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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Alterations in left ventricular volumes induced by Valsalva manoeuvre

Five patients were studied with left ventriculography during different phases of the Valsalva manoeuvre. Small doses of contrast medium allowed adequate repetitive visualization of the left ventricle for volume calculation. During strain phase, the volume of the left ventricle decreased by nearly 50 per cent in each case, and stroke volume and cardiac output also dropped strikingly. Release of straining was attended by a sharp rebound of left ventricular volume to control levels, with a transient surge of increased cardiac output 42 per cent above that of the resting state.

Brooker, J. Z.↗
NASA NTRS1994

Comparison of cardiovascular function during the early hours of bed rest and space flight

This paper reviews the cardiovascular responses of six healthy male subjects to 6 hours in a 5 degrees head-down bed rest model of weightlessness, and compares these responses to those obtained when subjects were positioned in head-up tilts of 10 degrees, 20 degrees, and 42 degrees, simulating 1/6, 1/3, and 2/3 G, respectively. Thoracic fluid index, cardiac output, stroke volume, and peak flow were measured using impedance cardiography. Cardiac dimensions and volumes were determined from two-dimensional guided M-mode echocardiograms in the left lateral decubitus position at 0, 2, 4, and 6 hours. Cardiovascular response to a stand test were compared before and after bed rest. The impedance values were related to tilt angle for the first 2 hours of tilt; however, after 3 hours, at all four angles, values began to converge, indicating that cardiovascular homeostatic mechanisms seek a common adapted state, regardless of effective gravity level (tilt angle) up to 2/3 G. Echocardiography revealed that left ventricular end-diastolic and end-systolic volume, stroke volume, ejection fraction, heart rate, and cardiac output had returned to control values by hour 6 for all tilt angles. The lack of a significant immediate change in left ventricular end-diastolic volume, despite decrements in stroke volume (P < .05) and heart rate (not significant), indicates that multiple factors may play a role in the adaptation to simulated hypogravity. The echocardiography data indicated that no angle of tilt, whether head-down or head-up for 4 to 6 hours, mimicked exactly the changes in cardiovascular function recorded after 4 to 6 hours of space flight. Changes in left ventricular end-diastolic volume during space flight and tilt may be similar, but follow a different time course. Nevertheless, head-down tilt at 5 degrees for 6 hours mimics some (stroke volume, systolic and diastolic blood pressure, mean arterial blood pressure, and total resistance), but not all, of the changes occurring in an equivalent time of space flight. The magnitude of the change in the mean heart rate response to standing was greater after six hours of tilt at -5 degrees or 10 degrees. Thus, results from the stand test after 6 hours of bed rest at -5 degrees and 10 degrees, but not at 20 degrees or 42 degrees, are similar to those obtained after space flight.

Space Flight↗
NASA NTRS2001

Mechanisms of blood pressure regulation that differ in men repeatedly exposed to high-G acceleration

The purpose of this study was to test the hypothesis that repeated exposure to high acceleration (G) would be associated with enhanced functions of specific mechanisms of blood pressure regulation. We measured heart rate (HR), stroke volume (SV), cardiac output (), mean arterial blood pressure, central venous pressure, forearm and leg vascular resistance, catecholamines, and changes in leg volume (%DeltaLV) during various protocols of lower body negative pressure (LBNP), carotid stimulation, and infusions of adrenoreceptor agonists in 10 males after three training sessions on different days over a period of 5-7 days using a human centrifuge (G trained). These responses were compared with the same measurements in 10 males who were matched for height, weight, and fitness but did not undergo G training (controls). Compared with the control group, G-trained subjects demonstrated greater R-R interval response to equal carotid baroreceptor stimulation (7.3 +/- 1.2 vs. 3.9 +/- 0.4 ms/mmHg, P = 0.02), less vasoconstriction to equal low-pressure baroreceptor stimulation (-1.4 +/- 0.2 vs. -2.6 +/- 0.3 U/mmHg, P = 0.01), and higher HR (-1.2 +/- 0.2 vs. -0.5 +/- 0.1 beats. min(-1). mmHg(-1), P = 0.01) and alpha-adrenoreceptor response (32.8 +/- 3.4 vs. 19.5 +/- 4.7 U/mmHg, P = 0.04) to equal dose of phenylephrine. During graded LBNP, G-trained subjects had less decline in and SV, %DeltaLV, and elevation in thoracic impedance. G-trained subjects also had greater total blood (6,497 +/- 496 vs. 5,438 +/- 228 ml, P = 0.07) and erythrocyte (3,110 +/- 364 vs. 2,310 +/- 96 ml, P = 0.06) volumes. These results support the hypothesis that exposure to repeated high G is associated with increased capacities of mechanisms that underlie blood pressure regulation.

