Irregular breathing in young lambs and newborn infants during heat stress.

Ten healthy unanaesthetized full-term lambs, aged 4-12 days, were studied during moderate radiant heat stress, and 21 full-term newborn infants were studied during moderate convective heat stress. The rate of breathing and the breathing pattern were recorded, using strain gauges made of mercury-filled rubber tubing placed around the thorax and abdomen. In both the lambs and the infants the respiratory rate increased during heat stress. When this increase began, both the lambs and infants had short periods of very rapid breathing followed by short apnoeas. The concentrations of carbon dioxide and water in a flow-through system collecting expired air increased during the short periods of rapid breathing and then decreased again during the subsequent short apnoeic period.