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Biomedical subjects

R R Gonzalez

Publications and source records attributed to R R Gonzalez.

At least 55 records · Page 3Linked to original sources
PubMed1988

Thermoregulatory model for immersion of humans in cold water.

The mathematical models of thermoregulation of Stolwijk and Hardy, and Montgomery were used to develop a model suitable for the simulation of human physiological responses to cold-water immersion. Data were obtained from experiments where 13 healthy male volunteers were totally immersed under resting and nude conditions for 1 h in water temperatures of 20 and 28 degrees C. At these temperatures, the mean measured rectal temperature (Tre) fell by approximately 0.9 and 0.5 degrees C, respectively, yet mean measured metabolic rate (M) rose by approximately 275 and 90 W for the low body fat group (n = 7) and 195 and 45 W for the moderate body fat group (n = 6). To predict the observed Tre and M values, the present model 1) included thermal inputs for shivering from the skin independent of their inclusion with the central temperature to account for the observed initial rapid rise in M, 2) determined a thermally neutral body temperature profile such that the measured and predicted initial values of Tre and M were matched, 3) confined the initial shivering to the trunk region to avoid an overly large predicted initial rate of rectal cooling, and 4) calculated the steady-state convective heat loss by assuming a zero heat storage in the skin compartment to circumvent the acute sensitivity to the small skin-water temperature difference when using conventional methods. The last three modifications are unique to thermoregulatory modeling.

Body Temperature Regulation↗
PubMed1988

Thermoregulatory responses of middle-aged and young men during dry-heat acclimation.

Thermoregulatory responses during heat acclimation were compared between nine young (mean age 21.2 yr) and nine middle-aged men (mean age 46.4 yr) who were matched (P greater than 0.05) for body weight, surface area, surface area-to-weight ratio, percent body fat, and maximal aerobic power. After evaluation in a comfortable environment (22 degrees C, 50% relative humidity), the men were heat acclimated by treadmill walking (1.56 m/s, 5% grade) for two 50-min exercise bouts separated by 10 min of rest for 10 consecutive days in a hot dry (49 degrees C ambient temperature, 20% relative humidity) environment. During the first day of heat exposure performance time was 27 min longer (P less than 0.05) for the middle-aged men, whereas final rectal and skin temperatures and heart rate were lower, and final total body sweat loss was higher (P less than 0.05) compared with the young men. These thermoregulatory advantages for the middle-aged men persisted for the first few days of exercise-heat acclimation (P less than 0.05). After acclimation no thermoregulatory or performance time differences were observed between groups (P greater than 0.05). Sweating sensitivity, esophageal temperature at sweating onset, and the sweating onset time did not differ (P greater than 0.05) between groups either pre- or postacclimatization. Plasma osmolality and sodium concentration were slightly lower for the young men both pre- and postacclimatization; however, both groups had a similar percent change in plasma volume from rest to exercise during these tests.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1988

Prediction of human thermoregulatory responses and endurance time in water at 20 and 24 degrees C.

A multi-compartmental mathematical model for predicting human thermoregulatory responses was applied to immersion in moderately cold water. Data were used from experiments where eight healthy male volunteers were immersed nude and up to the neck for 1 h in water at 20 and 24 degrees C under conditions of rest and exercise. Rectal temperature and metabolic rate were measured before and during immersion. Once agreement between the model prediction and experimental observation was obtained, the model was used for prediction beyond the duration of the experiment. Stabilization of core temperature was predicted after 4-5 h of immersion for rest and after 2-4 h for exercise. Stabilization for resting individuals has been observed in other experiments under similar conditions. These results suggest that linear extrapolations based on linear body cooling rates are inadequate for predicting endurance times in moderately cold water. In this study, predicted endurance times were based on the concept of relative exercise intensity and are in agreement with the limited data available.

Body Temperature Regulation↗
PubMed1988

Autologous red blood cell reinfusion: effects on stress and fluid regulatory hormones during exercise in the heat.

