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PubMed1991

Intrathoracic airstream temperatures during acute expansions of thoracic blood volume.

1. To determine the validity of employing intrathoracic heat flux as a reflection of changes in bronchial blood flow, we used a thermal probe to record airstream temperatures within the tracheobronchial tree in five normal and five asthmatic subjects during isocapnic hyperventilation challenges with and without inflation of the lower limb bladders of a pressure suit. 2. During hyperpnoea, airstream temperatures fell progressively in both subject groups. When blood volume was acutely shifted from the legs into the thorax via anti-shock trousers, airstream temperatures within the tracheobronchial tree rose and were significantly higher than the temperature recorded during hyperpnoea alone. In the normal subjects, once hyperpnoea ceased, the rate of airway re-warming was similar whether or not the anti-shock trousers were inflated. In the asthmatic subjects, however, shifting blood into the thorax attenuated the obstructive response to hyperpnoea and slowed the rate of re-warming. 3. These data demonstrate that changes in airway blood volume are reflected in fluctuations in intrathoracic heat exchange and that disruption of the end hyperpnoea thermal gradient attenuates the airway obstruction that follows hyperpnoea. Since the bronchial blood supply is the major source of heat to the airways, this circulation may play an important role in thermally induced asthma.

Asthma↗
PubMed1997

[Effect of different Anti-G suits on lower limb blood flow].

To study effects of different Anti-G suits (AGS) and different inflation pressure on human cardiac system, changes in lower limb arterial blood flow (BF), heart rate and blood pressure in 5 male subjects with three bladder coverage AGS and a capstain AGS were observed and recorded until inflation pressure reached to its maximum. The percent of bladder coverage was about 30%, 65% and 90% of lower body for three bladder AGS. All AGS were inflated to maximum pressure in +1Gz seating position. The results showed that calf BF, could be blocked by bladder AGS, and the relationship between the mean pressure for BF block and the percentage of bladder coverage was y = 29.66 - 16.35x. (P < 0.0001, r = -0.9229). While the thigh and calf BF was not blocked in subjects with the capsule AGS. The results indicate that the effect of "the higher bladder coverage AGS + lower IP" is probably equal to that of "the lower bladder coverage AGS + higher IP" in holding calf BF.

Aerospace Medicine↗
PubMed1985

Cerebral venous sinus pressure in seated dogs: impact of PEEP, cervical venous compression, and abdominal compression.

The authors studied the effects of positive end-expiratory pressure (10 cmH2O PEEP), abdominal compression, and neck compression on dural venous sinus pressure (VSP) in seated dogs. Abdominal compression increased the central venous pressure (CVP) as well as both the systemic arterial pressure and the cardiac output and thus may offer a useful substitute for an antigravity suit. Except when CVP was greater than 8 mmHg, there was little or no correlation between CVP and VSP. Moreover, each method increased VSP, but this effect was closely related to VSP prior to application of the method (pre-VSP). On comparing the VSP changes in relation to the pre-VSP levels when they were either above or below -1.0 mmHg, significant differences were noted in VSP increases, i.e., -0.4 +/- 1.3 (mean +/- SEM) and 4.3 +/- 1.2 mmHg by PEEP, 1.9 +/- 0.3 and 6.4 +/- 0.4 mmHg by abdominal compression, and 10.2 +/- 1.3 and 1.5 +/- 0.5 mmHg by neck compression, respectively. This indicates that PEEP and abdominal compression were more effective in increasing relatively highly negative pre-VSP (less than -1.0 mmHg), while neck compression greatly increased pre-VSP when it was at or above a slightly negative pressure (-1.0 mmHg). The authors conclude that a single application of any one of these three methods during sitting-position surgery may not be effective in increasing cerebral dural sinus pressure.

Abdomen↗
PubMed2005

Contributions of lower limb and abdominal compression to ventilation inhomogeneity in hypergravity.

