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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Distribution of pulmonary ventilation and perfusion during short periods of weightlessness

Airborne experiments were conducted on four trained normal male subjects (28-40 yr) to study pulmonary function during short periods (22-27 sec) of zero gravity obtained by flying a jet aircraft through appropriate parabolic trajectories. The cabin was always pressurized to a sea-level altitude. The discussion is limited to pulmonary ventilation and perfusion. The results clearly demonstrate that gravity is the major factor causing nonuniformity in the topographical distribution of pulmonary ventilation. More importantly, the results suggest that virtually all the topographical nonuniformity of ventilation, blood flow, and lung volume observed under 1-G conditions are eliminated during short periods of zero gravity.

Michels, D. B.↗
NASA NTRS1972

Digital simulation and experimental evaluation of the CO2-H(plus) control of pulmonary ventilation

Previous models of the CO2-H(+) control of ventilation have been concerned either with the response to CO2 inhalation, or the response to perfusion of the surface of the medulla with mock cerebrospinal fluid having a high P sub CO2. Simulation of both responses with the same model has not been attempted. The purpose of the present study was two fold; first to develop such a model and, second, to obtain experimental data from human subjects for both developing this model and for evaluating this and future models.

Milhorn, H. T., Jr.↗
NASA NTRS1994

Inhomogeneity of pulmonary ventilation during sustained microgravity as determined by single-breath washouts

Gravity is known to cause inhomogeneity of ventilation. Nongravitational factors are also recognized, but their relative contribution is not understood. We therefore studied ventilatory inhomogeneity during sustained microgravity during the 9-day flight of Spacelab SLS-1. All seven crew members performed single-breath nitrogen washouts. They inspired a vital capacity breath of 100% oxygen with a bolus of argon at the start of inspiration, and the inspiratory and expiratory flow rates were controlled at 0.5 l/s. Control measurements in normal gravity (1 G) were made pre- and postflight in the standing and supine position. Compared with the standing 1-G measurements, there was a marked decrease in ventilatory inhomogeneity during microgravity, as evidenced by the significant reductions in cardiogenic oscillations, slope of phase III, and height of phase IV for nitrogen and argon. However, argon phase IV volume was not reduced, and considerable ventilatory inhomogeneity remained. For example, the heights of the cardiogenic oscillations during microgravity for nitrogen and argon were 44 and 24%, respectively, of their values at 1 G, whereas the slopes of phase III for nitrogen and argon were 78 and 29%, respectively, of those at 1 G. The presence of a phase IV in microgravity is strong evidence that airway closure still occurs in the absence of gravity. The results were qualitatively similar to those found previously during short periods of 0 G in parabolic flight.

Guy, Harold J. B.↗
NASA NTRS2002

Effect of 6 degrees head-down tilt on cardiopulmonary function: comparison with microgravity

BACKGROUND: Head-down tilt (HDT) of 6 degrees is a commonly used model of weightlessness, but there are few comparisons with actual microgravity. HYPOTHESIS: Our study was designed to prove that the changes in cardiopulmonary function seen in HDT would be similar to those seen in microgravity. METHODS: We compared measurements of cardiovascular and pulmonary function from three separate spaceflights of 14 to 17 d duration, with data collected during a 17-d period of HDT. RESULTS: HDT proved a good model of the cardiovascular response to microgravity, resulting in increases in cardiac output and stroke volume of a similar magnitude to those seen in microgravity, with a concomitant reduction in heart rate. By contrast, HDT was a poor model of the effects of microgravity on pulmonary ventilation and gas exchange. CONCLUSION: Pulmonary function in HDT approximated the changes seen in the 1-G supine posture, while in microgravity this was much closer to that seen in the 1-G upright position. The differences probably reflect the fact that changes in cardiovascular function result primarily from fluid shifts within the entire body, whereas changes in pulmonary ventilation are primarily a result of mechanical influences on the lung and chest and abdominal wall.

