Respiratory function during thermal tachypnoea in sheep

1. Four Merino wethers were exposed to dry bulb temperatures ranging from approximately 20 to 60 degrees C, and the concurrent changes in respiratory frequency, tidal volume, respiratory minute volume, alveolar ventilation, dead space ventilation, carbon dioxide output, rectal temperature, and arterial and mixed venous blood, CO(2) content, CO(2) partial pressure and pH were established.2. The respiratory response to heat exposure showed two phases. Respiratory minute volume was initially increased by a rise in the respiratory frequency, while tidal volume decreased. After more prolonged exposure there was a second phase in which respiratory minute volume was further increased by an increase in the tidal volume; respiratory frequency was now slower than in the first phase but was still well above control values.3. The increase in respiratory minute volume during the first phase of the response was restricted almost entirely to the respiratory dead space; changes in blood CO(2) and pH were slight. In the second phase, respiratory minute volume showed a much greater increase, and a change of alveolar ventilation to about 5 times the control level resulted in severe respiratory alkalosis.4. Contrary to findings in cattle, the slower, deeper form of respiration could be elicited even with rectal temperature in the normal range. This change in respiration appears to be the result of either peripheral thermoreceptor function or mechanical demands of the respiratory system. The neglect of control of acid-base balance during the second phase indicates the existence of a dominant thermal stimulus or modification of respiratory control mechanisms.

The relation between spontaneous activity, metabolic rate and the 24 hour cycle in mice at different environmental temperatures

1. Oxygen consumption rates and levels of spontaneous activity were recorded simultaneously for mice, both singly and in groups, over 24 hr periods at temperatures ranging from 8 to 37 degrees C.2. There was marked 24 hr variation in both metabolic rate and activity, with maxima during the night; the amplitude of the variation diminished at the lower environmental temperatures.3. At 28-33 degrees C environmental temperatures, increased activity was associated with an increased oxygen consumption rate.4. At 8 and 15 degrees C, increased activity was accompanied by only a small increase in oxygen consumption.5. These results show that thermogenesis from spontaneous activity can take the place of thermoregulatory heat production in the cold.

Oxygen consumption during pouch development of the macropod marsupial Setonix brachyurus

1. Measurements of O(2) consumption at 9 or 10 temperatures in the 20-40 degrees C ambient temperature range were made on joeys with ages selected to cover the 180-day period of pouch occupancy.2. The rate of O(2) consumption of joeys younger than 100 days increased directly with ambient temperature.3. After 100 days of age the O(2) consumption rate at low temperatures rose and at about 140 days of age a constant rate was maintained over the full ambient temperature range.4. Heat transfer from joey to mother commenced after 100 days of age.5. At 150-180 days of age the rate of O(2) consumption at 20 degrees C was approximately 12 times greater than at ages less than 100 days. A thermal neutral zone was established in the range 32-36 degrees C by joeys older than 150 days.6. At the usual pouch temperature of 36.5 degrees C, O(2) consumption per unit wet body weight rose from 12 ml./kg.min at birth to 17 ml./kg.min at the end of pouch life. On a unit dry body weight basis it fell from 120 to 56 ml./kg.min. This decline parallels the decrease in growth rate.

The role of a central temperature receptor in shivering in man

1. Five subjects with spinal cord transections and one subject unconscious from a head injury have been studied when the deep tissue temperature (;central' temperature) was artificially lowered but normally innervated skin was kept warm, usually 34-36 degrees C.2. Shivering and/or increased metabolism was evoked when the central temperature was 34.9-37 degrees C.3. These observations are compatible with the view that there is a central receptor which can cause shivering when stimulated by a fall in central temperature.