Gravito-inertial load in the head-to-foot direction (Gz) and compression of the lower body half by an anti-G suit (AGS) are both known to influence ventilation distribution in the lungs. To study the interaction of Gz and AGS and to asses the separate contributions from lower limbs and abdominal compressions to large and small-scale ventilation inhomogeneities nine males performed SF6/He vital capacity (VC) single-breath washouts at 1, 2, and 3 Gz in a centrifuge, with abdominal and/or lower limbs compressions. SF6/He and (SF6-He) phase III slopes were used for determination of overall and small-scale ventilation inhomogeneity. Closing volume and phase IV height were used as measures of large-scale inhomogeneity. VC decreased marginally with G-load but markedly with lower limbs compression. Small-scale ventilation inhomogeneity increased slightly with G-load, but substantially with AGS pressurization. Small-scale ventilation inhomogeneity increased with AGS pressurization. Large-scale inhomogeneity increased markedly with G-load. Translocation of blood to the lungs might be the key determinant for changes in small-scale ventilation inhomogeneity when pressurizing an AGS.

Abdomen↗
PubMed1992

Hemodynamic and hormonal effects of prolonged anti-G suit inflation in humans.

This study examined the hemodynamic consequences of prolonged lower body positive-pressure application and their relationship to changes in the plasma concentration of the major vasoactive hormones. Six men [36 +/- 2 (SE) yr] underwent 30 min of sitting and then 3 h of 70 degrees head-up tilt. An antigravity suit was applied (60 Torr legs, 30 Torr abdomen) during the last 2 h of tilt. In a similar noninflation experiment, the endocrine responses were measured in the suited subjects tilted for 3 h. Two-dimensional echocardiography was used to calculate ventricular volume and cardiac output. Measurements were made 30 min before and 30 and 90 min after inflation. Immediately after inflation, mean arterial pressure increased by 7 +/- 2 Torr and heart rate decreased by 16 +/- 4 beats/min. Left ventricular end-diastolic volume and systolic volume increased significantly (P less than 0.05) at 30 and 90 min of inflation. Cardiac output increased after 30 min of inflation and returned to the preinflation level at 90 min. Plasma norepinephrine and plasma renin activity were maximally suppressed after 15 and 90 min of inflation, respectively (P less than 0.05). No such hormonal changes occurred during control. Plasma sodium, potassium, and osmolality remained unchanged during both experiments. Thus, prolonged application of lower body positive pressure induces 1) a transient increase in cardiac output and 2) a marked and sustained decrease in plasma norepinephrine and plasma renin activity, which reflect an inflation-induced decrease in sympathetic activity.

Adult↗
PubMed1989

Antigravity suit inflation: kidney function and cardiovascular and hormonal responses in men.

To investigate the effects of lower body positive pressure (LBPP) on kidney function while controlling certain cardiovascular and endocrine responses, seven men [35 +/- 2 (SE) yr] underwent 30 min of sitting and then 4.5 h of 70 degrees head-up tilt. An antigravity suit was applied (60 Torr legs, 30 Torr abdomen) during the last 3 h of tilt. A similar noninflation experiment was conducted where the suited subjects were tilted for 3.5 h. To provide adequate urine flow, the subjects were hydrated during the course of both experiments. Immediately after inflation, mean arterial pressure increased by 8 +/- 3 Torr and pulse rate decreased by 16 +/- 3 beats/min. Plasma renin activity and aldosterone were maximally suppressed (P less than 0.05) after 2.5 h of inflation. Plasma vasopressin decreased by 40-50% (P less than 0.05) and plasma sodium and potassium remained unchanged during both experiments. Glomerular filtration rate was not increased significantly by inflation, whereas inflation induced marked increases (P less than 0.05) in effective renal plasma flow (ERPF), urine flow, osmolar and free water clearances, and total and fractional sodium excretion. No such changes occurred during control. Thus, LBPP induces 1) a significant increase in ERPF and 2) significant changes in kidney excretory patterns similar to those observed during water immersion or the early phase of bed rest, situations that also result in central vascular volume expansion.

