Regulation of respiration in goat and its adaptation to chronic and life-long hypoxia

The effects of chronic and life-long hypoxia on the chemical regulation of ventilation was investigated in four groups of unanesthetized goats using conventional steady state techniques for determining the ventilatory response to hypercapnia at different levels of hypoxia. The results showed that in the goat, as in man, the effect of acute hypoxia on ventilation could be both independent of (additive), and dependent on (multiplicative), hypercapnia. Neither chronic hypoxia, nor life-long hypoxia at 5000 m modified the characteristic ventilatory response of sea level goats to acute hypoxia. However, in the goats maintained at 5000 m for 10 to 30 days, CO₂ sensitivity doubled and Pa_co2 threshold decreased by 8 mm Hg; concomitantly, arterial P_CO2 and [HCO^-₃] reached their nadirs within two days of exposure to altitude but increased gradually thereafter towards sea level values. A similar preservation of the sea level response was also shown in a goat which had life-long arterial hypoxia due to congenital cyanotic heart disease. Since the ventilatory responses to acute hypoxia and hypercapnia did not decrease as exposure to altitude was prolonged, the gradual return of theP_CO2 and [HCO^-₃] towards normal could not be attributed to hypoventilation. On the other hand because this increase in P_CO2 and [HCO^-₃] has not been observed in suborder other than ruminants, it may reflect heightened CO₂ production by the rumen of the goat at altitude, and/or increased absorption of CO₂ from the rumen into the blood during chronic hypoxia.