Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Immersion”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11Linked to original sources
PubMed2004

Comparison of hemodynamics during hyperthermal immersion and exercise testing in apparently healthy females aged 50-60 years.

BACKGROUND: Owing to excessive worries regarding adverse cardiac events, hyperthermal balneotherapy for patients with coronary artery disease is underprescribed. However, very few cardiac events occur in similar heat stress during Finnish sauna bathing. Exercise testing has proven to be a safe diagnostic procedure even in survivors of myocardial infarction. METHODS: We compared the effects of hyperthermal immersion and exercise testing on cardiac hemodynamics in 21 apparently healthy women aged 50-60 years. The maximal symptom-limited bicycle exercise test was performed according to the modified protocol of Wasserman. Hyperthermal immersion was carried out in 40 degrees C water and was completed by increasing the core temperature by about 2 degrees C. The left ventricular function was evaluated using continuous measurement of thoracic electric bioimpedance during both tests. The blood pressure, index of contractility and heart rate were measured directly, whereas the cardiac index, left cardiac work index and systemic vascular resistance index were calculated. RESULTS: The hemodynamic response, as assessed at continuous non-invasive monitoring, showed substantial differences between hyperthermal immersion and exercise testing. Overall, we found a significantly lower hemodynamic load during hyperthermal immersion in comparison with exercise testing. Entering the bath, there was a significant decrease in the left cardiac work, contractility and blood pressure. We recorded a slight increase in the heart rate towards peak hyperthermal immersion. However, other modulators such as the mean arterial pressure, index of contractility, cardiac index and left cardiac work index decreased even below resting values. CONCLUSIONS: Excessive hyperthermal immersion induced a lower hemodynamic load in apparently healthy women than standard maximal exercise testing.

Analysis of Variance↗
PubMed2005

[Comparison of resuscitation with Parkland formula and with improved protocol on hemodynamics in projectile-burn combined wound in dogs with seawater immersion].

OBJECTIVE: To compare hemodynamic effects of resuscitation with Parkland formula or with the improved protocol on projectile-burn combined wound in dogs with seawater immersion. METHODS: A model of projectile-burn combined wound in dogs with seawater immersion was reproduced, and 20 dogs were randomized into three groups: projectile-burn combined wound with seawater immersion (immersion group, n=8), Parkland formula resuscitation (lactated Ringer's solution 4 ml/kg per 1%total body surface area for 24 hours, standard resuscitation group, n=6), and improved protocol groups (lactated Ringer's solution 2.5 ml/kg per 1% total body surface area colloid solution 6% hetastarch 0.5 ml/kg per 1% total body surface area for 24 hours, improved group, n=6). Changes of hemodynamics and central temperature (CT) before injury, and 4, 7, 10, 20 and 28 hours after injury were observed. The mortality was observed. RESULTS: After resuscitation with Parkland formula, CT as well as hemodynamic indexes and amount of urine were improved, but central venous pressure (CVP) and the amount of urine were higher in early period of resuscitation. CVP was (14.7+/-3.1)cm H2O and the amount of urine was (2.38+/-0.18)ml.h(-1).kg(-1) at 7 hours after injury. Hemodynamics was not stable during later period of experiment. After resuscitation with the improved protocol, the hemodynamics ameliorated better than resuscitation with Parkland formula. No animals died in improved group, but 4 and 1 died respectively in immersion group and standard resuscitation group. CONCLUSION: Fluid resuscitation according to the improved protocol is more suitable for projectile-burn combined wound in dogs with seawater immersion than resuscitation with Parkland formula.

Animals↗
PubMed1990

[Studies on the mechanism of gastric mucosal injury induced by water-immersion stress in rats].

