The effect of environmental temperature on respiratory ventilation in the pig

Abstract

Over the range of environmental temperatures 0–25°C tidal volume and minute volume increase as the temperature decreases in the 3-month-old pig. When oxygen consumption doubles in response to cold, the minute volume increases by only 40 % and there is a fall in the oxygen content of the expired air. Calculations of heat lost by evaporation suggest that the increase in the amount of oxygen extracted from the air represents a significant saving in evaporative heat loss. At high environmental temperatures, tidal volume falls to about a quarter of the value in the thermoneutral zone and frequency increases. Minute volume increases by a factor of 4 as body temperature increases to over 42°C. There is no secondary decline in respiratory frequency at high body temperatures as in some other species, but tidal volume increases slightly between body temperatures of 41.0 and 43.0°C. The oxygen cost of panting is estimated to be less than 17% of the total at a body temperature of 40.0 to 40.3°C.