Adult↗
PubMed1990

Pathogenesis of hyperadrenergic orthostatic hypotension. Evidence of disordered venous innervation exclusively in the lower limbs.

The pathogenesis of hyperadrenergic orthostatic hypotension was studied in eight patients. Correction of the abnormal orthostatic changes by an inflated pressure suit (MAST) confirmed previous evidence of excessive gravitational pooling of blood in the leg veins. Intravenous L-norepinephrine infusion raised diastolic blood pressure in the same relationship to the infusion-induced increments in plasma norepinephrine concentrations as in normal subjects, indicating normal arteriolar responses. Contractile responses of the veins to infused L-norepinephrine were measured with a linear variable differential transformer (LVDT). The venous responses of hand veins in the patients fell within the 95% confidence limits of the responses of normal hand veins, as did the responses of foot veins in the seven normal subjects. However, foot veins of the patients with hyperadrenergic orthostatic hypotension, and both hand and foot veins of patients with "diffuse" autonomic failure, were supersensitive to norepinephrine, as reflected by a steeper slope of the regression of log (norepinephrine infusion rate) on percentage reduction in venous distensibility, and a significantly lower ED50 (i.e., norepinephrine infusion rate that induced 50% reduction in venous distensibility). The findings suggest anatomical or functional postganglionic denervation of lower limb veins causing excessive gravitational blood pooling with consequent orthostatic hypotension in these patients.

Adult↗
PubMed1986

Effect of antigravity suit inflation on cardiovascular, PRA, and PVP responses in humans.

Blood pressure, pulse rate (PR), serum osmolality and electrolytes, as well as plasma vasopressin (PVP) and plasma renin activity (PRA), were measured in five men and two women [mean age 38.6 +/- 3.9 (SE) yr] before, during, and after inflation of an antigravity suit that covered the legs and abdomen. After 24 h of fluid deprivation the subjects stood quietly for 3 h: the 1st h without inflation, the 2nd with inflation to 60 Torr, and the 3rd without inflation. A similar control noninflation experiment was conducted 10 mo after the inflation experiment using five of the seven subjects except that the suit was not inflated during the 3-h period. Mean arterial pressure increased by 14 +/- 4 (SE) Torr (P less than 0.05) with inflation and decreased by 15 +/- 5 Torr (P less than 0.05) after deflation. Pulse pressure (PP) increased by 7 +/- 2 Torr (P less than 0.05) with inflation and PR decreased by 11 +/- 5 beats/min (P less than 0.05); PP and PR returned to preinflation levels after deflation. Plasma volume decreased by 6.1 +/- 1.5% and 5.3 +/- 1.6% (P less than 0.05) during hours 1 and 3, respectively, and returned to base line during inflation. Inflation decreased PVP from 6.8 +/- 1.1 to 5.6 +/- 1.4 pg/ml (P less than 0.05) and abolished the significant rise in PRA during hour 1. Both PVP and PRA increased significantly after deflation: delta = 18.0 +/- 5.1 pg/ml and 4.34 +/- 1.71 ng angiotensin I X ml-1 X h-1, respectively. Serum osmolality and Na+ and K+ concentrations were unchanged during the 3 h of standing.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1997

Efficacy of compression of different capacitance beds in the amelioration of orthostatic hypotension.

