Ventilatory responses to CO 2, and hypoxia in the two-toed sloth Choloepus Hoffmanni

Abstract

Sloths are unusual in that they have a low metabolic rate, a low body temperature and a low rate of secretion of thyroxine in comparison with most other mammals. Since it is known that any one of these features, if induced in a characteristic mammal, results in some altered state of the ventilatory control system, and its responses to hypoxic and/or hypercapnic stimuli, the sloth was studied in order to determine whether its control of breathing was in any way unusual. Two mature animals, one female and one male, were studied on many occasions, under unanesthetized and unrestrained conditions, and under graded CO 2, hypoxic, and asphyxie states. There was considerable day-to-day variation, and the two sloths had generally different responses, but when compared with other species, their responses were well within the range of typical mammals. In its normal resting position, as studied, the sloth has certain decerebrate characteristics, and this feature, as well as other aspects of neuro-muscular function, are discussed in terms of the respiratory patterns observed.