Biomedical subjects

E R Nadel

Publications and source records attributed to E R Nadel.

At least 37 records · Page 2Linked to original sources

PubMed1995

Body temperature modification of osmotically induced vasopressin secretion and thirst in humans.

We examined the effect of increased body core temperature (Tes) on the plasma arginine vasopressin concentration ([AVP]p) and thirst responses to increased plasma osmolality (Posm) induced by 3% NaCl infusion for 120 min in seven healthy humans. Tes was increased by immersion of the lower legs in 41 degrees C water in a 28 degrees C room (passive heating; HT). Immersion of the lower legs in 34.5 degrees C water on a separate day served as the control (thermoneutral; NT). The 120-min hypertonic saline infusion was initiated 30 min after the onset of leg immersion and was followed by a 30-min rehydration period. Tes in HT increased by 0.21 +/- 0.04 degree C before infusion and by 0.86 +/- 0.08 degree C at the end of infusion. The change in Tes in NT before and after the infusion was negligible. Posm was increased by 15.0 +/- 1.0 mosmol/kgH2O by infusion in both NT and HT. [AVP]p increased by 3.48 +/- 0.72 pg/ml in NT and by 7.59 +/- 1.02 pg/ml in HT. Thus the increase in [AVP]p at a given increase in Posm was markedly higher in HT than in NT. The plasma renin activity response to hypertonic saline infusion in both conditions was similar. Subjective thirst rating and cumulative water intake during rehydration were higher in HT than in NT.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1994

Sodium appetite, thirst, and body fluid regulation in humans during rehydration without sodium replacement.

After a 7-h H2O and Na+ depletion period (DP), produced by intermittent light exercise (8 bouts) at 35 degrees C, we examined thirst and taste palatability responses to 10 different NaCl solutions during 23 h of rehydration (RH) at 25 degrees C. During DP, net H2O and Na+ loss were 27.2 +/- 2.9 ml/kg and 3.29 +/- 0.45 meq/kg, respectively. Plasma osmolality (POsm) and plasma Na+ concentration ([Na+]p) increased significantly during DP by 3.4 +/- 1.2 mosmol/kgH2O and 3.0 +/- 1.0 meq/kgH2O, respectively. Plasma volume (PV) decreased by 6.5 +/- 1.9%. Thirst rating, renal fractional reabsorption of H2O, and plasma arginine vasopressin concentration (PAVP) increased as POsm increased. This increased thirst was accompanied by increased palatability ratings to H2O. During RH, subjects drank deionized H2O ad libitum and ate a Na(+)-free diet for 23 h. POsm and [Na+]p returned to control levels within 1 h RH and remained at or below the control thereafter. PV remained reduced by approximately 5% throughout RH. The increased thirst and PAVP returned to their respective control levels within 1 h of RH as POsm decreased, but thirst rating increased against between 17 and 23 h of RH without increase in POsm or PAVP. Palatability ratings to a 1 M NaCl solution at and after 3 h RH and palatability ratings to 0.3 M at 17 and 23 h RH were significantly higher than control. Plasma aldosterone concentration (PAldo) increased after DP, decreased with drinking, and increased again between 6 and 23 h of RH, accompanied by a marked decrease in fractional Na+ excretion to < 0.07%. Thus both Na+ preference and thirst in humans are influenced by body fluid and electrolyte status. The increased Na+ palatability (Na+ appetite) was preceded by osmotically induced thirst, and accompanied by nonosmotically driven thirst [extracellular fluid (ECF) thirst] and increased PAldo. The "Na+ appetite" and "ECF thirst" along with increased renal Na+ retention could contribute to ECF volume regulation after thermally induced H2O and Na+ depletion.

Adult↗

PubMed1994

Measurement of plasma volume in rats with use of fluorescent-labeled albumin molecules.