This study assessed the effects of induced erythrocythemia on stress and fluid regulatory hormones during walking exercise in the heat. Six unacclimated male subjects received approximately 600 ml of a sterile saline solution containing 50% volume-to-volume of autologous erythrocytes. Three heat stress tests (HSTs) were attempted: one approximately 2 weeks prior to the reinfusion procedure, a second 48 h after the reinfusion procedure, and a third 1 week later, corresponding to 9 d subsequent to reinfusion. Each HST comprised three consecutive 45-min exercise and 15-min rest intervals (VO2 approximately 2.0 L.min-1, 1.56 m.s-1, 6% incline, 35 degrees C, 45% rh). Blood was withdrawn before the HST and 30 min into each exercise (EX) bout. In all three HST's plasma cortisol (PC) levels were significantly (p less than 0.01) reduced during the first EX bout compared to preexercise levels, and then progressively increased during the second and third EX intervals during HST 1. During HST 2 (48 h postinfusion), however, PC levels were significantly (p less than 0.05) reduced in two blood samples (EX 2, 3) compared to the same blood samples from HST-1 (preinfusion). Plasma renin activity (PRA) and aldosterone (ALD) were significantly (p less than 0.01) increased by the exercise/heat stress, but were unaffected by erythrocythemia either 48 h or 9 d subsequent to reinfusion. PRA and ALD were correlated (r = 0.84, p less than 0.001) under all conditions. We concluded from this study that acutely induced erythrocythemia reduced the stress response to consecutive exercise/heat intervals as manifested in PC responses during HST 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Role of body fat in the prediction of the metabolic response for immersion in cold water.

Several empirical models for predicting the metabolic response to a lowered body temperature have been evaluated against available data of young healthy males immersed in cold water under resting conditions. Nude immersions took place in 20 and 24 degrees C water for 1 h, and clothed immersions took place in 10 and 15 degrees C for 3 h. The data were pooled according to low and high percent body fat (%BF). Decreases in the mean weighted skin temperature (Tsk) ranged from 5.3 to 11.9 degrees C and decreases in the core temperature (Tc) ranged from 0.56 to 1.54 degrees C, while increases in the metabolic rate over the immersion period ranged from 34 to 256 W. Through regression analysis, an inverse relationship between %BF and the metabolic response for a given lowered Tsk and lowered Tc was established. When this relationship was explicitly applied to the models, significant improvements in their predictive capability were found. Variables such as body weight, body surface area, and the rate of change of Tsk were not found to contribute to the predictive capability of the models.

Adipose Tissue↗
PubMed1987

Erythrocyte reinfusion and maximal aerobic power. An examination of modifying factors.

Induced erythrocythemia is associated with a variable increase in maximal oxygen uptake. To examine the roles of the magnitude of change in hemoglobin concentration and the individual's initial aerobic fitness in this effect, we combined individual data from our own research and three other studies. In each study freeze-preserved erythrocytes from the product of 2 units of blood were reinfused, and maximal oxygen uptake was measured within 24 to 72 hours after reinfusion. The 30 subjects had an initial aerobic power of 36 to 88 mL of oxygen per kilogram per minute. The combined results from these studies indicate that after erythrocyte reinfusion the increase in hemoglobin concentration is fairly homogeneous (mean +/- SD, 1.36 +/- 0.6 g/dL [13.6 +/- 6 g/L]), nearly all individuals demonstrate an increase in maximal oxygen uptake (0.357 +/- 0.216 L/min), the magnitude of increase in hemoglobin concentration is not related to the magnitude of increase in maximal oxygen uptake, and the magnitude of increase in maximal oxygen uptake is related to the individual's initial aerobic fitness. Individuals with an initial aerobic fitness between 50 and 65 mL X kg-1 X min-1 experience approximately twice the increase in maximal oxygen uptake after erythrocyte reinfusion of individuals with greater fitness and also of lesser fitness.

