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Biomedical subjects

L C Senay

Publications and source records attributed to L C Senay.

36 records · Page 2Linked to original sources
PubMed1976

Acclimatization in a hot, humid environment: energy exchange, body temperature, and sweating.

Four trained young men, worked for 4 h/day at 43-50% of their maximum aerobic capacity for 3 days at 25 degrees C db, 18 degrees C wb and then for 10 consecutive days at 45 degrees C db, 32 degrees C wb. Their thermal status was assessed using direct calorimetry. As a group, the men showed classical acclimization responses, but there were marked individual differences. The calorimetric analysis revealed that reductions in strain were associated with minor changes in heat balance confined to the first and last hours of exposure. Events occurring within the first 4 days appeared to have little effect on body temperatures. Significant decreases in body temperature took place only when sweat and evaporation rate increased. A 10% increase in evaporation rate was accompanied by a 30% increase in sweat rate and a 200% increase in unevaporated sweat; thus, there is a wasteful overproduction of sweat. By the 10th day skin temperature was confined to the level necessary to evaporate sufficient sweat to achieve thermal balance with a fully wet body surface. The efficiency of heat transport within the body did not change with acclimatization.

Acclimatization↗
PubMed1976

Acclimization in a hot, humid environment: cardiovascular adjustments.

Four trained young men worked for 4 h/day at 40-50% of their maximum aerobic capacity first for 3 days at 25 degrees C db, 18 degrees C wb, and then for 10 consecutive days at 45 degrees C db, 32 degrees C wb. This portion of the study was mainly concerned with central circulatory changes during acclimatization. The central circulatory adaptation to work in heat could be divided into four distinct phases: phase I (day 1) was characterized by a progressive fall in stroke volume (SV) during heat exposure but cardiac output (CO) was maintained above control values by high heart rates. Phase II (days 2 and 3) was marked by increases in SV ande decreases in heart rate but with little change in CO from phase I. During phase III (days 4-8 of acclimatization), CO increased due to increases in SV. Phase IV (days 6-8) was associated with decreases in rectal and skin temperature towards control levels. SV and HR both decline in this phase so that CO was not elevated greatly above control levels. The results indicated that central circulatory and temperature regulating events are not casually associated in acclimatization.

Acclimatization↗
PubMed1976

Acclimatization in a hot, humid environment: body fluid adjustments.

Four trained men worked 4 h/day at 40-50% of their maximum aerobic capacity first for 3 days at 25 degrees C db, 18 degrees C wb and then for 10 consecutive days at 45 degrees C db, 32 degrees C wb. Between days 1 and 2 of heat exposure mean total circulating protein (TCP) and plasma volume (PV) increased 11.6% and 9%, respectively. Preexposure TCP and PV increased until day 6 of heat exposure. Of the protein fractions beta-globulins underwent the largest relative increase. During work movement of protein into and out of the vascular compartment was similar in control and acclimatizing subjects but the latter generally maintained a greater amount of protein and fluid within the vascular volume. There was no evidence of salt and water retention. The increase in vascualr volume was ascribed to transfer of interstitial protein and water to the vascular volume. Regression coefficients indicated significant correlations for changes in plasma volume versus heart rate, stroke volume, and cardiac output during acclimatization. It was concluded that the most critical event in heat acclimatization is the expansion of the plasma volume.

Acclimatization↗
PubMed1975

Plasma volumes and constituents of heat-exposed men before and after acclimatization.

Five men underwent a 2-wk exercise regimen and were then exposed to 45 degrees C db, 28 degrees C wb, wind speed 1 m/s for 12 h while at rest. Body weight was maintained with 0.1% saline. One week later the exposure was repeated without rehydration. After heat acclimatization, the 12-h experiments were repeated. Frequent body weights, rectal temperatures, and venous blood samples were obtained. Results indicated that hemodilution upon acute heat exposure is partially due to protein influx into the vascular volume and the hemodilution allowed considerable loss of body water before plasma volume returned to preexposure values. Water within the vascular volume appeared to be in equilibrium with that in other body compartments before but not after acclimatization. Acclimatization altered the rate of protein transfer (and water movement) such that hemodilution was accomplished more rapidly than before acclimatization. Early hemodilution was quite labile and depended upon subject hydration during the first hour of heat exposure.

