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All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

The endocrine system in space flight

A trial natriuretic factor (ANF), a hormone recently shown to regulate sodium and water excretion, has been measured in blood specimens obtained during flight. After 30 or 42 h of weightlessness, mean ANF was elevated. After 175 or 180 h, ANF has increased by 59 percent, and it changed little between that time and soon after landing. There is probably an increase in ANF early inflight associated with the fluid shift, followed by a compensatory decrease in blood volume. Increased renal blood flow may cause the later ANF decrease. Erythropoietin (Ep), a hormone involved in the control of red blood cell proudction, was measured in blood samples taken during the first Spacelab mission and was significantly decreased on the second day of flight, suggesting also an increase in renal blood flow. Spacelab-2 investigators report that the active vitamin D metabolite 1 alpha, 25-dihydroxyvitamin D-3 increased early in the flight, indicating that a stimulus for increased bone resorption occurs by 30 h after launch.

Leach, C. S.↗
NASA NTRS1986

Aerobic Fitness Does Not Contribute to Prediction of Orthostatic Intolerance

Several investigations have suggested that orthostatic tolerance may be inversely related to aerobic fitness (VO (sub 2max)). To test this hypothesis, 18 males (age 29 to 51 yr) underwent both treadmill VO(sub 2max) determination and graded lower body negative pressures (LBNP) exposure to tolerance. VO(2max) was measured during the last minute of a Bruce treadmill protocol. LBNP was terminated based on pre-syncopal symptoms and LBNP tolerance (peak LBNP) was expressed as the cumulative product of LBNP and time (torr-min). Changes in heart rate, stroke volume cardiac output, blood pressure and impedance rheographic indices of mid-thigh-leg initial accumulation were measured at rest and during the final minute of LBNP. For all 18 subjects, mean (plus or minus SE) fluid accumulation index and leg venous compliance index at peak LBNP were 139 plus or minus 3.9 plus or minus 0.4 ml-torr-min(exp -2) x 10(exp 3), respectively. Pearson product-moment correlations and step-wise linear regression were used to investigate relationships with peak LBNP. Variables associated with endurance training, such as VO(sub 2max) and percent body fat were not found to correlate significantly (P is less than 0.05) with peak LBNP and did not add sufficiently to the prediction of peak LBNP to be included in the step-wise regression model. The step-wise regression model included only fluid accumulation index leg venous compliance index, and blood volume and resulted in a squared multiple correlation coefficient of 0.978. These data do not support the hypothesis that orthostatic tolerance as measured by LBNP is lower in individuals with high aerobic fitness.

Convertino, Victor A.↗
NASA NTRS2011

Human Cardiovascular Adaptation to Weightlessness

Entering weightlessness (0 G) induces immediately a shift of blood and fluid from the lower to the upper parts of the body inducing expansion of the cardiac chambers (Bungo et al. 1986; Charles & Lathers 1991; Videbaek & Norsk 1997). For many years the effects of sudden 0 G on central venous pressure (CVP) was discussed, and it puzzled researchers that CVP compared to the 1-G supine position decreased during the initial hours of spaceflight, when at the same time left atrial diameter increased (Buckey et al. 1996). By measuring esophageal pressure as an estimate of inter-pleural pressure, it was later shown that this pressure decreases more than CVP does during 0 G induced by parabolic flights (Videbaek & Norsk 1997). Thus, transmural CVP is increased, which distends the cardiac chambers. This unique lung-heart interaction whereby 1) inter-pleural pressure decreases and 2) central blood volume is expanded is unique for 0 G. Because transmural CVP is increased, stroke volume increases according to the law of Frank-Starling leading to an increase in cardiac output, which is maintained increased during months of 0 G in space to levels of some 25% above that of the 1-G seated position (Norsk unpublished). Simultaneously, sympathetic nervous activity is at the level of the upright 1-G posture, which is difficult to explain based on the high stroke volume and decreased blood pressure and systemic vascular resistance. This paradox should be explored and the mechanisms revealed, because it might have implications for estimating the cardiovascular risk of travelling in space.

