Engineering topics
Publications and source records attributed to Pool, Sam L..
This paper presents the aeromedical lessons learned from the Space Shuttle Columbia Accident Investigation. The contents include: 1) Introduction and Mission Response Team (MRT); 2) Primary Disaster Field Office (DFO); 3) Mishap Investigation Team (MIT); 4) Kennedy Space Center (KSC) Mishap Response Plan; 5) Armed Forces Institute of Pathology (AFIP); and 6) STS-107 Crew Surgeon.
The National Academy of Sciences Committee on Space Biology and Medicine points out that space medicine is unique among space sciences, because in addition to addressing questions of fundamental scientific interest, it must address clinical or human health and safety issues as well. Efforts to identify how microgravity affects human physiology began in earnest by the United States in 1960 with the establishment of the National Aeronautics and Space Administration (NASA's) Life Sciences program. Before the first human space missions, prediction about the physiological effects of microgravity in space ranged from extremely severe to none at all. The understanding that has developed from our experiences in space to date allows us to be guardedly optimistic about the ultimate accommodations of humans to space flight. Only by our travels into the microgravity environment of space have we begun to unravel the mysteries associated with gravity's role in shaping human physiology. Space medicine is still at its very earliest stages. Development of this field has been slow for several reasons, including the limited number of space flights, the small number of research subjects, and the competition within the life sciences community and other disciplines for flight opportunities. The physiological changes incurred during space flight may have a dramatic effect on the course of an injury or illness. These physiological changes present an exciting challenge for the field of space medicine: how to best preserve human health and safety while simultaneously deciphering the effects of microgravity on human performance. As the United States considers the future of humans in long-term space travel, it is essential that the many mysteries as to how microgravity affects human systems be addressed with vigor. Based on the current state of our knowledge, the justification is excellent indeed compelling- for NASA to develop a sophisticated capability in space medicine. Teams of physicians and scientists should be actively engaged in fundamental and applied research designed to ensure that it is safe for humans to routinely and repeatedly stay and work in the microgravity environment of space.
The National Aeronautics and Space Administration (NASA) has used iodination as a method of microbial disinfection of potable water systems in United States spacecraft and long-duration habitability modules. A review of the effects on the thyroid following consumption o iodinated water by NASA astronauts was conducted. Pharmacological doses of iodine consumed by astronauts transiently decreased thyroid function, as reflected in serum TSH values. Although the adverse effects of excess iodine consumption in susceptible individuals are well documented, exposure to high doses of iodine during space flight did not result in a statistically significant increase in long-term thyroid disease in the astronaut population.
The therapeutic effectiveness of medications during spaceflight is considered in light of extensive anecdotal and experimental evidence. Attention is given to a range of medications for space motion sickness, sleeplessness, and physical discomfort. About 70 individual cases are reviewed in which crewmembers used such medications as: (1) scopolamine hydrobromide, dextroamphetamine sulfate, and promethazine hydrochloride for motion sickness; (2) metoclopramide hydrochloride and naloxone hydrochloride for bowel motility; and (3) aspirin and acetaminophen for headache and back pain. The effectiveness of orally ingested medications for space motion sickness is shown to be very low, while promethazine hydrochloride is effective when administered intramuscularly. The medications for pain are shown to be generally effective, and the use of sleep-inducing medications is limited by potentially detrimental performance effects.
Crews and passengers on future long-duration Earth orbital and interplanetary missions must be provided quality health services - to combat illnesses and accidental injuries, and for routine preventive care. People on Earth-orbital missions can be returned relatively easily to Earth, but those on interplanetary missions cannot. Accordingly, crews on long-duration missions will likely include at least one specially trained person, perhaps a physician's assistant, hospital corpsman, nurse, or physician who will be responsible for providing onboard health services. Specifically, we must determine the most effective way to administer health care to a remotely located population. NASA with the cooperation of the Department of Health, Education, and Welfare is pursuing a program for providing health services to remote locations on Earth as a necessary step to developing and verifying this capability on a spacecraft. The STARPAHC program is described.
Visual suppression of the vestibulo-ocular reflex was studied in 16 subjects on 4 Space Shuttle missions. Eye movements were recorded by electro-oculography while subjects fixated a head mounted target during active sinusoidal head oscillation at 0.3 Hz. Adequacy of suppression was evaluated by the number of nystagmus beats, the mean amplitude of each beat, and the cumulative amplitude of nystagmus during two head oscillation cycles. Vestibulo-ocular reflex suppression was unaffected by space flight. Subjects with space motion sickness during flight had significantly more nystagmus beats than unaffected individuals. These susceptible subjects also tended to have more nystagmus beats before flight.
Saccadic eye movements were studied in six subjects during two Space Shuttle missions. Reaction time, peak velocity and accuracy of horizontal, visually-guided saccades were examined preflight, inflight and postflight. Conventional electro-oculography was used to record eye position, with the subjects responding to pseudo-randomly illuminated targets at 0 deg and + or - 10 deg and 20 deg visual angles. In all subjects, preflight measurements were within normal limits. Reaction time was significantly increased inflight, while peak velocity was significantly decreased. A tendency toward a greater proportion of hypometric saccades inflight was also noted. Possible explanations for these changes and possible correlations with space motion sickness are discussed.