Orthostatic hypotension (OH) is the most disabling and serious manifestation of adrenergic failure, occurring in the autonomic neuropathies, pure autonomic failure (PAF) and multiple system atrophy (MSA). No specific treatment is currently available for most etiologies of OH. A reduction in venous capacity, secondary to some physical counter maneuvers (e.g., squatting or leg crossing), or the use of compressive garments, can ameliorate OH. However, there is little information on the differential efficacy, or the mechanisms of improvement, engendered by compression of specific capacitance beds. We therefore evaluated the efficacy of compression of specific compartments (calves, thighs, low abdomen, calves and thighs, and all compartments combined), using a modified antigravity suit, on the end-points of orthostatic blood pressure, and symptoms of orthostatic intolerance. Fourteen patients (PAF, n = 9; MSA, n = 3; diabetic autonomic neuropathy, n = 2; five males and nine females) with clinical OH were studied. The mean age was 62 years (range 31-78). The mean +/- SEM orthostatic systolic blood pressure when all compartments were compressed was 115.9 +/- 7.4 mmHg, significantly improved (p < 0.001) over the head-up tilt value without compression of 89.6 +/- 7.0 mmHg. The abdomen was the only single compartment whose compression significantly reduced OH (p < 0.005). There was a significant increase of peripheral resistance index (PRI) with compression of abdomen (p < 0.001) or all compartments (p < 0.001); end-diastolic index and cardiac index did not change. We conclude that denervation increases vascular capacity, and that venous compression improves OH by reducing this capacity and increasing PRI. Compression of all compartments is the most efficacious, followed by abdominal compression, whereas leg compression alone was less effective, presumably reflecting the large capacity of the abdomen relative to the legs.

Adult↗
PubMed1996

Centrifuge man-rating of a conceptual internal abdominal bladder restraint in an extended coverage anti-G suit.

An extended coverage anti-G suit, has been demonstrated to improve +Gz tolerance substantially. In some pilots/subjects, however, the abdominal bladder of the anti-G suit may expand excessively upward and inward causing discomfort and pain. This man-rating was performed to evaluate the effects on +Gz protection of an internal abdominal bladder restraint in the Swedish Tactical Flight Combat Suit (TFCS) used in conjunction with pressure breathing during G (PBG). The tests were executed in the Armstrong Laboratory Centrifuge at Brooks AFB with four Swedish test fighter pilots. The centrifuge profiles included gradual onset runs (GOR, relaxed) and rapid onset runs (ROR, with straining), as well as simulated aerial combat maneuver (SACM) runs up to +9 Gz until subjects experienced light loss or fatigue or surpassed 228 s. All subjects withstood 60 s at +9 Gz during GOR and ROR runs with and without abdominal bladder restraint. No difference There was no difference in SACM duration times. In three of four subjects, abdominal pain or discomfort experienced without abdominal bladder restraint disappeared with the addition of a bladder restraint. Ratings of perceived exertion (after 5 peaks at +9 Gz in the SACM), subjective +Gz tolerance, overall comfort, fatigue, and heat stress demonstrated no relevant differences with and without abdominal bladder restraint. Therefore, to enhance comfort, it seems possible to modify the TFCS by adding an abdominal bladder internal restraint without compromising its operational +Gz protection.

Abdomen↗
PubMed1997

[Changes in individual profiles of cerebral hemispheric asymmetry during somatosensory stimulation due to wearing of G-suits by healthy adults and children].

Presented are results of the investigations of individual profiles of the brain interhemispheric asymmetry (IPIHA) in healthy grown-ups and children prior to, during, and immediately after somatosensory stimulation. The somatosensory stimulation was performed by one-time wearing of space g-loading suit PENGUIN and its modification ADELIE. IPIHA was studied by the main functional asymmetries including motor hand asymmetry, sensory asymmetry of the visual hemispheres, body mass center asymmetry (BMA) using a computerized stabilimeter indirectly measuring the muscle tone of contralateral extensor. Results demonstrate differences in IPIHA of grown-ups and children, persons with right- and left-hand motor asymmetry. It was shown that peculiar features of standing posture acquisition with and without visual control are original IPIHA and age dependent. Initial stability was higher in grown-ups than children and right-handed grown-ups and left-handed children. IPIHA and stability of the vertical posture can be modified even during single somatosensory stimulation. Unequal effects of the somatosensory stimulation on IPIHA in right- and left-handed subjects of varying age dictate the necessity to allow for these differences when assessing effects of the somatosensory stimulation in grown-ups and developing criteria of effective therapy of patients with CNS pathology, specifically, infantile cerebral paralysis.

