Search PubMed⌕ Search

Biomedical subjects

J E Greenleaf

Publications and source records attributed to J E Greenleaf.

At least 127 records · Page 7Linked to original sources
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

Role of thermal and exercise factors in the mechanism of hypervolemia.

Our purpose was to determine whether the chronic increase in plasma volume (PV), resulting from heat exposure (HE) and exercise training (ET), was due only to elevated rectal temperature (Tre) or whether there were additional nonthermal factors related to the exercise. Eight men were divided into two groups. The HE group sat for 2 h/day (Tdb = 42 degrees C, 93% rh) for 8 consecutive days; Tre was raised by 1.72 +/- 0.04 degrees C to 38.5 degrees C each day. The ET group rode a bicycle ergometer for 2 h/day for 8 days (Tdb = 25 degrees C, 60% rh) at a load (60-65 Vo2max) that gave the same area under their Tre curve. PV increased by 177 ml (4.9%, P less than 0.05) in the HE group and by 427 ml (12.0%, P less than 0.05) in the ET group. This exercise-induced hypervolemia was associated with thermal factor(s) that contributed 40% and nonthermal factors that accounted for the remaining 60%. Some nonthermal, exercise-induced factors were twofold greater increases in plasma osmotic and vasopressin levels during exercise, and a fivefold increase in resting plasma protein (albumin) content.

Adult↗
PubMed1980

Exercise training-induced hypervolemia: role of plasma albumin, renin, and vasopressin.

To investigate the time course and mechanism of the increase in blood volume (BV) during isotonic exercise training, blood hemoglobin, hematocrit, and plasma volume (PV), osmotic, electrolyte, renin activity (PRA), vasopressin (AVP), and protein fractions were measured periodically in eight trained men 20-22 yr (Vo2max = 57 ml . min-1 . kg-1) before, during, and after ergometer exercise training (approximately 160 W, 65% Vo2max) for 2 h/day for 8 days. During training, plasma total osmolar and albumin contents increased to maintain a constant plasma osmolality and protein concentration during PV expansion. After training, BV increased by 457 ml (+8.1% P less than 0.05), due to an increase in PV of 427 ml (+12.1%, P less than 0.05); red cell volume was essentially constant (delta = +30 ml, NS). Plasma hypervolemia during training was associated with two major factors: 1) a ninefold elevation in PRA and AVP during exercise that facilitated Na+ and H2O retention, and 2) a progressive, chronic increase in plasma albumin content that provided increased H2O-binding capacity for the blood. Thus an efficient procedure for increasing PV is the daily performance of high-intensity isotonic leg exercise (65% Vo2max) for 2 h/day.

Adult↗
PubMed1980

Na+ and Ca2+ ingestion: plasma volume-electrolyte distribution at rest and exercise.

Plasma volume (PV), protein, and electrolyte shifts were measured in two groups of five men in the supine position during rest, exercise (40-47% VO2max), and recovery in cool (Ta = 26.5 degrees C) and hot (Ta = 39.4 degrees C) environments. They drank 16-17 ml/kg hypertonic (1.5%) NaCl, isotonic (0.9%) NaCl, or hypertonic (1.5%) calcium gluconate solutions during the preexercise rest period. Hyper-Na consumption retarded the rise in PV (hypervolemia) at rest in the cool but not in the heat. Ingestion of iso-Na and hyper-Na resulted in twofold greater hypervolemia at rest in the heat. During exercise and recovery, PV was highest with hyper-Na in the heat. Hyper-Ca prevented the normal hypervolemic response at rest in both environments. The normal hypervolemic responses during exercise were not influenced by any drink composition. The results suggest hypertonic drinks may be better for maintaining PV levels during exercise in heat; but calcium must be used with care.

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

Plasma volume and electrolyte shifts with heavy exercise in sitting and supine positions.