Aerobiosis↗
PubMed1987

Influence of polycythemia on blood volume and thermoregulation during exercise-heat stress.

We studied the effects of autologous erythrocyte infusion on blood volume and thermoregulation during exercise in the heat. By use of a double-blind design, nine unacclimated male subjects were infused with either 600 ml of a NaCl-glucose-phosphate solution containing a approximately 50% hematocrit (n = 6, reinfusion) or 600 ml of this solution only (n = 3, saline). A heat stress test (HST) was attempted approximately 2-wk pre- and 48-h postinfusion during the late spring months. After 30 min of rest in a 20 degrees C antechamber, the HST consisted of a 120-min exposure (2 repeats of 15 min rest and 45 min treadmill walking) in a hot (35 degrees C, 45% rh) environment while euhydrated. Erythrocyte volume (RCV, 51Cr) and plasma volume (PV, 125I) were measured 24 h before each HST, and maximal O2 uptake (VO2max) was measured 24 h after each HST. Generally, no significant effects were found for the saline group. For the reinfusion group, RCV (11%, P less than 0.01) and VO2max (11%, P less than 0.05) increased after infusion, and the following observations were made: 1) the increased RCV was associated with a reduction in PV to maintain the same blood volume as during the preinfusion measurements; 2) polycythemia reduced total circulating protein but did not alter F-cell ratio, plasma osmolality, plasma protein content, or plasma lactate at rest or during exercise-heat stress; 3) polycythemia did not change the volume of fluid entering the intravascular space from rest to exercise-heat stress; and 4) polycythemia tended to reduce the rate of heat storage during exercise-heat stress.

Blood Proteins↗
PubMed1987

Local sweating and cutaneous blood flow during exercise in hypobaric environments.

The effect of acute hypobaric hypoxia on local sweating and cutaneous blood flow was studied in four men and four women (follicular phase of menstrual cycle), who exercised at 60% of their altitude-specific peak aerobic power for 35 min at barometric pressures (PB) of 770 Torr (sea level), 552 Torr (2,596 m), and 428 Torr (4,575 m) at an ambient temperature of 30 degrees C. We measured esophageal temperature (Tes), mean skin temperature (Tsk, 8 sites), and local sweating (ms) from dew-point sensors attached to the skin at the chest, arm, and thigh. Skin blood flow (SkBF) of the forearm was measured once each minute by venous occlusion plethysmography. There were no gender differences in the sensitivity (slope) or the threshold of either ms/Tes or SkBF/Tes at any altitude. No change in the Tes for sweating onset occurred with altitude. The mean slopes of the ms/Tes relationships for the three regional sites decreased with increasing altitude, although these differences were not significant between the two lower PBS. The slope of SkBF/Tes was reduced in five of the eight subjects at 428 Torr. Enhanced body cooling as a response to the higher evaporative capacity of the environment is suggested as a component of these peripheral changes occurring in hypobaric hypoxia.

Adult↗
PubMed1987

Biophysical and physiological integration of proper clothing for exercise.

