Lack of long-term facilitation of ventilation after exposure to hypoxia in goats.

Episodic hypoxia has been shown to induce augmented normoxic ventilatory drive or long-term facilitation (LTF, continued hyperventilation after termination of hypoxic stimulation) in awake dogs and awake goats. The main objective of these experiments was to examine whether continuous isocapnic hypoxia in awake goats elicits LTF and additionally, to determine if goats exhibit hypoxic ventilatory decline (roll-off) during the hypoxic exposure. Goats were exposed to either 4 h of isocapnic hypoxia (n = 10) or 30 min of isocapnic hypoxia (n = 7). Ventilation (VE), tidal volume and frequency were measured before, during and following the end of the isocapnic hypoxia (PaO2 40 Torr) exposure. During the 4 h period of hypoxia, VE increased in a time-dependent manner in a typical pattern of acclimatization, reaching a mean of 40.8 +/- 3.6 L/min at the end of 4 h. Five minutes after return to normoxia, VE was 13.0 +/- 0.8 L/min, not different than control VE (13.1 +/- 0.9 L/min) measured prior to the hypoxic exposure and remained unchanged from this value for another 30 min. During the 30 min hypoxic exposure, VE increased upon exposure to hypoxia, remained significantly elevated throughout the hypoxic exposure, but promptly returned to control levels upon return to normoxia. These results indicate that continuous isocapnic hypoxia elicits neither long term facilitation of ventilation nor hypoxic ventilatory decline in awake goats.