Non-NASA Center↗
NASA NTRS1975

Cardiorespiratory responses to orthostasis and the effects of propranolol

Cardiac output and gas exchange were determined serially using the single-breath method of Kim et al. before, during, and after orthostasis on six subjects after beta-adrenergic blockage and in duplicate controls. In the latter, heart rate increased and pulse pressure dropped immediately on tilting to 60 deg and remained stable while cardiac output and stroke volume declined gradually over 21 min upright. On propranolol, heart rate was 10 bpm lower supine and 20 bpm less at 60 deg but cardiac output was only slightly lower before and following tilt-up. However, after 15 min upright, stroke volume and cardiac output recovered on propranolol exceeding the controls after 21 min without change in heart rate. Returning to supine, heart rate dropped in all tests with a transitory increase in stroke volume, cardiac output and arteriovenous O2 difference. At the same time, apparent O2 uptake increased temporarily, reflecting the return of pooled venous blood to the lungs. Orthostatic tolerance did not appear to be affected by beta-adrenergic blockade.

Loeppky, J. A.↗
NASA NTRS2001

Marked exacerbation of orthostatic intolerance after long- vs. short-duration spaceflight in veteran astronauts

OBJECTIVE: The incidence of postflight orthostatic intolerance after short-duration spaceflight is about 20%. However, the incidence after long-duration spaceflight was unknown. The purpose of this study was to test the hypothesis that orthostatic intolerance is more severe after long-duration than after short-duration flight. METHODS: We performed tilt tests on six astronauts before and after long-duration (129-190 days) spaceflights and compared these data with data obtained during stand tests before and after previous short-duration missions. RESULTS: Five of the six astronauts studied became presyncopal during tilt testing after long-duration flights. Only one had become presyncopal during stand testing after short-duration flights. We also compared the long-duration flight tilt test data to tilt test data from 20 different astronauts who flew on the short-duration Shuttle missions that delivered and recovered the astronauts to and from the Mir Space Station. Five of these 20 astronauts became presyncopal on landing day. Heart rate responses to tilt were no different between astronauts on long-duration flights and astronauts on short-duration flights, but long-duration subjects had lower stroke volumes and cardiac outputs than short-duration presyncopal subjects, suggesting a possible decrease in cardiac contractile function. One subject had subnormal norepinephrine release with upright posture after the long flight but not after the short flight. Plasma volume losses were not greater after long flights. CONCLUSION: Long-duration spaceflight markedly increases orthostatic intolerance, probably with multiple contributing factors.

