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Biomedical subjects

Y Epstein

Publications and source records attributed to Y Epstein.

At least 91 records · Page 5Linked to original sources
PubMed1987

Predicting metabolic cost of running with and without backpack loads.

In the past, a mathematical equation to predict the metabolic cost of standing or walking (Mw) was developed. However, this equation was limited to speeds less than 2.2 m.s-1 and overestimated the metabolic cost of walking or running at higher speeds. The purpose of this study was, therefore, to develop a mathematical model for the metabolic cost of running (Mr), in order to be able to predict the metabolic cost under a wide range of speeds, external loads and grades. Twelve male subjects were tested on a level treadmill under different combinations of speed and external load. Speed varied between 2.2 to 3.2 m.s-1 using 0.2 m.s-1 intervals and external loads between 0-30 kg with 10 kg intervals. Four of the subjects were also tested at 2 and 4% incline while speed and load remained constant (2.4 m.s-1, 20 kg). The model developed is based on Mw and is proportionately linear with external load (L) carried as follows: Mr = Mw-0.5 (1-0.01L)(Mw -15L-850), (watt) The correlation coefficient between predicted and observed values was 0.99 (P less than 0.01) with SER of 7.7%. The accuracy of the model was validated by its ability to predict the metabolic cost of running under different conditions extracted from the literature. A highly significant correlation (r = 0.95, P less than 0.02, SER = 6.5%) was found between our predicted and the reported values. In conclusion, the new equation permits accurate calculation of energy cost of running under a large range of speeds, external loads and inclines.

Adult↗
PubMed1987

Changes of white blood cell count during prolonged exercise.

Leukocytosis was postulated to accompany short- and medium-length exercise; in this report, we have studied the changes in leukocyte count during and following prolonged exercise. White blood cell (WBC) counts were obtained in 15 endurance-trained subjects before, during, and at a recovery period after an ultralong exercise (120 km march), lasting 24 h. WBC counts increased after 16 h march from a baseline value of 8.5 +/- 0.3 10(9) l-1 to 11.3 +/- 0.8 10(9) l-1 (P less than 0.05) and then declined to 7.1 +/- 0.9 10(9) l-1 after 24 h march with no further significant changes during 64 h of recovery. These observations were supported by previous findings in three separate marches performed by a second group (40, 70, and 120 km). A parallel increase in plasma creatine phosphokinase activity from 127 +/- 4.4 ul-1 to 539 +/- 106.3 ul-1 was observed after 16 h march (P less than 0.01), indicating muscle cell damage. Our findings suggest that in extremely long marches, WBC counts return to baseline values before exercise is terminated. This phenomenon may reflect WBC infiltration to damaged muscle tissue.

Adult↗
PubMed1987

Changes in serum magnesium concentration after strenuous exercise.

Serum magnesium concentration (S-Mg) was measured in 20 highly trained young men (mean age 19.5, +/- 0.5, range 18-20.5) before, and at 1 hour, 24 hours, 72 hours, and 3 months after a 120 km hike. As found in previous studies, S-Mg was significantly decreased at the end of the hike (p less than 0.001, [corrected] Student's t-test). In this group S-Mg had risen significantly after 24 hours in relation to the value at 1 hour (but not to starting value); yet, at 72 hours and 3 months later, it was once more significantly lower than the starting value (p less than 0.001 and p less than 0.05, respectively, Student's t-test). A marked elevation in serum creatine kinase activity (CK) suggests that the rise in S-Mg observed at 24 hours is the result of either exertional rhabdomyolysis or loss of membrane integrity, as a result of the strenuous exertion, since the CK had fallen sharply by 72 hours after the hike. The biphasic, statistically significant, lowering of S-Mg which persisted after 3 months suggests that strenuous exertion induces magnesium deficiency.

Adolescent↗
PubMed1987

Cooling different body surfaces during upper and lower body exercise.

The effect of varying the body surface area being cooled by a liquid microclimate system was evaluated during exercise heat-stress conditions. Six male subjects performed a total of six exercise (O2 uptake = 1.2 l/min) tests in a hot environment (ambient temperature = 38 degrees C, relative humidity = 30%) while dressed in clothing having low moisture permeability and high insulation. Each subject completed two upper body exercise (U; arm crank) tests: 1) with only the torso surface (T) cooled; and 2) with the surfaces of both the torso and upper arms (TA) cooled [coolant temperature at the inlet (Ti) was 20 degrees C for all upper body tests]. Each subject also completed four lower body exercise (L; walking) tests: 1) with only the T cooled (Ti = 20 degrees C); 2) with only the T cooled (Ti = 26 degrees C); 3) with torso, upper arm, and thigh surface (TAT) cooled (Ti = 20 degrees C); and 4) with TAT cooled (Ti = 26 degrees C). During U exercise, TA cooling had no effects compared with cooling only T. During L exercise, sweat rates, heart rates, and rectal temperature (Tre) changes were less with TAT cooling compared with cooling only the T. Altering Ti had no effect on Tre changes, but higher heart rates were observed with 26 than with 20 degrees C. These data indicate that cooling arms during upper body exercise provides no thermoregulatory advantage, although cooling the thigh surfaces during lower body exercise does provide an advantage.

