Steven H. Platts

NASA, Washington, West Virginia, United States

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Publications (43)76.16 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Abdomen-high, lower body graded compression garments (GCGs) may represent the next-generation of orthostatic intolerance protection with applications for exploration missions and commercial space flight. To evaluate the efficacy of the GCG to prevent orthostatic intolerance after a 14-day 6° head-down tilt bed rest (BR) and to determine whether wearing thigh-high compression garments impairs recovery from BR. Sixteen (12 M, 4 F) subjects participated in a 15-min 80° head-up tilt test 5 day before BR (BR-5), on the last morning of BR (BR+0), and on day 1 (BR+1) and 3 after BR (BR+3). No subjects wore the GCG on BR-5, and all subjects wore the GCG during testing on BR+0. Control subjects (n = 8) wore the GCG only through testing on BR+0. Treatment subjects (n = 8) wore the GCG on BR+0 and thigh-high garments on BR+1 and BR+2. No subjects were presyncopal during tilt on BR+0 while wearing the GCG. Despite lower plasma volume index (BR-5: 1.52 ± 0.06, BR+0: 1.32 ± 0.05 l/m(2)), the tilt-induced increase in heart rate (ΔHR, 17 ± 2 bpm) and decrease in stroke volume (ΔSV, -28 ± 3 ml) on BR+0 were less than on BR-5 (24 ± 2 bpm, -43 ± 4 ml). On BR+1 ΔHR in the control group (33 ± 4 bpm) was higher than in the treatment group (23 ± 2 bpm) but there were no group differences on BR+3. Wearing the GCG prevented the orthostatic intolerance that is normally present after BR. Thigh-high garments provided protection after BR, and wearing these garments did not impair recovery.
    Arbeitsphysiologie 12/2013; · 2.66 Impact Factor
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    ABSTRACT: Microgravity-induced physiologic changes could impair a crewmember's performance upon return to a gravity environment. The Functional Task Test aims to correlate these physiologic alterations with changes in performance during mission-critical tasks. In this study, we evaluated spaceflight-induced cardiovascular changes during 11 functional tasks in 7 Shuttle astronauts before spaceflight, on landing day, and 1, 6, and 30 days after landing. Mean heart rate was examined during each task and autonomic activity was approximated by heart rate variability during the Recovery from Fall/Stand Test, a 2-min prone rest followed by a 3-min stand. Heart rate was increased on landing day during all of the tasks, and remained elevated 6 days after landing during 6 of the 11 tasks. Parasympathetic modulation was diminished and sympathovagal balance was increased on landing day. Additionally, during the stand test 6 days after landing, parasympathetic modulation remained suppressed and heart rate remained elevated compared to preflight levels. Heart rate and autonomic activity were not different from preflight levels 30 days after landing. We detected changes in heart rate and autonomic activity during a 3-min stand and a variety of functional tasks, where cardiovascular deconditioning was still evident 6 days after returning from short-duration spaceflight. The delayed recovery times for heart rate and parasympathetic modulation indicate the necessity of assessing functional performance after long-duration spaceflight to ensure crew health and safety.
    Acta Astronautica 11/2013; 92(1):10-14. · 0.70 Impact Factor
  • Journal for Vascular Ultrasound 06/2013; 37(2):91-94.
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    ABSTRACT: Space Shuttle astronauts wore an inflatable antigravity suit during reentry and landing, and astronauts and cosmonauts wear an elastic-compression garment (with lacing) during Soyuz re-entry and landings and in the first few days of recovery. However, neither garment is an ideal countermeasure to spaceflight-induced orthostatic intolerance. Our laboratory has been investigating an elastic graded compression garment (GCG) that applies graduated pressures from the feet to the abdomen for use following International Space Station missions and possibly during exploration missions. Before and after Shuttle missions, 14 astronauts participated in a 3.5-min stand test. The stand test was conducted without garments preflight. On landing day, 7 astronauts wore the GCG while 7 astronauts did not (controls). Heart rate and blood pressure were measured in all astronauts during prone rest and standing. Stroke volume and cardiac output were measured only in GCG subjects. No astronauts in either group became presyncopal during the stand test preflight or postflight. The change in heart rate from prone to standing was lower in the GCG subjects on landing day than in the control subjects. Within the GCG subjects only, the increase in total peripheral resistance from prone to standing was higher after spaceflight. The GCG prevented tachycardia and increased total peripheral resistance with standing after spaceflight. The GCG shows promise as a countermeasure against post-spaceflight orthostatic intolerance, can be easily donned, and is relatively comfortable to wear, but has not been validated after long-duration spaceflight.
