Aspects of nasal heat exchange in resting reindeer.

Abstract

SUMMARY1. Total respiratory heat loss (t.r.h.l.) in resting reindeer has been calculated from exhaled air temperature (Te) and respiratory minute volume (T) obtained during heat and cold stress in both summer and winter.2. Exhaled air temperature decreased with decreasing ambient temperature (Ta)in both summer and winter. The lowest T; recorded was +6 0C at a Ta of -45 0C in winter and the highest + 38 0C at a T. of + 29 0C in summer. At any T., Te was higher in winter than in summer. v was constant with increasing Ta up to + 25 0C and -10 0C in summer and winter, respectively. Further increase in Ta resulted in thermal tachypnea. During summer t.r.h.l. did not change significantly in the ambient temperature range from -25 to + 25 0C. In winter, however, t.r.h.l. increased linearly with increasing ambient temperature from -30 to + 15 'C. Minimum t.r.h.l. was found to coincide with the animals' lower critical temperature. 3. We suggest that the heat exchange in the upper respiratory tract of resting reindeer is actively regulated to attain fine tuning of thermal balance in this high arctic mammal undergoing great seasonal changes in fur insulation.

Adaptations to polar life in mammals and birds

“…Blix and Johnsen (1983) found that, at any given ambient temperature, the temperature of air expired by the reindeer is consistently lower in summer (when fur insulation is low) than in winter (when it is high). This implies that the animal is capable of adjusting the efficiency of the nasal heat exchange to maintain thermal balance along with the great seasonal changes in body insulation ( Fig.…”

“…Here, the nasal surfaces have developed into a highly convoluted mass, reminiscent of a car radiator, with an air space of <1 mm between the lamellae . This structure allows ∼65% of the heat and ∼80% of the water added to the inspired air to be regained on expiration at an ambient temperature of −25°C in both reindeer and seals (Blix and Johnsen, 1983;Blix, 1987, 1989).…”

“…The lower critical temperature and the total conductance of the animal, as determined in the laboratory, is a good indication of the thermal adaptation of the species, but cannot be taken as a measure of when the wild animal will reach its thermal limits. Wind and precipitation may drastically increase the conductance of the animal, and Øritsland and Ronald (1973), by contrast, have shown that solar radiation may significantly contribute to warming in harp Blix and Johnsen (1983). (C) A simplified diagram of arterial and venous vasculature of the left side of a reindeer head.…”

Regulation of nasal heat exchange in reindeer

“…On the other hand, when the animal is in a state of extreme heat dissipation (in a hot environment, or during running), respiratory minute volume will increase substantially (Blix and Johnsen, 1983). However, an increase in respiratory minute volume without circulatory adjustments, will result in a substantial decrease of nasal mucosal temperature and a subsequent reduction in expired air temperature, which would compromise the dissipation of heat bv way of the respiratory tract.…”

“…This mode of heat conservation, which is based on cooling of the expired air, and thereby condensation of water, particularly at low ambient temperatures, is possible because of the existence of a temperature gradient along the length of the nasal passages (Johnsen et ai, 1985a). Furthermore, Blix and Johnsen (1983) have shown that there is a summer to winter difference of about 12°C in exhaled air temperature at, for instance, -10°C ambient temperature, in these animals. At this ambient temperature respiratory minute volume and frequency were the same in summer and winter.…”