Changes in the degree of gastric mucosal injury, gastric acid output, secretion of gastric barrier mucus and gastric motility were made in 5 groups of rat: I, Restraint alone plus saline under room temperature; II, Water-immersion plus saline; III, Water-immersion plus atropine (0.5 mg/kg); IV, Water-immersion plus phenoxybenzamine (10 mg/kg); V, Water-immersion plus pentobarbital (30 mg/kg). The results were as follows: (1) Water-immersion stress resulted in severe gastric mucosal lesions, an increase in the gastric acid output, a decrease in the secretion of gastric barrier mucus and an increase in gastric motility. (2) Atropine attenuated gastric mucosal injury significantly, inhibited gastric acid output and gastric motility, while gastric barrier mucus was increased. (3) Sodium pentobarbital also significantly attenuated gastric mucosal injury and inhibited gastric motility, but had no effect on gastric acid output. (4) Phenoxybenzamine failed to affect on gastric mucosal injury, gastric acid output, gastric barrier mucus secretion and gastric motility. These results suggest that the gastric hypercontractility, the reduction of gastric barrier mucus and the increase in gastric acid output participate in varying degrees in the formation of gastric mucosal injury induced by water-immersion stress, but when gastric motility is inhibited and gastric barrier mucus increases, only the existence of gastric acid can not induce severe gastric mucosal injury.

Animals↗
PubMed2006

Immersion in thermoneutral water: effects on arterial compliance.

BACKGROUND: Since thermoneutral head-out water immersion induces an increase in central blood volume and cardiac output along with a decrease in peripheral vascular resistance, we examined here whether thermoneutral immersion leads rapidly to an increase in arterial compliance. METHODS: Changes in hemodynamic status and arterial compliance induced by thermoneutral head-out water immersion to the midchest were studied in 26 healthy volunteers (15 women, 11 men) using a non-invasive pulse wave measurement system. Several hemodynamic parameters including stroke volume (SV) and large and small artery compliance were studied in a quiet room with a stable environmental temperature (25 degrees C) and during thermoneutral (34.5 degrees C) head-out water immersion. RESULTS: In a preliminary study, an agreement between SV estimated by radial pulse contour analysis and that obtained by Doppler echocardiography was observed in ambient air. An increase in SV led to an increase in cardiac output (12%) 10 min after the start of immersion. Heart rate and arterial pressure remained unchanged. Systemic vascular resistance was significantly decreased and total arterial compliance estimated by the SV to aortic pulse pressure ratio was significantly increased. Radial pulse contour analysis confirmed these results with an increase in both large and small artery compliance. CONCLUSION: In conclusion, radial pulse contour analysis provides an interesting method for assessing hemodynamic changes under environmental constraints. Our results were consistent with a prompt increase in arterial compliance during acute water immersion.

Adult↗
PubMed1989

[Evaluation of the skin sympathetic function by the decrease of skin temperature at the finger tip immersed into cold water].

The change of the skin temperature at the finger tip immersed into cold water was measured in normal volunteers and in patients with disturbances of various portions of sympathetic nervous system with copper-constant thermocouple. The skin temperature of the normal subjects decreased soon after the immersion, partly due to cooling by the cold water, and partly due to the decrease of the skin blood flow. The skin sympathetic activity recorded from three normal subjects using the technique of microneurography presented an increase during the decreasing phase of the skin temperature. The skin temperature of the patients who received stellate ganglion block did not fall and maintained higher level compared to that of normal subjects. These data indicated that the decreasing phase of the skin temperature of the immersed finger is related to the increase of skin sympathetic activity. Cases of vascular neuropathy (lesion in post-ganglionic fiber), Shy-Drager syndrome and pure autonomic failure (lesion in pre-ganglionic fiber), cervical spondylosis and cervical disc herniation (lesion in descending tract of sympathetic system in spinal cord), and bleeding in pons tegmentum (lesion in descending tract in brain stem) were examined and all of them presented poor decrease of the skin temperature during the immersion. The skin temperature decreased, but incompletely in the patients, who had suffered from thalamic infarct and post-central gyrus infarct, and did not feel any sense on the immersion. These results indicate that the decreasing phase of the skin temperature of the finger immersed into cold water depends more upon the efferent than upon the afferent system, and this test is useful for evaluation of the skin sympathetic function.

Adult↗
PubMed1986

[Plasma beta endorphin in man during partial immersion in water using the therapeutic method].