Plasma volume (PV) and electrolyte shifts were measured before and for 60 min after a continuous peak oxygen uptake (VO2 peak) test in four men (26-45 yr) on a bicycle ergometer. Mean (+/-SE) sitting VO2peak (3.16 +/- 0.32 1/min) was the same as supine VO2peak (3.13 +/- 0.33 1/min). In recovery (R + 1.5 min), mean PV had decreased by 477 ml (-16.1%, P less than 0.05) in the sitting and by 548 ml (-17.6%, P less than 0.05) in the supine positions, whereas total osmolality increased progressively with its peak at R + 3.5 min. The percentage losses of protein, total Ca2+, and ionized Cai2+ were about half as great as the percentage loss in PV, indicating a selective retention of these constituents. Calculated osmolality (sigma Na+, K+, Cl-, Cai2+) returned to control levels within 1.5 min after sitting exercise but required about 15 min after supine exercise. These small increases in protein concentration were not likely to significantly aid restitution of plasma volume and the ions were probably in equilibrium across the capillary membrane. So a change in hydrostatic and/or systemic blood pressures most likely provided the force for restitution of plasma volume.

Adult↗
PubMed1979

Plasma volume during stress in man: osmolality and red cell volume.

Our purpose was 1) to test the hypothesis that in man there is a range of plasma osmolality within which the red cell volume (RCV) and mean corpuscular volume (MCV) remain essentially constant and 2) to determine the upper limit of this range. During a variety of stresses--submaximal and maximal exercise, heat and altitude exposure, +Gz acceleration, and tilting--changes in plasma osmolality between -1 and +13 mosmol/kg resulted in essentially no change in the regression of percent change in plasma volume (PV) calculated from a change in hematocrit (Hct) on that calculated from a change in Hct + hemoglobin (Hb), i.e., the RCV and MCV were constant. Factors that do not influence RCV are the level of metabolism, heat exposure at rest, and short-term orthostasis (heat-to-foot acceleration). Factors that may influence RCV are exposure to high altitude and long-term orthostasis (head-up tilting). Factors that definitely influence RCV are prior dehydration and extended (greater than 2 h) periods of stress. Thus, either the Hct or the Hct + Hb equations can be used to calculate percent changes in PV under short-term (less than 2 h) periods of stress when the change in plasma osmolality is less than 13 mosmol/kg.

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

Thresholds for Na+ and Ca++ effects on thermoregulation.

The evidence for threshold concentrations of Na+ and Ca++ that alter body temperature when introduced into (a) the hypothalamus and cerebral ventricles, and (b) intravenously and by oral ingestion is examined. For hypothamic and ventricular perfusion the threshold for any increase in core temperature (Tc) at rest with excess Na+ is about 10 mM, while there is a linear relationship between the level of excess Ca++ and the decrease in Tc, with a correlation co-efficient of 0.85. With intravenous and oral ingestion the resting threshold plasma concentration for an excess Na+ effect is about 5 mEq/1 per 0.1 degrees C rise in Tc, and the excess Ca++ level is about 1 mEq/1 per 0.1 degrees C decrease in Tc. With exercise, there is a dose-dependent attenuation of the rise in core temperature that is also about 0.1 degrees C per mM excess Ca++.

Administration, Oral↗
PubMed1977

Cardiorespiratory responses to exercise after bed rest in men and women.