Adult↗
PubMed1986

Increase in rat intestinal permeability to endotoxin during hyperthermia.

Victims of heat stroke exhibit several clinical features which are also encountered in endotoxaemia. In order to investigate these similarities hyperthermic rats were used to explore the possibility that high body temperature results in increased permeability of intestinal wall to endotoxin. 125I endotoxin was introduced into intestinal segments taken from non-heat exposed rats. The segments were then incubated at 37 degrees C or 45 degrees C. Intestinal segments from heat stressed rats were similarly prepared and incubated at 37 degrees C. Leakage of endotoxin from segments taken from heat stressed rats was three times greater than from those from non-heat stressed rats, as were the segments from non-heat stressed rats which were incubated at 45 degrees C. These results indicate that the intestinal membrane is damaged by heat and that an increase in outward leakage of microbial endotoxins from the gut then occurs. This might contribute to the pathophysiological picture of heatstroke.

Animals↗
PubMed1985

Effect of food intake on exercise fatigue in trained and untrained subjects.

The effects of carbohydrate and fat intake on exercise-induced fatigue was investigated in 30 untrained--(VO2max of 40.6 +/- 2.7 ml X kg-1 X min-1) and 24 trained-subjects (VO2max of 52.3 +/- 2.7 ml X kg-1 X min-1) performing a 34 km march with a 25 kg backpack. Marching time was 8 1/2 h and 6 1/3 h in the untrained and trained-subjects respectively. The subjects were divided into 3 dietary groups. One group had free access to sugar cubes, the second group was offered almonds and the third one served as a control. Triglyceride levels decreased by 65 mg X dl-1 in untrained, and by 115 mg X dl-1 in trained subjects, while blood glucose remained at normal levels. In the untrained subjects, ingestion of almonds delayed the subjective sensation of exhaustion, while 50% of the controls and the sugar consuming subjects complained of exhaustion. The data suggest that ingestion of food containing fat delays exercise induced exhaustion or fatigue to a greater extent than does carbohydrate ingestion.

Adolescent↗
PubMed1985

Fatal heatstroke after a short march at night: a case report.

A case of heatstroke is reported in a young recruit who participated in a 4-km march at night. Body temperature was not measured at the time of collapse. Hyperventilation and aggressive behavior misled to the incorrect diagnosis of hysteric reaction. Upon arrival at the Medical Center 4h later, the patient experienced deep coma, renal failure, shock, and uncontrolled bleeding. Inspite of intensive treatment, the patient died 27 h after collapse. A positive blood culture suggests the involvement of septicemia in the fulminant picture of the disease. The importance of immediate measurement of rectal temperature in any case of collapse after exercise is emphasized.

Adolescent↗
PubMed1984

Serum creatine kinase activity following a 120-km march.

Serum creatine kinase (SCK) was measured in 19 well-trained athletes before, immediately after and 24 and 72 h after a 120-km, non-stop march. The mean level before the march was 97.6 +/- 46.6 (SD), immediately after the march 1072.8 +/- 708 microns/l, and 72 h later 185.6 +/- 106.2 microns/l. It is concluded that elevated SCK levels may persist for 72 h after a long march.

Adult↗
PubMed1984

The scotopic threshold of the human retina during static physical effort.

The scotopic threshold of 15 subjects was measured with a 1 degree circular white stimulus light placed at 15 degrees below the fixation level during 45 min at rest followed by 20 min constant pedalling on an ergometric bicycle with the head stationary. Loads were adjusted individually so that the effort extended by each subject required 60-75% of his maximum oxygen uptake. Similar results were obtained under both resting and effort conditions, indicating that the dark adaptation threshold remained unaffected by vigorous static effort.

Adolescent↗
PubMed1983

External inspiratory resistance of protective respiratory devices: effects on physical performance and respiratory function.

Twenty subjects wearing protective respirators were studied during submaximal exercise (80% of VO2max) on a treadmill. The protective devices were fitted with canister filters of low expiratory resistance and different inspiratory resistances: (0.3, 1.8, 2.8, 3.4, 3.9, and 4.6 cm H2O X sec/liter). The effect of inspiratory resistance on physical endurance, various physiological parameters, and subjective sensations was examined. With the increase in inspiratory resistance, a significant decrease in physical performance, decrease in tidal volume, increased ratio of inspiratory to expiratory time, increased peak inspiratory pressure, and increased CO2 retention were observed. The difficulty in inspiration correlated significantly to inspiratory resistance and seems to be the main reason for cessation of the effort. No acceptable upper limit for the inspiratory resistance of the canister filters was found. Any decrease in the inspiratory resistance of the mask's filter enhanced endurance and performance.

Adult↗
PubMed1983

Changes in hypothalamic and extra-hypothalamic vasopressin content of water-deprived rats.

