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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Effect of perturbations and a meal on superior mesenteric artery flow in patients with orthostatic hypotension

Our aims were to evaluate to role of superior mesenteric blood flow in the pathophysiology of orthostatic hypotension in patients with generalized autonomic failure. METHODS: Twelve patients with symptomatic neurogenic orthostatic hypotension and 12 healthy controls underwent superior mesenteric artery flow measurements using Doppler ultrasonography during head-up tilt and tilt plus meal ingestion. Autonomic failure was assessed using standard tests of the function of the sympathetic adrenergic, cardiovagal and postganglionic sympathetic sudomotor function. RESULTS: Superior mesenteric flow volume and time-averaged velocity were similar in patients and controls at supine rest; however, responses to cold pressor test and upright tilt were attenuated (p < 0.05) in patients compared to controls. Head-up tilt after the meal evoked a profound fall of blood pressure and mesenteric blood flow in the patients; the reduction of mesenteric blood flow correlated (r = 0.89) with the fall of blood pressure in these patients, providing another manifestation of failed baroreflexes. We make the novel finding that the severity of postprandial orthostatic hypotension regressed negatively with the postprandial increase in mesenteric flow in patients with orthostatic hypotension. CONCLUSION: Mesenteric flow is under baroreflex control, which when defective, results in, or worsens orthostatic hypotension. Its large size and baroreflexivity renders it quantitatively important in the maintenance of postural normotension. The effects of orthostatic stress can be significantly attenuated by reducing the splanchnic-mesenteric volume increase in response to food. Evaluation of mesenteric flow in response to eating and head-up tilt provide important information on intra-abdominal sympathetic adrenergic function, and the ability of the patient to cope with orthostatic stress.

Non-NASA Center↗
NASA NTRS1997

Left ventricular diastolic filling with an implantable ventricular assist device: beat to beat variability with overall improvement

OBJECTIVES: We studied the effects of left ventricular (LV) unloading by an implantable ventricular assist device on LV diastolic filling. BACKGROUND: Although many investigators have reported reliable systemic and peripheral circulatory support with implantable LV assist devices, little is known about their effect on cardiac performance. METHODS: Peak velocities of early diastolic filling, late diastolic filling, late to early filling ratio, deceleration time of early filling, diastolic filling period and atrial filling fraction were measured by intraoperative transesophageal Doppler echocardiography before and after insertion of an LV assist device in eight patients. A numerical model was developed to simulate this situation. RESULTS: Before device insertion, all patients showed either a restrictive or a monophasic transmitral flow pattern. After device insertion, transmitral flow showed rapid beat to beat variation in each patient, from abnormal relaxation to restrictive patterns. However, when the average values obtained from 10 consecutive beats were considered, overall filling was significantly normalized from baseline, with early filling velocity falling from 87 +/- 31 to 64 +/- 26 cm/s (p < 0.01) and late filling velocity rising from 8 +/- 11 to 32 +/- 23 cm/s (p < 0.05), resulting in an increase in the late to early filling ratio from 0.13 +/- 0.18 to 0.59 +/- 0.38 (p < 0.01) and a rise in the atrial filling fraction from 8 +/- 10% to 26 +/- 17% (p < 0.01). The deceleration time (from 112 +/- 40 to 160 +/- 44 ms, p < 0.05) and the filling period corrected by the RR interval (from 39 +/- 8% to 54 +/- 10%, p < 0.005) were also significantly prolonged. In the computer model, asynchronous LV assistance produced significant beat to beat variation in filling indexes, but overall a normalization of deceleration time as well as other variables. CONCLUSIONS: With LV assistance, transmitral flow showed rapidly varying patterns beat by beat in each patient, but overall diastolic filling tended to normalize with an increase of atrial contribution to the filling. Because of the variable nature of the transmitral flow pattern with the assist device, the timing of the device cycle must be considered when inferring diastolic function from transmitral flow pattern.

Non-NASA Center↗
NASA NTRS1997

Changes in skeletal muscle biochemistry and histology relative to fiber type in rats with heart failure