Adolescent↗
PubMedDate not supplied

Orthostatic hypertension. Pathogenetic studies.

Among 1800 referred hypertensive patients, 181 had recumbent diastolic blood pressures (DBP) below 90 mm Hg and standing DBP above 90 mm Hg. Orthostatic increments in DBP were greater in these orthostatic hypertensive patients than in 181 persistently hypertensive patients and 134 normotensive subjects. In 12 patients with orthostatic hypertension, the orthostatic fall in cardiac output (27.3 +/- 2.9%, measured by a respiratory method) was double that in 8 normotensive subjects (13.3 +/- 3.7%, p less than 0.01). An inflated pressure suit over the pelvis and lower limbs prevented the excessive fall in cardiac output and significantly reduced (p less than 0.02) the excessive rise in standing DBP in orthostatic hypertensive patients. Gravitational pooling of blood in the legs and reduction of blood in the head was measured by external gamma counting of autologous erythrocytes labeled with sodium pertechnetate Tc 99m through ports in fixed positions over the leg and the temple. Orthostatic intravascular pooling was significantly greater (p less than 0.01) in orthostatic hypertensive subjects than in normotensive subjects, and the magnitudes of orthostatic pooling and orthostatic increases in DBP were closely correlated (r = +0.85). Plasma norepinephrine concentrations were similar in recumbency and after sustained handgrip exercise, but significantly greater (p less than 0.01) after 5 to 60 mins of standing in orthostatic hypertensive subjects than in normotensive subjects. Our results indicate that orthostatic hypertension is common and that its mechanism in representative patients involves excessive orthostatic blood pooling, which results in decreased venous return, decreased cardiac output, increased sympathetic stimulation (presumably through low-pressure cardiopulmonary receptors), and excessive arteriolar, but not venular, constriction.

Adolescent↗
PubMed1986

Immediate ventilatory response to sudden changes in venous return in humans.

We changed venous return transiently by postural manoeuvres, and by lower body positive pressure, to see what happened simultaneously to ventilation. Cardiac output was measured by a Doppler technique. In seven subjects, after inflation of a pressure suit to 80 and 40 mmHg at 30 deg head-up tilt, both cardiac output and ventilation increased. Ventilation increased rapidly to a peak in the first 5 s, cardiac output more slowly to a steady state in about 20 s, at 80 mmHg inflation. After inflation to 80 mmHg in six subjects at 12.5 deg head-up and 30 deg head-down tilt, cardiac output did not change in the first, and fell in the second case. There were no significant changes in ventilation. On release of pressure there were transient increases in both cardiac output and ventilation, with ventilation lagging behind cardiac output, in contrast to (2) above. In five subjects, elevation of the legs at 30 deg head-up tilt caused a rise in both cardiac output and ventilation, but in two subjects neither occurred. In all seven subjects there was a transient increase in cardiac output and ventilation when the legs were lowered. Ventilation and cardiac output changes were approximately in phase. We were therefore unable to dissociate entirely increasing cardiac output from increasing ventilation. The relation between them was certainly not a simple proportional one.

Adult↗
PubMed2002

Heat stress effects for USAF anti-G suits with and without a counter-pressure vest.