NASA Discipline Cardiopulmonary↗
NASA NTRS1994

Lung volumes during sustained microgravity on Spacelab SLS-1

Gravity is known to influence the topographical gradients of pulmonary ventilation, perfusion, and pleural pressures. The effect of sustained microgravity on lung volumes has not previously been investigated. Pulmonary function tests were performed by four subjects before, during, and after 9 days of microgravity exposure. Ground measurements were made in standing and supine postures. Tests were performed using a bag-in-box and flowmeter system and a respiratory mass spectrometer. Measurements of tidal volume (V(sub T)), expiratory reserve volume (ERV), inspiratory and expiratory vital capacities (IVC, EVC), functional residual capacity (FRC), and residual volume (RV) were made. During microgravity, V(sub T) decreased by 15%. IVC and EVC were slightly reduced during the first 24 hrs of microgravity and returned to 1 g standing values within 72 hrs after the onset of microgravity. FRC was reduced by 15% and ERV decreased by 10-20%. RV was significantly reduced by 18%. The reductions in FRC, ERV, and V(sub T) during microgravity are probably due to the cranial shift of the diaphragm and an increase in intrathoracic blood volume.

Elliott, Ann R.↗
NASA NTRS1975

Respiration, respiratory metabolism and energy consumption under weightless conditions

Changes in the physiological indices of respiration, respiratory metabolism and energy consumption in spacecrews under weightlessness conditions manifest themselves in increased metabolic rates, higher pulmonary ventilation volume, oxygen consumption and carbon dioxide elimination, energy consumption levels in proportion to reduction in neuroemotional and psychic stress, adaptation to weightlessness and work-rest cycles, and finally in a relative stabilization of metabolic processes due to hemodynamic shifts.

Kasyan, I. I.↗
NASA NTRS1990

Effects of acute hypoxia on cardiopulmonary responses to head-down tilt

Six male subjects were exposed on two separate occasions to simulated microgravity with 28 deg head-down tilt (HD) for 1 h with baseline followed by recovery at + 17 deg head-up. Pulmonary ventilation, gas exchange, spirometry, and central and cerebral blood flow characteristics were compared while breathing ambient air and reduced F(I)O2 equivalent to 14,828 ft. With hypoxia (HY), the increased tidal volume served to attenuate the drop in arterial saturation by reducing deadspace ventilation. Arterial and mixed venous PO2, values, estimated from peripheral venous samples and cardiac output (CO), were both maintained during HD in HY. Mixed venous PO2 was elevated by an increase in CO associated with a reduction in systemic resistance. Changes in spirometric indices during HD were not accentuated by HY, making the presence of interstitial edema unlikely. Cerebral flow and resistance showed minor reductions with HD. Tissue oxygenation and cardiopulmonary function were not notably effected by HD during HY, but a combination of these two stressors may predispose subjects to subsequent orthostatic intolerance during initial recovery.

Loeppky, J. A.↗
NASA NTRS1995

CO2-O2 interactions in extension of tolerance to acute hypoxia

Objectives and results of experimental projects a re summarized. The scope of information desired included (1) physiological and performance consequences of exposures to simulated microgravity, in rest and graded physical activity, (2) separate influences of graded degrees of atmospheric hypercapnia and hypoxia, and (3) composite effects of hypoxia and hypercapnia. The research objectives were selected for close relevance to existing quantitative information concerning interactions of hypercapnia and hypoxia on respiratory and brain circulatory control. They include: (1) to determine influences of normoxic immersion on interrelations of pulmonary ventilation, arterial PCO2 and PO2, and brain blood flow, in rest and physical work; (2) to determine influence of normoxic immersion on respiratory reactivity to atmospheric hypercapnia at rest; (3) to determine influence of atmospheric hypoxia on respiratory reactivity to hypercapnia at rest and in work; and (4) to provide physiological baselines of data concerning adaptations in acute exposures to aid in investigation of rates of adaptation or deteriorations in physiological or performance capability during subsequent multi-day exposures. A list of publications related to the present grant period is included along with an appendix describing the Performance Measurement System (human perceptual, cognitive and psychomotor functions).