Acclimatization↗
PubMed1975

Untrained females: effects of submaximal exercise and heat on body fluids.

Five untrained females having no history of heat exposure worked in a cool (16-20 degrees C db, 28% rh) environment on day 1 and a warm environment on day 2 (45 degrees C db, 28% rh). Exercise level (bicycle ergometer) was 30% of individual Vo2 max values and work time on both days was 45 min. Venous blood samples were obtained at rest, after 40 min of exercise and 25 min after exercise ceased. Analysis of blood samples indicated an 8.3% increase in Hct during exercise on day 1 and a plasma volume reduction of 12.8% though total circulating protein increased 11.5%. Except for K+ all parameters approximated control values within 25 min postexercise. On day 2, exercise in heat caused a 12% increase in Hct and a plasma volume reduction of 17.7%. Mean total protein did not significantly change from resting values. These data indicated that for a given % Vo2 max, untrained females suffer considerably greater reductions in plasma volumes than do exercised males. Similar to males, dilatation of the cutaneous vascular bed in unacclimatized females resulted in loss of protein from the vascular volume.

Adult↗
PubMed1973

Body fluids and temperature responses of heat-exposed women before and after ovulation with and without rehydration.

1. Four females (21-25 yr) were exposed to 43.3 degrees C dry bulb, 28-29 degrees C wet bulb, for 10 hr both early and late in two menstrual cycles. During the experiments in one cycle, the subjects were rehydrated while during the experiments in another cycle, the subjects were allowed to progressively dehydrate.2. Rates of weight loss and oral temperatures were determined hourly while venous blood samples were obtained before and then after 1, 2, 3, 4, 6, 8, and 10 hr of heat exposure.3. Pre-ovulatory results were compared with post-ovulatory results and dehydration experiments with rehydration experiments. In addition, the data on these female subjects were compared with those presented elsewhere for similarly treated male subjects.4. When compared to males, these resting females did not significantly haemodilute when heat exposed. In addition, the female subjects apparently suffered a decrease in plasma volume and body water at a rate some 1.5 times that of similarly exposed males.5. In general,% change in total protein/unit volume of plasma for these female subjects was similar to previously published results for males. However, there were significant differences in the manner in which albumin and globulin fractions changed before and after ovulation.6. The rates of body weight loss for these subjects were similar to those determined for males. No difference was noted between pre- and post-ovulatory rates of weight loss. Dehydration significantly depressed the rates of weight loss during heat exposure.7. Stimulation of sweating (assessed as weight loss) appeared to require similar amounts of heat storage before and after ovulation though initial post-ovulatory temperatures were generally higher.8. Progressive dehydration of females before ovulation was accompanied by rates of increase in oral temperatures that were similar to those seen for similarly exposed males.9. When females progressively dehydrated after ovulation, there was no statistically significant correlation between temperature rise and weight loss as had been noted in pre-ovulatory experiments. In addition, for all subjects, the rise in body temperature with dehydration was less after than before ovulation. Two subjects showed an ability to decrease their body temperature in the face of continued dehydration.10. Based on these results, the differences in the responses of males and females to heat exposure were ascribed mainly to two causes: a, inherent differences such as skin surface: blood volume ratios, and b, the inability of females to maintain their vascular volume during heat exposure.

Adult↗
PubMed1972

Changes in plasma volume and protein content during exposures of working men to various temperatures before and after acclimatization to heat: separation of the roles of cutaneous and skeletal muscle circulation.