BACKGROUND: Aircrew have reported increased heat stress when wearing the USAF Combined Advanced Technology Enhanced Design G-Ensemble or COMBAT EDGE (CE). The perceived thermal burden has been attributed to the fact that CE includes an inflatable counter-pressure vest to ease the work of positive pressure breathing during G (PBG). This study compared the heat load of CE with that of the standard USAF anti-G system (STD) without the vest, and measured heat stress effects on G-tolerance in both suits. METHODS: This study had 12 subjects (6 of them aircrew) who participated. Simulated preflight thermal stress (20 min walking at 35 degrees C with 85% relative humidity and radiant heat) was followed by return to a cooler environment (21 degrees C). G-tolerance and subjective stress levels were determined on the human centrifuge before and after the heat stress. Body weight, rectal and skin temperatures, and blood parameters were also assessed. RESULTS: Baseline relaxed tolerance for +Gz gradual onset runs (GORs) were (mean +/- SD) 7.6 +/- 1.3 G for CE and 7.1 +/- 0.8 G for STD (p < 0.05). Maximal rectal temperature following heat stress peaked at 38.1 +/- 0.4 degrees C for both CE and STD, and mean nude weight loss was 1.10 +/- 0.24 kg for both. Relaxed GOR tolerances after heat stress were 7.1 +/- 1.3 for CE and 6.3 +/- 0.9 for STD (p < 0.01). The heat stress significantly reduced G tolerance for both CE and STD (p < 0.01). CONCLUSIONS: Simulated preflight activity in hot conditions revealed no significant difference between CE and STD with regard to maximal core and skin temperature elevations or dehydration levels. CE supported a significantly higher baseline relaxed G-tolerance than STD, an advantage that persisted after heat stress and dehydration.

Adult↗
PubMed1998

The design of arm pressure covers to alleviate pain in high G maneuvers.

HYPOTHESIS: Arm pain has been noted especially when increased coverage anti-G suits are worn in combination with PBG (pressure breathing during G) in high G centrifuge test runs. Arm pain has forced the termination of test runs and has the potential to cause a serious decrement in a pilot's ability to function effectively during high-G flight. Based on the theory that arm pain is caused by fluid pooling in the arm, four new pressure cover systems for the arm were designed and tested. METHODS: Seven test subjects wore each design in a series of runs in a dynamic flight simulator (DFS). Subjects experienced both gradual and rapid onset rate runs with G levels ranging from +3.0 G to +9.0 G. Data were collected on the maximum G's achieved, pain location, and pain intensity. Subjective responses on the comfort and function of each design and overall arm cover design preferences were also obtained via a questionnaire. RESULTS: Analysis of the DFS data, using a two-factor ANOVA (subjects, designs), revealed that each of the new designs provided significantly better protection from arm pain than the control condition (no protection) and that each of the designs significantly improved the maximum G level attained during rapid onset acceleration in the range of +1 G. CONCLUSION: No positive correlation was found between subject ranking of the four new design concepts at the conclusion of the study in terms of the pain reduction they provided and the pain levels reported during DFS testing.

Adult↗
PubMed2003

Staged decompression to 3.5 psi using argon-oxygen and 100% oxygen breathing mixtures.

INTRODUCTION: The current extravehicular activity (EVA) space suit at 4.3 psia causes hand and arm fatigue and is too heavy for Martian EVA. A 3.5 psia EVA pressure suit requires increased preoxygenation time but would reduce structural complexity, leak rate, and weight while increasing mobility, comfort, and maintainability. On Mars, nitrogen and argon are available to provide the inert gas necessary for a fire-resistant habitat atmosphere, eliminating need for transport. This study investigated breathing argon/oxygen and 100% oxygen gas mixtures during staged decompression prior to exposure to 3.5 psia. METHOD: During this study, 40 subjects each completed 3 hypobaric exposures to 3.5 psia for 3 h in a reclined position: (A) a 4-h 25-min 14.7-psia (ground level) denitrogenation (100% oxygen breathing) prior to exposure to 3.5 psia; (B) the same as A, utilizing a 7.3-psia stage denitrogenation; and (C) the same as B, with 62% argon-38% oxygen (ARGOX) during the stage. Venous gas emboli (VGE) were monitored with echocardiography. RESULTS: Decompression sickness (DCS) incidence at 3.5 psia with ARGOX at 7.3 psia (C) was significantly higher than with oxygen breathing with or without staged decompression: there was 78% DCS for C compared with 33% and 55% DCS, respectively, for A and B. The corresponding VGE incidences were 73% (C) compared with 33% (A) and 45% (B). CONCLUSION: Preoxygenation at a 7.3-psia stage resulted in a higher DCS risk at 3.5 psia than ground level preoxygenation. It is suggested that an 8.0-psia stage pressure could eliminate this difference. Unfavorable results after preoxygenation with ARGOX indicate argon on-gassing was significant.