We describe a method for measuring plasma volume (PV) in small animals that allows small sample sizes but does not require the use of radioisotopes and thus is a convenient approach for making repeated measurements. Texas Red covalently bound to albumin (TR-A) was used in a typical indicator-dilution technique to measure PV. The relative fluorescent intensity of TR-A is linear to its concentration (up to 0.15 mg/ml) at an excitation lambda of 590 nm and an emission lambda of 610 nm. Catheters were inserted through the right jugular vein of anesthetized rats and threaded into the vena cava. A 0.5-ml control blood sample was taken, a measured quantity of TR-A was injected, and the catheter was flushed with saline. A 0.5-ml postinjection sample was taken 5 min after TR-A injection. PV was calculated by comparing the difference between the relative fluorescent intensity of control and postinjection plasma samples to a standard. The PV of 22 rats [362 +/- 14 (SE) g] was 14.1 +/- 0.4 ml (39.6 +/- 0.9 ml/kg body wt) measured by the TR-A method and 12.8 +/- 0.4 ml (35.9 +/- 1.0 ml/kg body wt) measured by a standard radioiodinated albumin method. There was a strong correlation between PV measured by both methods in the same rat (r = 0.90, P < 0.01). Infusion experiments indicated that the TR-A method can detect acute changes in PV, and repeated measurements of PV made on a chronically instrumented rat demonstrated that the method can reliably measure PV on consecutive days.

Animals↗

PubMed1994

Body fluid balance in dehydrated healthy older men: thirst and renal osmoregulation.

We examined osmotic control of thirst and free water clearance in healthy older (65+, n = 10) and younger (Y, n = 6) subjects during a 3-h rehydration period after an approximately 2.4% decrease in body weight. Plasma volume (PV), plasma osmolality (Posm), renal function, and thirst were measured before and after dehydration and during rehydration. In 65+, baseline PV was lower (43.1 +/- 1.6 vs. 48.1 +/- 2.5 ml/kg), Posm was higher (287 +/- 1 vs. 281 +/- 2 mosmol/kgH2O), and perceived thirst was lower than in Y. During dehydration, the osmotic threshold for increased thirst was shifted to a higher Posm in 65+. Total fluid intake was greater in Y than in 65+ (16.6 +/- 4.1 vs. 8.9 +/- 2.0 ml/kg); however, the relation between thirst and the rate of fluid intake was identical. Thus the blunted rehydration in 65+ is related to a lower overall sensation of thirst. The stimulus-response characteristics of osmotic control of free water clearance was similar in 65+ and Y; however, 65+ operated around a higher Posm and on a less-steep portion of the stimulus-response curve. These data support the hypothesis that the hyperosmotic hypovolemic state of healthy older individuals is not a result of a simple water deficit but represents a shift in the operating point for control of body fluid volume and composition.

Adolescent↗

PubMed1994

Cardiovascular and renal function during exercise-induced blood volume expansion in men.

To test the hypothesis that reduced baroreflex sensitivity is a direct result of exercise, we measured forearm vascular conductance (FVC) responses to graded lower body negative pressure (LBNP) 2, 20, and 44 h after intense exercise. Eight 4-min bouts of exercise at 85% of maximum oxygen uptake produced 3.5 +/- 0.7 and 3.9 +/- 1.0% blood volume (BV) expansions at 20 and 44 h of recovery, respectively. BV was unchanged from control values 2 h after exercise. The reduction in FVC was significantly less than control values during 30 and 40 mmHg of LBNP at 2 and 20 h of recovery, respectively, whereas heart rate and cardiac stroke volume responses were unchanged. Thus, a reduced FVC response to LBNP preceded BV expansion, demonstrating that exercise itself can elicit an attenuation of baroreflex function. To test the hypothesis that volume sensitivity of renal function is attenuated by intense exercise, we measured cardiovascular variables, plasma hormone concentrations, and renal output. At 20 h of recovery, resting mean arterial blood pressure and cardiac output were increased by 6 +/- 1 mmHg and 0.6 +/- 0.2 l/min, respectively, but resting plasma aldosterone and overnight Na+ excretion rate were unchanged. At 44 h of recovery, plasma aldosterone was decreased by 26 +/- 9% and overnight Na+ excretion rate was increased by 51 +/- 26%. Thus, appropriate endocrine and renal responses to increased BV were delayed until 44 h of recovery. Our findings suggest that a postexercise attenuation of baroreflex function participates in the induction of BV expansion by intense exercise.