One of the primary consequences of left ventricular dysfunction (LVD) after myocardial infarction is a decrement in exercise capacity. Several factors have been hypothesized to account for this decrement, including alterations in skeletal muscle metabolism and aerobic capacity. The purpose of this study was to determine whether LVD-induced alterations in skeletal muscle enzyme activities, fiber composition, and fiber size are 1) generalized in muscles or specific to muscles composed primarily of a given fiber type and 2) related to the severity of the LVD. Female Wistar rats were divided into three groups: sham-operated controls (n = 13) and rats with moderate (n = 10) and severe (n = 7) LVD. LVD was surgically induced by ligating the left main coronary artery and resulted in elevations (P < 0.05) in left ventricular end-diastolic pressure (sham, 5 +/- 1 mmHg; moderate LVD, 11 +/- 1 mmHg; severe LVD, 25 +/- 1 mmHg). Moderate LVD decreased the activities of phosphofructokinase (PFK) and citrate synthase in one muscle composed of type IIB fibers but did not modify fiber composition or size of any muscle studied. However, severe LVD diminished the activity of enzymes involved in terminal and beta-oxidation in muscles composed primarily of type I fibers, type IIA fibers, and type IIB fibers. In addition, severe LVD induced a reduction in the activity of PFK in type IIB muscle, a 10% reduction in the percentage of type IID/X fibers, and a corresponding increase in the portion of type IIB fibers. Atrophy of type I fibers, type IIA fibers, and/or type IIB fibers occurred in soleus and plantaris muscles of rats with severe LVD. These data indicate that rats with severe LVD after myocardial infarction exhibit 1) decrements in mitochondrial enzyme activities independent of muscle fiber composition, 2) a reduction in PFK activity in type IIB muscle, 3) transformation of type IID/X to type IIB fibers, and 4) atrophy of type I, IIA, and IIB fibers.

NASA Discipline Musculoskeletal↗
NASA NTRS1997

Pulmonary tissue volume, cardiac output, and diffusing capacity in sustained microgravity

In microgravity (microG) humans have marked changes in body fluids, with a combination of an overall fluid loss and a redistribution of fluids in the cranial direction. We investigated whether interstitial pulmonary edema develops as a result of a headward fluid shift or whether pulmonary tissue fluid volume is reduced as a result of the overall loss of body fluid. We measured pulmonary tissue volume (Vti), capillary blood flow, and diffusing capacity in four subjects before, during, and after 10 days of exposure to microG during spaceflight. Measurements were made by rebreathing a gas mixture containing small amounts of acetylene, carbon monoxide, and argon. Measurements made early in flight in two subjects showed no change in Vti despite large increases in stroke volume (40%) and diffusing capacity (13%) consistent with increased pulmonary capillary blood volume. Late in-flight measurements in four subjects showed a 25% reduction in Vti compared with preflight controls (P < 0.001). There was a concomittant reduction in stroke volume, to the extent that it was no longer significantly different from preflight control. Diffusing capacity remained elevated (11%; P < 0.05) late in flight. These findings suggest that, despite increased pulmonary perfusion and pulmonary capillary blood volume, interstitial pulmonary edema does not result from exposure to microG.

Clinical Trial↗
NASA NTRS1997

Effect of fluid ingestion on orthostatic responses following acute exercise

Orthostatic tolerance is impaired following an acute bout of exercise. This study examined the effect of fluid ingestion following treadmill exercise in restoring the cardiovascular responses to an orthostatic stress. Five men (age, 29.6 +/- 3.4 yrs) were exposed to a graded lower body negative (LBNP) pressure protocol (0 to -50 mmHg) during euhydration without exercise (C), 20 minutes after exercise dehydration (D), 20 minutes after exercise and fluid ingestion (FI20), and 60 minutes after exercise and fluid ingestion (FI60). Fluid ingestion (mean +/- SE) consisted of water-ingestion equivalent to 50% of the body weight lost during exercise (520 +/- 15 ml). Exercise dehydration resulted in significantly higher heart rates (119 +/- 8 vs 82 +/- 7 bpm), lower systolic blood pressures (95 +/- 1.7 vs 108 +/- 2.3 mmHg), a smaller increase in leg circumference (3.7 +/- 4 vs 6.9 +/- 1.0 mm), and an attenuated increase in total peripheral resistance (2.58 +/- 1.2 vs 4.28 +/- 0.9 mmHg/L/min) at -50 mmHg LBNP compared to the C condition. Fluid ingestion (both 20 and 60), partially restored the heart rate, systolic blood pressure, and total peripheral resistance responses to LBNP, but did not influence the change in leg circumference during LBNP (4 +/- 0.3 for R20 and 2.8 +/- 0.4 mm for R60). These data illustrate the effectiveness of fluid ingestion on improving orthostatic responses following exercise, and suggest that dehydration is a contributing factor to orthostatic intolerance following exercise.