STS Shuttle Project↗
NASA NTRS1986

Cardiovascular dynamics associated with tolerance to lower body negative pressure

The purpose of this investigation was to identify cardiovascular responses associated with tolerance to lower body negative pressure (LBNP). Eighteen men, ages 29-51 years, were categorized as high (HT) or low (LT) LBNP-tolerant based on a graded presyncopal-limited LBNP exposure criterion of -60 mm Hg relative to ambient pressure. Groups were matched for physical characteristics and pre-LBNP cardiovascular measurements, with the exceptions of greater (p less than 0.05) end-diastolic volume and cardiac output in the HT group. During peak LBNP, cardiac output was similar in both groups, although the HT group displayed a greater heart rate (p less than 0.05). In both groups, venous return appeared to limit cardiac output resulting in decreased arterial pressure. Tolerance to LBNP did not appear solely dependent on the absolute amount of blood pooled in the legs since the HT group demonstrated a greater (p less than 0.05) peak LBNP-induced increase in midthigh-leg volume. Greater tolerance to LBNP was associated with a larger pre-LBNP cardiac output reserve and higher compensatory increases in heart rate and peripheral resistance.

Sather, T. M.↗
NASA NTRS1994

Response to graded Lower Body Negative Pressure (LBNP) after space flight

The effects of space flight on orthostatic function were studied. LBNP tests (0 to -60 mmHg) were administered to 7 crew members preflight and 2 to 6 hrs after 6 to 9 day shuttle missions. Cardiac stroke volumes were obtained each minute by echo Doppler. Orthostatic responses are given. The data suggest a decline in postflight orthostatic function, as assessed by LBNP, due to reduced cardiac filling despite potentiated heart rate and vasoconstrictor reflex responses in most crew members.

Fortney, S.↗
NASA NTRS1994

Cardiopulmonary adaptation to weightlessness

The lung is profoundly affected by gravity. The absence of gravity (microgravity) removes the mechanical stresses acting on the lung paranchyma itself, resulting in a reduction in the deformation of the lung due to its own weight, and consequently altering the distribution of fresh gas ventilation within the lung. There are also changes in the mechanical forces acting on the rib cage and abdomen, which alters the manner in which the lung expands. The other way in which microgravity affects the lung is through the removal of the gravitationally induced hydrostatic gradients in vascular pressures, both within the lung itself, and within the entire body. The abolition of a pressure gradient within the pulmonary circulation would be expected to result in a greater degree of uniformity of blood flow within the lung, while the removal of the hydrostatic gradient within the body should result in an increase in venous return and intra-thoracic blood volume, with attendant changes in cardiac output, stroke volume, and pulmonary diffusing capacity. During the 9 day flight of Spacelab Life Sciences-1 (SLS-1) we collected pulmonary function test data on the crew of the mission. We compared the results obtained in microgravity with those obtained on the ground in both the standing and supine positions, preflight and in the week immediately following the mission. A number of the tests in the package were aimed at studying the anticipated changes in cardiopulmonary function, and we report those in this communication.

short duration↗
NASA NTRS1988

Correlation of macro and micro cardiovascular function during weightlessness and simulated weightlessness

The investigation of cardiovascular function necessarily involves a consideration of the exchange of substances at the capillary. If cardiovascular function is compromised or in any way altered during exposure to zero gravity in space, then it stands to reason that microvascular function is also modified. We have shown that an increase in cardiac output similar to that reported during simulated weightlessness is associated with a doubling of the number of post-capillary venules and a reduction in the number of arterioles by 35%. If the weightlessness of space travel produces similar changes in cardiopulmonary volume and cardiac output, a reasonable expectation is that astronauts will undergo venous neovascularization. We have developed an animal model in which to correlate microvascular and systemic cardiovascular function. The microcirculatory preparation consists of a lightweight, thermo-neutral chamber implanted around intact skeletal muscle on the back of a rat. Using this technique, the performed microvasculature of the cutaneous maximus muscle may be observed in the conscious, unanesthetized animal. Microcirculatory variables which may be obtained include venular and arteriolar numbers, lengths and diameters, single vessel flow velocities, vasomotion, capillary hematocrit anastomoses and orders of branching. Systemic hemodynamic monitoring of cardiac output by electromagnetic flowmetry, and arterial and venous pressures allows correlation of macro- and microcirculatory changes at the same time, in the same animal. Observed and calculated hemodynamic variables also include pulse pressure, heart rate, stroke volume, total peripheral resistance, aortic compliance, minute work, peak aortic flow velocity and systolic time interval. In this manner, an integrated assessment of total cardiovascular function may be obtained in the same animal without the complicating influence of anesthetics.