Adult↗

PubMed1993

Forearm vascular responses to baroreceptor unloading at the onset of dynamic exercise.

To determine the extent to which reflexes accompanying muscular exercise (associated with central command) interact with cardiopulmonary (CP) baroreceptor-mediated reflexes controlling forearm vascular resistance (FVR), we examined the forearm vasoconstrictor response at the onset of dynamic exercise, with and without CP baroreflex unloading, in 10 physically active men. CP baroreceptors were unloaded by application of lower body negative pressure (LBNP) at rest and during five 4-min bouts of supine exercise at 25 and 32 degrees C. Exercise intensities were 10 (essentially no load) and 100 W, and LBNP was applied at -10, -20, -30, and -40 mmHg during rest and at -20 and -40 mmHg during exercise. Resting FVR was 33.0 +/- 3.2 and 14.0 +/- 2.7 resistance units, and cardiac stroke volume (SV) was 117 +/- 7 and 126 +/- 9 ml/beat at 25 and 32 degrees C, respectively. We found a linear relationship between the increase in FVR and decrease in SV during LBNP; the slope of the relationship was significantly lower at 32 degrees C (FVR = 51.7-0.29SV) than at 25 degrees C (FVR = 123-0.79SV). At the onset of 100-W exercise without LBNP, FVR increased significantly to 50.2 +/- 9.0 and 21.2 +/- 3.2 units at 25 and 32 degrees C, respectively, whereas SV was unchanged. Application of -40-mmHg LBNP reduced SV significantly to 68 +/- 5 and 71 +/- 6 ml/beat and increased FVR significantly to 89.0 +/- 11.3 and 36.3 +/- 7.6 units at 25 and 32 degrees C, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1993

Effect of exercise training on cardiopulmonary baroreflex control of forearm vascular resistance in humans.

We studied the stimulus-response characteristics of cardiopulmonary baroreflex control of forearm vascular resistance (FVR) in four groups of male volunteer subjects: i) unfit, ii) physically fit, iii) before and after 10 wk of endurance training (chronic blood volume expansion), and iv) before and after acute blood volume expansion. We assessed the relationship between reflex stimulus, i.e., changes in central venous pressure and response, i.e., FVR, during unloading of cardiopulmonary mechanoreceptors with lower body negative pressure (LBNP, 0 to -20 mm Hg). The slope of the linear relationship between FVR and CVP, the index of the responsiveness of this baroreflex, was significantly diminished (> 50%) in the fit subjects compared with the unfit. The slope of the FVR-CVP relationship was inversely correlated with the subject's total blood volume, suggesting that blood volume expansion was related to the attenuated CP baroreflex. In the exercise training study, maximal oxygen consumption and blood volume increased following 10 wk of endurance training (N = 14) but were unchanged in the time control group (N = 7). The slope of the FVR-CVP relationship was significantly reduced (32%) following 10 wk of training but was unchanged in the time control group. The reduction in slope of the FVR-CVP relationship was inversely related to the increase in blood volume associated with exercise training. Acute blood volume expansion 8 ml.kg-1 body weight with 5% human serum albumin solution) significantly reduced the slope of the FVR-CVP relationship. These data support the hypothesis that the attenuated forearm vascular reflex in physically fit individuals is related to a training-induced hypervolemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗

PubMed1993

Effects of dynamic exercise on cardiovascular regulation during lower body negative pressure.

