Ventilatory effects of prolonged systemic (CNS) hypoxia in awake goats

Hypoxia isolated to the carotid body (CB) can induce time-dependent progressive hyperventilation (ventilatory acclimatization) in the absence of brain hypoxia. The studies reported in this paper were designed to determine if CNS hypoxia in the absence of CB hypoxia would affect ventilation over a 4 h period. In addition, the effect of 4 h of CNS hypoxia on the ventilatory responses to central chemoreceptor stimulation and to isolated CB stimulation were also determined. The studies were carried out in awake goats with CB blood gases controlled by an extracorporeal circuit while systemic (CNS) blood gases were determined independently by the level of inhaled gases. Systemic arterial PO2 was reduced to 40 Torr while the CB was maintained normoxic and normocapnic. Systemic arterial PCO2 was kept isocapnic. The data obtained indicate that 4 h of CNS hypoxia produced mild hyperventilation that reached a peak after 30 min of hypoxia and was sustained for the entire period of hypoxia. There was no evidence of a time-dependent progressive hyperventilation, i.e. no acclimatization. In contrast to studies in which whole body hypoxia is induced, CNS hypoxia did not result in any changes in the ventilatory responses to either central or peripheral chemoreceptor stimulation after return to normoxic conditions. These findings suggest no significant role for CNS mechanisms induced by hypoxia in ventilatory acclimatization to hypoxia in goats.