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Biomedical subjects

S D Livingstone

Publications and source records attributed to S D Livingstone.

16 recordsLinked to original sources
PubMed1990

Respiratory heat loss during work at various ambient temperatures.

The purpose of this investigation was to establish the temperature and humidity of the expired air of subjects working at various metabolic rates at ambient temperatures between -40 degrees C and 20 degrees C in order to calculate respiratory heat loss. Measurements of the respired air temperature and water vapour content were made for five subjects while they either stood or walked on a treadmill. The results indicated that the maximum respired air temperature varied slightly with the ambient air temperature but changes in metabolic rate, respiration rate and breathing frequency had no apparent effect on the expired air temperature under the conditions studied. The relative humidity of the respired air was found to be close to saturation in the extreme-cold environments. Heat loss due to respiration was between 25 and 30% of the resting metabolic and between 15 and 20% of the working metabolic rate.

Adult↗
PubMed1990

Body composition and skin temperature variation.

Temperature variations near four common torso skin temperature sites were measured on 17 lightly clad subjects exposed to ambient temperatures of 28, 23, and 18 degrees C. Although variations in skin temperature exceeding 7 degrees C over a distance of 5 cm were observed on individuals, the mean magnitude of these variations was 2-3 degrees C under the coolest condition and less at the warmer temperatures. There was no correlation between the temperature variation and skinfold thickness at a site or with estimations of whole body fat content. These findings imply that errors in mean skin temperature measurement could arise from probe mislocation and/or subcutaneous fat distribution and that the problem becomes more acute with increasing cold stress. However, the magnitudes of these errors cannot be easily predicted from common anthropometric measurements.

Adipose Tissue↗
PubMed1989

Heat loss caused by immersing the hands in water.

The effect of immersing the hands up to the wrist in cold water to alleviate heat strain was examined in volunteers wearing chemical protective clothing and gloves. Each subject, who was monitored with skin and rectal thermistors, was observed while walking on a treadmill at two different work rates (283 +/- 47 and 455 +/- 58 watts) at 23 degrees C and at a resting state at 35 degrees C. After 20 min of work at 23 degrees C or after 120 min in the hot room, the hands were immersed in water at temperatures of 10, 15, 20, 25, and 30 degrees C. The amount of heat lost via the hands ranged between 124 +/- 14 and 31 +/- 4 watts (W) and was greater, the colder the water and harder the work. In most cases, this amount of cooling was sufficient to decrease skin temperature and lower the rate of increase of core temperature. We concluded that this method may be used to decrease resting time when working in the heat.

Adult↗
PubMed1988

Measurement of torso skin temperature under clothing.

The influence of clothing on skin temperature distributions of the torso was investigated during and after cold exposure. Volunteers were cooled for one hour at 5 degrees C while wearing clothing designed to have insulation which was intended to be relatively uniformly distributed. Three different thicknesses of clothing were used. Following thermistor measurements of skin temperatures during the cold exposures, clothing was quickly removed from the upper parts of the body to enable thermographic investigations of the temperature distributions of the front of the bare torso. The evolution of temperature distributions were then studied at different ambient temperatures (5 degrees C and 20 degrees C) as a function of the thickness of the insulation which had previously been worn. The patterns of the temperature distributions, and the range and standard deviation of torso temperatures were all found to be relatively constant in spite of the different thicknesses of clothing worn or in the time-variant mean torso temperatures which resulted. The front torso sites normally used for the determination of mean skin temperatures were found to be on portions of the torso which were cooler than the surrounding regions. It was concluded that a site midway between the umbilicus and a nipple yields a more accurate estimate of mean torso temperature in the conditions of the present study.

Body Temperature Regulation↗
PubMed1979

Skin temperature changes in paradoxical sleep in man in the cold.

Mean skin temperature (Tsk) calculated from seven sites and rectal temperature (Tre) were recorded every minute for a total of 88 man-nights in eight young men sleeping at night in both cold (during the Artic winter) and neutral (laboratory) environments, and were related to the EEG stages of sleep, especially to paradoxical sleep (PS). In the neutral environment, Tre was always above 36 degrees C and Tsk increased during PS. In the cold conditions, during PS, Tsk increased when Tre was high, and decreased when Tre was below 36 degrees C. It was concluded that, although it is not known why a core temperature of about 36 degrees C is the critical point of change in the direction of Tsk variations during PS, the direction in which Tsk will vary during PS is dependent on the core temperature at the time.

Adult↗
PubMed1979

Similarity in the number of lifespan heartbeats among non-hibernating homeothermic animals.