Adolescent↗
PubMed2003

The effect of straining maneuvers on G-protection during assisted pressure breathing.

INTRODUCTION: Pilots flying high-performance aircraft increase their acceleration tolerance by using straining maneuvers and anti-G suits. Recently, assisted positive pressure breathing has been added in some aircraft systems. This study assessed the effect of anti-G straining maneuvers on the G-protective properties of one such system, the AGE-39 anti-G ensemble used in the Swedish JAS 39 Gripen aircraft. METHODS: Ten subjects were studied in a centrifuge using each of the following: 1) the AGE-39 in combination with anti-G straining maneuvers (AGSM) throughout each high-G exposure (full maneuver; FM); 2) the AGE-39 in combination with AGSM only during the initial part of each high-G exposure (reduced maneuver; RM). G-tolerance was established during exposures to rapid onset rate (ROR) G profiles with plateau levels ranging from 6.5 to 9.0 G. RESULTS: Mean G-tolerance was > or = 8.8 G (range: 8.5 to > or = 9.0 G) in the RM condition and > or = 9.0 G in all subjects in the FM condition. Mean arterial pressure was 30-50 mm Hg higher (p < 0.001) in the FM than in the RM condition at any given ROR G-load. CONCLUSIONS: AGE-39 in combination with a brief period of straining provide efficient G-protection as illustrated by the finding that all subjects could tolerate 8.5 G while performing AGSM during the initial part of the high-G exposures. However, at 9.0 G, 40% of the subjects had to perform AGSM throughout the duration of the G-exposure. That arterial pressure was only 30-50 mm Hg higher in the FM than RM condition suggests that in the presence of straining maneuvers, pressure breathing makes only a minute contribution to the arterial-pressure response.

Adult↗
PubMed2000

[The role of individual reaction s of thermal and water-electrolyte metabolism to suited immersion].

Role of individual reactions of thermal and water-electrolyte metabolism and their relation to the mechanisms of hormonal control were studied during suited immersion (SI). The investigation consisted of 177 man/exposures from 3 hrs up to 3 days of 46 male volunteers. Parameters of mass, heat and water-electrolyte metabolism, and hormonal control were determined on a background of monitoring consumption of special ratios. Based on the complex evaluation of tolerance of weight-free SI for 1 to 3 days, parameters of thermal and hydroionic homeostasis were found to be the predictor variables. Extreme types of reactions to SI were in the ratio of 1:4 (tolerant/intolerant subjects). An extreme reaction appears to be an individual constitutional characteristic of the body the dimensions of which are equal during repeated immersion. As for the water-electrolyte parameters, extreme levels of SI tolerance were significantly different in the amount and velocity of renal excretion of liquids and liquid losses due to perspiration (897 +/- 253 ml and 2010 +/- 218 ml in SI tolerant and intolerant subjects, serotonin variability in everyday life and serotonin dynamics during SI (significant increase in tolerant subjects and no dynamics in intolerant subjects after 24 hrs in SI). The complex evaluation of the reaction showed nonstationary thermal state and reduction of oral temperature by 1 degree C in SI intolerant subjects after initial 1-1.5 days of exposure. In the course of 3 days, the negative water balance showed an increase; body mass losses were in parallel with the development of motion sickness and hyperventilation, and disturbance in the rhythm of the sympathoadrenal activity. The renin-aldosterone system reacted most actively out of all the hormonal systems and did not adapt to SI within a day and a half. Thermal state of SI tolerant subjects was stationary during 1-1.5-d immersion; oral temperature dropped by 0.2-0.4 degree C, liquid losses and AP deviations were relatively small and blood osmolality remained unchanged on a background of stable adaptive reactions of various components of the neuroendocrine system. Adaptation to SI occurred in the period from one day to a day and a half.

Adaptation, Physiological↗