1. Ten male subjects were trained in stair stepping for 2 weeks. Group A (six subjects) was thereupon sequentially exposed for 45 min to dry bulb temperatures of 20, 40 and 30 degrees C, a vapour pressure of 10-11 mm Hg and a wind speed of 1 m/sec in a climate tunnel. While temperature changes were being effected the subjects rested in an antechamber. Group B (four subjects) was exposed to a sequence of 40, 20 and 30 degrees C. Work rate was the same for all subjects, i.e. 216 kg m/min ( approximately to an oxygen consumption of 0.9 l./min). Duplicate experiments were run on both groups of subjects before and after acclimatization to heat.2. Throughout, periodic samples of venous blood, water and protein movement into or out of the extravascular compartment was assessed during exercise periods wherein blood flow was increased to exercising muscles (Group A, 20 degrees C) or to both exercising muscles and skin (Group B, 40 degrees C; Groups A and B, 30 degrees C.)3. Mild exercise in a cool environment before and after acclimatization to heat was accompanied by expansion of the vascular volume and an increase in the amount of circulating protein.4. Mild exercise in a warm environment for 45 min was accompanied by haemoconcentration and loss of protein from the vascular volume before subjects were heat acclimatized. The results were reversed following heat acclimatization; i.e. exposure of Group B to 40 degrees C and of Groups A and B to 30 degrees C was accompanied by haemodilution and addition to (or maintenance of) plasma protein concentration.5. Effects of heat acclimatization on exposure of Group A to 40 degrees C were also noted.6. The effects of heat acclimatization were ascribed to:(a) a change in permeability of cutaneous capillaries to large molecules,(b) an increased availability of translocatable protein within cutaneous interstitial spaces, and(c) a combination of both a and b.7. Further, the results supported a previous suggestion that addition or loss of water and protein from the vascular volume is dependent on the ratio of cutaneous to muscle blood flow.

Acclimatization↗
PubMed1970

Movement of water, protein and crystalloids between vascular and extra-vascular compartments in heat-exposed men during dehydration and following limited relief of dehydration.

1. Five male subjects were exposed to a hot environment (43-44 degrees C dry bulb, 28-29 degrees C wet bulb) and allowed to dehydrate for 4 hr. Water was then provided ad libitum for drinking during a 20-min period; thereafter the subjects continued at rest in the hot room for an additional 140 min.2. Through periodic samples of venous blood, water and protein movement into or out of the intravascular compartment were assessed during dehydration and during and following water ingestion that partially relieved dehydration.3. Consideration of changes in blood osmolarity, plasma protein content and haematocrit values led to the conclusion that protein was added to plasma during heat exposure and that plasma, as previously supposed, did not lose water at rates greater than that of the whole body under such conditions.4. Haemodilution occurred when dehydration was partially relieved by drinking water and this dilution was maintained even when sweat loss exceeded the amount of water ingested.5. For similar levels of bodily dehydration before and after water ingestion, body temperatures were lower when haemodilution was present.6. A hypothesis that relates changes in plasma volume and constituents with levels of exercise is presented.

Adult↗
PubMedDate not supplied

An inquiry into the role of cardiac filling pressure in acclimatization to heat.

During the first exposure of exercising subjects to hot environments (30-50 degrees C), cardiac output, heart rate, and body temperature increase over that seen in cool environments, while stroke volume decreases. If daily heat exposures occur, during the second heat exposure, heart rates and rectal temperatures are decreased from day 1 while cardiac output is maintained. This decrease in physiological strain occurs with little or no increase in evaporative heat loss. The alleviating agent appears to be an expansion of plasma volume. Several brief studies have indicated decreases in cardiac filling pressure during exercise in heat, and though inferential, it appears that the progressive increase in plasma volume during the first five to six days of heat exposure assists in maintaining cardiac filling pressure. Later, with increased evaporative heat loss due to increased sweat secretion, the mechanism of supplying increased volume to maintain cardiac filling is changed; fluid is transferred from extravascular to intravascular compartment, thus protecting venous return and cardiac filling pressure. These statements are based on limited data, and there is need of experiments designed to confirm or deny certain conclusions as to the role of cardiac filling pressure in acclimatization to heat.

Acclimatization↗