NASA Discipline Number 00-00↗
NASA NTRS1980

Effect of hypokinesia on cardiac contractile function and nervous regulation of the heart

Longterm hypokinesia caused cardiac deadaptation in rabbits, which resulted in the diminishing of the left ventricular rate of contraction and relaxation, joined later by decreased vascular resistance. As a results, the ejection rate as well as stroke volume and cardiac output were normal. The decrease of the relaxation speed was more obvious at a high heart rate and results in shortening of the diastolic pause and diminishing of cardiac output. Hearts of the hypokinetic animals were characterized by normal maximal pressure developed by a unit of muccardial mass aorta clamping, decreased adrenoreactivity, and increased cholinoreactivity. This complex of changes is contrary to changes observed in adaptation to exercise, but is similar to changes observed in compensatory hypertrophy of the heart.

Meyerson, F. Z.↗
NASA NTRS2001

Maximal exercise as a countermeasure to orthostatic intolerance after spaceflight

Previous investigators have suggested that maximal exercise performed 24 h before the end of bed rest, a spaceflight analog, restores prebed rest plasma volume, baroreflex responses, and orthostatic tolerance. PURPOSE: In this case report, we examined the effect of a similar exercise protocol 24 h before a Shuttle landing on the orthostatic responses of four crewmembers (EX) after spaceflights of 8-14 d. Four additional crewmembers (CON) served as controls and did not perform exercise during the final day of the flight. METHODS: Each crewmember performed a 10-min stand test approximately 10 d before launch (L-10) and within 1-2 h of landing (R+0). Cardiac stroke volume was measured (Doppler ultrasound) supine and during each min of standing for three EX and three CON subjects. RESULTS: Preflight, all crewmembers completed the stand test and each group had similar heart rate and blood pressure responses. Postflight, all subjects also completed the 10-min stand test. Each group had similarly elevated supine and standing heart rates, elevated diastolic and mean arterial blood pressures, and reduced pulse pressures compared to L-10. However, postflight cardiac output, mean +/- SEM, (EX: 4.5+/-0.6 L x min(-1); CON: 3.1+/-0.3 L x min(-1)) and stroke volume (EX: 43+/-7 mL x beat; CON: 30+/-6 mL x beat) were higher after 10 min standing in the EX subjects compared to CON subjects. CONCLUSIONS: For these four crewmembers, maximal exercise performed 24 h before landing may have helped maintain stroke volume but did not maintain heart rate and blood pressure responses during standing compared to preflight.

Flight Experiment↗
NASA NTRS1999

Marked Exacerbation of Orthostatic Intolerance After Long vs. Short-Duration Spaceflight in Veteran Astronauts

The incidence of postflight orthostatic intolerance following short-duration spaceflight is about 20%. However, the incidence following long-duration spaceflight is unknown. We performed tilt tests on six astronauts before and after their long-duration (129 - 190 days) spaceflights and compared these data to those obtained during stand tests before and after their previous short-duration missions and also to tilt test data from 20 different short-duration (8 - 16 days) flight astronauts. Five of these six became presyncopal during tilt testing after long-duration flights: only one had become presyncopal during stand testing after short-duration flights. Five of the twenty astronauts who flew on other short-duration flights, became presyncopal during upright tilt on landing day. Long-duration presyncopal subjects had lower stroke volumes, lower cardiac outputs and higher peripheral vascular resistance than short-duration presyncopal subjects, but their heart rate responses were not different. One subject had subnormal norepinephrine release with upright posture after a long but not short flight. Plasma volume losses were not greater after long flights. Long-duration spaceflight markedly increases orthostatic intolerance, probably related to altered autonomic function.

