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  • 1
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    Cardiovascular dynamics during the initial period of head-down tilt (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The cardiovascular response to 1 h of 60-deg head-down tilt was studied in 12 male subjects, ages 30-39 years, to simulate the early effects of weightlessness. Fluid shifts, hemodynamic variables, and indices of myocardial contractility were evaluated by utilizing electrocardiography, systolic time intervals, impedance cardiography, sphygmomanometry, and measurement of calf circumference. Most cardiovascular variables remained stable throughout the initial 30 min of the protocol, even though translocation of fluid from the legs to the thorax commenced immediately with the onset of head-down tilt. In contrast, minutes 30-60 were characterized by reduced stroke volume, cardiac output, mean stroke ejection rate, and Heather index concomitant with an elevation in mean arterial pressure. Intrathoracic fluid volume continued to increase, while leg volume continued to decrease. This latter physiological response suggests intrathoracic sequestration of fluid volume; blood was apparently redistributed to the pulmonary circulation rather than being retained in the great veins.
    Keywords: AEROSPACE MEDICINE
    Type: Aviation, Space, and Environmental Medicine (ISSN 0095-6562); 58; 3-8
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  • 2
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    Aerobic fitness in women and responses to lower body negative pressure (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The role of tolerance to orthostatic stress in the maintenance of high aerobic fitness in women was investigated by examining the responses of heart rate, stroke volume, cardiac output, Heather index of contractility, arterial pressure, peripheral resistance, change in calf circumference, and thoracic impedance of healthy female subjects to lower body negative pressure (LBNP) applied for 5 min at -50 mm Hg or until a subject became presyncopal. The testing protocol involved a stepwise reduction in pressure and consisted of two parts: an LBNP test in supine position followed by a treadmill test to peak aerobic capacity. Women were found to exhibit the same response pattern to LBNP as was previously reported by Convertino et al. (1984) for men. The results do not support the hypothesis that orthostatic tolerance in women is inversely related to aerobic fitness, as demonstrated by a finding that the peak aerobic capacity of subjects who became presyncopal did not differ from the peak of the tolerant subjects, and that hemodynamic responses to LBNPL were not a function of aerobic capacity.
    Keywords: AEROSPACE MEDICINE
    Type: Aviation, Space, and Environmental Medicine (ISSN 0095-6562); 58; 1149-115
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  • 3
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    Hysteresis in response to descending and ascending lower-body negative pressure (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Changes in the indices of fluid redistribution and cardiovascular responses during graduated orthostatic stress were measured in 12 men subjected for 25 min to lower-body negative pressure (LBNP) test protocol that involved stepwise decreases (from the starting pressure of -8 to the final -50 mm Hg), followed by stepwise increases (back to -8 mm Hg) of LBNP. The values of many variables measured during the descending phase of LBNP were significantly different from the respective values measured during the ascending phase. These differences appear to be caused by a component of fluid translocation that occurs during LBNP and cannot be reversed within the duration of the procedure. It is hypothesized that this slowly-reversed component is the sequestration of fluid in the interstitial and the lymphatic compartments.
    Keywords: AEROSPACE MEDICINE
    Type: Journal of Applied Physiology (ISSN 0161-7567); 63; 719-725
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  • 4
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    Association of sex and age with responses to lower-body negative pressure (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The effects of age and sex on the human-body responses to -50 torr LBNP were investigated in subjects who have undergone LBNP tests at the Kennedy Space Center. The comparison of results obtained on women and age-matched men indicated that men had larger relative increases in calf circumference and greater increases in peripheral resistance during the exposure to LBNP than the women; on the other hand, women displayed greater increases in thoracic impedance and heart rate. The comparison of the results on men of different ages (between 29 and 56 y) indicated that older subjects had greater increases in peripheral resistance and less heart rate elevation in response to LBNP. It is suggested that the age-related circulatory differences were due to a reduction in vagal response and a switch to predominant sympathetic nervous system influence in older men.
    Keywords: AEROSPACE MEDICINE
    Type: Journal of Applied Physiology (ISSN 0161-7567); 65; 1752-175
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  • 5
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    Considerations in prescribing preflight aerobic exercise for astronauts (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The physiological effects of prolonged exposure to weightlessness are discussed together with the effects of aerobic exercise on human characteristics affected by weightlessness. It is noted that, although early data on orthostatic intolerance after spaceflight led to a belief that a high level of aerobic fitness for astronauts was detrimental to orthostatic tolerance on return to earth, most of the data available today do not suport this contention. Aerobic fitness was found to be beneficial to cardiovascular function and to mental performance; therefore, it may be important in performing extravehicular activities during flight.
