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Biomedical subjects

E Shvartz

Publications and source records attributed to E Shvartz.

At least 19 recordsLinked to original sources
PubMed1996

Endurance fitness and orthostatic tolerance.

BACKGROUND: Several lower body negative pressure studies conducted in recent years have suggested that aerobically fit individuals have poo-orthostatic tolerance (OT). HYPOTHESIS: There will be significant differences between OT of highly fit endurance runners and unfit individuals. METHODS: Subjects were 17 men and 17 women aged 29-42 yr who were administered two orthostatic tests (20 min standing) before, and 5 min following a VO2max test. There were 6 men and 6 women who were highly trained endurance runners with VO2max of 63 and 50 ml.kg-1.min-1 for the men and women, respectively; 6 men and 6 women had average fitness (VO2max of 40 and 32 ml.kg-1.min-1, respectively), and the remaining 5 men and 6 women had poor fitness (VO2max of 32 and 26 ml.kg-1.min-1, respectively). RESULTS: The trained men and women showed good OT before and after exercise, which was characterized by very low orthostatic heart rates (54 and 64 bpm before, 70 and 75 bpm after exercise, for the men and women, respectively); relatively large pulse pressures (PP); and a lack of any adverse subjective reactions. The untrained subjects' orthostatic heart rates were 30-40 bpm higher than in the trained subjects, (18 bpm higher after, vs. before exercise) their PP was narrower, and there were 7 cases of orthostatic weakness (dizziness, yawning) and 8 fainting episodes. (6 cases before, 9 cases after exercise). CONCLUSIONS: Aerobically fit individuals have good OT while unfit individuals show poor OT. Since the maintenance of good OT is important in the Space Shuttle flights, endurance training enhances crew/vehicle safety.

Adult↗
PubMed1990

Advantages of a low-oxygen environment in space cabins.

The advantages of having a low-oxygen environment in space cabins are discussed. The major advantage is a sharply reduced fire hazard, which is a major threat in manned space flights. At 1 atm, for example, 15% O2 (9,000 ft altitude equivalent) would not support most fires and could accommodate the crew with respect to hypoxia, decompression sickness (DCS), and other requirements. Chronic exposure to such a hypoxic environment (altitude acclimatization) could improve major areas of crew health and safety including alleviating deconditioning effects, decreasing susceptibility to DCS, and improving tolerance to severe hypoxia.

Ecological Systems, Closed↗
PubMed1990

Aerobic fitness norms for males and females aged 6 to 75 years: a review.

An extensive literature review was performed of studies where VO2max was measured directly in healthy, untrained subjects in the USA, Canada and 7 European countries to establish absolute (L/min) and relative (ml.kg-1.min-1) VO2max norms in males and females aged 6-75 years. Mean norms (L/min) in males show an increase from 1.0 L/min at age 6 years, to 2.0 and 3.4 L/min at ages 12 and 18 years, respectively, after which they decline with age to 3.2, 2.7, and 1.6 L/min for ages 30, 50, and 75 years, respectively. The corresponding values for females aged 6, 12, 18, 30, 50, and 75 years are 0.9, 1.8, 2.2, 1.8, and 1.1 L/min, respectively. Sex differences in relative VO2max are smaller than the above. Mean values for males for the above age groups are 47.5, 50, 48, 35, and 25 ml.kg-1.min-1, respectively, with corresponding values for females of 42.5, 44, 41, 28, and 17.5 ml.kg-1.min-1, respectively. These norms (L/min) are slightly lower than Robinson's 1938 data on males; they are only 1.5% lower compared with Astrand's adult males norms; but 2.5 to 10% lower than Astrand's norms for adult females. Present norms (ml.kg-1.min-1) for middle aged and older women are 25% lower than the corresponding Astrand's norms.

Adolescent↗
PubMed1983

Hemodynamic responses during prolonged sitting.

Eight young men (group A) underwent 5 h of quiet sitting, preceded by 30 min of recumbency, 20 min of standing, and 20 s of walking, and five other young men (group B) underwent 70 min of sitting, preceded by recumbency only, to determine the effects of prolonged sitting and previous posture on hemodynamic responses (measured by impedance plethysmography). Group A showed more calf blood pooling and a decrease in thigh blood flow during sitting in comparison with the control group, but after 1 h of sitting hemodynamic responses of the two groups were similar. Sitting for 5 h (1st vs. 5th h) resulted in an increase in calf venous pooling (17%) and a decrease in calf BF (13%), a reduction in gravitational pooling in the thigh (corresponding to increased pooling in the calf), increases in diastolic and mean arterial pressures (6 and 7.3 mmHg, respectively), and minor changes in heart rate, stroke volume, and cardiac output. The results show that it is necessary to sit for 1 h before hemodynamic responses can be assessed in this position, regardless of the posture maintained previously. The main effect of prolonged sitting is pooling in the calf, which is compensated for by an increase in peripheral resistance.