Fritsch-Yelle, Janice M.↗
NASA NTRS2012

Examining Individual Differences in Temporal Profiles of Cardiovascular Responses to the Head Down Tilt during Fluid Loading

Upon returning to Earth after an extended exposure to micro-gravity in space many astronauts have experienced symptoms of light headedness and fainting associated with post-flight orthostatic intolerance (low blood pressure). The main reason for this condition is the reduced fluid volume in the body while in space. A preventative treatment was proposed to prevent this condition by fluid loading to restore lost plasma volume by giving crew members salt tablets and water prior to re-entry. In order to simulate micro-gravity effects on earth test subjects are placed in a supine position with their head below the level of their heart (6 head down tilt-HDT). The purpose of the present study is to define individual differences in the time course of cardiac stroke volume responses to HDT (6 hours) and the effectiveness of fluid loading for mitigating orthostatic intolerance when standing . Echocardiography and impedance cardiography data will be collected on 8 men and 8 women to examine heart function to HDT. A second objective is to determine if the effects of fluid loading vary due to individual differences (e.g., age, gender, height, weight, physical fitness, etc.).

orthostatic intolerance↗
NASA NTRS1999

Cardiovascular Session Summary

It was apparent that the bed-rest and spaceflight data indicated that decreases in plasma volume and cardiac atrophy along with cardiac remodeling were fundamental changes which predisposed many astronauts to post flight orthostatic intolerance. Despite the recently acquired in-flight and post-flight muscle sympathetic nerve activity findings suggesting that the sympathetic nerve responses were appropriate there remains significant contrary data from bed-rest studies, post- flight stand tests and hind-limb unweighted rat studies that suggest that the vasoconstrictive responses were compromised at least insufficient in susceptible individuals. The key issues raised is whether a diminished increase in sympathetic activity from baseline without changes in 254 First Biennial Space Biomedical Investigators'Workshop Cardiovascular peak response or receptor adaptations is an abnormal response or is an individual variance of response to the accentuated decrease in stroke volume. Data relating autonomic neural control of heart rate were presented to suggest that the vagal and sympathetic control of heart rate was attenuated. Also, bed-rest and space flight induced attenuated baroreflex control of heart rate was shown to be restored to pre-bedrest function by one bout of maximal dynamic exercise. However, these data were confounded by relying on the use of R-R interval as a measure of efferent responses of the baroreflex during a condition in which the baseline heart rate was changed. Clearly the idea that the autonomic control of heart rate may be changed by microgravity needs further investigation. This direction is suggested despite the fact that in the triple product (HR x SV x TPR = MAP) assessment of the regulation of arterial blood pressure during orthostasis the role of the HR reflex may be less influential than that associated. with cardiac atrophy (SV changes) and aberrant sympathetic vasoconstriction (resistance) changes. Although sympathetic nerve activity responses in-flight and post-flight on neurolab appeared appropriate, enough bed-rest and post-flight stand test data, along with animal model data suggest that vasoconstriction was compromised. The mechanism of this compromised vasoconstriction needs to be delineated. Other major findings concerning microgravity and physiological regulatory systems are that: I . Thermoregulatory adaptation appear to suggest some decrements in the control of cutaneous vasodilation and sweating; 2. Calcium resorption and dietary calcium need to be defined for differing durations of spaceflight, especially as the effects of excess calcium on vasomotor function appears to be detrimental; 3. Neurohumoral mechanisms of microgravity induced changes in neural function and the regulation of plasma volume and total body water, bone resorption and autonomic neural control of the circulation need further delineation; 4. As performance of work tasks become prolonged, the mechanisms of blood pressure regulation in microgravity needs to be used in the recovery period from prolonged work tasks.