NASA Center JSC↗
NASA NTRS1996

Evaluation of transit-time and electromagnetic flow measurement in a chronically instrumented nonhuman primate model

The Physiology Research Branch at Brooks AFB conducts both human and nonhuman primate experiments to determine the effects of microgravity and hypergravity on the cardiovascular system and to identify the particular mechanisms that invoke these responses. Primary investigative efforts in our nonhuman primate model require the determination of total peripheral resistance, systemic arterial compliance, and pressure-volume loop characteristics. These calculations require beat-to-beat measurement of aortic flow. This study evaluated accuracy, linearity, biocompatability, and anatomical features of commercially available electromagnetic (EMF) and transit-time flow measurement techniques. Five rhesus monkeys were instrumented with either EMF (3 subjects) or transit-time (2 subjects) flow sensors encircling the proximal ascending aorta. Cardiac outputs computed from these transducers taken over ranges of 0.5 to 2.0 L/min were compared to values obtained using thermodilution. In vivo experiments demonstrated that the EMF probe produced an average error of 15% (r = .896) and 8.6% average linearity per reading, and the transit-time flow probe produced an average error of 6% (r = .955) and 5.3% average linearity per reading. Postoperative performance and biocompatability of the probes were maintained throughout the study. The transit-time sensors provided the advantages of greater accuracy, smaller size, and lighter weight than the EMF probes. In conclusion, the characteristic features and performance of the transit-time sensors were superior to those of the EMF sensors in this study.

Non-NASA Center↗
NASA NTRS1996

[Heart functions in monkeys during a 2-week antiorthostatic hypokinesia]

Dynamics of the left heart ventricular muscle contractility and compliance was studied in 4 monkeys in the head down position (antiorthostatic hypokinesia) with the body angle 10 during 2 weeks. Functional tests on a tilt table and under two conditions of centrifuge rotation were performed prior to and after the antiorthostatic hypokinesia. No changes in the left heart ventricular muscle contractility was found. However, the sensitivity level of the baroreflex control decreased. Compliance of the left heart myocardial fibre increased in the first hours and days of the antiorthostatic hypokinesia.

NASA Discipline Regulatory Physiology↗
NASA NTRS1996

Application of acute maximal exercise to protect orthostatic tolerance after simulated microgravity

We tested the hypothesis that one bout of maximal exercise performed at the conclusion of prolonged simulated microgravity would improve blood pressure stability during an orthostatic challenge. Heart rate (HR), mean arterial blood pressure (MAP), norepinephrine (NE), epinephrine (E), arginine vasopressin (AVP), plasma renin activity (PRA), atrial natriuretic peptide (ANP), cardiac output (Q), forearm vascular resistance (FVR), and changes in leg volume were measured during lower body negative pressure (LBNP) to presyncope in seven subjects immediately prior to reambulation from 16 days of 6 degrees head-down tilt (HDT) under two experimental conditions: 1) after maximal supine cycle ergometry performed 24 h before returning to the upright posture (exercise) and 2) without exercise (control). After HDT, the reduction of LBNP tolerance time from pre-HDT levels was greater (P = 0.041) in the control condition (-2.0 +/- 0.2 min) compared with the exercise condition (-0.4 +/- 0.2 min). At presyncope after HDT, FVR and NE were higher (P < 0.05) after exercise compared with control, whereas MAP, HR, E, AVP, PRA, ANP, and leg volume were similar in both conditions. Plasma volume (PV) and carotid-cardiac baroreflex sensitivity were reduced after control HDT, but were restored by the exercise treatment. Maintenance of orthostatic tolerance by application of acute intense exercise after 16 days of simulated microgravity was associated with greater circulating levels of NE, vasoconstriction, Q, baroreflex sensitivity, and PV.

NASA Discipline Cardiopulmonary↗
NASA NTRS1996

Animal models and their importance to human physiological responses in microgravity

Two prominent theories to explain the physiological effects of microgravity relate to the cascade of changes associated with the cephalic shifts of fluids and the absence of tissue deformation forces. One-g experiments for humans used bed rest and the head-down tilt (HDT) method, while animal experiments have been conducted using the tail-suspended, head-down, and hindlimbs non-weightbearing model. Because of the success of the HDT approach with rats to simulate the gravitational effects on the musculoskeletal system exhibited by humans, the same model has been used to study the effects of gravity on the cardiopulmonary systems of humans and other vertebrates. Results to date indicate the model is effective in producing comparable changes associated with blood volume, erythropoiesis, cardiac mass, baroreceptor responsiveness, carbohydrate metabolism, post-flight VO2max, and post-flight cardiac output during exercise. Inherent with these results is the potential of the model to be useful in investigating responsible mechanisms. The suspension model has promise in understanding the capillary blood PO2 changes in space as well as the arterial PO2 changes in subjects participating in a HDT experiment. However, whether the model can provide insights on the up-or-down regulation of adrenoreceptors remains to be determined, and many investigators believe the HDT approach should not be followed to study gravitational influences on pulmonary function in either humans or animals. It was concluded that the tail-suspended animal model had sufficient merit to study in-flight and post-flight human physiological responses and mechanisms.