The following study was designed to evaluate plasma beta-endorphin (beta-EP) variations in healthy volunteers during thermoneutral head-out water immersion while prevalently in the standing position. The type of immersion was similar to that currently adopted for therapeutic rehabilitation. Plasma beta-EP was evaluated by RIA previous beta-lipotropin stripping and Sep-Pack cartridge methanol extraction. Plasma beta-EP levels significantly decreased during water immersion from a value of 12.71 +/- 2.04 pmol/l to 7.46 +/- 1.09 pmol/l at 15 min (P less than 0.05) and to 6.08 +/- 1.87 pmol/l at 30 min (P less than 0.01). Thirty min after the end of immersion, plasma beta-EP levels showed a slight increase to 6.98 +/- 1.88 pmol/l but were still significantly below the basal level (P less than 0.05). These results are consistent with the previously demonstrated decrease of ACTH and prolactin and the increase of plasma dopamine and decrease of norepinephrine, suggesting that thermoneutral head-out water immersion is not a stressful condition in healthy subjects. Further studies are necessary in order to clarify the mechanism involved in beta-EP decrease in normal subjects during thermoneutral head-out water immersion.

Adrenocorticotropic Hormone↗
PubMed1987

Effect of hydrostatic pressure on plasma concentrations of norepinephrine during cold water immersion.

Head-out immersion of humans in cold water concurrently stimulates low-pressure receptors and cutaneous cold receptors. In theory, the low-pressure receptors inhibit sympathetic nerve activity to the extent of modifying plasma norepinephrine responses to chilling of the skin. Human plasma norepinephrine concentrations ([NE]p's) were measured when low-pressure receptors were stimulated by 6 h of head-out immersion in thermoneutral water (35 degrees C). The experimental protocol was repeated when cold receptors were activated by a separate exposure to 14.8 degrees C air. Furthermore, both types of receptors were activated by 6 h of immersion in cold water (29.8 degrees C). The control exposure maintained [NE]p close to a constant value of 0.34 ng/ml. Thermoneutral water reduced [NE]p to 0.18 ng/ml after 30 min of immersion, but the change was not statistically significant (two-way ANOVA). [NE]p increased to peak values of 1.5 ng/ml in cold air (P less than 0.05) and 1.1 ng/ml in cold water (P less than 0.5), with no significant differences observed between [NE]p's in cold air and cold water. Equal rates of body heat loss occurred during the exposures to cold air and cold water. Since [NE]p's were comparably raised by separate exposures to cold water and cold air, stimulation of low-pressure receptors by immersion did not significantly depress peripheral vasomotor nerve activity during head-out immersion in cold water.

Adult↗
PubMed1984

Circulatory functions during immersion and breath-hold dives in humans.

An unusual circulatory state exists in humans immersed in water at or near 35 degrees C. This circulatory state is characterized by a persistent and elevated stroke index (SI) but heart rate (HR) changes little; hence an increased cardiac index (CI) results. In comparison of measurements in air and immersion in water up to the neck level that are based on the weighted averages of 45 subjects from 8 studies, SI increased by 29%, CI increased by 24%, and HR decreased by 6%. Evidence is presented to support the finding that the increase in stroke volume is a result of enhanced preload of the heart, and that alterations in afterload and contractility play an unimportant role in affecting cardiac performance during immersion in thermoneutral water up to the level of the neck. The circulatory state represents hyperperfusion, since there is no concurrent rise in metabolic demand or heat stress. To what extent this preexisting circulatory state affects the cardiovascular responses to breath-hold (BH) diving is in most part unknown. However, the BH bradycardiac responses are more potent in a natural setting than in the laboratory where the breath hold is performed with only face immersion in water. In contrast, in the natural setting, the divers perform BH dives while they are immersed up to the neck in cold water (much lower than 35 degrees C) and are exercising. It is desirable in future studies to compare systematically other aspects of circulatory responses to BH dives while immersed in water and while exercising.

Biomechanical Phenomena↗
PubMed1984

Volume regulation in man during neck-out immersion in a medium with high specific gravity (Dead Sea water).

The effect of immersion for 4 h on arterial blood pressure and the rate or urinary sodium excretion was studied in five subjects both in fresh water and in Dead Sea water (specific gravity 1.19) at 34 C. Following 100 min of immersion, mean systolic and diastolic blood pressure decreased (P less than 0.01) in subjects immersed in fresh water, and increased (P less than 0.05) in those immersed in Dead Sea water. While immersion in fresh water led to hypotension, it was associated with an increased natriuresis. In contrast, the hypertensive response to immersion in Dead Sea water was not associated with an increased natriuresis. It is concluded that under the unique conditions of this experiment, urinary excretion of sodium becomes independent of systemic arterial blood pressure, and is presumably governed by neurohumoral influences originating in the baroreceptors of the low pressure system.