An investigation was made of the available data on heart rates and maximum lifespan of a number of vertebrates from a variety of sources; only data pertinent to resting adult non-anesthesized homeothermic mammals and birds in a state of thermal neutrality were subsequently analyzed. All known hibernators were excluded because of their extreme, and largely unknown, range of heartbeat from season to season. Plots of heart rate (beats per minute) against reciprocal of lifespan in years showed surprisingly good fits (r = +0.90 for mammals and r = +0.64 for birds). Computation of the total number of heartbeats in the maximum recorded lifespans of the mammalian and avian species involved in this study showed that the mean cumulative heartbeat number for 31 mammalian species was 100 +/- 8 S.E.M. x 10(7) beats and for 23 avian species was 326 +/- 22 S.E.M. x 10(7) beats. This paper documents this analysis, which supports the concept of a close similarity in lifespan heartbeats among mammalian species and among avian species.

Animals↗
PubMed1978

Effect of a local cold stress on peripheral temperatures of Inuit, Oriental, and Caucasian subjects.

Male subjects comprised of six Inuit from Igloolik, N.W.T., and five Orientals and six Caucasians from Toronto, Ont., volunteered for tests to determine the effect of localized cold stress on peripheral temperatures. In each subject, skin temperatures of the right index finger, the arm, and the cheek, as well as blood pressure and heart rate, were measured before, during, and after foot immersion in water of 10 degrees C temperature for 10 min. There was an immediate decrease in finger temperature on foot immersion in all three subject groups; however, the Inuit finger temperatures recovered very quickly to control values, the Caucasian finger temperatures began to increase after decreasing for 7.5 min, and the Oriental finger temperatures decreased continuously during the foot immersion and remained cool even 10 min after the removal of the cold stimulus. The cold stimulus did not affect the cheek or arm temperatures of any of the groups. In all subjects, systolic and diastolic blood pressures and heart rates increased on foot immersion, gradually returning towards normal values. No intergroup differences were seen in these parameters.

Adult↗
PubMed1978

Effects on handgrip strength due to arm immersion in a 10 degree C water bath.

Thirteen male and female human subjects participated in an experiment to determine if cold water immersion of the arm increases post-immersion handgrip strength. The test involved immersion of a subject's fore-arm into a 10 degrees C water bath for 30 min once a week in a 3-week series, involving a control test and two immersion experiments. Handgrip strength was measured 20 min before and then once every 20 minutes after the cold bath immersion for 4 h, for a total of 18 readings. Grip strength significantly decreased as a consequence of immersion of the forearm. However, strength recovery to approximately normal values took place within 40 min. No increases in post-immersion strength were observed.

Adult↗
PubMed1976

Effect of alterations in ambient temperature on blood flow in the skin.

The effect of changing ambient temperature on skin temperature was recorded in human subjects; also, its effect on blood flow was measured using venous occlusion and optical plethysmography. When cold stimulus was removed in stages using a heating cabinet, it was found that a biphasic flow response occurred in the fingers with each step change in temperature. There was a rapid transient rise followed by a decline to an equilibrium flow level. The transient rise occurred even when the temperature rose from 37 to 40 degrees C, although at this level the equilibrium remained unchanged. It is suggested that the transient rise was due to stimulation of Hensel's dynamic warmth receptors, whereas the rise in equilibrium temperature was due to removal of cold stimulus, which at low ambient temperatures maintains reflex vasoconstriction through activation of static cold receptors. Upper arm skin responded to removal of cold stimulus by a fall in temperature. Immersion of a different limb in cold water produced vasoconstriction in fingers but vasodilatation in the upper arm skin. It is suggested that this may be due to neurogenic vasodilatation, though the present work gives no indication as to pathways.

Adult↗
PubMed1976

Changes in cold-induced vasodilation during Arctic exercises.

The effect of exposure to cold on cold-induced vasodilation (CIVD) was examined in military personnel who had experienced a 2-wk stay in the Artic. During this time, the daily regimen consisted of long marches over difficult terrain and sleep in unheated tents with diurnal temperatures ranging from -10 to -40 degrees C. In tests conducted before and after the 2-wk period, CIVD was measured in the left middle finger of each subject by its immersion in ice water. After the 2-wk period, the value of mean finger temperature during the test had decreased relative to that observed before the test, the time required before the first vasodilative temperature increase occurred had become greater, and the finger temperature value at which the vasodilative increase was initiated has been lowered. These changes manifest a deleterious effect of cold exposure on the CIVD, contrary to expectations, and suggest that the effect of short-term cold exposure is to produce a general rather than peripheral acclimation in these subjects.

Adaptation, Physiological↗
PubMed1976

Cold-induced shivering in men with thermoneutral skin temperatures.

Twenty-two male Caucasians, aged 20-47 yr, were exposed in a cold room to air temperatures of -33 degrees C while lying in sleeping bags for 2 h. Skin and rectal temperatures as well as electromyographic activity of the chin, forearm, and thigh, were recorded. Shivering occurred in all the subjects, even though skin temperatures were maintained between 31 and 33 degrees C. It is suggested that a counter-current heat exchange occurs whereby the warm blood of the common carotid artery is cooled by cool venous blood in the jugular veins. This cooled arterial blood, in irrigating the hypothalamus, causes shivering.

Adult↗