PubMed Health⌕ Search

Biomedical subjects

C B Wenger

Publications and source records attributed to C B Wenger.

At least 37 records · Page 2Linked to original sources
PubMed1982

Effects on heat tolerance of physical training in water and on land.

A 4-wk training program was undertaken by 15 untrained non-heat-acclimated males who were divided into three groups matched on maximal aerobic capacity (VO2max) and trained either in water or on land to determine how physical training (PT) in these different media affects heat tolerance. Subjects trained on a cycle ergometer for 1 h/day, 5 days/wk at 75% VO2max, with the exercise intensity progressively increased to maintain a constant training stimulus. Group I exercised on land, whereas groups II and III exercised while immersed to the neck in water of either 32 degrees C (II) or 20 degrees C (III). Daily exercise increased core temperature (Tc) in groups I and II but not in group III. Training elicited similar increases (approximately 15%) in VO2max in the three groups. Before and after PT, all subjects exercised at approximately 30% VO2max for 3 h at 49 degrees C, 20% rh. Compared with before training, groups I and II showed a decrease in final Tc and heart rate (HR) in the posttraining heat exposure. Sweat rate increased 25% in group II but remained the same in group I. Group III demonstrated a decrease in final HR, but final Tc was higher than before training. Sweat rate did not increase in group III and was lower than the other groups. It was concluded that PT can improve the cardiovascular response to dry heat without affecting thermoregulatory capacity. PT appears to enhance heat tolerance only if Tc is permitted to rise during exercise, thus stimulating the temperature-regulating center for heat dissipation.

Adaptation, Physiological↗
PubMed1981

Effect of acute alterations of blood volume on circulatory performance in humans.

Six subjects exercised (60% VO2 max) in a 35 degree C environment on the day prior to (C1) and 1 h after withdrawal (PW) of 10% of each subject's blood volume, and 2 wk later on the day prior to (C2) and 1 h after infusion (PI) of the stored blood. Esophageal and mean skin temperatures (Tes and Tsk), forearm blood flow (FBF), cardiac output (Q), heart rate (HR), and blood samples were taken at intervals. Blood withdrawal had no major effect on either Q or stroke volume (SV), as plasma volume was largely restored prior to exercise. Following blood infusion Q and SV during exercise were significantly increased 1.4 1.min-1 and 15 ml.beat-1 above C2 levels and HR was significantly reduced at any Tes. Blood withdrawal decreased the slope of the FBF:Tes relationship. The resulting decrease in cutaneous perfusion caused a significantly greater body heat storage during PW. In contrast during PI, the slope of the FBF:Tes relation was somewhat increased. We conclude that cardiac stroke volume and cutaneous blood flow vary in proportion to changes in absolute blood volume. The rise in body temperature during exercise was significantly greater in hypovolemia but was not significantly reduced following volume expansion.

Adult↗
PubMed1981

Effect of blood volume on sweating rate and body fluids in exercising humans.

Five relatively fit men performed cycle ergometer exercise (65-70% VO2max) for up to 30 min at 30 degrees C, 40% rh. The data from control (normo-volemic), hypovolemic [8.7% reduction in blood volume (BV) induced by diuretics], and hypervolemic [7.9% expansion of BV induced by infusion if isotonic serum albumin] tests revealed significant effects of BV on body fluid and sweating responses. During control exercise, BV decreased an average (+/- SE) 370 +/- 64 ml at 20 min. A significantly smaller loss occurred after 20 min of hypovolemic exercise (270 +/- 29 ml). The decrease in BV during 30 min of hypervolemic exercise (541 +/- 43 ml) was significantly greater than during control (421 +/- 50 ml). Blood volume reduction also significantly altered the control of sweating rate independent of changes in plasma osmolality. The slope of the sweating rate-to-esophageal temperature relationship (SR/Tes) was significantly reduced from the mean value of 1.07 +/- 0.16 and 1.09 +/- 0.18 mg X min-1 X cm-2 X degrees C-1 during control tests, measured from the chest and arm, respectively, to 0.64 +/- 0.11 and 0.63 +/- 0.11 mg X min-1 X cm-2 X degrees C-1 during hypovolemia. The SR/Tes slope was unchanged in hypovolemia over active tissues (calf). Hypervolemia had no effect on the control of sweating at any site. Both the body fluid and sweating responses during hypovolemia act to conserve circulating blood volume during exercise.