The purpose of this study was to compare the cardiovascular control mechanisms that defend arterial blood pressure against blood pooling between rest and moderate dynamic exercise. We studied ten physically active men during rest and five 12-min graded supine cycle ergometer exercise bouts with and without application of LBNP in 25 degrees C and 35 degrees C. Exercise intensities were 10, 50, and 100 watts (W), each for 4 min, and LBNP was applied at 0 (control), -20, -40, and -60 mm Hg in 25 degrees C and -40 mm Hg in 35 degrees C. At rest, cardiac stroke volume (SV) decreased from 120 +/- 5 ml during control to 94 +/- 6, 67 +/- 5 and 49 +/- 3 ml during -20, -40, and -60 mm Hg LBNP, respectively, and to 55 +/- 3 ml during -40 mm Hg at 35 degrees C. Exercise elevated SV toward the control level during LBNP due to muscle pumping action. Heart rate (HR) did not increase significantly during application of LBNP until SV decreased by 20-25 ml during LBNP, both during rest and exercise. The magnitude of HR increase per decrease in SV, once an increase in HR occurred, was similar between rest and exercise, regardless of exercise intensity. The change in total peripheral resistance (TPR) with respect to SV was linear, confirming that peripheral vascular adjustments were proportional to changes in the heart's preload. The slopes of the TPR-SV relation were similar during rest and exercise, although shifted to the left with increasing exercise intensity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1993

A survey for assessing physical activity among older adults.

In 1988, the Yale Physical Activity Survey (YPAS) was designed and then administered to healthy older populations of volunteers (aged 60-86) to establish its 2-wk repeatability and relative validity. Among the 76 volunteers in the repeatability substudy, correlation coefficients between the two administrations of the survey for the eight YPAS summary indices ranged from 0.42 (P = 0.0002) to 0.65 (P = 0.0001). Among the 25 subjects in the validation substudy, weekly energy expenditure (r = -0.47; P = 0.01) and daily hours spent sitting (r = 0.53; P = 0.01) correlated with resting diastolic blood pressure, while the YPAS activity dimensions summary index (composed of questions on vigorous activity, leisurely walking, moving, sitting, and standing) correlated positively with estimated VO2max (r = 0.58; P = 0.004) and inversely with percent body fat (r = -0.43; P = 0.03). The YPAS index of vigorous activity also correlated positively with estimated VO2max (r = 0.60; P = 0.003) and the moving index correlated marginally with body mass index (r = -0.37; P = 0.06). We conclude that the YPAS demonstrates adequate repeatability, and some validity by correlating with several physiologic variables reflecting habitual physical activity. The value of the YPAS, however, in accurately assessing low intensity activity remains to be established.

Activities of Daily Living↗

PubMed1992

Effects of varied air velocity on sweating and evaporative rates during exercise.

This study was designed to determine the extent to which changes in the evaporative power of the environment (Emax) affect sweating and evaporative rates. Six male subjects undertook four 60-min bouts of cycle ergometer exercise at 56% maximal O2 uptake (VO2max).Emax was varied by differences in ambient temperature and airflow; two exercise bouts took place at 24 degrees C and two at 35 degrees C, with air velocity at < 0.2 and 3.0 m/s in both. Total sweat production was estimated from body weight loss, whereas whole body evaporative rate was measured continuously from a Potter beam balance. Body core temperature was measured continuously from a thermocouple in the esophagus (T(es)), with mean skin temperature (Tsk) computed each minute from thermocouples at eight sites. Total body sweat loss was significantly greater (P < 0.05) in the 0.2- than in the 3.0-m/s condition at both 24 and 35 degrees C. Tsk was higher (P < 0.05) in the still-air conditions at both temperatures, but final T(es) was significantly higher (P < 0.05) in still air only in the 35 degrees C environment. Thus the reduced Emax in still air caused a greater heat storage, thereby stimulating a greater total sweat loss. However, in part because of reduced skin wettedness, the slope of the sweat rate-to-T(es) relation at 35 degrees C in the 3.0-m/s condition was 118% that at 0.2 m/s (P < 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

Comparison of the forearm and calf blood flow response to thermal stress during dynamic exercise.