    Aviation Space and Environmental Medicine 05/2013; 84(5):459-66. · 0.78 Impact Factor
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    Dataset: Gender
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    Dataset: Gender
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    ABSTRACT: Spaceflight-induced orthostatic intolerance has been studied for decades. Although ~22% of the astronaut corps are women, most mechanistic studies use mostly male subjects, despite known gender differences in autonomic control and postflight orthostatic intolerance. We studied adrenergic, baroreflex, and autonomic indices during continuous infusions of vasoactive drugs in men and women during a 60-day head-down bed rest. Volunteers were tested before bed rest (20 men, 10 women) and around days 30 (20 men, 10 women) and 60 (16 men, 8 women) of bed rest. Three increasing doses of phenylephrine (PE) and sodium nitroprusside (SNP) were infused for 10 minutes following an infusion of normal saline. A 20-minute rest period separated the PE and SNP infusions. Autonomic activity was approximated by spectral indices of heart rate and blood pressure variability, and baroreflex sensitivity was measured by the spontaneous baroreflex slope. Parasympathetic activity and baroreflex sensitivity decreased with bed rest, with women experiencing a larger decrease in baroreflex sensitivity by day 30 than men. The sympathetic dominance of men and parasympathetic dominance of women in blood pressure control were preserved throughout bed rest. During PE infusions, women experienced saturation of the R-R interval high frequency (RR HF) whereas men did not, revealing a gender difference in the parabolic relationship between RR HF, a measurement of respiratory sinus arrhythmia, and R-R interval. These gender differences in blood pressure control during simulated microgravity reveal the need to study gender differences in long-duration spaceflight to ensure the health and safety of the entire astronaut corps.
    AJP Heart and Circulatory Physiology 02/2013; · 4.01 Impact Factor
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    ABSTRACT: Successful acquisition of high-quality ultrasound images for medical diagnoses and scientific research entails several years of intensive training. This time commitment, combined with training requirements for space flight operations, precludes astronauts from proficiently conducting ultrasound examinations without assistance. Therefore, experts in the Johnson Space Center Cardiovascular Laboratory developed a technique called Remote Guidance in which astronauts who possess limited ultrasound training before they launch perform ultrasound examinations in space while receiving real-time feedback about ultrasound probe positioning, scanning technique, study protocol, and image quality through two-way, real-time communication with sonographers on the ground. For instances when time and distance make two-way communication impractical, such as during a mission to Mars or an asteroid, we have developed a form of “just-in-time training” called Virtual Guidance that allows astronauts to autonomously obtain diagnostic ultrasound images by viewing ultrasound tutorials using audio-video glasses while simultaneously performing ultrasound scans. We recently conducted two trials in which we demonstrated the ability of untrained scanners to complete carotid artery and ophthalmic examinations using Virtual Guidance as their only form of instruction. Virtual Guidance can be an important training tool to ensure high-quality ultrasound imaging for scientific and medical applications during future space exploration missions and also could be valuable on Earth in remote areas or applications when a trained sonographer is not readily accessible.
    Journal for Vascular Ultrasound. 01/2013; 37(2).