Adult↗
PubMed1983

Physiologic responses to exercise in normal and obese women.

The present study examines the possibility that the reduced activity commonly found in obese individuals could stem from a reduced physiological responsiveness to exercise. Responses to bicycle ergometer exercise (300 kpm/min) of four obese and four normal weight women were observed in a metabolic ward. This resulted in decreases in exercise heart rate and oxygen consumption, indicating an improvement in mechanical efficiency and suggesting an increase in physical working capacity. It also resulted in some decreases of resting oral temperature. The differences in the response to exercise between the obese and the normal weight groups were small and not statistically significant. The normal weight subjects showed a trend for greater decreases in heart rate and O2 consumption during exercise, while in the obese resting oral temperature tended to be more reduced. The results suggest that obesity in our subjects was not related to a deranged physiological response to physical activity.

Adolescent↗
PubMed1982

Effect of the circutone seat on hemodynamic, subjective, and thermal responses to prolonged sitting.

Eight young men were twice administered--on two different days--a series of hemodynamic (using an impedance plethysmograph), subjective, and skin temperature measurements during 5 h of quite sitting. On one day, a Circutone seat (massage-type seat cushion) was activated for 14 min/h, and on the other day it was not. During the "Circutone off" day, 5 h of sitting resulted in a continuous decrease in calf blood flow and an increase in venous blood pooling in the calf; an increase in blood pressure and a stable cardiac output (4.6 l/min); very low urine output; large increases in skin temperatures at the body areas in contact with the seat (thigh and lower back); and increases in various subjective responses of discomfort. The Curcutone activation resulted in a substantial exchange of the stagnant blood in the calf and thigh; a tendency to increase thigh and calf blood flow; a decrease in venous pooling in the thigh; and less subjective discomfort. The Circutone activation had no effect on skin temperature. The results indicate that the Circutone seat improved seat comfort by improving local circulation, especially in the thigh, which probably accounted for the improved subjective reactions.

Blood Circulation↗
PubMed1982

Hemodynamic responses in orthostasis following 5 hours of sitting.

Six young men were administered an orthostatic test, 20 min of quiet standing before and after 5 h of quiet sitting, to determine the effect of sitting fatigue on orthostatic responses. Hemodynamic responses were recorded with an impedance plethysmograph. During the 5 h sitting period, there was a 15.6% decrease in calf blood flow, a 19.4% increase in venous pooling in the calf, and an increase in blood pressure. A comparison between the two standing tests showed increases in blood pressure and in total peripheral resistance, decreases in heart rate (7 beats/min), cardiac output (12.7%) and calf blood flow (18.5%), and 70% increase in calf venous pooling after sitting. The results show that prolonged sitting constitutes a mild orthostatic stress where an increase in venous pooling is compensated by an increase in blood pressure. When this is followed by standing, insufficient compensations are made to the large amounts of pooling resulting from both postures. Despite the maintenance of a stable blood pressure (same as at the end of the sitting period) there is an insufficient increase in total peripheral resistance and heart rate resulting in a relatively low cardiac output. Thus, prolonged sitting constitutes a liability for subsequent performance in an upright position unless methods to minimize venous pooling are employed.

Adult↗
PubMed1981

Exercise training hypotension: implications for plasma volume, renin, and vasopressin.

To determine the function of changes in plasma volume (PV), plasma renin activity (PRA), and arginine vasopressin (AVP) in the mechanism of the reduction of resting blood pressure during exercise training, resting supine, sitting, and standing systolic (SBP) and 5th-phase diastolic (DBP) blood pressures were measured in 10 men (19-24 yr) before and after an 8-day (2 h/day) training period on a cycle ergometer. The control group (5 men) exercised at 1.4 1/min [44% peak O2 uptake (VO2 max)] at 23.8 degrees C Tdb and 50% rh, and the acclimation group at 1.5 1/min (46% VO2 max) at 39.8 degrees C Tdb and 50% rh. After acclimation, resting supine and sitting DPB decreased (P less than 0.05) by 6 and 9 mmHg, respectively. There were no significant changes in DBP in the controls or in SBP in either group. After training, PV increased by 12.2% in controls and by 17.6% after acclimation. The resting hypotension could not be attributed to changes in resting levels of PV, AVP, or PRA. However, large decreases in PV and large increases in AVP and especially PRA during acclimation exposures suggest these responses may play a role in the chronic hypotensive response.