Adult↗
PubMed1984

Renal handling of urate during water immersion in the nephrotic syndrome.

Renal handling of urate was examined in 11 patients with nephrotic syndrome before, during, and after 4 h of water immersion up to the neck. Urinary urate excretion, urate clearance, and fractional excretion of urate all increased significantly during water immersion, and decreased in the hour following water immersion. During water immersion fractional excretion of urate rose to a maximum of 16 ml/ml of glomerular filtrate, and fell towards control levels on removal from the bath. It is concluded that either there is a decrease in proximal tubular urate reabsorption or secretion caused by water immersion. In contrast, diurnal control studies showed no significant change in fractional excretion of urate during the same period of the day. It is postulated that the increased fractional excretion of urate on water immersion is due to hypervolemia induced by the hydrostatic pressure of the water on the lower limbs and abdomen.

Adolescent↗
PubMed1994

Flow velocity in carotid artery in humans during immersions and underwater swimming.

Heart rate and flow velocity in the common carotid artery were examined on eight subjects in various underwater conditions. The heart rate decreased more markedly during whole-body immersion than during head-out immersion. The end-diastolic flow velocity and the flow-velocity integral in a cardiac cycle during whole-body immersion increased more markedly than during head-out immersion. Differences in heart rate and flow velocity were not detected between sitting and prone positions in whole-body immersion. Heart rate increased at the beginning and after underwater swimming. The peak systolic flow velocity increased significantly after the end of underwater swimming. The flow-velocity integral in a cardiac cycle decreased during underwater swimming, but in a minute did not change significantly. These results suggest that facial immersion is important in eliciting pronounced carotid artery flow-velocity response in addition to the heart-rate response and that underwater exercise influences these responses. However, underwater posture apparently does not influence them.

Adult↗
PubMed1993

Water immersion and salt-sensitivity in essential hypertension.

It has been demonstrated that an exaggerated natriuretic response to central hypervolaemia is not necessarily associated with hypertension; many hypertensive subjects manifest either an appropriate or a blunted natriuresis in response to ECFV expansion attained by head-out water immersion. In this study, we tested the hypothesis that an underlying condition of salt-sensitivity may explain the heterogeneity of the natriuretic response of essential hypertension. Both salt-sensitivity tests and 2h water-immersion studies were randomly performed in 18 untreated essential hypertensives under a selected and controlled diet. Salt-sensitivity was defined as a significant drop in mean arterial pressure of 10% or greater, calculated as the difference between the average of the 25 readings under the high and the low salt period. Water immersion did result in a significant natriuretic and calciuretic response in the whole hypertensive group (n = 18, p < 0.001 and p < 0.05, respectively), while the examination of the individual excretion disclosed either exaggerated and appropriate or blunted urinary response. When the hypertensive group was classified in relation to salt-sensitivity, the greater fall in mean arterial pressure during low salt diet (salt-sensitivity) was associated with the more pronounced natriuretic response during water immersion (r = -0.66, p < 0.003). An identical correlation (r = -0.58, p < 0.01) was also found between changes in mean arterial pressure (low salt diet) and urinary calcium excretion (water immersion) in the same hypertensives. The water immersion-induced suppression of plasma aldosterone and the increase in plasma atrial natriuretic peptide did result from comparable magnitude in the salt-sensitive and in salt-resistant subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1998

Physiologic and perceptual responses to hypercarbia during warm- and cold-water immersion.

Thermoregulatory, respiratory, and perceptual responses to acute CO2 exposure during light exercise (75 W) were assessed in 12 U.S. Navy divers clad only in swim trunks while immersed to the neck in water at 18 degrees and 34 degrees C. The CO2 exposures consisted of a linear 10-min ramp increase in the inspired fraction of CO2 (FICO2) from 0 to 6% followed by 5 min of breathing 6% CO2. The ability to detect and rate the severity of hypercarbia, as well as subjective changes in thermal comfort, were assessed by comparing subjective ratings given during the CO2 exposures with those given during immersion trials where the FICO2 was maintained at 0%. Hypercarbia was recognized earlier and, at a given PETCO2, was perceived to be greater during cold- than during warm-water immersions (P < 0.01). The CO2 exposures did not affect the thermal balance of divers as assessed by changes in heat flux and rectal temperature. However, increased feelings of warmth were reported during both the cold and warm immersions when breathing raised concentrations of CO2 (P < 0.01). During the cold immersions, acute exposure to 6% CO2 significantly decreased forearm blood flow (P < 0.05), but did not affect finger blood flow. It is concluded that PETCO2 levels can reach unacceptably high concentrations (> 60 mmHg) before hypercarbia can be reliably detected by working divers. Furthermore, the ability to detect hypercarbia is poorer when immersed in warm water than when in cold water.