Lambertsen, C. J.↗
NASA NTRS1999

Exercise Training During +Gz Acceleration

The overall purpose is to study the effect of passive (without exercise) and active (with exercise) +Gz (head-to-foot) acceleration training, using a short-arm (1.9m radius) centrifuge, on post- training maximal oxygen uptake (VO2 max, work capacity) and 70 deg head-up tilt (orthostatic) tolerance in ambulatory subjects to test the hypothesis that (a) both passive and active acceleration training will improve post-training tilt-tolerance, and (b) there will be no difference in tilt-tolerance between passive and active exercise acceleration training because increased hydrostatic and blood pressures, rather than increased muscular metabolism, will provide the major adaptive stimulus. The purpose of the pilot study was to test the hypothesis that there would be no significant difference in the metabolic responses (oxygen uptake, heart rate, pulmonary ventilation, or respiratory exchange ratio) during supine exercise with moderate +Gz acceleration.

Greenleaf, J. E.↗
NASA NTRS2001

Endoscopic surgery in weightlessness: the investigation of basic principles for surgery in space

BACKGROUND: Performing a surgical procedure in weightlessness, also called 0-gravity (0-g), has been shown to be no more difficult than in a 1-g environment if the requirements for the restraint of the patient, operator, surgical hardware, are observed. The performance of laparoscopic and thorascopic procedures in weightlessness, if feasible, would offer several advantages over the performance of an open operation. Concerns about the feasibility of performing minimally invasive procedures in weightlessness have included impaired visualization from the absence of gravitational retraction of the bowel (laparoscopy) or thoracic organs (thoracoscopy) as well as obstruction and interference from floating debris such as blood, pus, and irrigation fluid. The purpose of this study was to determine the feasibility of performing laparoscopic and thorascopic procedures and the degree of impaired surgical endoscopic visualization in weightlessness. METHODS: From 1993 to 2000, laparoscopic and thorascopic procedures were performed on 10 anesthetized adult pigs weighing approximately 50 kg in the National Aeronautics and Space Administration (NASA) Microgravity Program using a modified KC-135 airplane. The parabolic simulation system for advanced life support was used in this project, and 20 to 40 parabolas were used for laparoscopic or thorascopic investigation, each containing approximately 30 s of 0-g alternating with 2-g pullouts. The animal model was restrained in the supine position on a floor-level Crew Medical Restraint System, and the abdominal cavity was insufflated with carbon dioxide. The intraabdominal and intrathoracic anatomy was visualized in the 1-g, 0-g, and 2-g periods of parabolic flight. Bleeding was created in the animals, and the behavior of the blood in the abdominal and thoracic cavities was observed. In the thoracic cavity, gas insufflation and mechanical retraction was used at times unilaterally to decrease pulmonary ventilation enough to increase the thoracic domain. RESULTS: Visualization was improved in laparoscopy, from tethering of the bowel by the elastic mesentery, and from the strong tendency for debris and blood to adhere to the abdominal wall because of surface tension forces. The lack of adequate thoracic domain made thorascopy more difficult. Fluid in the thoracic cavity did not impair visualization because the fluid at 0-g does not loculate posteriorly, but disperses along the thoracic wall and mediastinal reflections. CONCLUSIONS: Performing minimally invasive procedures instead of open surgical procedures in a weightless environment has theoretical advantages, especially in the ability to prevent cabin atmosphere contamination from surgical fluids (blood, pus, irrigation). Visualization will become more important and practical as the endoscopic hardware is miniaturized from its current form, as endoscopic technology becomes more advanced, and as more surgically capable medical crew officers are present in future long-duration space exploration missions.

short duration↗
NASA NTRS1992

VA/Q distribution during heavy exercise and recovery in humans: implications for pulmonary edema