Acclimatization↗
PubMed1981

Orthostatic fluid-electrolyte and endocrine responses in fainters and nonfainters.

A tilt-table test was administered to five young men before (test 1) and after (test 2) 8 days of heat acclimation (2-h daily exercise at 50% VO2max at 40 degrees db, 30 degrees C wb) and to five other young men before and after the same exercise at 24 degrees C to determine fluid-electrolyte and endocrine responses in orthostasis in fainters and nonfainters. Half of the 10 subjects showed improved orthostatic reactions from test 1 to test 2 (disappearance of nausea and dizziness and improved heart rate and blood pressure), and the other 5 subjects showed no improvement. The improvement, especially in the nonfainters, was related to increases in posttilt plasma volume (PV) and plasma concentration of potassium. During test 1, plasma renin activity (PRA) increased five times from supine to orthostatis, with a corresponding increase in plasma vasopressin (ADH) of 50 times. The corresponding increases in test 2 were lower by 50 and 75% compared with those occurring in test 1 for PRA and ADH, respectively. PRA was five times higher in nonfainters than in fainters in test 1, whereas ADH showed an opposite trend. The orthostatic-induced increase in ADH seems to be related to volume control independent of PRA. This increase is reduced with improvement in orthostatic reactions, probably because of an increase in PV.

Adult↗
PubMed1980

Fluid shifts and endocrine responses during chair rest and water immersion in man.

To determine the effect of external water pressure per se on intercompartmental fluid volume shifts, plasma and urine electrolytes, osmotic and endocrine responses were compared in four men (21-22 yr) during 8 h of water immersion (TH2O = 34.4 degrees C) and during 8 h of chair rest (Ta = 22.5 degrees C), followed by16 h of bed rest in both regimens. Water intake was 1,800 ml during 8-h exposures. Urine volume during immersion was 2,954 ml/8 h and 1,538 ml/8 h (P less than 0.01) during chair rest; the respective decreases in extracellular volume (ECV) were 2,230 ml/8 h and 1,892 ml/8 h. Losses from the intersititial volume (1.81 vs. 1.67 liters) and plasma volume (0.43 vs. 0.23 liters) during immersion and chair rest, respectively, were approximately proportional to theri normal ratios. With a negative H2O balance (corrected for blood withdrawal) during immersion of 1,234 ml and a positive balance (190 ml) during chair rest, there appeared to be a shift of ECV to the intracellular compartment in both regimens. There was suppression of both plasma arginine vasopressin (AVP) and renin activity (PRA) during chair rest and immersion. It appears that the increased central blood volume, as opposed to increased plasma osmolality, is the primary stimulus for AVP suppression. In hyperhydrated subjects, about half (6.7%) of the immersion plasma volume loss of 12.6% could be attributed to orthostatic responses associated with the upright body position during chair rest and the remaining half to the external water pressure.

Adult↗
PubMed1980

Body acceleration distribution and O2 uptake in humans during running and jumping.

Body acceleration distribution and its relation to the mode of generation were determined in eight young males (19-26 yr) who walked and ran on a treadmill operated at four speeds and jumped on a trampoline at four heights. With increasing treadmill speed, peak acceleration at the ankle (Aa = 3.0-12.0 Gz) always exceeded that at the back and forehead (Ab = 0.9-5.0 Gz, and Ah = 0.8-3.9 Gz); these acceleration profiles included higher frequency components than those during jumping. Corresponding ranges of oxygen uptake (VO2) and heart rate (HR) were 0.8-3.0 l/min and 90-180 beats/min, respectively. With increasing jumping height, acceleration levels were more symmetrically distributed (Aa = 3.0-7.0 Gz, Ab = 3.9-6.0 Gz, and Ah = 3.0-5.6 Gz); VO2 and HR ranges were 1.1-2.5 l/min and 102-175 beats/min, respectively. VO2 was linearly related to HR for both types of exercise. The results indicate that, for similar levels of HR and VO2, the magnitude of the biomechanical stimuli is greater with jumping on a trampoline than with running, a finding that might help identify acceleration parameters needed for the design of remedial procedures to avert deconditioning in persons exposed to weightlessness.

Adult↗
PubMed1980

Fluid-electrolyte shifts and thermoregulation: Rest and work in heat with head cooling.