In this chapter, I have presented a potpourri of examples of proper clothing to wear during various exercise demands in different environments. These examples are not wholly exact for all persons. For example, during the 1984 Olympics in Los Angeles, clothing wear related to the particular environment was totally different. We have already described the aerodynamic necessities of cyclists and runners. At the other extreme, equestrians had to contend with a warm, moderately humid environment, plus a solar load that added to the effective heat stress, while wearing clothing having clo values of nearly 0.8-0.9, plus headgear that limited evaporative heat loss. Obviously, garments with high water vapor permeation and bellows properties were necessary. Runners in the marathon faced equal thermal challenges. In addition, they incurred variable levels of hypovolemia and cardiovascular strain. A. Salazar, for example, was advised to omit shower sprays, and he ran with a prototype high-permeability singlet. The excessive wetting plus time to maneuver to the spray was deemed of no value, since Mr. Salazar chafes easily from wet clothes (L. Armstrong, personnel communication). One interesting response to this advice is to consider the clothed runner as a wet globe thermometer under forced convection. A high-contact fabric, especially one like cotton, does allow evaporative cooling, provided that the skin-ambient vapor pressure gradient is not diminished by high relative humidity. Salts in sweat may reduce the skin's vapor pressure ; however, Woodcock and Breckenridge point out that "secreted sweat (especially with heat acclimation) is so dilute that no appreciable lowering of vapor pressure would occur unless sweat were concentrated many times by evaporation." Thus, the degree of "human" wet bulb depression simulated by a completely wet runner may or may not be an advantage, since all other variables are also constant (i.e., humidity, weight of clothing as in Figure 13, etc.) or the level of hypovolemia is not excessive and the person is fully heat acclimated. Problems such as these may be theoretical, but they serve to show that the thermal biophysics and physiology of exercise follow similar fundamental pathways that can be highly pertinent. As we sought to point out in this chapter, these pathways have merged in the last 30 years with developments such as warmth without bulk for backpackers (which is a welcomed contrast to heavy arctic wear), materials that allow athletes to remain somewhat comfortable while sweating, and other advances that luckily have replaced the less appealing sports apparel such as the old woolen baseball uniform.(ABSTRACT TRUNCATED AT 400 WORDS)

Biophysical Phenomena↗
PubMed1987

Human thermoregulation after atropine and/or pralidoxime administration.

The effects of intramuscular saline (control), atropine (2 mg), and/or pralidoxime (600 mg) on heat exchange was evaluated in four healthy males during seated, cycle exercise (55% Vo2 peak) in a temperate environment (Ta = 30.3 degrees C, Pw = 1.0 kPa). Esophageal (Tes), rectal (Tre), and mean skin temperatures (Tsk), and chest and forearm sweating (ms) were continuously measured. Skin blood flow (FBF) from the forearm was measured twice each minute by venous occlusion plethysmography. Whole body sweating was calculated from weight changes. The expected result of atropine injection, decreased eccrine sweating (-60%, p less than 0.05) and elevated esophageal (+0.4 degree C, p less than 0.05) and skin temperatures (+2.1 degrees C, p less than 0.05) was observed relative to control. Heart rate (+28 b X min-1) and FBF (+9 ml X 100 ml-1 X min-1) were higher after atropine. Pralidoxime, in general, did not affect the core and skin temperature responses to the exercise differently from control; however, a slightly elevated FBF (+3 ml X 100 cc-1 X min-1, 33%) compensated for the reduction in whole body sweating (-45%, p less than 0.05] that we observed. The combination of the drugs resulted in significantly higher esophageal (0.4 degree C) and skin (0.9 degree C) temperatures than atropine alone, as has been previously shown. The thermoregulatory disadvantage of inhibited sweating by atropine was partially compensated for by enhanced skin blood flow in this environment where Ta less than Tsk. Pralidoxime was shown to decrease whole body sweating, by a mechanism as yet unexplained.

Adult↗
PubMed1987

Elite special forces: physiological description and ergogenic influence of blood reinfusion.

We measured the physical exercise capabilities of U.S. Army Special Forces soldiers (male) and determined the subsequent ergogenic influence of autologous blood reinfusion. Twelve subjects (Ss) completed maximal exercise treadmill testing in a comfortable (Ta = 20 degrees C, Tdp = 9 degrees C) environment. Six Ss were later transfused with a 600 ml autologous red blood cell (50% Hct) NaCl glucose-phosphate solution and completed identical maximal exercise tests 3 and 10 d posttransfusion. Pretransfusion, the 12 Ss had a maximal oxygen uptake (VO2max) of 4.36 +/- 0.56 L . min-1 and 55 +/- 4 ml . kg-1 . min-1 with a heart rate of 188 +/- 10 b . min-1 and ventilatory equivalent for oxygen of 37 +/- 3. For the 6 reinfused Ss, hemoglobin and red cell volume (RCV) increased by 10% (p less than 0.05) and 11% (p less than 0.05), respectively, posttransfusion. Reinfusion increased (p less than 0.05) VO2max from 4.28 +/- 0.22 L . min-1 (54 +/- 5 ml . kg-1 . min-1) to 4.75 +/- 0.42 L . min-1 (60 +/- 6 ml . kg-1 . min-1) and 4.63 +/- 0.21 L . min-1 (59 +/- 6 ml . kg-1 . min-1) at 3 and 10 d posttransfusion, respectively. No significant relationship was found between the individual change in RCV and VO2max values pre- to posttransfusion. We conclude that Special Forces soldiers have high levels of aerobic fitness that can be further increased by blood reinfusion for at least 10 d.