Adult↗
PubMed2000

Measurement of Contact Angles for Fumed Silica Nanospheres Using Enthalpy of Immersion Data.

The hydrophobicity of fine particles is important for their behavior at interfaces, for example, in stabilizing emulsions. In this study, contact angles were evaluated for silanized fumed silica nanospheres with mean primary diameter of about 12 nm, using heat flow microcalorimetry. Three systems were investigated: water-air-nanospheres, toluene-air-nanospheres, and toluene-water-nanospheres. For the water-air-nanospheres system, n-propanol at various concentrations in water was used to aid in dispersing the nanospheres, and the enthalpy of immersion between water, air, and nanospheres was obtained by extraploting to zero n-propanol concentration. Measurements of enthalpy of immersion for toluene-air-nanospheres system were straightforward, as all the nanospheres samples were dispersible in toluene. The enthalpy of immersion for toluene-water-nanospheres system was calculated from the data for the aforementioned first and the second systems. For water-air-nanosphere systems, contact angles were in the range of 14 to 118 degrees, corresponding to enthalpy of immersion from -0.0905 to 0.0041 J/m(2). For the case of toluene-air-nanospheres systems, the contact angles varied from 72 to 94 degrees with corresponding enthalpy of immersion from -0.0295 to -0.0189 J/m(2). For toluene-water-nanospheres systems, however, contact angles were in the range of 0 to 96 degrees, corresponding to enthalpy of immersion from -0.0717 to -0.0175 J/m(2). Copyright 2000 Academic Press.

Journal Article↗
PubMed1996

A comparison of human thermoregulatory response following dynamic exercise and warm-water immersion.

We tested the hypothesis that the prolonged elevated plateau of esophageal temperature (Tes) following moderate exercise is a function of some exercise-related factors and not the increase in heat content and Tes during exercise, by comparing the response to increase Tes during exercise (endogenous heating) and warm-water immersion (exogenous heating). Nine healthy, young [24.0 (1.9) years] subjects performed two separate experiments: (1) 15 min of treadmill exercise at 70% (VO2max) and 15 min rest in a climatic chamber at 29 degrees C, followed by 15 min of immersion in a 42 degrees C water bath and a further 60 min of recovery in the climatic chamber [exercise-water (EW)]; and (2) 15 min of immersion in a 42 degrees C water bath followed by 60 min of recovery in the climatic chamber [water-only (WO)]. Esophageal (Tes) and skin (Tsk) temperatures were recorded at 5-s intervals throughout. The Tes at which the forearm to finger temperature gradient (Tfa-Tfi) abruptly decreases was used to identify the threshold for forearm cutaneous vessel dilation (Thdil) during exercise. Pre-exercise Tes values were 36.64 degrees C and 36.74 degrees C for EW and WO respectively. The EW post-exercise Tes value fell to a stable level of 37.12 degrees C and this value differed by 0.48 degree C (P < 0.05) from baseline, but was similar to Thdil (37.09 degrees C). Despite a 1.2 degrees C increase in Tes during the subsequent warm-water immersion, Tes returned to the post-exercise value (37.11 degrees C). The WO post-immersion Tes fell to a stable plateau of 36.9 degrees C, which was not statistically different from the pre-immersion Tes. The data for both warm-water treatments support the hypothesis that increases in Tes and heat content alone are not the primary mechanisms for the post-exercise elevation in Tes and Thdil. These data also support our previous observation that the exercise-induced elevation in Thdil persists into recovery.

Adult↗
PubMed2004

Repeated cold showers as a method of habituating humans to the initial responses to cold water immersion.