  • Aviation Space and Environmental Medicine 01/2013; 84:459 – 66. · 0.78 Impact Factor
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    ABSTRACT: With missions planned to travel greater distances from Earth at ranges that make real-time two-way communication impractical, astronauts will be required to perform autonomous medical diagnostic procedures during future exploration missions. Virtual guidance is a form of just-in-time training developed to allow novice ultrasound operators to acquire diagnostically-adequate images of clinically relevant anatomical structures using a prerecorded audio/visual tutorial viewed in real-time. Individuals without previous experience in ultrasound were recruited to perform carotid artery (N = 10) and ophthalmic (N = 9) ultrasound examinations using virtual guidance as their only training tool. In the carotid group, each untrained operator acquired two-dimensional, pulsed and color Doppler of the carotid artery. In the ophthalmic group, operators acquired representative images of the anterior chamber of the eye, retina, optic nerve, and nerve sheath. Ultrasound image quality was evaluated by independent imaging experts. Of the studies, 8 of the 10 carotid and 17 of 18 of the ophthalmic images (2 images collected per study) were judged to be diagnostically adequate. The quality of all but one of the ophthalmic images ranged from adequate to excellent. Diagnostically-adequate carotid and ophthalmic ultrasound examinations can be obtained by previously untrained operators with assistance from only an audio/video tutorial viewed in real time while scanning. This form of just-in-time training, which can be applied to other examinations, represents an opportunity to acquire important information for NASA flight surgeons and researchers when trained medical personnel are not available or when remote guidance is impractical.
    Aviation Space and Environmental Medicine 10/2012; 83(10):995-1000. · 0.78 Impact Factor
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    ABSTRACT: Astronauts have worn an inflatable antigravity suit (AGS) during Space Shuttle re-entry and landing to protect against hypotension and syncope, but ambulation with an inflated AGS requires significant effort and may prevent successful completion of an unaided emergency egress from the vehicle. NASA is considering the use of alternative garments to provide protection against post-spaceflight orthostatic intolerance. The purpose of this study was to compare the metabolic cost of walking in NASA's current AGS with that of walking in a commercially available elastic compression garment (thigh-high stockings), a candidate garment for use after exploration missions. There were 10 volunteers (5 men, 5 women) who walked on a treadmill at 5.6 km x h(-1) for 5 min, a simulation of unaided egress previously used in our laboratory, in 3 different conditions presented in random order: wearing exercise clothes, wearing elastic compression garments, and wearing the AGS. Oxygen consumption (Vo2), carbon dioxide production (Vco2), and ventilation (V(E)) were compared using repeated-measures ANOVA and Tukey's Honestly Significant Difference test. Vo2 while wearing the AGS was 12% greater than when wearing the elastic compression garments and 15% greater than while wearing exercise clothes. There were no differences between the elastic compression garments and exercise clothes only conditions. Vco2 and VE also were greater while walking in the AGS than walking in the elastic compression garments or exercise clothes. Wearing elastic compression garments as a countermeasure to post-spaceflight orthostatic intolerance may not impair unaided egress from a space vehicle.
    Aviation Space and Environmental Medicine 06/2011; 82(6):648-53. · 0.78 Impact Factor
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    ABSTRACT: We studied 15 men (8 treatment, 7 control) before and after 21 days of 6º head-down tilt to determine whether daily, 1-h exposures to 1.0 G(z) (at the heart) artificial gravity (AG) would prevent bed rest-induced cardiovascular deconditioning. Testing included echocardiographic analysis of cardiac function, plasma volume (PV), aerobic power (VO(2)pk) and cardiovascular and neuroendocrine responses to 80º head-up tilt (HUT). Data collected during HUT were ECG, stroke volume (SV), blood pressure (BP) and blood for catecholamines and vasoactive hormones. Heart rate (HR), cardiac output (CO), total peripheral resistance, and spectral power of BP and HR were calculated. Bed rest decreased PV, supine and HUT SV, and indices of cardiac function in both groups. Although PV was decreased in control and AG after bed rest, AG attenuated the decrease in orthostatic tolerance [pre- to post-bed rest change; control: -11.8 ± 2.0, AG: -6.0 ± 2.8 min (p = 0.012)] and VO(2)pk [pre- to post-bed rest change; control: -0.39 ± 0.11, AG: -0.17 ± 0.06 L/min (p = 0.041)]. AG prevented increases in pre-tilt levels of plasma renin activity [pre- to post-bed rest change; control: 1.53 ± 0.23, AG: -0.07 ± 0.34 ng/mL/h (p = 0.001)] and angiotensin II [pre- to post-bed rest change; control: 3.00 ± 1.04, AG: -0.63 ± 0.81 pg/mL (p = 0.009)] and increased HUT aldosterone [post-bed rest; control: 107 ± 30 pg/mL, AG: 229 ± 68 pg/mL (p = 0.045)] and norepinephrine [post-bed rest; control: 453 ± 107, AG: 732 ± 131 pg/mL (p = 0.003)]. We conclude that AG can mitigate some aspects of bed rest-induced cardiovascular deconditioning, including orthostatic intolerance and aerobic power. Mechanisms of improvement were not cardiac-mediated, but likely through improved sympathetic responsiveness to orthostatic stress.
