Radio-frequency rewarming in resuscitation from severe hypothermia

Twenty-seven dogs and monkeys were restored to normal body temperature from near-lethal limits of cold, using a radio-frequency rewarming technique. Induction cable applicators were chosen for their facility of arrangement and comparative safety. There was no evidence of optimum frequency among the three radio frequencies used. However, the rate of rewarming was dependent upon the spacing of coils from the body, with most satisfactory rewarming resulting from the use of 1/2 in. thick rubber pads. Dogs were rewarmed at an average rate of 11.1° C. per hour, using the 1/2 in. spacing and a frequency of 13.56 megacycles per second.

Thermal sensations of workers in light industry in summer; a field study in southern England

Workers in factories and a postal sorting office were questioned concerning their subjective thermal sensations, and the replies assessed according to a scale of standard sensations. Measurements of the thermal environment were made concurrently. The investigation was confined to workers engaged in light or sedentary activity during summer months in southern England.

The upper limit of the comfort zone is determined in terms of the temperatures at which more than 20% of people questioned experienced thermal discomfort.

Discontinuities in the linear relationships between thermal sensation, described on a numerical scale, and the thermal indices of the environment are shown to occur under conditions which suggest the onset of sweating beneath the clothing. The comfort zone is also determined in terms of these critical temperatures.

The regression constants relating thermal sensation to thermal conditions are determined, and the optimum conditions for comfort are deduced. The accuracy of prediction of thermal sensation from thermal measurements is examined.

The importance of clothing in requirements for thermal comfort is illustrated in two ways. Postal workers wearing regulation uniform were found to require conditions cooler than those required by factory workers wearing clothing of their own choosing. Male and female factory workers were found to require thermal conditions not significantly different, this being attributed to their selection of clothing appropriate to their personal thermal requirements.

I am indebted to Prof. G. P. Crowden for granting facilities for this research and for encouragement throughout. Dr T. C. Angus and Dr T. Bedford gave valuable advice, and Mr P. J. Williams rendered technical assistance. The co-operation of the managements and workers at the factories was greatly appreciated.

Vascular convection of heat from active muscle to overlying skin

Both thermocouple and radiometer measurements revealed marked elevations in temperature of skin immediately over actively working muscles of the forearm and leg. Such localized increases in the surface temperature were confined to skin overlying rhythmically contracting muscle. They were attributed to a direct vertical vascular convection of heat from the muscle to the overlying skin because they were prevented by blocking perfusion or by surgical severance of skin from underlying tissue and because of the character of the temperature gradient in the intervening tissue. The argument for a venous rather than an arterial convection was based on a) the effects of compression of the superficial veins on the temperature changes, b) the absence of effect on the latter by electrophoresis of adrenaline into the skin, which greatly reduced arterial perfusion of the skin, c) the absence of evidence of arterial dilation in the skin and d) the lack of relation of the location of arterial twigs to the topography of the temperature rise.

Submitted on August 11, 1958

Oxygen consumption, body temperature and heart rate of woodchucks entering hibernation

Oxygen consumption, heart rate and temperatures from various parts of the body were measured in woodchucks ( Marmota monax) entering hibernation. Comparisons were made with the chilling of woodchucks anesthetized with sodium pentobarbital, with and without the ganglionic blocking agent bis(trimethylammonium)hexane dibromide. Heart rate and oxygen consumption began to decline before any drop in body temperature as animals entered hibernation. The process was usually not continuous, for periodically the heart speeded, oxygen consumption and muscle action potentials increased and, shortly thereafter, the temperature rose transiently with the anterior portion of the body warming faster than the posterior. These partial rewarmings were less and less frequent as the total period of hibernation became longer. As hibernators chilled, the heart was the warmest area, with the thorax warmer than the abdomen. Dead woodchucks curled in the hibernating position chilled faster than the hibernators with the central portion of the abdomen chilling the slowest. In the supine, anesthetized animal, with or without the ganglionic blocking agent, the flow of blood altered the chilling so that the area near the heart remained slightly warmer than the abdomen. If curled in the hibernating position, the heart region remained much warmer than the abdomen because blood flow was curtailed by the restricted position. Chilling of the hibernator was identical to the curled, anesthetized animal except that the thoracic region of the former remained warmer due to periodic rewarmings, and also shivering in this well-muscled area. It is concluded that entrance into hibernation is not strictly temperature-dependent and that the animal is vasodilated during this process.

