Abstract
By observing phrenic nerve discharges in dogs, the threshold PCO2 (PTCO2) for the respiratory system was examined during the course of passive hyperventilation lasting for 4-8 hours.
1. The degree of hyperventilation was so strong as to decrease alveolar PCO2 to about 10mmHg.
2. The PTCO2 was lowered with lapse of time of hyperventilation. The regression line for the relationship between arterial (PTaCO2) and alveolar (PTACO2) PTCO2, and duration of hyperventilation in hour (H) were: PTaCO2=-1.4H+29.3, and PTACO2=-1.2H+28.7.
3. The regression line for relationship between arterial PCO2 and plasma bicarbonate ([BHCO3]) at the threshold condition was; PTaCO2=1.4 [BHCO3] T+3.3.
4. In spite of decreasing the PTCO2, arterial pH at the threshold condition was nearly kept constant.
