Metabolic Heat Dissipation Research Articles

The effects of anoxia and hydrogen sulphide on survival, activity and metabolic rate in the coot clam, Mulinia lateralis (Say)

The mactrid clam Mulinia lateralis (Say) shows ephemeral success in colonizing a variety of marine substrata, most commonly “soupy”, reducing muds. Depending on temperature and body size, LT50 values during exposure to anoxia and hydrogen sulphide range from 2 to 11 days, at the lower end of the range reported for infaunal bivalve molluscs. Unlike most bivalves, M. lateralis maintains high levels of feeding, shell valve, and locomotory activities under anoxia, which may be an adaptation to escape periodic burial in unstable, oxygen-deficient sediment. The rate of metabolic heat dissipation under anoxia is the same as under normoxic conditions, which implies a greatly elevated rate of anaerobic glycolysis (Pasteur effect) during anoxic exposure. This may explain the rather short anoxic survival times in this species, and emphasizes its adaptation to short-term as opposed to chronic oxygen deficiency, which may occur in dense deposit-feeding communities from which M. lateralis is excluded.

Advanced Prototype Firefighter Protective Clothing: Heat Dissipation Characteristics 1

Continuing efforts to develop new firefighter protective clothing have resulted in an advanced prototype garment demonstrating improved dissipation of metabolic heat under laboratory exercise conditions. The performance of three variations of the advanced prototype design were compared to standard turn-out gear and tested for heat retention. Analysis of biophysical data obtained from four volunteer subjects revealed heat loss advantages associated with the innovative design and fabric characteristics of the prototype garment. Additional modifications and changes in the design were recommended.

Assessment of Ventilation Characteristics of Standard and Prototype Firefighter Protective Clothing1

Specialized clothing is an integral part of a firefighter's protective system. However, existing fire fighter clothing, which attempts to protect against environmental hazards, also restricts dissipation of metabolic heat. This restriction can lead to severe heat stress and may result in subsequent hazards to the health and safety of the firefighter. A new prototype design has been developed that exhibits some improved heat-dissipation characteristics under controlled laboratory settings. Two versions of the prototype design were tested for ventilation and compared with the ventilation of standard turnout gear. Laboratory information was obtained using one male and one female test subject participating in a series of treadmill exercise tests. Biophysical data collected show that the proto type design provides improvements in clothing ventilation over the standard turnout gear presently in use. Analysis of results suggests that reduction in firefighter heat stress can be achieved, and con tinued development of the prototype design is recommended.

Physiological Responses to Temperature Stress by an Australian Murid, Rattus lutreolus

The native Australian murid, Rattus lutreolus , regulates its body temperature well at ambient temperatures between 10°C and approximately 31°C, being assisted by a basically low thermal conductance that is indirectly related to ambient temperature within this range. Above this range, significant hyperthermia commences, and is accompanied by a pronounced increase in the rate of evaporative water loss. I suggest that the change in rate of water loss may be due mostly to increased cholinergic activity that promotes salivation and insensible cutaneous water loss. At high temperatures, R. lutreolus continues to exhibit controlled hyperthermia, to a stage where equality of ambient and body temperatures is achieved at approximately 41.5°C. This response is permitted by the extremely effective dissipation of metabolic heat that results from insensible cutaneous water loss, licking, drooling, and hyperventilation. Regardless of its geographic location, R. lutreolus encounters its greatest heat stress in the field when occupying burrows during the day. It is therefore advantageous that this species possesses a depressed B.M.R. (0.52 ± 0.05 SD ml CO2/gm hr) and normothermic body temperature (36.7 ± 0.1 SD °C). Although burrows are probably humid, and evaporative cooling therefore restricted, the temperatures actually experienced by the rats probably rarely exceed approximately 30°C, so that R. lutreolus would seldom need to exercise its considerable potential for evaporative cooling at high temperatures.

Metabolism, pulmocutaneous water loss and respiration of eight species of ground squirrels from different environments

1. 1. The night time metabolism of eight species of ground squirrels ( Spermophilus spp.) is described by the allometric relationship: metabolism ( ml/hr) = 3·2G 0·66 ± 0·1176 (2 S.E.)—60 per cent of the metabolism for other mammals of comparable size. 2. 2. The circadian cycle of T b has an amplitude of 1·9°C, with a nocturnal T b of 35·7 ± 0·2 (2 S.E.) . 3. 3. The Q 10 of metabolism vs. T b between 1·96 and 5·4. 4. 4. The dry conductance of six species decreased at T a of 35°C and above. 5. 5. Breathing rate was 2·25−2·75 times minimal values resulting in 100 per cent dissipation of metabolic heat at T a between 38·7 and 42°C, inclusive. 6. 6. There were distinct differences between species in their tolerance to high T a .