To examine the hypothesis that the skin blood flow response to body heating is not uniform over the entire body surface, we compared forearm (FBF) and calf (CBF) blood flow responses to an increase in core temperature (esophageal temperature, Tes) during dynamic exercise. We studied 13 physically active men during semi-recumbent one leg exercise and/or intermittent supine cycle exercise at 35 degrees C. During 30 min of one leg exercise, Tes, FBF, and CBF in the nonactive leg increased from 36.94 +/- 0.09 degrees C, 5.7 +/- 1.2, and 5.6 +/- 0.6 ml.(min.100 ml)-1 at rest to 37.97 +/- 0.10 degrees C, 27.0 +/- 2.4, and 11.1 +/- 0.8 ml.(min.100 ml)-1, respectively. The increase in blood flow per unit increase in Tes was much less in the calf than in the forearm. The ratio of the peak to resting blood flow averaged 6.5 in the forearm and 2.5 in the calf. During 60 min of intermittent supine two leg exercise, Tes, FBF, and CBF increased from 36.96 +/- 0.06 degrees C, 7.9 +/- 1.5, and 5.6 +/- 0.7 ml.(min.100 ml)-1 at rest to 37.91 +/- 0.07 degrees C, 23.6 +/- 3.0, and 11.4 +/- 1.9 ml.(min.100 ml)-1, respectively. Skin blood flow (SkBF) in the forearm and calf was estimated by using a simple cylindrical model, assuming skin thickness and resting muscle blood flow to be 0.2 cm and 2 ml.(min.100 ml)-1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1991

Elevated central venous pressure: a consequence of exercise training-induced hypervolemia?

Resting blood volumes and arterial and central venous pressures (CVP) were measured in 14 men before and after exercise training to determine whether training-induced hypervolemia is accompanied by a change in total vascular capacitance. In addition, resting levels of plasma arginine vasopressin (AVP), atrial natriuretic peptide (ANP), aldosterone (Ald), and norepinephrine (NE) were measured. The same measurements were conducted in seven subjects who did not undergo exercise and acted as controls. Exercise training consisted of 10 wk of controlled cycle exercise for 30 min/day, 4 days/wk at 75-80% of maximal O2 uptake (VO2max). A training effect was verified by a 20% increase in VO2max, a resting bradycardia, and a 9% increase in blood volume. Mean arterial blood pressure was unaltered by exercise training, but resting CVP increased by 16% (P less than 0.05). The percent change in blood volume from before to after training was linearly related to the percent change in CVP (r = 0.903, P less than 0.05). As a consequence of elevations in both blood volume and CVP, the volume-to-pressure ratio was unchanged after exercise training. Plasma AVP, ANP, Ald, and NE were unaltered. Our results indicate that elevated CVP is a consequence of training-induced hypervolemia without alteration in total effective venous capacitance.

Adult↗

PubMed1991

Effect of hypovolemia on forearm vascular resistance control during exercise in the heat.

To determine the influence of hypovolemia on the control of forearm vascular resistance (FVR) during dynamic exercise, we studied five physically active men during 60 min of supine cycle ergometer exercise bouts at 35 degrees C in control (normovolemic) and hypovolemic conditions. Hypovolemia was achieved by 3 days of diuretic administration and resulted in an average decrease in plasma volume of 15.9%. Relative to normovolemia, hypovolemia caused an attenuation of the progressive rise in forearm blood flow (P less than 0.05) and an increase in heart rate (P less than 0.05) during exercise. Because mean arterial blood pressure during hypovolemic exercise was well maintained, the attenuation of forearm blood flow was due entirely to a relative increase in FVR. At the onset of dynamic exercise, FVR was increased significantly in control and hypovolemic conditions by 13.2 and 27.1 units, respectively. The increase in FVR was significantly different between control and hypovolemic conditions as well. We attributed the increased vasoconstrictor bias during hypovolemia to cardiopulmonary baroreceptor unloading and/or an increased sensitivity to cardiopulmonary baroreceptor unloading. We concluded that reduced blood flow to the periphery during exercise in the hypovolemic condition was caused entirely by an increase in vascular resistance, thereby preserving arterial blood pressure and adequate perfusion to the organs requiring increased flow.