Ventilation-perfusion (VA/Q) inequality has been shown to increase with exercise. Potential mechanisms for this increase include nonuniform pulmonary vasoconstriction, ventilatory time constant inequality, reduced large airway gas mixing, and development of interstitial pulmonary edema. We hypothesized that persistence of VA/Q mismatch after ventilation and cardiac output subside during recovery would be consistent with edema; however, rapid resolution would suggest mechanisms related to changes in ventilation and blood flow per se. Thirteen healthy males performed near-maximal cycle ergometry at an inspiratory PO2 of 91 Torr (because hypoxia accentuates VA/Q mismatch on exercise). Cardiorespiratory variables and inert gas elimination patterns were measured at rest, during exercise, and between 2 and 30 min of recovery. Two profiles of VA/Q distribution behavior emerged during heavy exercise: in group 1 an increase in VA/Q mismatch (log SDQ of 0.35 +/- 0.02 at rest and 0.44 +/- 0.02 at exercise; P less than 0.05, n = 7) and in group 2 no change in VA/Q mismatch (n = 6). There were no differences in anthropometric data, work rate, O2 uptake, or ventilation during heavy exercise between groups. Group 1 demonstrated significantly greater VA/Q inequality, lower vital capacity, and higher forced expiratory flow at 25-75% of forced vital capacity for the first 20 min during recovery than group 2. Cardiac index was higher in group 1 both during heavy exercise and 4 and 6 min postexercise. However, both ventilation and cardiac output returned toward baseline values more rapidly than did VA/Q relationships. Arterial pH was lower in group 1 during exercise and recovery. We conclude that greater VA/Q inequality in group 1 and its persistence during recovery are consistent with the hypothesis that edema occurs and contributes to the increase in VA/Q inequality during exercise. This is supported by observation of greater blood flows and acidosis and, presumably therefore, higher pulmonary vascular pressures in such subjects.

NASA Discipline Cardiopulmonary↗
NASA NTRS2001

Cardiopulmonary Responses to Supine Cycling during Short-Arm Centrifugation

The purpose of this study was to investigate cardiopulmonary responses to supine cycling with concomitant +G(sub z) acceleration using the NASA/Ames Human Powered Short-Arm Centrifuge (HPC). Subjects were eight consenting males (32+/-5 yrs, 178+/-5 cm, 86.1+/- 6.2 kg). All subjects completed two maximal exercise tests on the HPC (with and without acceleration) within a three-day period. A two tailed t-test with statistical significance set at p less than or equal to 0.05 was used to compare treatments. Peak acceleration was 3.4+/-0.1 G(sub z), (head to foot acceleration). Peak oxygen uptake (VO2(sub peak) was not different between treatment groups (3.1+/-0.1 Lmin(exp -1) vs. 3.2+/-0.1 Lmin(exp -1) for stationary and acceleration trials, respectively). Peak HR and pulmonary minute ventilation (V(sub E(sub BTPS))) were significantly elevated (p less than or equal to 0.05) for the acceleration trial (182+/-3 BPM (Beats per Minute); 132.0+/-9.0 Lmin(exp -1)) when compared to the stationary trial (175+/-3 BPM; 115.5+/-8.5 Lmin(exp -1)). Ventilatory threshold expressed as a percent of VO2(sub peak) was not different for acceleration and stationary trials (72+/-2% vs. 68+/-2% respectively). Results suggest that 3.4 G(sub z) acceleration does not alter VO2(sub peak) response to supine cycling. However, peak HR and V(sub E(sub BTPS)) response may be increased while ventilatory threshold response expressed as a function of percent VO2(sub peak) is relatively unaffected. Thus, traditional exercise prescription based on VO2 response would be appropriate for this mode of exercise. Prescriptions based on HR response may require modification.

