Alveolar CO, during breath holding and exercise

their breath after breathing I oo y0 02, the PACES 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 demon-strate 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 Pcoz 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 COz, or at least the sensitivity is not decreased. breath holds on subsequent ones would be eliminated. At rest the subject sat quietly on the bicycle erogmeter. During active exercise the subject pedaled at a constan