Plasma volume and thermoregulatory responses were measured, during head and neck cooling with a liquid-cooled neoprene headgear, in four men (21-43 years old) during 60 min of rest, 60 min of ergometer exercise (45% VO2 max), and 30 min of recovery in the supine position at 40.1 degrees C DBT and 40% rh. Compared with control (noncooling) responses, cooling decreased thigh sweating and increased mean skin temperature (Tsk) at rest, and attenuated the increases in thigh sweating by 0.26 mg/min x cm2 (-22.4%, p < 0.05), heart rate by 10 b/min (-8.5%, N.S.), rectal temperature (Tre) by 0.3 degrees C (N.S.), and ventilation by 12.5% (N.S.) during exercise. In recovery, cooling facilitated the decreases in thigh sweat rate, heart rate, Tre, and forearm blood flow, and enhanced the increase in Tsk toward control levels. Cooling had no effect upon plasma protein, osmotic, or electrolyte shifts during rest, exercise, or recovery. Plasma volume (PV) loss during exercise was 11.2% without cooling and 10.9% with cooling. Cooling increased PV by 3% (p < 0.05) during rest, and this differential was maintained throughout the exercise and recovery periods.

Adult↗
PubMed1979

Heat intolerance in former heatstroke patients.

Nine young men who had suffered from heatstroke on previous occasions (heat-intolerant subjects) and 10 young volunteers (control subjects) were examined to determine their physiologic responses to exercise in temperate (23 degrees C) and hot environments (40 degrees C). The tests included an orthostatic test, work loads of 40 W and 80 W, and oxygen consumption (Vo2) determination. Although all the control subjects completed the exercise under severe heat load (3 h), none of the heat-intolerant subjects succeeded in completing this test due to high rectal temperatures and high heart rates. Sweat rates were similar in both groups, with Vo2 slightly higher in the control subjects. Orthostatic responses were similar in each group. The results suggest that inefficient thermoregulation, possibly due to decreased heat conductance from core to periphery, contributes to heat intolerance in former heatstroke patients.

Adult↗
PubMed1979

Deconditioning-induced exercise responses as influenced by heat acclimation.

Five young men were tested on a bicycle ergometer before (Test 1) and after (Test 2) 8 d of heat acclimation (exercise at 50% of Vo2max at 39.8 degrees C DB, 30.0 degrees C WB) and after 8 h of water immersion (Test 3). A control group of five subjects underwent a similar procedure in a temperate environment of 23.8 degrees C. Heat acclimation resulted in the usual decreases in exercise heart rate (30 beats/min) and rectal temperature (0.6 degrees C) and an increase in sweat rate (19%). The control group showed effects of moderate training by decreases in exercise heart rate (11 beats/min), rectal temperature (0.3 degrees C), and sweat rate (24%). Water immersion resulted in substantial diuresis in both groups, despite 1800 ml of water consumed by each subject. In the acclimation group, exercise responses in Test 2 were better than in Test 1, with little improvement shown by the control group. The acclimation group maintained exercise responses in Test 3 as in Test 1, with more adverse responses shown by the control group. The results show that heat acclimation provides an effective method to prevent the adverse effects of water-immersion deconditioning on exercise tolerance.

Acclimatization↗
PubMed1978

Maximal oxygen uptake, heat tolerance and rectal temperature.

To determine the relation of rectal temperature (Tre) to Vo2max and heat tolerance, eight untrained, eight trained and five heat acclimated subjects (respective means +/- SE for Vo2max in ml/kg.min of 37.5 +/- 1.6; 55.7 +/- 1.5; and 54.5 +/- 3.2) were tested in 3 conditions: 60 min of exercise at a fixed load of 35 W at room temperature of 23 degrees C; 60 min of exercise at 35% Vo2max also at 23 degrees C, and 3-hr of exercise in heat (40 degrees C DB, 30 degrees C WB). The heat-acclimated group showed the best heat tolerance, while the untrained group showed the poorest responses in heat. Exercise at 35 W resulted in higher heart rates shown by the untrained, compared with the other subjects, while equilibrium Tre were 37.6, 37.9, and 38.2 degrees C, in the heat-acclimated, trained and untrained groups, respectively, with corresponding differences for resting Tre (36.7, 36.9, and 37.1 degrees C). During exercise at 35% Vo2max, the heat-acclimated group showed lower Tre than the trained group despite working at the same relative loads. Tre during exercise at 35 W at 23 degrees C correlated r = -70 with Vo2max and r = 0.80 with Tre during exercise in heat. These results show that Vo2max accounts for only part of the variability which determines the level of Tre in cool conditions with heat acclimatization accounting for the remainder of this relationship.

Acclimatization↗