Vener, J. M.↗
NASA NTRS1998

Sleep and respiration in microgravity

Sleep studies conducted during the STS-90 Neurolab mission are explored. The relationship between sleep, melatonin, and circadian phase is reviewed. The study contained both sleep and awake components. The objectives of the sleep component were to test five hypotheses: that circadian rhythms of core body temperature and urinary melatonin are synchronized to required sleep-wake schedules, that spaceflight results in substantial disruption of sleep, that the pattern of chest and abdominal wall motion alters during the different sleep stages in microgravity, that arterial oxygen saturation is reduced during some stages of sleep in microgravity, and that pre-sleep administration of melatonin during microgravity results in improved sleep quality. The awake component tested three hypotheses: that ventilatory response to carbon dioxide is increased during exposure to microgravity and that this exacerbates sleep disruption, that ventilatory response to hypoxia is increased by exposure to microgravity, and that the improved sleep resulting from the pre-sleep administration of melatonin enhances next day cognition when compared to placebo.

Non-NASA Center↗
NASA NTRS1995

Voluntary control of breathing does not alter vagal modulation of heart rate

Variations in respiratory pattern influence the heart rate spectrum. It has been suggested, hence, that metronomic respiration should be used to correctly assess vagal modulation of heart rate by using spectral analysis. On the other hand, breathing to a metronome has been reported to increase heart rate spectral power in the high- or respiratory frequency region; this finding has led to the suggestion that metronomic respiration enhances vagal tone or alters vagal modulation of heart rate. To investigate whether metronomic breathing complicates the interpretation of heart rate spectra by altering vagal modulation, we recorded the electrocardiogram and respiration from eight volunteers during three breathing trials of 10 min each: 1) spontaneous breathing (mean rate of 14.4 breaths/min); 2) breathing to a metronome at the rate of 15, 18, and 21 breaths/min for 2, 6, and 2 min, respectively; and 3) breathing to a metronome at the rate of 18 breaths/min for 10 min. Data were also collected from eight volunteers who breathed spontaneously for 20 min and breathed metronomically at each subject's mean spontaneous breathing frequency for 20 min. Results from the three 10-min breathing trials showed that heart rate power in the respiratory frequency region was smaller during metronomic breathing than during spontaneous breathing. This decrease could be explained fully by the higher breathing frequencies used during trials 2 and 3 of metronomic breathing. When the subjects breathed metronomically at each subject's mean breathing frequency, the heart rate powers during metronomic breathing were similar to those during spontaneous breathing. Our results suggest that vagal modulation of heart rate is not altered and vagal tone is not enhanced during metronomic breathing.

Non-NASA Center↗
NASA NTRS1997

Pulmonary blood flow distribution in sheep: effects of anesthesia, mechanical ventilation, and change in posture

BACKGROUND: Recent studies providing high-resolution images of pulmonary perfusion have questioned the classical zone model of pulmonary perfusion. Hence the present work was undertaken to provide detailed maps of regional pulmonary perfusion to examine the influence of anesthesia, mechanical ventilation, and posture. METHODS: Pulmonary perfusion was analyzed with intravenous fluorescent microspheres (15 microm) in six sheep studied in four conditions: prone and awake, prone with pentobarbital-anesthesia and breathing spontaneously, prone with anesthesia and mechanical ventilation, and supine with anesthesia and mechanical ventilation. Lungs were air dried at total lung capacity and sectioned into approximately 1,100 pieces (about 2 cm3) per animal. The pieces were weighed and assigned spatial coordinates. Fluorescence was read on a spectrophotometer, and signals were corrected for piece weight and normalized to mean flow. Pulmonary blood flow heterogeneity was assessed using the coefficient of variation of flow data. RESULTS: Pentobarbital anesthesia and mechanical ventilation did not influence perfusion heterogeneity, but heterogeneity increased when the animals were in the supine posture (P < 0.01). Gravitational flow gradients were absent in the prone position but present in the supine (P < 0.001 compared with zero). Pulmonary perfusion was distributed with a hilar-to-peripheral gradient in animals breathing spontaneously (P < 0.05). CONCLUSIONS: The influence of pentobarbital anesthesia and mechanical ventilation on pulmonary perfusion heterogeneity is small compared with the effect of changes in posture. Analysis of flow gradients indicate that gravity plays a small role in determining pulmonary blood flow distribution.