Oxygen consumption and body temperature during sleep in cold environments

Six young soldiers slept at the following ambient temperatures: 25.5° to 26℃ (78–80℉), 15° to 18.5°C (60°–65℉) and -32° to -34.5℃ (-25°--30℉). Rectal (Tr) and skin temperatures were recorded and mean weighted skin temperature (Ts) was calculated at -hour intervals every night; oxygen consumption (Vo2) was measured at 6-minute intervals on occasional nights. During sleep at a ‘comfortable’ temperature (25.5℃) Tr, Ts and Vo2 decreased below the resting levels measured just before retiring. During sleep in cold environments, Tr and Ts dropped to still lower levels with the lowest values recorded at an early hour of the night. Vo2 during sleep in the cold did not differ from values recorded during sleep at 25.5℃. Lowest values measured during sleep in the coldest environment were 35.5°C, 30.5℃ and 78 Cal/m2 for Tr, Ts and body heat debt, respectively. These values may represent the limits of body cooling compatible with substantially continuous sleep in the cold.

Submitted on February 19, 1959

Temperature distribution over the human head, especially in the cold

Two separate practical problems are the reduction of the total heat loss of the head, as by insulated helmets, and protection from frostbite, as by face masks. Solution of both problems benefits from knowledge of the distribution of skin temperature. Temperatures were measured with thermocouples at several points on three subjects, in the steady state, at environmental temperature of 0°C. Topographical differences were similar for the three subjects. Temperatures at a large number of points were measured in a single subject, and isothermal maps were drawn from the results. They show that the areas needing most protection from frostbite are the tip of the nose, the rim of the ears, the chin and the cheekbones. The areas of highest temperature (greatest heat loss) are those covered by the conventional insulated helmets. A face mask need not cover the area round the mouth where tactile sensitivity may make it uncomfortable. The isothermal map is correlated with the anatomical distribution of arterial blood supply.

Submitted on August 3, 1959

Survival time of hypothermic white rats (15 degrees C) and ground squirrels (10 degrees C)

The survival times of intensively cooled white rats decrease with their body temperatures. When cooled by Giaja's technique and maintained afterwards at a body temperature of 15°C rats survived 9 hours, but they could be revived by rewarming only during the first 5.5 hours of survival (biological survival). Similar biological survival times were found when the rats were cooled by other techniques, whether the cooling was much quicker or much slower. The survival time was also independent of the rate of rewarming from hypothermia. Survival was shortened by cooling after administration of sodium pentobarbital. Biological survival of young 40-gm rats at 15°C body temperature was 19 hours, 14 hours longer than that of hypothermic adults. Level of O2 consumption of hypothermic young rats differed from those of hypothermic adult animals.

Physiological effects of continuous or intermittent work in the heat

To define thermal limits for everyday work, a possible criterion which has been put forward described the climates (“prescriptive” climates) in which the level of bodily thermoregulation remained steady for a given rate of work. The present experiments were intended to determine the effect on results, obtained from brief exposures involving continuous work, of extending the exposure to a period of 8 hr and of presenting a given total energy expenditure (2,100 kcal) in different patterns of work and rest. During 8-hr exposures to three climates with dry and wet bulb temperatures of 29.4 and 23.9, 36.7 and 25.6, and 41.1 and 28.3 C, respectively, two subjects expended approximately 2,100 kcal in both 1) a nearly continuous level of activity and 2) intermittent bouts of much harder work interspaced by longer periods of rest. Evaluation and comparison of the results show that extension of exposures to periods of up to 8 hr per se did not demonstrably change the levels of rectal temperature, pulse rate, or weight loss found by the 2nd hr of exposure in the climates examined. Further, in prescriptive climates (in which the level of thermoregulation depends on the rate of work rather than on the environment), when the energy expenditure was 2,100 kcal in 8 hr, either continuously at a moderate rate, or intermittently at a high rate with compensatory rest pauses, the physiological cost was similar, as judged by rectal temperature, pulse rate, and weight loss.

Submitted on June 15, 1962