VENTILATORY RESPONSE TO OXYGEN AFTER EUCAPNIC HYPOXIA IN CONSCIOUS DOGS

In humans the ventilatory [minute ventilation (VI)] response to sustai ned hypoxia is biphasic: an initial brisk increase followed by a decli ne is usually seen. However, in adult dogs, the ventilatory response t o a similar stimulus shows no decline. To evaluate if central ventilat ory drive is altered by sustained hypoxia, we measured the lowest vent ilation (nadir) as the lowest moving average of seven sequential breat hs within 200 s after transition to hyperoxia (100% O2) after 3 differ ent. exposures: room air, 4-min (brief) eucapnic hypoxia (arterial O2 saturation = approximately 80%), and 12-min (prolonged) eucapnic hypox ia. The nadir hyperoxic VI after brief hypoxia (2.7 +/- 0.2 l/min) was similar to that after room air (2.6 +/- 0.2 l/min; P > 0.05), with bo th less than prior room air mean VI (P < 0.05). The nadir after prolon ged hypoxia (3.5 +/- 0.3 l/min) was significantly greater than that af ter brief hypoxia (P < 0.05). This suggests that central ventilatory d rive increases in conscious dogs after sustained eucapnic hypoxia. The reason for the difference in central ventilatory response to hypoxia between conscious dogs and adult humans is unexplained.