NASA Discipline Cardiopulmonary↗
NASA NTRS1972

Pattern of filling in the pulmonary capillary bed.

Artificially ventilated and perfused dog lungs were rapidly frozen under various physiological conditions. In 2-micron-thick sections the number of red blood cells (RBCs) per 10-micron length of alveolar septum was counted. Under conditions in which alveolar pressure exceeded venous pressure, variation in RBC concentration within areas supplied by single arterioles accounted completely for variation between areas supplied by different arterioles. Except at very high perfusion pressures when venous pressure exceeded alveolar pressure, there was no significant correlation between RBC concentrations of pairs of adjacent septa.

Warrell, D. A.↗
NASA NTRS1997

Pulmonary function in space

The lung is exquisitely sensitive to gravity, and so it is of interest to know how its function is altered in the weightlessness of space. Studies on National Aeronautics and Space Administration (NASA) Spacelabs during the last 4 years have provided the first comprehensive data on the extensive changes in pulmonary function that occur in sustained microgravity. Measurements of pulmonary function were made on astronauts during space shuttle flights lasting 9 and 14 days and were compared with extensive ground-based measurements before and after the flights. Compared with preflight measurements, cardiac output increased by 18% during space flight, and stroke volume increased by 46%. Paradoxically, the increase in stroke volume occurred in the face of reductions in central venous pressure and circulating blood volume. Diffusing capacity increased by 28%, and the increase in the diffusing capacity of the alveolar membrane was unexpectedly large based on findings in normal gravity. The change in the alveolar membrane may reflect the effects of uniform filling of the pulmonary capillary bed. Distributions of blood flow and ventilation throughout the lung were more uniform in space, but some unevenness remained, indicating the importance of nongravitational factors. A surprising finding was that airway closing volume was approximately the same in microgravity and in normal gravity, emphasizing the importance of mechanical properties of the airways in determining whether they close. Residual volume was unexpectedly reduced by 18% in microgravity, possibly because of uniform alveolar expansion. The findings indicate that pulmonary function is greatly altered in microgravity, but none of the changes observed so far will apparently limit long-term space flight. In addition, the data help to clarify how gravity affects pulmonary function in the normal gravity environment on Earth.

short duration↗
NASA NTRS1993

Alveolar ventilation to perfusion heterogeneity and diffusion impairment in a mathematical model of gas exchange

This study describes a two-compartment model of pulmonary gas exchange in which alveolar ventilation to perfusion (VA/Q) heterogeneity and impairment of pulmonary diffusing capacity (D) are simultaneously taken into account. The mathematical model uses as input data measurements usually obtained in the lung function laboratory. It consists of two compartments and an anatomical shunt. Each compartment receives fractions of alveolar ventilation and blood flow. Mass balance equations and integration of Fick's law of diffusion are used to compute alveolar and blood O2 and CO2 values compatible with input O2 uptake and CO2 elimination. Two applications are presented. The first is a method to partition O2 and CO2 alveolar-arterial gradients into VA/Q and D components. The technique is evaluated in data of patients with chronic obstructive pulmonary disease (COPD). The second is a theoretical analysis of the effects of blood flow variation in alveolar and blood O2 partial pressures. The results show the importance of simultaneous consideration of D to estimate VA/Q heterogeneity in patients with diffusion impairment. This factor plays an increasing role in gas alveolar-arterial gradients as severity of COPD increases. Association of VA/Q heterogeneity and D may produce an increase of O2 arterial pressure with decreasing QT which would not be observed if only D were considered. We conclude that the presented computer model is a useful tool for description and interpretation of data from COPD patients and for performing theoretical analysis of variables involved in the gas exchange process.

NASA Discipline Environmental Health↗