    Keywords: AEROSPACE MEDICINE
    Type: Aviation, Space, and Environmental Medicine (ISSN 0095-6562); 58; 1014-102
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  • 6
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    Hemolysis in runners as evidenced by low serum haptoglobin: Implications for preflight monitoring of astronauts (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Hematological parameters and serum haptoglobin were examined in 21 male employees of the Kennedy Space Center who were at 3 levels of physical activity: 7 subjects regularly ran more than 40 km (25 miles) per week (Group I); 7 ran 13 to 24 km (8 to 15 miles) per week (II), and 7 were sedentary (III). Blood was drawn on a different day of the week for five weeks. Differences between day of the week, visit number, and activity level were examined. No differences were observed for day of week or visit number; thus mean values for each variable were calculated for each subject. Variables did not differ among groups. However, trends with level of training were observed in some critical variables. Hemoglobin (Hb) and hematocrit (Hct) conformed to a staircase effect with Group I (14.5 gm/dl and 41.3 percent) lower than Group III (15.1 gm/dl and 42.9 percent). Reticulocyte count was higher and haptoglobin levels lower in Group I (1.35% and 75.7 gm/dl) than Group III (.99 percent and 132.9 gm/dl), with haptoglobin for the high mileage Group I in the clinically abnormal range. Since haptoglobin binds free Hb following RBC destruction, these results suggest that intravascular hemolysis occurs in trained male runners. These results may have special meaning for astronauts training before long-duration spaceflights, since the further reduction in red blood cells which is reported to occur during spaceflight could become detrimental to their health and performance.
    Keywords: AEROSPACE MEDICINE
    Type: NASA-TM-100304 , NAS 1.15:100304
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  • 7
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    Relationships between coronary heart disease risk factors and serum ionized calcium in Kennedy Space Center Cohort (1987)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Kennedy Space Center (KSC) employees are reported to be at high risk for coronary heart disease (CHD). Risk factors for CHD include high serum total cholesterol levels, low levels of high-density lipoprotein cholesterol (HDLC), elevated triglyceride, smoking, inactivity, high blood pressure, being male, and being older. Higher dietary and/or serum calcium Ca(++) may be related to a lower risk for CHD. Fifty men and 37 women participated. Subjects were tested in the morning after fasting 12 hours. Information relative to smoking and exercise habits was obtained; seated blood pressures were measured; and blood drawn. KCS men had higher risk values than KCS women as related to HDLC, triglycerides, systolic blood pressure, and diastolic blood pressure. Smoking and nonsmoking groups did not differ for other risk factors or for serum Ca(++) levels. Exercise and sedentary groups differed in total cholesterol and triglyceride levels. Serum Ca(++) levels were related to age, increasing with age in the sedentary group and decreasing in the exercisers, equally for men and women. It is concluded that these relationships may be significant to the risk of CHD and/or the risk of bone demineralization in an aging population.
    Keywords: AEROSPACE MEDICINE
    Type: NASA-TM-100979 , NAS 1.15:100979
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  • 8
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    Spatial Audio on the Web: Or Why Can't I hear Anything Over There? (1997)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: Auditory complexity, freedom of movement and interactivity is not always possible in a "true" virtual environment, much less in web-based audio. However, a lot of the perceptual and engineering constraints (and frustrations) that researchers, engineers and listeners have experienced in virtual audio are relevant to spatial audio on the web. My talk will discuss some of these engineering constraints and their perceptual consequences, and attempt to relate these issues to implementation on the web.
    Keywords: Acoustics
    Type: Getting Out of the Box: Effective Design Practices for Audio on the Net; Jun 13, 1997 - Jun 15, 1997; Seattle, WA; United States
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  • 9
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    Analysis of the Role of Update Rate and System Latency in Interactive Virtual Acoustic Environments (1997)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: The ultimate goal of virtual acoustics is to simulate the complex acoustic field experienced by a listener freely moving around within an environment. This paper discusses some of the engineering constraints that may be faced during implementation and the perceptual consequences of these constraints. In particular, the perceptual impact of parameters like the update rate and overall system latency of interactive spatial audio systems is addressed.
    Keywords: Acoustics
    Type: Audio Engineering Society Conference; Sep 26, 1997 - Sep 29, 1997; New York, NY; United States
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  • 10
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    Perceptual Fidelity Versus Engineering Compromises in Virtual Acoustic Displays (1997)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: Immersive, three-dimensional displays are increasingly becoming a goal of advanced human-machine interfaces. While the technology for achieving truly useful multisensory environments is still being developed, techniques for generating three-dimensional sound are now both sophisticated and practical enough to be applied to acoustic displays. The ultimate goal of virtual acoustics is to simulate the complex acoustic field experienced by a listener freely moving around within an environment. Of course, such complexity, freedom of movement and interactivity is not always possible in a 'true' virtual environment, much less in lower-fidelity multimedia systems. However, many of the perceptual and engineering constraints (and frustrations) that researchers, engineers and listeners have experienced in virtual audio are relevant to multimedia. In fact, some of the problems that have been studied will be even more of an issue for lower fidelity systems that are attempting to address the requirements of a huge, diverse and ultimately unknown audience. Examples include individual differences in head-related transfer functions, A lack of real interactively (head-tracking) in many multimedia displays, and perceptual degradation due to low sampling rates and/or low-bit compression. This paper discusses some of the engineering constraints faced during implementation of virtual acoustic environments and the perceptual consequences of these constraints. Specific examples are given for NASA applications such as telerobotic control, aeronautical displays, and shuttle launch communications. An attempt will also be made to relate these issues to low-fidelity implementations such as the internet.
    Keywords: Acoustics
    Type: Acoustical Society of America Conference; Dec 01, 1997 - Dec 05, 1997; San Diego, CA; United States
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