Adult↗

PubMed1991

Plasma volume expansion in humans after a single intense exercise protocol.

We used intense intermittent exercise to produce a 10% expansion of plasma volume (PV) within 24 h and tested the hypothesis that PV expansion is associated with an increase in plasma albumin content. The protocol consisted of eight 4-min bouts of exercise at 85% maximal O2 uptake with 5-min recovery periods between bouts. PV, plasma concentrations of albumin and total protein (TP), and plasma osmolality were measured before and during exercise and at 1, 2, and 24 h of recovery from exercise. During exercise, PV decreased by 15%, while plasma TP and albumin content remained at control levels. At 1 h of recovery, plasma albumin content was elevated by 0.17 +/- 0.04 g/kg body wt, accounting for the entire increase in plasma TP content. PV returned to control level at 1 h of recovery without fluid intake by the subjects, despite a 820 +/- 120-g reduction in body weight. At 2 h of recovery, plasma TP content remained significantly elevated, and plasma TP and albumin concentration were significantly elevated. At 24 h of recovery, PV was expanded by 4.5 +/- 0.7 ml/kg body wt (10 +/- 1%), estimated from hematocrit and hemoglobin changes, and by 3.8 +/- 1.3 ml/kg body wt (8 +/- 3%), measured by Evans blue dye dilution. Plasma albumin content was increased by 0.19 +/- 0.05 g/kg body wt at 24 h of recovery. If 1 g of albumin holds 18 ml of water, this increase in plasma albumin content can account for a 3.4-ml/kg body wt expansion of the PV. No significant changes in plasma osmolality occurred during recovery, but total plasma osmotic content increased in proportion to PV.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1991

Cardiopulmonary baroreflex control of forearm vascular resistance after acute blood volume expansion.

We report the stimulus-response characteristics of cardiopulmonary (CP) baroreflex control of forearm vascular resistance (FVR) in young adult male volunteers before and after: 1) blood volume expansion (8 ml/kg infusion of 5% human serum albumin solution, n = 5) and 2) a redistribution of blood volume toward the heart (6 degrees head-down tilt (HDT), n = 6). We assessed the relationship between reflex stimulus (i.e., changes in central venous pressure (CVP] and response (i.e., FVR) during unloading of CP mechanoreceptors with lower body negative pressure (0 to -20 mm Hg). Changes in CVP were estimated from changes in venous pressure of a large peripheral vein of the dependent arm with the subject in the right lateral decubitus position. In all conditions, reflex forearm vasoconstriction occurred in response to a reduction in estimated CVP. The absolute change in FVR per unit of CVP was reduced from -4.24 +/- 1.68 to -2.15 +/- 1.16 units/mm Hg (p less than 0.05) following blood volume expansion but was similar before (-3.34 +/- 0.89 units/mm Hg) and during 6 degrees HDT (-3.30 +/- 0.92 units/mm Hg). The reduced sensitivity of the CP baroreflex following volume expansion was manifested primarily as a smaller FVR response to LBNP (p less than 0.05). Blood volume expansion and 6 degrees HDT increased resting estimated CVP by 1.5 and 0.9 mm Hg, respectively (p less than 0.05) and resting levels of FVR decreased slightly.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1991

Diminished baroreflex control of forearm vascular resistance following training.