Norsk, Peter↗
NASA NTRS2014

Effects of Mild Hypercapnia During Head-Down Bed Rest on Ocular Structures, Cerebral Blood Flow, aud Visual Acuity in Healthy Human Subjects

The cephalad fluid shift induced by microgravity has been hypothesized to cause an elevation in intracranial pressure (ICP) and contribute to the development of the Visual Impairment/Intracranial Pressure (VIIP) syndrome, as experienced by some astronauts during long-duration space flight. Elevated ambient partial pressure of carbon dioxide (PCO2) on ISS may also raise ICP and contribute to VIIP development. We seek to determine if the combination of mild CO2 exposure, similar to that occurring on the International Space Station, with the cephalad fluid shift induced by head-down tilt, will induce ophthalmic and cerebral blood flow changes similar to those described in the VIIP syndrome. We hypothesize that mild hypercapnia in the head-down tilt position will increase choroidal blood volume and cerebral blood flow, raise intraocular pressure (IOP), and transiently reduce visual acuity as compared to the seated or the head-down tilt position without elevated CO2, respectively.

Laurie, S. S.↗
NASA NTRS1986

Effect of posture on arterial baroreflex control of heart rate in humans

The effects of blood-volume redistribution induced by postural changes on baroreflex activity are investigated. The central blood volume and baroreceptor functions of ten males between 23-51 years old were examined while they were in the head-up tilt (HUT), head-down tilt (HDT), and supine positions. It is observed that during HDT at 15 deg the pulse interval over the first five cardiac cycles following neck suction onset is 51 + or - 18 ms longer, at 30 deg it is 61 + or - 20 ms longer, and at 45 deg it is 74 + or - 35 ms longer than at supine; during HUT at 15 deg the pulse interval is 25 + or - 9 ms shorter than when supine, but for the 30 and 45 deg there is no significant difference in pulse interval detected. The data reveal that posture does modify arterial baroreflex control of heart rate.

Harrison, M. H.↗
NASA NTRS1993

Reliability of Autonomic Responses and Malaise Across Multiple Motion Sickness Stimulation Tests

There is general agreement that a high degree of variability exists between subjects in their autonomic nervous system responses to motion sickness stimulation. Additionally, a paucity of data exists that examines the variability within an individual across repeated motion sickness tests. Investigators have also examined the relationship of autonomic responses to motion sickness development. These investigations have used analyses at discrete points in time to describe this relationship. This approach fails to address the time course of autonomic responses and malaise development throughout the motion sickness test. Our objectives were to examine the reliability of autonomic responses and malaise using the final minute of the motion sickness test across five testing occasions, to examine the reliability of the change in autonomic responses and the change in malaise across five testing occasions, and to examine the relationship between changes in autonomic responses and changes in malaise level across the entire motion sickness test. Our results indicate that, based on the final minute of testing, the autonomic responses of heart rate, blood volume pulse, and respiration rate are moderately stable across multiple tests. Changes in heart rate, blood volume pulse, respiration rate, and malaise throughout the test duration were less stable across the tests. We attribute this instability to variations in individual susceptibility and the error associated with estimating a measure of autonomic gain.

Stout, Cynthia S.↗
NASA NTRS1995

Reliability of psychophysiological responses across multiple motion sickness stimulation tests

Although there is general agreement that a high degree of variability exists between subjects in their autonomic nervous system responses to motion sickness stimulation, very little evidence exists that examines the reproducibility of autonomic responses within subjects during motion sickness stimulation. Our objectives were to examine the reliability of autonomic responses and symptom levels across five testing occasions using the (1) final minute of testing, (2) change in autonomic response and the change in symptom level, and (3) strength of the relationship between the change in symptom level and the change in autonomic responses across the entire motion sickness test. The results indicate that, based on the final minute of testing, the autonomic responses of heart rate, blood volume pulse, and respiration rate are moderately stable across multiple tests. Changes in heart rate, blood volume pulse, respiration rate, and symptoms throughout the test duration are less stable across the tests. Finally, autonomic responses and symptom levels are significantly related across the entire motion sickness test.