NASA Discipline Cardiopulmonary↗
NASA NTRS1996

Lessons from operational cardiovascular studies in space

The Space Shuttle program has produced a database of information on the cardiovascular responses to spaceflight, based on in-flight as well as pre- and post-flight assessments undertaken as part of the assessment of the health, safety, and efficiency of Shuttle crews. The methods used in routine cardiovascular assessments of Space Shuttle astronauts are reviewed, and the major findings of these investigations are presented.

NASA Program Data Analysis↗
NASA NTRS1996

Use-dependent loss of active sympathetic neurogenic vasodilation after nitric oxide synthase inhibition in conscious rats. Evidence for the presence of preformed stores of nitric oxide-containing factors

In this study, we examined whether air-jet stress-induced active sympathetic hindlimb vasodilation in conscious rats involves the release of preformed stores of nitric oxide-containing factors. We determined the effects of repeated episodes of air-jet stress (six episodes given 5 minutes apart) on mean arterial pressure and vascular resistances in the mesenteric bed and intact and sympathetically denervated hindlimb beds of conscious rats treated with saline or the nitric oxide synthesis inhibitor N omega-nitro-L-arginine methyl ester (L-NAME, 25 mumol/kg IV). In saline-treated rats, air-jet stress produced alerting behavior, minor changes in blood pressure, pronounced mesenteric vaso-constriction, and immediate and marked vasodilation in the sympathetically intact hindlimb but a minor vasodilation in the sympathetically denervated hindlimb. Each air-jet stress produced virtually identical responses. In L-NAME-treated rats, the first air-jet stress produced vasodilator responses in the sympathetically intact and sympathetically denervated hindlimbs that were similar to those in the saline-treated rats. However, each subsequent air-jet stress produced progressively smaller vasodilator responses in the sympathetically intact but not the sympathetically denervated hindlimb. There was no loss of air-jet stress-induced alerting behavior or mesenteric vasoconstriction, suggesting that L-NAME did not interfere with the central processing of the air-jet or the resultant changes in autonomic nerve activity. The progressive diminution of air-jet stress-induced vasodilation in the intact hindlimb of L-NAME-treated rats may be due to the use-dependent depletion of preformed stores of nitric oxide-containing factors that cannot be replenished in the absence of nitric oxide synthesis.

NASA Discipline Regulatory Physiology↗
NASA NTRS1996

Certain cardiovascular indices predict syncope in the postural tachycardia syndrome

Patients with postural tachycardia syndrome (POTS) represent a patient population with orthostatic intolerance; some are prone to syncope, others are not. The underlying neurocardiovascular mechanisms are not completely understood. The current study was undertaken to assess if certain cardiovascular indices are predictive of syncope in POTS. We compared the response to tilt-up and the Valsalva maneuver in four groups: POTS patients who fainted (POTS-f; n = 11;31 +/- 11 years): POTS patients who did not faint (POTS-nf; n = 9; 29 +/- 9 years); normal controls (NLS; n = 13; 39 +/- 11 years); patients with generalized autonomic failure with orthostatic hypotension and syncope (n = 10; 59 +/- 14 years). Beat-to-beat heart rate (HR), systolic arterial pressure, diastolic arterial pressure (DAP) and pulse pressure (PP) were monitored using Finapres. Cardiac output, stroke volume (SV) and end-diastolic volume (EDV), and calculated total peripheral resistance (TPR) were recorded using thoracic electrical bioimpedance. An autonomic reflex screen which quantitates the distribution and severity of autonomic failure was also done. With the patient supine, all POTS patients (POTS-nf; POTS-f) had increased HR (p < 0.001) and reduced SV/EDV (p < 0.001) when compared with NLS. On tilt-up, POTS-f patients were significantly different from both NLS and POTS-nf patients; the most consistent alteration was a fall instead of an increase in TPR; other changes were a greater reduction in PP, a reduction (instead of an increment) in DAP, and a different pattern of changes during the Valsalva maneuver (excessive early phase II, attenuated or absent late phase II). Our results suggest alpha-adrenergic impairment with increased pooling or hypovolemia in POTS-f patients. We conclude that it is possible to identify the mechanism of syncope in POTS patients, and perhaps other patients with orthostatic intolerance and an excessive liability to syncope.

