Long description

This figure shows graphically the pattern of change in peripheral blood flow, evaporative water loss and oxygen consumption (a measure of BMR) with change in ambient temperature. The area of the graph is divided into three regions: cold environment, thermoneutral zone and hot environment. Point A, the lower limit of the thermoneutral zone, is labelled 'lower critical temperature'; and point C, the upper limit of the thermoneutral zone, is labelled 'upper critical temperature'. In a cold environment, peripheral blood flow and evaporative water loss (both of which result in heat loss) are low and constant; while BMR is initially high but decreases with increase in temperature. Within the thermoneutral zone, BMR stays at a constant low level while peripheral blood flow climbs steadily. Evaporative water loss is low and constant until the temperature marked B, which is between A and C near the upper limit of the thermoneutral zone. The region from A to B is identified as the zone of least thermoregulatory effort, for beyond B, evaporative water loss begins to increase. In the hot environment, all three parameters increase with increase in temperature.