The stimulus-response characteristics of cardiopulmonary baroreflex control of forearm vascular resistance (FVR units in mm Hg.min.100 ml.ml-1) were studied in 14 volunteers before and after 10 wk of endurance training. We assessed the relationship between reflex stimulus (changes in central venous pressure, CVP) and response (FVR) during unloading of cardiopulmonary baroreceptors with lower body negative pressure (LBNP, 0 to -20 mm Hg). Changes in CVP during LBNP were estimated from pressure changes in a large peripheral vein in the dependent arm of the subject in the right lateral decubitus position. Maximal oxygen uptake (VO2max) and total blood volume increased with endurance training from 37.8 +/- 1.4 ml.min-1.kg-1 and 63.6 +/- 2.1 ml.kg-1 to 45.3 +/- 1.4 ml.min-1.kg-1 and 69.3 +/- 2.8 ml.kg-1, respectively (P less than 0.05). Reflex forearm vasoconstriction occurred in response to a reduction in estimated CVP, and the absolute change in FVR per unit of CVP was reduced from -5.96 +/- 0.79 to -4.06 +/- 0.52 units.mm Hg-1 (P less than 0.05) following exercise training but was unchanged from -6.10 to 0.57 to -6.22 +/- 0.94 units.mm Hg-1 for the time control group (N = 7). Resting values for FVR were similar before and after exercise training; however, resting estimated CVP was elevated from 9.5 +/- 0.5 mm Hg before training to 11.3 +/- 0.6 mm Hg after training.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1990

Effect of saline infusion during exercise on thermal and circulatory regulations.

To quantify the effect of an acute increase in plasma volume (PV) on forearm blood flow (FBF), heart rate (HR), and esophageal temperature (Tes) during exercise, we studied six male volunteers who exercised on a cycle ergometer at 60% of maximal aerobic power for 50 min in a warm [(W), 30 degrees C, less than 30% relative humidity (rh)] or cool environment [(C), 22 degrees C, less than 30% rh] with isotonic saline infusion [Inf(+)] or without infusion [Inf(-)]. The infusion was performed at a constant rate of 0.29 ml.kg body wt-1.min-1 for 20-50 min of exercise to mimic fluid intake during exercise. PV decreased by approximately 5 ml/kg body wt within the first 10 min of exercise in all protocols. Therefore, PV in Inf(-) was maintained at the same reduced level by 50 min of exercise in both ambient temperatures, whereas PV in Inf(+) increased toward the preexercise level and recovered approximately 4.5 ml/kg body wt by 50 min in both temperatures. The restoration of PV during exercise suppressed the HR increase by 6 beats/min at 50 min of exercise in W; however, infusion had no effect on HR in C. In W, FBF in Inf(+) continued to increase linearly as Tes rose to 38.1 degrees C by the end of exercise, whereas FBF in Inf(-) plateaued when Tes reached approximately 37.7 degrees C. The infusion in C had only a minor effect on FBF.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1990

Cutaneous vascular reflexes during exercise in the heat.

Eight relatively fit men performed cycle ergometer exercise (50% VO2max) for 30 min at 35 degrees C, less than 40% rh. To determine the importance of changes in cardiac filling pressure on the cutaneous vascular responses during exercise, we compared data from eight control (normovolemic) and four hypovolemic (19.5% decrease in plasma volume (PV) induced by diuretics) experiments. Cardiac output was maintained at 13.9 +/- 0.8 l.min-1 during steady state exercise in the two conditions. However, heart rate was higher (P less than 0.05) and stroke volume (SV) was slightly, although not statistically lower during hypovolemic exercise. Forearm venous compliance (FVC) was significantly lower during hypovolemic exercise than during control exercise (P less than 0.05). The increases in forearm blood flow and arterial blood pressure during exercise were not affected significantly by hypovolemia. FVC and SV in both conditions were linearly related to changes in central venous pressure during exercise (r2 = 0.88 and 0.78, respectively). Since changes in arterial pressure during exercise were not correlated with the observed arteriomotor and venomotor responses, we concluded that low pressure baroreceptors may have induced peripheral vascular reflexes, which act to maintain cardiac output during exercise in the heat.

Adult↗