NASA Discipline Number 14-10↗
NASA NTRS1996

An optimized index of human cardiovascular adaptation to simulated weightlessness

Prolonged exposure to weightlessness is known to produce a variety of cardiovascular changes, some of which may influence the astronaut's performance during a mission. In order to find a reliable indicator of cardiovascular adaptation to weightlessness, we analyzed data from nine male subjects after a 24-hour period of normal activity and after a period of simulated weightlessness produced by two hours in a launch position followed by 20 hours of 6 degrees head-down tilt plus pharmacologically induced diuresis (furosemide). Heart rate, arterial pressure, thoracic fluid index, and radial flow were analyzed. Autoregressive spectral estimation and decomposition were used to obtain the spectral components of each variable from the subjects in the supine position during pre- and post-simulated weightlessness. We found a significant decrease in heart rate power and an increase in thoracic fluid index power in the high frequency region (0.2-0.45 Hz) and significant increases in radial flow and arterial pressure powers in the low frequency region (<0.2 Hz) in response to simulated weightlessness. However, due to the variability among subjects, any single variable appeared limited as a dependable index of cardiovascular adaptation to weightlessness. The backward elimination algorithm was then used to select the best discriminatory features from these spectral components. Fisher's linear discriminant and Bayes' quadratic discriminant were used to combine the selected features to obtain an optimal index of adaptation to simulated weightlessness. Results showed that both techniques provided improved discriminant performance over any single variable and thus have the potential for use as an index to track adaptation and prescribe countermeasures to the effects of weightlessness.

NASA Discipline Number 14-10↗
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 NTRS1995

Spectral indices of cardiovascular adaptations to short-term simulated microgravity exposure

We investigated the effects of exposure to microgravity on the baseline autonomic balance in cardiovascular regulation using spectral analysis of cardiovascular variables measured during supine rest. Heart rate, arterial pressure, radial flow, thoracic fluid impedance and central venous pressure were recorded from nine volunteers before and after simulated microgravity, produced by 20 hours of 6 degrees head down bedrest plus furosemide. Spectral powers increased after simulated microgravity in the low frequency region (centered at about 0.03 Hz) in arterial pressure, heart rate and radial flow, and decreased in the respiratory frequency region (centered at about 0.25 Hz) in heart rate. Reduced heart rate power in the respiratory frequency region indicates reduced parasympathetic influence on the heart. A concurrent increase in the low frequency power in arterial pressure, heart rate, and radial flow indicates increased sympathetic influence. These results suggest that the baseline autonomic balance in cardiovascular regulation is shifted towards increased sympathetic and decreased parasympathetic influence after exposure to short-term simulated microgravity.

NASA Discipline Cardiopulmonary↗
NASA NTRS1995

'Non-hypotensive' hypovolaemia reduces ascending aortic dimensions in humans

1. The notion that small, 'non-hypotensive' reductions of effective blood volume alter neither arterial pressure nor arterial baroreceptor activity is pervasive in the experimental literature. We tested two hypotheses: (a) that minute arterial pressure and cardiac autonomic outflow changes during hypovolaemia induced by lower body suction in humans are masked by alterations in breathing, and (b) that evidence for arterial baroreflex engagement might be obtained from measurements of thoracic aorta dimensions. 2. In two studies, responses to graded lower body suction at 0 (control), 5, 10, 15, 20 and 40 mmHg were examined in twelve and ten healthy young men, respectively. In the first, arterial pressure (photoplethysmograph), R-R interval, and respiratory sinus arrhythmia amplitude (complex demodulation) were measured during uncontrolled and controlled breathing (constant breathing frequency and tidal volume). In the second, cross-sectional areas of the ascending thoracic aorta were calculated from nuclear magnetic resonance images. 3. Lower body suction with controlled breathing resulted in an increased arterial pulse pressure at mild levels (5-20 mmHg; ANOVA, P < 0.05) and a decreased arterial pulse pressure at moderate levels (40 mmHg; ANOVA, P < 0.05). Both R-R intervals and respiratory sinus arrhythmia were negatively related to lower body suction level, whether group averages (general linear regression, r > 0.92) or individual subjects (orthogonal polynomials, 12 of 12 subjects) were assessed. 4. Aortic pulse area decreased progressively and significantly during mild lower body suction, with 47% of the total decline occurring by 5 mmHg. 5. These results suggest that small reductions of effective blood volume reduce aortic baroreceptive areas and trigger haemodynamic adjustments which are so efficient that alterations in arterial pressure escape detection by conventional means.

NASA Discipline Cardiopulmonary↗
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↗