NASA Discipline Neuroscience↗
NASA NTRS2005

WISE-2005: Integrative Cardiovascular Responses with LBNP during 60-Day Bed Rest in Women

During 2005, 24 women will take part in the Women International Space-simulation for Exploration (WISE). In this paper we report on the first phase that studied 4 Exercise (EX+LBNP), 4 nutrition (NUT), and 4 no countermeasure control (CON) subjects. The EX+LBNP group completed regular exercise on a treadmill inside LBNP, flywheel resistive exercise and static periods of LBNP, and had recovery days. The NUT group received daily protein supplements. Integrative cardiovascular responses were obtained and here we report data for heart rate during LBNP, blood volume and angiotensin 11. LBNP was applied at 0, -10, -20 and -30 mmHg for 2-minutes for each stage. Blood was sampled prebed rest and on HDT-60. After 60-days head down bed rest, HR in the CON group increased by 6.1+/-2.8 bpm at rest and by 20.7+/-5.0 bpm at -30 mmHg LBNP. The EX+LBNP group had increases of 3.6+/-5.6 and 11.6+/-5.4 bpm, while the NUT group HR increased 2.6+/-3.1 and 9.4+/-3.6 bpm. The EX+LBNP group had almost no change in blood volume or plasma angiotensin II from pre-bed rest to HDT60, while both the CON and NUT groups had larger increases in plasma volume and almost double concentrations of angiotensin II. These data show a positive effect in the EX+LBNP group on the heart rate response as well as an unexpected possible benefit in the NUT group. Further studies are required to confirm possible cardiovascular benefits of the protein supplement.

Hughson, R. L.↗
NASA NTRS2000

Comparison of Echocardiographic Measurements Before and After Short and Long Duration Spaceflight

Previous echocardiography studies in astronauts before and after short duration (4 - 17 days) missions have demonstrated a decrease in resting left ventricular (LV) stroke volume (SV), but maintained ejection fraction (EF) and cardiac output. Similar studies before and after long duration (129 - 144 days) spaceflight have been rare and their overall results equivocal. The purpose of this work was to compare the echocardiographic measurements (M-mode, 2-D and Doppler) from short duration (n = 13) and long duration (n = 4) crewmembers. Compared to short duration astronauts, long duration crewmembers had a significantly greater percent decrease in EF (+6+/-0.02 vs.-10.5+/-0.03, p = 0.005) and percent fractional shortening (+7+/-0.03 vs. -11+/-0.07, p = 0.0 15), and an increase in LV end systolic volume (-12+/-0.06 vs. +39+/-0.24, p = 0.011). These data suggest a reduction in cardiac function that relates to mission duration. As the changes in blood pressure and circulating blood volume (9% - 12%) are reported to be similar after short and long duration flights, the drop in EF after longer spaceflights is likely due to a decrease in cardiac function rather than altered blood volume.

Fritsch-Yelle, Janice M.↗
NASA NTRS2002

Comparison of echocardiographic changes after short- and long-duration spaceflight

BACKGROUND: Previous echocardiographic studies of astronauts before and after short-duration (4-17 d) missions have demonstrated a decrease in resting left ventricular stroke volume, but maintained ejection fraction (EF) and cardiac output. Similar studies before and after long-duration (129-144 d) spaceflight have been rare and their overall results equivocal. METHODS: Echocardiographic measurements (M-mode, 2-D, and Doppler) were obtained from short-duration (n = 13) and long-duration (n = 4) crewmembers to evaluate cardiac chamber sizes and function. RESULTS: Compared with short-duration astronauts, long-duration crewmembers had decreases in EF (+6+/-0.02 vs. -10.5+/-0.03%, p = 0.005) and percent fractional shortening (+7+/-0.03 vs. -11+/-0.07%, p = 0.015), and an increase in left ventricular end systolic volume (-12+/-0.06 vs. +39+/-0.24%, p = 0.011). CONCLUSIONS: These data suggest a reduction in cardiac function that relates to mission duration. As the changes in BP and circulating blood volume are reported to be similar after short- and long-duration flights, the smaller EF after longer spaceflights may be due to a decrease in cardiac function rather than altered blood volume.

short duration↗
NASA NTRS1985

Simulation of a G-tolerance curve using the pulsatile cardiovascular model

A computer simulation study, performed to assess the ability of the cardiovascular model to reproduce the G tolerance curve (G level versus tolerance time) is reported. A composite strength duration curve derived from experimental data obtained in human centrifugation studies was used for comparison. The effects of abolishing automomic control and of blood volume loss on G tolerance were also simulated. The results provide additional validation of the model. The need for the presence of autonomic reflexes even at low levels of G is pointed out. The low margin of safety with a loss of blood volume indicated by the simulation results underscores the necessity for protective measures during Shuttle reentry.