    Arbeitsphysiologie 05/2011; 112(2):605-16. · 2.66 Impact Factor
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    ABSTRACT: Astronauts experience both orthostatic hypotension and space motion sickness during re-entry. Midodrine, an alpha1-adrenergic agonist, is used to treat orthostatic hypotension. Promethazine, a histamine H1-receptor antagonist, is prescribed for space motion sickness. Many astronauts need both midodrine and promethazine. This study evaluated the interactive effects of midodrine and promethazine on hemodynamic responses to upright tilt. Subjects (5 men; 3 women) were studied four times: control (no drug); midodrine only; promethazine only; or midodrine plus promethazine. Hemodynamic parameters, plasma norepinephrine, renin activity, and aldosterone were measured supine and upright. Rates of presyncope were 38% with no drug; 0% with midodrine alone; 100% with promethazine alone; and 63% with both drugs. Supine to upright decreases in systolic pressure were greater with promethazine alone than control (P < 0.01); midodrine (P < 0.05) or both drugs (P < 0.05). Supine to upright increases in plasma norepinephrine, renin activity, and aldosterone all were significantly reduced with promethazine alone compared to control (P < 0.05, P < 0.05, P < 0.05) and midodrine alone (P < 0.05, P < 0.01, P < 0.01). Cardiac output fell more with promethazine alone than with no drug (P < 0.05) or with midodrine plus promethazine (P < 0.05). Promethazine significantly increased the incidence of orthostatic hypotension in subjects, even when combined with midodrine. Inhibition of sympathetic responses, likely via enhancement of the inhibitive effects of GABA, by promethazine may underlie the increased orthostatic hypotension. Promethazine also appears to inhibit responses of the renin angiotensisn system during orthostatic challenge.
    Aviation Space and Environmental Medicine 01/2011; 82(1):9-12. · 0.78 Impact Factor
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    ABSTRACT: Orthostatic intolerance (OI) is a significant challenge for astronauts after long-duration spaceflight. Depending on flight duration, 20–80% of astronauts suffer from post-flight OI, which is associated with reduced vascular resistance. This paper introduces a novel algorithm for continuously monitoring changes in total peripheral resistance (TPR) by processing the peripheral arterial blood pressure (ABP). To validate, we applied our novel mathematical algorithm to the pre-flight ABP data previously recorded from twelve astronauts ten days before launch. The TPR changes were calculated by our algorithm and compared with the TPR value estimated using cardiac output/heart rate before and after phenylephrine administration. The astronauts in the post-flight presyncopal group had lower pre-flight TPR changes (1.66 times) than those in the non-presyncopal group (2.15 times). The trend in TPR changes calculated with our algorithm agreed with the TPR trend calculated using measured cardiac output in the previous study. Further data collection and algorithm refinement are needed for pre-flight detection of OI and monitoring of continuous TPR by analysis of peripheral arterial blood pressure.
    Acta Astronautica 01/2011; 68(7):770-777. · 0.70 Impact Factor
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    ABSTRACT: Post-spaceflight orthostatic intolerance affects approximately 30% of short-duration and 80% of long-duration crewmembers. While the current NASA antigravity suit is effective during Space Shuttle re-entry, it is not designed to be worn postflight and has several drawbacks. The purpose of this study was to evaluate the use of commercially available, thigh-high, gradient compression garments to prevent post-spaceflight orthostatic intolerance. Before spaceflight, five male Shuttle astronauts were fitted for compression garments. Postflight stand time, blood pressure, heart rate, stroke volume, cardiac output, and peripheral resistance during 10-min, 80 degrees head-up tilt test within 4 h of landing in these astronauts were retrospectively compared to a group of nine male astronauts not wearing the compression garments. On landing day, three of nine non-countermeasure astronauts developed presyncopal symptoms and could not complete the test, while no countermeasure subjects became presyncopal. Compared to the non-countermeasure subjects, the countermeasure subjects had higher systolic blood pressure (116 +/- 3 vs. 134 +/- 2 mmHg), stroke volume (42 +/- 5 vs. 57 +/- 6 ml), and cardiac output (3.1 +/- 0.3 vs. 4.6 +/- 0.4 L). Heart rate was not different between groups. In this small pilot study, the rate of presyncope in the non-countermeasure group was similar to that reported previously in subjects without a compression garment. In contrast, thigh-high graded compression garments mitigated the symptoms of orthostatic intolerance by improving stroke volume, cardiac output, and systolic blood pressure responses to standing.