A correlative radioimmunoassay (RIA) and immunocytochemical (ICC) study was carried out on vasopressin (VP) distribution and content in brains of normal and 3-day water-deprived rats. By RIA there were statistically significant differences in brain VP per pg/mg between normal and osmotically stressed specimens in hypothalamus (338.4 versus 134.4), thalamus (4.8 versus 0.9), septum (18.0 versus 3.4), striatum (1.6 versus 0.7) and amygdala (17.3 versus 1.3), but not in other brain regions measured. Pituitary VP decreased from 71.1 to 8.7 ng/mg, and plasma VP rose from 3.6 to 19.3 pg/ml during water deprivation. Application of the peroxidase-anti-peroxidase ICC method of Sternberger to vibratome sections showed that VP-immunoreactivity in dehydrated specimens decreased in perikarya of paraventricular nucleus and suprachiasmatic nucleus, while intrahypothalamic immunoreactive magnocellular fibers appeared more conspicuous due to proliferation of large Herring bodies. In extrahypothalamic sites VP-immunoreactivity in water-deprived rats was visibly reduced in periventricular thalamus and septum. Thus it is apparent that both intra- and extrahypothalamic VP are affected by osmotic stress, and these results are discussed within the context of current ideas relating to co-activation of neurosecretory cells that project to different sites.

Animals↗
PubMed1982

March myoglobinemia: a hazard to renal function.

Serum muscle enzyme levels, myoglobin levels, and renal function were measured in a group of 20 army recruits who had volunteered for a prolonged period of primary, specially designed, gradual training. Blood samples were taken before training and before and after each hike. Levels of serum myoglobin, creatinine phosphokinase, lactic dehydrogenase, and SGOT indicated muscle injury. Levels of urea creatinine, and uric acid and creatinine clearance evaluated renal function. Substantial elevation of muscle enzyme levels and persistent myoglobinemia were observed throughout the study. A highly significant decrease in creatinine clearance was demonstrated. After the last hike, the mean creatinine clearance was 70.41 mL/min, which is notably lower than the value at the beginning of the study. Prolonged physical exercise induces muscular damage, as evidenced by a rise in myoglobin and enzyme levels. Continuous muscle injury induces persistent myoglobinemia, a probable hazard to renal function.

Acute Kidney Injury↗
PubMed1982

Thermoregulatory responses of patients with extensive healed burns.

Two groups (A, n = 4; B, n = 6) of young male subjects with deep second- and third-degree healed burns (burned area: 48.6 +/- 3.6 and 23.7 +/- 3.1% of the total skin surface area in groups A and B, respectively) and a group of healthy subjects (C, n = 10) underwent a 3-h exposure to 40 degrees C, 50% rh, stepping on a bench 32 cm high, at a rate of 12 steps/min (Vo2 = 1.05 +/- 0.06 l X min-1). Rectal temperature (Tre), mean skin temperature (Tsk), and heart rate (HR) of group A were significantly higher than those of groups B and C; i.e., at the end of the 1st h Tre was 38.7, 37.9, and 37.7 degrees C; Tsk was 37.3, 36.4, and 37.0 degrees C; HR was 151, 105, and 110 beats X min-1 in groups A, B and C respectively. Maximal evaporative cooling capacity (Emax) was 4.9 +/- 0.1, 7.2 +/- 0.5, and 10.2 +/- 0.4 W X kg-1 in groups A, B and C, respectively, while the required evaporation capacity for thermoequilibrium (Ereq) was similar in all groups (6.7 +/- 0.1, 6.8 +/- 0.1, and 6.6 +/- 0.1 W X kg-1). Total sweat rate (msw) was 594 +/- 13, 602 +/- 29, and 485 +/- 34 g X h-1 in groups A, B and C, respectively, msw normalized to healthy skin area (msw/AH) was 671 +/- 75, 449 +/- 29, and 280 +/- 16 g X h-1 X m-2 in groups A, B and C, respectively. Sweating sensitivity normalized to healthy skin area (msw/AH X delta Tre) was similar in all three groups. It is suggested that the similarity between groups B and C can be explained by the compensatory sweating from the healthy skin of group B, which was sufficient because Emax greater than Ereq. In group A, Emax less than Ereq; therefore thermoequilibrium could not be maintained despite high compensatory sweat rate from the healthy skin. The similarity in msw/AH X delta Tre supports the assumption that elevation in Tre is the main drive of sweat regulation and that sweat rate is a function of delta Tre and healthy skin surface area.

Adult↗
PubMed1982

Physiological and psychological adaptation to respiratory protective devices.

This study was conducted to investigate the adaptation process to respiratory protective devices (RPD). Twenty healthy subjects were tested at 80% of their Vo2 max for 6 consecutive days with a fitted RPD with an airway resistance of 2.80 +/- 0.07 cm H2O s/1. It was concluded that working with RPD at a work capacity close to maximum for several minutes per day induces a rapid adaptation process. This is demonstrated by an improvement in physiological parameters rather than in subjective sensations.

Adaptation, Physiological↗