The hypothesis that the initial responses to cold water immersion could be attenuated by repeated cold showers was tested. Eighteen (13 men, 5 women) non-habituated subjects undertook two 3-min head-out seated immersions into stirred water at 10 degrees C wearing swim wear. The immersions were separated by 4 days during which time they took six cold showers. The subjects were randomly split into three groups with different showering regimes: 3 min at 10 degrees C on the back (10B); 3 min at 15 degrees C on the back (15B); and 30 s at 10 degrees C on the back followed by 30 s on the front (10BF). Over the first 30 s of immersion respiratory frequency ( f (R)) was reduced by 21% in groups 10B and 10BF from 54 (14) to 44 (16) breaths.min(-1) ( P <0.05), and 33 (8) to 26 (10) breaths.min(-1) ( P <0.05) respectively, following repeated showers. Group 15B showed no change in f (R). The tachycardia induced on immersion in water at 10 degrees C was not reduced by repeated showers except in group 15B during the last 150 s [from 119 (23) to 105 (25) beats.min(-1), P <0.05]. Repeated showering in water at 10 degrees C reduced the respiratory drive (as measured by f (R)) during head-out immersion in water at the same temperature. No such habituation was observed with repeated showers in warmer water (15 degrees C). It is concluded that when the body surface area cooled is the same, the rate of change of skin temperature is an important factor in determining the degree of habituation produced.

Adaptation, Physiological↗
PubMed2001

Determination of membrane immersion depth with O(2): a high-pressure (19)F NMR study.

Oxygen is known to partition with an increasing concentration gradient toward the hydrophobic membrane interior. At partial pressures (P(O2)) of 100 Atm or more, this concentration gradient is sufficient to induce paramagnetic effects that depend sensitively on membrane immersion depth. This effect is demonstrated for the fluorine nucleus by depth-dependent paramagnetic shifts and spin-lattice relaxation rates, using a fluorinated detergent, CF3(CF(2))(5)C(2)H(4)-O-maltose (TFOM), reconstituted into a lipid bilayer model membrane system. To interpret the spin-lattice relaxation rates (R) in terms of a precise immersion depth, two specifically fluorinated cholesterol species (6-fluorocholesterol and 25-fluorocholesterol), whose membrane immersion depths were independently estimated, were studied by (19)F NMR. The paramagnetic relaxation rates, R, of the cholesterol species were then used to parameterize a Gaussian profile that directly relates R to immersion depth z. This same Gaussian curve could then be used to determine the membrane immersion depth of all six fluorinated chain positions of TFOM and of two adjacent residues of specifically fluorinated analogs of the antibacterial peptide indolicidin. The potential of this method for determination of immersion depth and topology of membrane proteins is discussed.

Antimicrobial Cationic Peptides↗
PubMed2000

Effects of three days of dry immersion on muscle sympathetic nerve activity and arterial blood pressure in humans.

The present study was performed to determine how sympathetic function is altered by simulated microgravity, dry immersion for 3 days, and to elucidate the mechanism of post-spaceflight orthostatic intolerance in humans. Six healthy men aged 21-36 years old participated in the study. Before and after the dry immersion, subjects performed head-up tilt (HUT) test to 30 degrees and 60 degrees (5 min each) with recordings of muscle sympathetic nerve activity (MSNA, by microneurography), electrocardiogram, and arterial blood pressure (Finapres). Resting MSNA was increased after dry immersion from 23.7+/-3.2 to 40.9+/-3.0 bursts/min (p<0.005) without significant changes in resting heart rate (HR). MSNA responsiveness to orthostasis showed no significant difference but HR response was significantly augmented after dry immersion (p<0. 005). A significant diastolic blood pressure fall at 5th min of 60 degrees HUT was observed in five orthostatic tolerant subjects despite enough MSNA discharge after dry immersion. A subject suffered from presyncope at 2 min after 60 degrees HUT. He showed gradual blood pressure fall 10 s after 60 degrees HUT with initially well-maintained MSNA response and then with a gradually attenuated MSNA, followed by a sudden MSNA withdrawal and abrupt blood pressure drop. In conclusion, dry immersion increased MSNA without changing MSNA response to orthostasis, and resting HR, while increasing the HR response to orthostasis. Analyses of MSNA and blood pressure changes in orthostatic tolerant subjects and a subject with presyncope suggested that not only insufficient vasoconstriction to sympathetic stimuli, but also a central mechanism to induce a sympathetic withdrawal might play a role in the development of orthostatic intolerance after microgravity exposure.

Adult↗