The purpose of this study was to compare cardiorespiratory responses of men and women to submaximal and maximal workloads before and after bed rest (BR). Fifteen male college students (19-23 yr) and 8 female nurses (23-34 yr) underwent 14 d and 17 d, respectively of bed rest. The maximal work capacity test was performed in the supine position on a bicycle ergometer just before and immediately after bed rest. The women's maximal O2 uptake (maximal VO2) was 41% lower (P<0.05) than the men's before bed rest and 42% lower (P<0.05) after bed rest. During bed rest the women's maximal VO2 decreased from 2.06 to 1.86 liter/min (-9.7%, P<0.05), and that of the men decreased from 3.52 to 3.20 liter/min (-9.1%, P<0.05). Compared with pre-BR values, after bed rest the maximal ventilatory volume was essentially unchanged in the men (+1.8%) and women (+ 2.3%), but maximal heart rate was elevated from 185 to 193 b/min (+ 4.3%, P<0.05) in the men and from 181 to 187 b/min (3.3%, P<0.05) in the women. Submaximal VO2 was unchanged after bed rest in the men but was significantly reduced in the women; the women's Hct and RBC levels were lower (P<0.05) than comparable male data. Mean corpuscular volume was unchanged in both groups pre- and post-bed rest. It is concluded that the proportional deterioration in maximal VO2 following prolonged bed rest was essentially the same in young men and women.

Adult↗
PubMed1977

Fluid and electrolyte shifts during bed rest with isometric and isotonic exercise.

Fluid and electrolyte shifts were measured in seven men (19-21 yr) during three 2-wk bed rest (BR) periods, each of which was separated by a 3-wk ambulatory recovery period. During two of the three BR periods they performed isometric exercise and isotonic exercise. No prescribed exercise was given during the other BR period. On day 4 of BR, plasma volume decreased (P less than 0.05) 441 ml (-12.6%) with no exercise, 396 ml (-11.3%) with isometric, and 262 ml (-7.8%) with isotonic exercise; the decreases (NS) of extracellular volume were -4.4%, -2.6%, and -2.7%, respectively. By day 13 of BR, plasma volume stabilized at the lower level with isometric and isotonic exercise and continued to decline with no exercise; but the extracellular volume returned to or above control levels due to an overshoot of the interstitial volume of +320 to +430 ml (2.0-2.7%) that was about equal to the plasma volume loss. During BR there were isocontent losses from the plasma of protein, albumin, globulin, urea N2, uric acid, creatinine, Na, Cl, osmolarity, P, and glucose that were not influenced by either exercise regimen. However, the blood, red blood cell, and plasma volumes, and the Ca and K contents were stabilized during BR by both exercise regimens. The results suggest that during BR, preservation of the extracellular volume takes precedence over maintenance of the plasma volume, and this mechanism is independent of the effects of isometric or isotonic exercise.

Adult↗
PubMed1977

Fluid and electrolyte shifts in women during +Gz acceleration after 15 days' bed rest.

Twelve women (23-34 yr), comprising a bed-rest (BR) group of eight subjects and an ambulatory (AMB) group of four subjects, were centrifuged after 14 days of ambulatory control (C),after 15 days of a 17-day BR period, and on the third day of recovery (R). Venous blood was taken before and after the third +3.0 G acceleration run (1.8 G/min). Relative to (C), the +Gz tolerance after BR was reduced -49.0% (P less than 0.05) in the BR group and -38.7% (NS) in the AMB group; during (R) the BR group regained up to 89.4% and the AMB group up to 87.1% of their (C) tolerances. In each of the three test periods, the shifts in plasma Na, Cl, PO4, and osmotic contents, which accompanied +Gz, followed the outward shift of plasma volume (PV). The correlation of the shift of PV during acceleration with the +Gz tolerance was 0.72 (P less than 0.01). During acceleration, the PV and electrolyte loss for both groups after BR was about half the loss of (C) and (R). Compared with (C) and (R) values, potassium shifts were variable but the mean corpuscular volume and mean corpuscular Hb contents and concentrations were unchanged during all +Gz runs; The results indicate that: 1) the higher the (C) + Gz tolerance, the greater the tolerance decline due to BR; 2) relative confinement and reduced activity contribute as much to the reduction in tolerance as does the horizontal body position during BR; 3) bed-rest deconditioning has no effect on the erythrocyte volume during +3.0 Gz; and 4) about one-half the loss in tolerance after BR can be attributed to PV and electrolyte shifts.

Acceleration↗