Solomon, M.↗
NASA NTRS1995

Effects of 30 day simulated microgravity and recovery on fluid homeostasis and renal function in the rat

Transition from a normal gravitational environment to that of microgravity eventually results in decreased plasma and blood volumes, increasing with duration of exposure to microgravity. This loss of vascular fluid is presumably due to negative fluid and electrolyte balance and most likely contributes to the orthostatic intolerance associated with the return to gravity. The decrease in plasma volume is presumed to be a reflection of a concurrent decrease in extracellular fluid volume with maintenance of normal plasma-interstitial fluid balance. In addition, the specific alterations in renal function contributing to these changes in fluid and electrolyte homeostasis are potentially responding to neuro-humoral signals that are not consistent with systemic fluid volume status. We have previously demonstrated an early increase in both glomerular filtration rate and extracellular fluid volume and that this decreases towards control values by 7 days of simulated microgravity. However, longer duration studies relating these changes to plasma volume alterations and the response to return to orthostasis have not been fully addressed. Male Wistar rats were chronically cannulated, submitted to 30 days heat-down tilt (HDT) and followed for 7 days after return to orthostasis from HDT. Measurements of renal function and extracellular and blood volumes were performed in the awake rat.

Tucker, Bryan J.↗
NASA NTRS1998

Beta-Adrenergic Blockade Does not Prevent Polycythemia or Decrease in Plasma Volume in Men at 4300 m Altitude

When humans ascend to high altitude (ALT) their plasma volume (PV) and total blood volume (BV) decrease during the first few days. With continued residence over several weeks, the hypoxia-induced stimulation of erythropoietin increases red cell production which tends to restore BV. Because hypoxia also activates the beta-adrenergic system, which stimulates red blood cell production, we investigated the effect of adrenergic beta-receptor inhibition with propranolol on fluid volumes and the polycythemic response in 11 healthy unacclimatized men (21-33 years old exposed to an ALT of 4300 m (barometric pressure 460 Torr) for 3 weeks on Pikes Peak, Colorado. PV was determined by the Evans blue dye method (PV(sub EB)), BV by the carbon monoxide method (BV(sub CO)), red cell volume (RCV)was calculated from hematocrit (Hct) and BV(sub CO), and serum erythropoietin concentration ([EPO]) and reticulocyte count, were also determined. All determinations were made at sea level and after 9-11 (ALT-10) and 9-20 (ALT-20) days at ALT. At sea level and ALT, six men received propranolol (pro, 240 mg/day), and five received a placebo (pla). Effective beta-blockade did not modify the mean (SE) maximal values of [EPO] [pla: 24.9 (3.5) vs pro: 24.5 (1.5) mU/ml] or reticulocyte count [pla: 2.7 (0.7) vs pro: 2.2 (0.5)%]; nor changes in PV(sub EB)[pla: -15.8 (3.8) vs pro: -19.9 (2.8)%], RCV(sub CO) [pla: +7.0 (6.7) vs pro: +10.1 (6.1)%], or BV(sub CO) [pla: -7.3 (2.3) vs pro: -7.1 (3.9)%]. In the absence of weight loss, a redistribution of body water with no net loss is implied. Hence, activation of the beta-adrenergic system did not appear to affect the hypovolemic or polycythemic responses that occurred during 3 weeks at 4300 m ALT in these subjects.

Grover, R. F.↗
NASA NTRS1993

Hemodynamic and autonomic nervous system responses to mixed meal ingestion in healthy young and old subjects and dysautonomic patients with postprandial hypotension

