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Biomedical subjects

E Shvartz

Publications and source records attributed to E Shvartz.

At least 37 records · Page 2Linked to original sources
PubMed1977

Prediction of heat tolerance from heart rate and rectal temperature in a temperate environment.

To determine if heat tolerance could be predicted from responses to exercise in temperature conditions, 51 young men performed 15 min of bench stepping at an average work load of 80 W at 23 degrees C. On the following day they attempted to perform 3 h of bench stepping at 40 W in heat (39.3 degrees C dry bulb, 30.3 degrees C wet bulb). Of these subjects, 4 were heat intolerant, judged by previous heat stroke episodes during field marches, 12 were heat acclimated, and 35 were unacclimated. The heat-intolerant subjects showed the highest heart rates (HR) and rectal temperatures (Tre) at 23 degrees C and in heat, and the acclimated subjects showed the lowest corresponding values. HR and Tre in each environment were combined into a single score, from 10, indicating the poorest responses, to 100, indicating the best responses. These scores at 23 degrees C when correlated with the corresponding scores in heat resulted in a linear correlation coefficient of r = 0.94 with a standard error of estimate of 8.6%. Scores of the heat-intolerant subjects were below 35, and those of the acclimated subjects were between 70 and 100. Thus heat tolerance can accurately be predicted for HR and Tre responses to exercise at room temperature.

Acclimatization↗
PubMed1977

Responses to temperate, cold, and hot environments and the effect of physical training.

Ten young men underwent several tests before and after a training program: a bicycle ergometer test and 60 min of moderate exercise performed at a temperate 24 degrees C; the same work load performed in heat (40.0 degrees C DB, 30.4 degrees C WB) for 3 h; and cold (10 degrees C) exposure for 60 min. Training consisted of 13 1-h sessions of hard, strenuous, and exhaustive work performed in temperate conditions four times a week. Training resulted in substantial decreases in heart rate and rectal temperature responses to exercise in temperate, minor increases in hot, and no significant changes in cold conditions. Subjects who showed good responses to heat, also showed good responses at 24 degrees C, and poor compensatory responses to cold, which were indicated by relatively low heat production and rectal temperature values, and relatively high body heat loss and extremities temperature values. Subjects who showed poor heat tolerance also showed poor responses in temperate and good compensatory responses in cold conditions. Positive correlation coefficients were found between rectal temperatures in the three environments, and between heart rate and sweat rate responses in temperate and hot conditions. The results indicated that moderately severe training causes minor tolerance improvements in heat and no changes in cold, and that responses in temperate, cold, and hot environments are interdependent.

Acclimatization↗
PubMed1977

Exercise and heat orthostatism and the effect of heat acclimation and physical fitness.

Twelve trained and 16 untrained young men were administered five orthostatic tests while leaning upright against a wall, for 20 min--before exercise; after 60 min of exercise at a load of 40 W; after 15 min of exercise at a load of 80 W; after a Vo2 max test, and after 3 h of exercise at a load of 40 W in heat (39.4 degrees C DB, 30.3 degrees C WB). Eight of the untrained subjects were retested in the five orthostatic tests after 8 d of heat acclimation. The number of fainters in the orthostatic tests administered before exercise, after exercise at 40 W and 80 W, and after exercise in heat, were 3, 4, 6, and 13, respectively. There were no fainting episodes after the Vo2 max tests. Orthostatic responses in the different conditions were partially related. The trained subjects showed substantially better responses than the untrained ones (10% vs. 25% of fainting episodes), and heat acclimation resulted in marked improvement in orthostatism (decrease to 5% faintings). The results show that Vo2 max and heat tolerance account for most of the variability which determines orthostatic tolerance.

Acclimatization↗
PubMed1976

Effect of neck versus chest cooling on responses to work in heat.

Six young men performed bench-stepping at a load of 40 W, once at room temperature of 23 degrees C and 3 times in heat (39.5 degrees C db, 30.3 degrees C wb). Two of the heat exposures included cooling of either the neck or chest by circulating cool water having an inlet temperature of 8.3 degrees C. The heat exchanges for the neck and chest were of equal size and they consisted of PVC tubes, having a total length of 3m each, which covered 2.2% of the body surface area. Heat exchange between the tubing assemblies and the environment was prevented by proper insulation. As compared with no cooling in heat, each method of cooling resulted in no change in heart rate, a decrease of 0.5 degrees C in rectal temperature, small and insignificant decreases in skin temperature and 16-22% decreases in sweat rates. Heat removed from the neck and chest equalled 63.1 and61.9 W-m-2, respectively. This large heat removal and the substantial decreases in rectal temperature and sweat rate as a result of cooling 2.2% of the body surface area were explained in terms of the powerful effect of conductive cooling and the particular regions which were cooled.

Acclimatization↗
PubMed1975

Orthostatism and heat acclimation.

Three groups of subjects (6 subj in each group) underwent the following precedures: group A was given a 20-min head-up tilt at 21 degrees C followed by 4 h of exercise at 33.9 degrees C DB, 32.2 degrees C WB, and a repetition of tilting after exercise in heat; group B underwent the same procedure at 21 degrees C; group C was tilted at 21 degrees C, rested in heat for 4 h and was retilted in heat. The above procedures were repeated for 8 days, and on the last day groups B and C underwent the same treatment as group A. Group A showed the usual decreases in heart rate and rectal temperature and an increase in sweat rate on acclimation. This corresponded to marked improvements in heat-orthostatism. While five subjects in group A fainted during post-exposure tilting on the first exposure, none fainted on the last day. Resting in heat (group C) did not cause any acclimation to work in heat. This corresponded to poor heat-orthostatism after the work-heat procedure when five subjects fainted. Mild training at 21 degrees C (group B) resulted in minor improvements to work in heat as evident by some improvements in heart rate responses after the 1st and 2nd h of exposure. This corresponded to better heat-orthostatism and fewer men fainting than in group C. The results indicated that heat-orthostatism improves on acclimation to the same extent as exercise heart rate and rectal temperature.

Acclimatization↗
PubMed1975

Orthostatic responses in Caucasians and Bantu.

Nine Caucasian and 13 Bantu young men, all untrained and unacclimated to heat, were tilted head-up for 20 min before and after 4 h of exercise performed at a load of 35 W at room temperature of 23 degrees C and in heat (33.9 degrees C DB, 32.2 degrees C WB). In heat, all Bantu but only four Caucasians completed the 4 h of exposure. The change in systolic blood pressure from recumbency to orthostasis was negligible in the Bantu and adverse in the Caucasians, during pre-exercise tilting at 23 degrees C. Similar differences were found during tilting after exercise at 23 degrees C. Post-exercise orthostatic heart rate did not differ between the two groups despite higher exercise heart rats of the Bantu. Seven subjects in each group fainted during heart-orthostatism, and the difference in systolic blood pressure between recumbency and orthostasis in heat was substantially more adverse in the Caucasians. High relationships were found between exercise heart rate, orthostatic heart rate, and fainting episodes. The results suggested that Bantu make better orthostatic adjestments than Caucasians.

Adult↗