Adult↗
PubMed1986

Prediction modeling of physiological responses and human performance in the heat.

Over the last two decades, our laboratory has been establishing the data base and developing a series of predictive equations for deep body temperature, heart rate and sweat loss responses of clothed soldiers performing physical work at various environmental extremes. Individual predictive equations for rectal temperature, heart rate and sweat loss as a function of the physical work intensity, environmental conditions and particular clothing ensemble have been published in the open literature. In addition, important modifying factors such as energy expenditure, state of heat acclimation and solar heat load have been evaluated and appropriate predictive equations developed. Currently, we have developed a comprehensive model which is programmed on a Hewlett-Packard 41 CV hand held calculator. The primary physiological inputs are deep body (rectal) temperature and sweat loss while the predicted outputs are the expected physical work--rest cycle, the maximum single physical work time if appropriate, and the associated water requirements. This paper presents the mathematical basis employed in the development of the various individual predictive equations of our heat stress model. In addition, our current heat stress prediction model as programmed on the HP 41 CV is discussed from the standpoint of propriety in meeting the Army's needs and therefore assisting in military mission accomplishment.

Acclimatization↗
PubMed1986

Human thermoregulatory responses to cold air are altered by repeated cold water immersion.

The effects of repeated cold water immersion on thermoregulatory responses to cold air were studied in seven males. A cold air stress test (CAST) was performed before and after completion of an acclimation program consisting of daily 90-min cold (18 degrees C) water immersion, repeated 5 times/wk for 5 consecutive wk. The CAST consisted of resting 30 min in a comfortable [24 degrees C, 30% relative humidity (rh)] environment followed by 90 min in cold (5 degrees C, 30% rh) air. Pre- and postacclimation, metabolism (M) increased (P less than 0.01) by 85% during the first 10 min of CAST and thereafter rose slowly. After acclimation, M was lower (P less than 0.02) at 10 min of CAST compared with before, but by 30 min M was the same. Therefore, shivering onset may have been delayed following acclimation. After acclimation, rectal temperature (Tre) was lower (P less than 0.01) before and during CAST, and the drop in Tre during CAST was greater (P less than 0.01) than before. Mean weighted skin temperature (Tsk) was lower (P less than 0.01) following acclimation than before, and acclimation resulted in a larger (P less than 0.02) Tre-to-Tsk gradient. Plasma norepinephrine increased during both CAST (P less than 0.002), but the increase was larger (P less than 0.004) following acclimation. These findings suggest that repeated cold water immersion stimulates development of true cold acclimation in humans as opposed to habituation. The cold acclimation produced appears to be of the insulative type.

Acclimatization↗
PubMed1986

Effect of Portuguese man-of-war venom on isolated vascular segments.

The purpose of this study was to characterize the mode of action of nematocyst venom from the Portuguese man-of-war (Physalia physalis) on isolated rabbit arterial ring segments, and to see if these in vitro effects were similar to those observed in the intact skeletal muscle vasculature of the dog (see Loredo et al., J. Pharmacol. Exp. Ther. 232: 301-304, 1985). The venom (0.021-4.28 micrograms/ml) produced dose-dependent relaxations of norepinephrine precontracted arterial segments from various vascular beds. Venom-induced relaxations were blocked by sodium meclofenamate (10-20 micrograms/ml), but not by atropine (6 micrograms/ml), propranolol (4-12 micrograms/ml) or quinacrine (2-4 X 10(-5) M). These results were similar to those observed in the intact skeletal muscle vascular bed of the dog and further implicate the stimulation of endogenous prostaglandin synthesis as the mechanism by which P. physalis venom dilates vasculature.

