Effects of ambient temperature and altitude on ventilation and gas exchange in deer mice (Peromyscus maniculatus).

The effects of different ambient temperatures (Ta) on gas exchange and ventilation in deer mice (Peromyscus maniculatus) were determined after acclimation to low and high altitude (340 and 3,800 m). At both low and high altitude, oxygen consumption (VO2) decreased with increasing Ta at Ta from -10 to 30 degrees C. The VO2 was 15-20% smaller at high altitude than at low altitude at Ta below 30 degrees C. Increased VO2 at Ta below thermoneutrality was supported by increased minute volume (VI) at both low and high altitude. At most Ta, the change in VI was primarily a function of changing respiration frequency (f); relatively little change occurred in tidal volume (VT) or oxygen extraction efficiency (O2EE). At Ta = 0 degree C and below at high altitude, VI was constant due to declining VT and O2EE increased in order to maintain high VO2. At high altitude, VI (BTP) was 30-40% higher at a given Ta than at low altitude, except at Ta below 10 degrees C. The increased VI at high altitude was due primarily to a proportional increase in f, which attained mean values of 450-500 breaths/min at Ta below 0 degree C. The VI (STP) was equivalent at high and low altitude at Ta of 10 degrees C and above. At lower Ta, VI (STPD) was larger at low altitude. At both altitudes, respiratory heat loss was a small fraction (less than 10%) of metabolic heat production, except at high Ta (20-30 degrees C).