Adult↗
PubMed1980

Control of forearm venous volume during exercise and body heating.

Subjects ate ice to cool sufficiently to constrict the superficial forearm veins. After ice-eating, esophageal temperature (Tes) recovered from local cooling in 10-15 min, and thereafter reflected body core temperature. Eight skin temperatures (Tsk) were measured, and a weighted mean (Tsk) computed. The left wrist was suspended 5-6 in. above shoulder level, and left forearm skin temperature was maintained at 35 degrees C with a controlled-temperature air stream. Forearm venous volume (FVV) w-s the volume difference between the forearm drained by gravity and the forearm congested by a pneumatic cuff inflated to 32 Torr. Subjects were warmed either by storage of resting metabolic heat or by cycle exercise at 40-45% of maximal O2 consumption. Exercise experiments were conducted in ambient temperatures of 15, 25, and 35 degrees C, and resting experiments in 25 and 35 degrees C. FVV rose linearly with Tes, but during exercise FVV was lower than at the same Tes and Tsk during rest, and the difference was greater at high Tsk and FVV. Our data fit the equation FVV-FVV0 = (a1 Tes + a2 Tsk - b).[1 - phi (W).(Tsk - T-sk0)], where phi (W) is a function of exercise, and phi (W) = 0 at rest.

Adult↗
PubMed1980

Control of skin blood flow during exercise by thermal reflexes and baroreflexes.

Four male subjects exercised on cycle ergometers at 40-51% of maximal aerobic power in the upright and supine positions at air temperatures of 15, 25, and 40 degrees C. Esophageal temperature (Tes) was measured at heart level, and mean skin temperature was computed from a weighted average of eight skin temperature measurements. Forearm blood flow (ABF) was measured by venous occlusion plethysmography, and cardiac output was measured by a CO2 rebreathing technique. At air temperatures of 15 and 25 degrees C, cardiac stroke volume was slightly lower during upright exercise than it was during supine exercise, as was ABF at a given Tes. At 40 degrees C, however, stroke volume was much lower and ABF at a given Tes was considerably lower during upright as opposed to supine exercise. The reduced stroke volume during upright exercise in the heat shows that gravity compounds the effect of cutaneous venodilation by allowing blood to pool in dependent limbs and thus impairing cardiac filling. The proportionality between reduced stroke volume and reduced forearm blood flow suggests that the reduction in blood flow may be mediated by cardiopulmonary baroreflexes that are activated by reduced cardiac filling pressure.

Adult↗
PubMed1980

Effect of hydration state of circulatory and thermal regulations.

To determine the influence of hydration state upon circulatory controls, we studied four relatively fit subjects during duplicate 30-min cycle ergometer exercise bouts (55% VO2max) in euhydrated, hypohydrated, and hyperhydrated conditions. Ambient temperature was 35 degrees C. Hypohydration was achieved by 4 days of diuretic administration and resulted in a whole-body weight loss of 2.2 kg and a plasma volume decrease of approximately 700 ml. Hyperhydration was achieved by ADH administration plus ingestion of 2 liters water but caused only a minor increase volume. Hypohydration resulted in a significantly reduced cardiac output during exercise; this the result of a reduction in stroke volume of 17 ml.beat-1 without adequate elevation in heart rate. the internal temperature (Tes) threshold for cutaneous vasodilation was elevated by 0.42 degree C in hypohydrated conditions; but once vasodilation occurred, the slope of the arm blood flow:Tes relation was unchanged from control. Maximal arm blood flow was reduced by nearly 50% in hypohydration. These restrictions in cutaneous blood flow served to maintain an already compromised venous return, but due to the limitation of core-to-skin heat transfer, forced Tes to nearly 39 degrees C, significantly higher than in euhydrated conditions.