Raven, Peter↗
NASA NTRS1994

Cardiovascular regulation in humans in response to oscillatory lower body negative pressure

The frequency response characteristics of human cardiovascular regulation during hypotensive stress have not been determined. We therefore exposed 10 male volunteers to seven frequencies (0.004-0.1 Hz) of oscillatory lower body negative pressure (OLBNP; 0-50 mmHg). Fourier spectra of arterial pressure (AP), central venous pressure (CVP), stroke volume (SV), cardiac output (CO), heart rate (HR), and total peripheral resistance (TPR) were determined and first harmonic mean, amplitude, and phase angles with respect to OLBNP are presented. AP was relatively well regulated as demonstrated by small oscillations in half amplitude (3.5 mmHg) that were independent of OLBNP frequency and similar to unstressed control spectra. Due to the biomechanics of the system, the magnitudes of oscillations in calf circumference (CC) and CVP decreased with increasing frequency; therefore, we normalized responses by these indexes of the fluid volume shifted. The ratios of oscillations in AP to oscillations in CC increased by an order of magnitude, whereas oscillations in CVP to oscillations in CC and oscillations in AP to oscillations in CVP both tripled between 0.004 and 0.1 Hz. Therefore, even though the amount of fluid shifted by OLBNP decreased with increasing frequency, the magnitude of both CVP and AP oscillations per volume of fluid shifted increased (peaking at 0.08 Hz). The phase relationships between variables, particularly the increasing lags in SV and TPR, but not CVP, indicated that efferent responses with lags of 5-6 s could account for the observed responses. We conclude that, at frequencies below 0.02 Hz, the neural system of humans functioned optimally in regulating AP; OLBNP-induced decreases in SV (by as much as 50%) were counteracted by appropriate oscillations in HR and TPR responses. As OLBNP frequency increased, SV, TPR, and HR oscillations increasingly lagged the input and became less optimally timed for AP regulation.

NASA Discipline Cardiopulmonary↗
NASA NTRS2000

Real-time three-dimensional echocardiographic study of left ventricular function after infarct exclusion surgery for ischemic cardiomyopathy

BACKGROUND: Infarct exclusion (IE) surgery, a technique of left ventricular (LV) reconstruction for dyskinetic or akinetic LV segments in patients with ischemic cardiomyopathy, requires accurate volume quantification to determine the impact of surgery due to complicated geometric changes. METHODS AND RESULTS: Thirty patients who underwent IE (mean age 61+/-8 years, 73% men) had epicardial real-time 3-dimensional echocardiographic (RT3DE) studies performed before and after IE. RT3DE follow-up was performed transthoracically 42+/-67 days after surgery in 22 patients. Repeated measures ANOVA was used to compare the values before and after IE surgery and at follow-up. Significant decreases in LV end-diastolic (EDVI) and end-systolic (ESVI) volume indices were apparent immediately after IE and in follow-up (EDVI 99+/-40, 67+/-26, and 71+/-31 mL/m(2), respectively; ESVI 72+/-37, 40+/-21, and 42+/-22 mL/m(2), respectively; P:<0.05). LV ejection fraction increased significantly and remained higher (0.29+/-0.11, 0.43+/-0.13, and 0.42+/-0.09, respectively, P:<0.05). Forward stroke volume in 16 patients with preoperative mitral regurgitation significantly improved after IE and in follow-up (22+/-12, 53+/-24, and 58+/-21 mL, respectively, P:<0.005). New York Heart Association functional class at an average 285+/-144 days of clinical follow-up significantly improved from 3.0+/-0.8 to 1.8+/-0.8 (P:<0.0001). Smaller end-diastolic and end-systolic volumes measured with RT3DE immediately after IE were closely related to improvement in New York Heart Association functional class at clinical follow-up (Spearman's rho=0.58 and 0.60, respectively). CONCLUSIONS: RT3DE can be used to quantitatively assess changes in LV volume and function after complicated LV reconstruction. Decreased LV volume and increased ejection fraction imply a reduction in LV wall stress after IE surgery and are predictive of symptomatic improvement.

Non-NASA Center↗