    Aviation Space and Environmental Medicine 09/2010; 81(9):883-7. · 0.78 Impact Factor
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    ABSTRACT: Pathology driven alterations in the geometric shape of the heart have been found to result in regional changes in ventricular wall stress and a remodeling of the myocardium. If reductions in the gravitational forces acting on the heart produce similar changes in the overall contour of the ventricles, this modification might also induce adaptations in the cardiac structure during long-term spaceflight. In this study we examined the changes in left ventricle (LV) shape in spaceflight and during parabolic flights. The diastole dimensions of the human LV were assessed with echocardiography during spaceflight and in parabolic flights which replicated the gravity of the Moon, Mars, and spaceflight and were compared to findings in Earth's gravity. LV dimensions were translated into circularity indices and geometric aspect ratios and correlated with their corresponding gravitational conditions. During parabolic flight, a linear relationship (r = 0.99) was found between both the circularity index and geometric aspect ratio values and the respective gravitational fields in which they were measured. During spaceflight (N = 4) and parabolic flights (N = 3), there was an average 4.1 and 4.4% higher circularity index and a 5.3 and 8.1% lower geometric aspect ratio, respectively. A correlative trend was found between the degree of LV sphericity and the amount of gravitational force directed caudal to the longitudinal orientation of the body. The importance of this finding is uncertain, but may have implications regarding physiologic adaptations in the myocardial structure secondary to changes in LV wall stress upon prolonged exposure to microgravity.
    Aviation Space and Environmental Medicine 05/2010; 81(5):506-10. · 0.78 Impact Factor
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    ABSTRACT: A tendency to develop reentry orthostasis after a prolonged exposure to microgravity is a common problem among astronauts. The problem is 5 times more prevalent in female astronauts as compared to their male counterparts. The mechanisms responsible for this gender differentiation are poorly understood despite many detailed and complex investigations directed toward an analysis of the physiologic control systems involved. In this study, a series of computer simulation studies using a mathematical model of cardiovascular functioning were performed to examine the proposed hypothesis that this phenomenon could be explained by basic physical forces acting through the simple common anatomic differences between men and women. In the computer simulations, the circulatory components and hydrostatic gradients of the model were allowed to adapt to the physical constraints of microgravity. After a simulated period of one month, the model was returned to the conditions of earth's gravity and the standard postflight tilt test protocol was performed while the model output depicting the typical vital signs was monitored. The analysis demonstrated that a 15% lowering of the longitudinal center of gravity in the anatomic structure of the model was all that was necessary to prevent the physiologic compensatory mechanisms from overcoming the propensity for reentry orthostasis leading to syncope.
    Theoretical Biology and Medical Modelling 03/2010; 7:8. · 1.46 Impact Factor
  • Medicine and Science in Sports and Exercise - MED SCI SPORT EXERCISE; 01/2010
  • Medicine and Science in Sports and Exercise - MED SCI SPORT EXERCISE; 01/2010

Publication Stats

209 Citations
76.16 Total Impact Points

Institutions

  • 2009–2012
    • NASA
      • Cardiovascular Laboratory
      Washington, West Virginia, United States
  • 2004–2006
    • Universities Space Research Association
      • Division of Space Life Sciences
      Houston, Texas, United States
  • 2003–2004
    • University of Virginia
      • Department of Molecular Physiology and Biological Physics
      Charlottesville, VA, United States