Adult↗
PubMed1979

Circulatory regulation during exercise in different ambient temperatures.

Three relatively fit subjects performed duplicate 20- to 25-min cycle ergometer exercise bouts at moderate and heavy intensities (40% and 70% Vo2 max) in ambient temperatures of 20, 26, and 36 degrees C. They approached a steady state in internal body temperature (Tes) in all but the heavy exercise in the heat, where Tes rose consistently, averaging 38.84 degrees C at the termination of exercise. Cardiac output (Q), estimated by a rebreathing technique, was proportional to Vo2 and independent of the body temperatures, except during the lower exercise intensity in the heart, where Q averaged 1.31 . min -1 higher throughout. In any environment, forearm blood flow was linearly related to Tes above the Tes threshold for vasodilation, but during heavy exercise in the heat this relationship was severely attenuated above a Tes around 38.0 degrees C, when forearm blood flow exceeded 15 ml.min -1 .100 ml -1. Plasma volume decreases during exercise were primarily a function of the intensity of exercise. During heavy exercise in the heat the relative vasconstriction contributes to the maintenance of an adequate stroke volume preventing a fall in Q. In this case, circulatory regulation has precedence over temperature regulation.

Adult↗
PubMed1979

Control of skin circulation during exercise and heat stress.

At any given environmental and mean skin temperature, exercise brings about an increase in internal body temperature and skin blood flow. At high environmental temperatures, when skin temperature is elevated, skin blood flow at any given internal temperature reaches higher levels than at cooler skin temperatures. Increased cutaneous blood flow serves to deliver metabolic heat from the core to the skin, where the heat is lost to the environment by convective, radiative, and evaporative mechanisms. However, at high levels of skin blood flow, peripheral vascular pooling and fluid losses by filtration lead to reduced central venous pressure. This lowers cardiac stroke volume, and requires a higher heart rate to maintain a given cardiac output. Mechanisms which alleviate some of the cardiovascular strain produced by exercise in the heat include the following: acutely, reflexes which arise from receptors in working muscles produce vasoconstriction in a number of central and peripheral vascular beds. Other reflexes, arising from cardiac baroreceptors, produce additional peripheral vasoconstriction when cardiac filling is impaired. In the long term, physical conditioning and heat acclimation lead to increases in sweat output during thermal stress, leading to cooler skin and core temperature during exercise, and decreasing the level of skin blood flow needed for regulation of body temperature.

Arm↗
PubMed1978

Comparative thermoregulatory responses of resting men and women.

Three men and three women were exposed to transients of air temperature (range, 16--48 degrees C). Whole-body sweating rate, local tissue heat flows, and O2 consumption in the cold were linearly related to a weighted sum of tympanic and mean skin temperatures, called "central drive," During changes in air temperature, changes in subjects' scaled estimates of thermal sensation and discomfort led changes in the physiological responses and central drive. Women's thermoregulatory responses were similar to the men's, but were shifted toward higher (warmer) values of central drive. This shift was about 0.3 degrees C for responses to heat and about 0.6 degrees C for responses to cold. With respect to the women, the mean thus showed delayed responses to the cold, and approached steady state in the cold more slowly.

Body Temperature↗
PubMed1977

Skin blood flow and sweating changes following exercise training and heat acclimation.

Eight subjects underwent an exercise training program (10 days at 75% VO2max for 1 h/day at 25 degrees C db/13 degrees C wb) and a heat-acclimation program (10 days at 50% VO2max for 1 h/day at 35 degrees C db/32 degrees C wb). The relations of chest sweat rate and of forearm blood flow to internal temperature were determined for each subject at a 25 degrees C ambient temperature before training, between training and acclimation, and following acclimation. Training shifted the vasodilation and sweating thresholds toward lower internal temperatures, and acclimation further lowered these thresholds. All threshold shifts were statistically significant (P less than 0.05). Training and acclimation both appeared to increase the slope of the sweating relation, but these effects were not statistically significant. Changes in the slope of the blood flow relation were small and inconsistent. Since arm blood flow is higher at any given internal temperature after acclimation, the lower blood flow which is reported to accompany heat acclimation must result from the lower body temperatures.

