive exercise did not produce a result different from rest. By repeated breath-holding experiments at different work loads it was possible to demonstrate a systematic error due to the sampling site, the alveolar air. When this error was examined quantitatively, it was found that there is probably no difference in the Pco₂ at some critical sensing site at the breaking point under the different conditions of voluntary apnea. Our results imply that exercise may not change the sensitivity to CO₂, or at least the sensitivity is not decreased.