Animals↗
PubMed1985

Evaluation of vapor permeation through garments during exercise.

Five males [age 28 +/- 8 yr; maximum O2 uptake (VO2max) 50 +/- 6 ml O2 . kg-1 . min-1; body wt 70 +/- 3 kg; DuBois surface area 1.85 +/- 0.02 m2] exercised on a cycle ergometer, placed on a Potter scale, at 31% VO2max for up to 2 h at an ambient temperature (Ta) of 25 degrees C and a dew-point temperature of 15 degrees C. Air movement was varied from still air to 0.4 and 2 m/s. Each subject, in separate runs, wore a track suit (TS ensemble) of 60% polyester-40% cotton (effective clo = 0.5); a Gortex parka (GOR ensemble), covering a sweat shirt and bottom of TS (effective clo = 1.4); or the TS ensemble covered by polyethylene overgarment (POG ensemble). Esophageal, skin temperature (Tsk) at eight sites, and heart rate were continuously recorded. Dew-point sensors recorded temperatures under the garments at ambient and chest (windward site) and midscapular sites. Local skin wettedness (loc w) and ratio of evaporative heat loss (Esk) to maximum evaporative capacity were determined. An observed average effective permeation (Pe, W . m-2 . Torr-1) was calculated as Esk/loc w (Ps,sk - Pw), where w is the average of chest and back loc w and (Ps,sk - Pw) is the gradient of skin saturation vapor pressure at Tsk and Ta. Additionally, the local effective evaporative coefficient was determined for chest and back sites by Esk/(Ps,dpl - Pw). The GOR ensemble produced an almost as high a Pe as the TS ensemble (82-86% of Pe with TS in still air and 0.4- and 2-m/s conditions). Direct dew-point recording offers an easy practical dimension to the study of efficacy of latent heat loss and skin wettedness properties through garments.

Adult↗
PubMed1985

Vascular effects of Physalia physalis venom in the skeletal muscle of the dog.

The purpose of this study was to characterize the mode of action of the venom from Portuguese man-of-war (Physalia physalis) on the skeletal muscle vascular bed of dogs anesthetized with sodium pentobarbital (35 mg/kg). Venous outflow and the blood pressure difference across the hind-limb vascular bed were used to calculate changes in resistance due to close arterial injections of the venom (0.001-1 microgram/kg). The venom consistently produced dilations that were blocked by sodium meclofenamate (5 mg/kg). Atropine (1 mg/kg), propranolol, phentolamine, cimetidine (each 2 mg/kg) or tripelennamine (2.5 mg/kg) had no significant blocking effect. The venom also produced transient dilations on vascular beds predilated with histamine or prostaglandin E1, or preconstricted with norepinephrine (each 0.01 microgram/kg) or by sympathetic stimulation (12 V, 20 Hz). These data suggest that Physalia venom dilates skeletal muscle vasculature primarily by stimulation of endogenous prostaglandin synthesis.

Alprostadil↗
PubMed1985

Modification of Otis-McKerrow valve for measurement of respiratory water loss.

An apparatus is described that allows a continuous measurement of inspired and expired gas dew-point temperature for the calculation of water loss (Eres) during ventilation. A rapid response dew-point temperature measurement method is described which is based on a small Peltier module. The compact structure with near zero system dead space minimizes potential errors inherent in many techniques used to measure Eres. The simple design and rugged construction permit the incorporation of the apparatus into many manual or personal computer controlled oxygen consumption systems. Collection of data may be done in a variety of ambient temperatures, altitudes, and activity levels. There is also the potential for creating a portable system for field use.

Altitude↗