PubMed Health⌕ Search

Biomedical subjects

P J Brock

Publications and source records attributed to P J Brock.

17 recordsLinked to original sources
PubMed1985

Effect of physical training in cool and hot environments on +Gz acceleration tolerance in women.

Rectal temperature (Tre), sweat rate, plasma volume (PV), peak oxygen uptake (peak VO2), and relaxed +Gz acceleration tolerance (0.5 G X min-1 linear to grayout) were measured in 15 healthy women 21-41 years old before and after submaximal isotonic exercise training for 2 h X d-1 on a cycle ergometer. The women had 2 weeks of acceleration runs and Vo2 testing, followed by 8 d of exercise training, post-training acceleration runs on day 9, and peak Vo2 tests on day 10. They were divided into three groups: an exercise (heat) group, ambient temperature (Ta) 40.6 degrees C, relative humidity (rh) 42%, and a peak Vo2 of 52%; an exercise (cool) group, Ta = 18.7 degrees, rh = 48%, and Vo2 peak = 55%; and a sedentary control (cool) group. There was no change in peak ventilation, peak heart rate (HR), peak Vo2, or in resting PV in any group after training. Heart rate and Tre were significantly lower after training in both cool and hot environments; HR by 17 b X min-1 (p less than 0.05) and 27 b X min-1 (p less than 0.05), respectively, and Tre by 0.4 degrees C (p less than 0.05) and 0.4 degrees C (p less than 0.05), respectively. Sweat rates were not different in any group. In all groups, acceleration tolerances were not different after training; they ranged from 3.5 to 3.8 G (373 - 410 s). The loss (shift) in PV during acceleration ranged from -5.8% to -10.3% (nonsignificant).(ABSTRACT TRUNCATED AT 250 WORDS)

Acceleration↗
PubMed1985

Effects of exercise-heat acclimation on fluid, electrolyte, and endocrine responses during tilt and +Gz acceleration in women and men.

Plasma fluid, electrolyte, protein, renin, and vasoactive hormone (epinephrine, norepinephrine, vasopressin) responses were measured in six women (21-23 yr) and four men (21-38 yr) before and immediately following an orthostatic tolerance test (70 degrees head-up tilt) and a +Gz (head-to-foot) acceleration tolerance test (0.5 G X min-1 linear ramp to grayout). These tests were conducted before and after 12 consecutive days of exercise-heat acclimation when the subjects exercised on a cycle ergometer at a relative oxygen uptake of 44% to 49% peak oxygen uptake in a hot environment (Ta = 40 degrees C, 42% rh). During acclimation plasma volume increased by 10.6% (p less than 0.05) in the women and by 11.9% (p less than 0.05) in the men; in both groups exercise heart rate decreased significantly. After acclimation, acceleration tolerance was unchanged in both groups (range 3.1 to 3.4 G); the women's tilt tolerance was unchanged (range 33.6 to 39.5 min), but the men's tilt tolerance increased from 30.4 min before to 58.3 min (delta = 91%, p less than 0.05) after acclimation. Since the pattern of fluid, electrolyte, and protein shifts and acceleration tolerances in the women and men were virtually the same, the hormone responses were highly variable, and the men's tilt tolerance increased significantly after acclimation, it is clear that responses to tilting cannot be used to predict responses to acceleration. Analysis of data from the present study and the literature suggests that current exercise training regimes should be unrestricted for astronauts who have not previously been highly endurance trained.(ABSTRACT TRUNCATED AT 250 WORDS)

Acceleration↗
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↗
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

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

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↗