Acclimatization↗
PubMed1976

Nocturnal lowering of thresholds for sweating and vasodilation.

Six subjects exercised on a bicycle ergometer at 60-70% of maximal aerobic power in a 25 degrees C ambient. Experiments on each subject were conducted at night (4:00-5:30 A.M.) and in daytime (noon-4:30 P.M.). Chest sweating rate (msw) was measured with resistance hygrometry. Forearm blood flow (BF), with an arm skin temperature of 35.5 +/- 1.2 degrees C (SD), was measured with electrocapacitance plethysmography. Esophageal temperature (Tes) was measured with a thermocouple at the level of the left atrium, and mean skin temperature (Tsk) was calculated from a weighted average of temperatures at three sites. Tes was corrected to a skin temperature of 33 degrees C as follows: T'es = Tes + (Tsk - 33 degrees C)/8. This correction reflects the relative contributions of Tes and Tsk to control of msw:T'es and BF:T'es relations were not consistently changed. In any given subject, thresholds for sweating and vasodilation were shifted about equally. These shifts averaged 0.57 degrees C (range: 0.23-0.93 degrees C)for msw and 0.63 degrees C (range: 0.17-0.98 degrees C) for BF.

Adult↗
PubMed1975

Forearm blood flow during body temperature transients produced by leg exercise.

Subjects exercised for 30 min on a bicycle ergometer at 30, 50, and 70% of maximal aerobic power in ambient temperatures of 15, 25, and 35 degrees C and vapor pressures of less than 18 Torr. Exercise was used to vary internal temperature during an experiment, and different ambient temperatures were used to vary skin temperatures independently of internal temperature. Forearm skin temperature was fixed at about 36.5 degrees C. Esophageal temperature (Tes) was measured with a thermocouple at the level of the left atrium, and mean skin temperature (Tsk) was calculated from a weighted mean of thermocouple temperatures at eight skin sites. Forearm blood flow (BF) was measured by electrocapacitance plethysmography. Our data are well accounted for by an equation of the form BF = a1Tes + q2Tsk + b, independent of exercise intensity, although some subjects showed an equivocal vasodilator effect of exercise. The ratios a1/a2 (7.5, 9.6, 11.7) are quite similar to the ratios (8.6, 10.4) of the corresponding coefficients in two recent models of thermoregulatory sweating.

Adult↗
PubMed1975

Thermoregulatory control of finger blood flow.

Three men exercised on a bicycle ergometer at 30, 50, asd 70 per cent of maximal aerobic power in ambient temperatures of 15, 25, and 35 degrees C with water vapor pressure less than 18 Torr. Exercies was used to vary internal temperature during as experiment, and different ambient temperatures were used to vary skin temperatures independently of internal temperature. Finger temperature was fixed at about 35.7 degrees C. Espohageal temperature (Tes) was measured with a thermocouple at the level of the left atrium, and mean skin temperature (Tsk) was calcualted from a weighted mean of thermocouple temperatures at eight skin sites. Finger blood flow (BF) was measured by electrocapacitance plethysmography. Although some subjects showed small and equivocal vasomotor effects of exercise, our data are well accounted for by an equation of the form BF equal to alTes + a2Tsk + b, independent of exercise intensity. For these subjects, the ratios a1/a2 (5.9, 8.6, 9.4) were similar to the ratios of the corresponding coefficients recently reported for thermaoregulatory sweating (8.6, 10.4) and for forearm blood flow (9.6).

Adult↗
PubMed1974

Effects of buoyancy and of magnetic forces on osmotic pressure.

The commonly held view that the mechanism of osmotic pressure is a mass action effect at the semi-permeable membrane has recently been challenged by several authors who propose that solute molecules, in bombarding the free surface of the solution, subject the solvent to a negative hydrostatic pressure. Thus, they argue that osmotic pressure is a purely hydrostatic phenomenon. Experimental findings that they cite in support of their concept are here analyzed and shown to be consistent with the mechanism of a mass action effect at the semipermeable membrane.

Hydrostatic Pressure↗