PO2-ventilation response curve with normal pH and PCO2 in the dog.

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Abstract
Venti-latory response to hypoxia and hyperoxia was studied in anesthetized dogs with exclusion of secondary changes of CO2 and pH. The response was referred to both alveolar and arterial O2 pressure (PO2). The PO2-ventilation response curve in hypoxia showed a sigmoid course. The curve lay significantly above the usual normoxic level at an alveolar PO2 of 90-95 mm Hg and an arterial PO2 of 75-80 mm Hg. With increasing hypoxia it gradually rose, down to an alveolar PO2 of about 70 mm Hg and an arterial PO2 of some 60 mm Hg, then it became increasingly steeper, and finally reached a maximum at a PO2 of about 40 mm Hg. The PO2-ventilation response curve in hyperoxia clearly demonstrated the chemoreceptor activity in normoxia. The threshold PO2 for the chemoreflex drive seemed to lie at an alveolar PO2 of 170-180 mm Hg and an arterial PO2 of 130-140 mm Hg. The ventilatory response to normoxic drive was 30-40% of the resting level.