BACKGROUND. Although postprandial hypotension is a common cause of falls and syncope in elderly persons and in patients with autonomic insufficiency, the pathophysiology of this disorder remains unknown. METHODS AND RESULTS. We examined the hemodynamic, splanchnic blood pool, plasma norepinephrine (NE), and heart rate (HR) power spectra responses to a standardized 400-kcal mixed meal in 11 healthy young (age, 26 +/- 5 years) and nine healthy elderly (age, 80 +/- 5 years) subjects and 10 dysautonomic patients with symptomatic postprandial hypotension (age, 65 +/- 16 years). Cardiac and splanchnic blood pools were determined noninvasively by radionuclide scans, and forearm vascular resistance was determined using venous occlusion plethysmography. In healthy young and old subjects, splanchnic blood volume increased, but supine blood pressure remained unchanged after the meal. In both groups, HR increased and systemic vascular resistance remained stable. Forearm vascular resistance and cardiac index increased after the meal in elderly subjects, whereas these responses were highly variable and of smaller magnitude in the young. Young subjects demonstrated postprandial increases in low-frequency HR spectral power, representing cardiac sympatho-excitation, but plasma NE remained unchanged. In elderly subjects, plasma NE increased after the meal but without changes in the HR power spectrum. Patients with dysautonomia had a large postprandial decline in blood pressure associated with no change in forearm vascular resistance, a fall in systemic vascular resistance, and reduction in left ventricular end diastolic volume index. HR increased in these patients but without changes in plasma NE or the HR power spectrum. CONCLUSIONS. 1) In healthy elderly subjects, the maintenance of blood pressure homeostasis after food ingestion is associated with an increase in HR, forearm vascular resistance, cardiac index, and plasma NE. In both young and old, systemic vascular resistance is maintained. 2) Dysautonomic patients with postprandial hypotension fail to maintain systemic vascular resistance after a meal. This impairment in vascular response to meal ingestion may underlie the development of postprandial hypotension. 3) The measurement of mean HR or plasma NE does not adequately characterize autonomic cardiac control. Power spectral analysis suggests an impairment in the postprandial autonomic modulation of HR in healthy elderly and dysautonomic subjects, possibly predisposing to hypotension when vascular compensation is inadequate.

Non-NASA Center↗
NASA NTRS1990

Computer simulation of cardiovascular changes during extended duration space flights

The application of mathematical modeling and computer simulation to the study of spaceflight cardiovascular changes is examined using a multicompartment representation model of the entire human cardiovascular system including its control elements. The model simulates the beat-to-beat dynamic responses of the cardiovascular system to orthostatic stresses. Simulation results pertaining to long-term space flight, the combined effect of +G(z) and blood volume loss, and the effect of anti-G suit inflation are discussed, including past results on the original version of the model which has been used in a number of analysis applications at NASA. New results pertain to analysis of cardiovascular changes in extended duration space flights and demonstrate the use of this model in evaluation of physiological factors that contribute to orthostatic intolerance following an exposure to weightlessness, in particular, blood volume loss and changes in the sensitivity of baroreceptors.

Srinivasan, R. Srini↗
NASA NTRS1974

Depth of immersion as a determinant of the natriuresis of water immersion

The current study was undertaken to further assess the contribution of an immersion-induced hydrostatic pressure gradient on the redistribution of blood volume. The rate of sodium excretion by seated subjects was significantly increased by water immersion up to the chest and neck compared to waist immersion and controls. These results are consistent with the hypothesis that whereas immersion to the level of the diaphragm merely cancels the intravascular hydrostatic pressure gradient by providing an identical external gradient, immersion above the diaphragm level results in increased water pressure which tends to favor a shift in blood volume from the lower extremities.

Epstein, M.↗
NASA NTRS2015

Numerical Modeling of Ophthalmic Response to Space

To investigate ophthalmic changes in spaceflight, we would like to predict the impact of blood dysregulation and elevated intracranial pressure (ICP) on Intraocular Pressure (IOP). Unlike other physiological systems, there are very few lumped parameter models of the eye. The eye model described here is novel in its inclusion of the human choroid and retrobulbar subarachnoid space (rSAS), which are key elements in investigating the impact of increased ICP and ocular blood volume. Some ingenuity was required in modeling the blood and rSAS compartments due to the lack of quantitative data on essential hydrodynamic quantities, such as net choroidal volume and blood flowrate, inlet and exit pressures, and material properties, such as compliances between compartments.

intracranial pressure↗
NASA NTRS1985

A detailed analysis of the erythropoietic control system in the human, squirrel, monkey, rat and mouse

The erythropoiesis modeling performed in support of the Body Fluid and Blood Volume Regulation tasks is described. The mathematical formulation of the species independent model, the solutions to the steady state and dynamic versions of the model, and the individual species specific models for the human, squirrel monkey, rat and mouse are outlined. A detailed sensitivity analysis of the species independent model response to parameter changes and how those responses change from species to species is presented. The species to species response to a series of simulated stresses directly related to blood volume regulation during space flight is analyzed.

Nordheim, A. W.↗