The fundamental biomedical issues involved in manned space flight are examined in review chapters contributed by leading U.S. experts. Sections are devoted to the history of manned space flight, the space environment, space-flight systems and procedures, physiological adaptation to space flight, health maintenance of space crewmembers, and medical problems of space flight. Extensive diagrams, drawings, graphs, photographs, and tables of numerical data are provided.
Unpaced voluntary horizontal head oscillation was used to study the Vestibulo-Ocular Reflex (VOR) on Shuttle flights STS 7 and 8. Ten subjects performed head oscillations at 0.33 Hz + or - 30 deg amplitude under the followng conditions: VVOR (visual VOR), eyes open and fixed on a stationary target; VOR-EC, with eyes closed and fixed on the same target in imagination; and VOR-S (VOR suppression), with eyes open and fixed on a head-synchronized target. Effects of weightlessness, flight phase, and Space Motion Sickness (SMS) on head oscillation characteristics were examined. A significant increase in head oscillation frequency was noted inflight in subjects free from SMS. In subjects susceptible to SMS, frequency was reduced during their Symptomatic period. The data also suggest that the amplitude and peak velocity of head oscillation were reduced early inflight. No significant changes were noted in reflex gain or phase in any of the test conditions; however, there was a suggestion of an increase in VVOR and VOR-ES gain early inflight in asymptomatic subjects. A significant difference in VOR-S was found between SMS susceptible and non-susceptible subjects. There is no evidence that any changes in VOR characteristics contributed to SMS.
Eye-head motion was studied pre-, in- and postflight during single voluntary head turns. A transient increase in vestibulo-ocular reflex (VOR) gain occurred early in the flight, but later trended toward normal. This increased gain was produced by a relative increase in eye counterrotation velocity. Asymmetries in gain with right and left turns also occurred, caused by asymmetries in eye counterrotation velocities. These findings were remarkably similar to those from Soviet primate studies using gaze fixation targets, except the human study trended more rapidly toward normal. These findings differ substantially from those measuring VOR gain by head oscillation, in which no significant changes were found inflight. No visual disturbances were noted in either test condition or in normal activities. These head turn studies are the only ones to date documenting any functional change in VOR in weightlessness.
This paper attempts to underscore the importance of continued studies on the effects of space on human physiology. With particular reference to the Space Station, it is pointed out that there are two aspects which are challenging to life scientists: first is the development of a research capability for the life sciences which will be used to conduct investigations necessary to extend the time humans can remain in space; second is the challenge to develop a medical capability to provide prevention, diagnosis, and therapy. A discussion of physiological changes that have been observed in spacecrews follows along the lines of the two aspects mentioned.
The vestibulo-ocular reflex (VOR) may be altered by weightlessness. Since this reflex plays a large role in visual stabilization, it was important to document any changes caused by space flight. This is a report on findings on STS-4 through 6 and is part of a larger study of neurosensory adaptation done on STS-4 through 8. Voluntary horizontal head oscillations at 1/3 Hz with amplitude of 30 deg right and left of center were recorded by a potentiometer and compared to eye position recorded by electroculography under the following conditions: eyes open, head fixed, tracking horizontal targets switched 0, 15, and 30 degrees right and left (optokinetic reflex - OKR - and calibration); eyes open and fixed on static external target with oscillation, (vestibulo ocular reflex, eyes closed - VOR EC); eyes open and wearing opaque goggles with target fixed in imagination (vestibulo-ocular reflex, eyes shaded - VOR ES); and eyes open and fixed on a head synchronized target with head oscillation (VOR suppression). No significant changes were found in voluntary head oscillation frequency or amplitude in those with (n=5), and without (n=3), space motion sickness (SMS), with phase of flight or test condition. Variations in head oscillation were too small to have produced detectable changes in test results.
An inflight, clinically-oriented investigation of space motion sickness (SMS) was begun on STS-4 and revealed the following: compared to motion sickness (MS) on earth, automatic signs are significantly different in SMS vs. MS in that sweating is not present, pallor or flushing may be present, and vomiting is episodic, sudden, and brief. Postflight there is a period of resistance to all forms of MS. There is some evidence for individual reduction in sensitivity on repeated flights. Electrooculogram, audio-evoked potentials, measurement of fluid shifts, and other studies are inconsistent with a transient vestibular hydrops or increased intracranial pressure as a cause.
Gastrointestinal symptoms in space motion sickness (SMS) are significantly different from those in ordinary motion sickness (MS). Recording and tabulation of sounds was the only technique that could be used as a measure of motility during spaceflight operations. There were 17 subjects, six unaffected by SMS, who made ambulatory recordings preflight and inflight. With one exception, all those affected had sharply reduced sounds, while those unaffected had increases or moderate reductions. The mechanism of vomiting in SMS appears to be secondary to this ileus, in contrast to vomiting in ordinary MS, where the emesis center is thought to be directly triggered by the vestibular system.
Studies of leg volumes in space by multiple girth measurements showed reductions of 1.9 l (12.8 percent of leg volume), with 1.1 l from the nondominant leg, on Skylab 4. On landing, 65 percent of postflight leg volume increase was complete at 1.5 h. Measurement of the dominant leg during the equivalent period on Shuttle showed a mean loss of 0.9 l which was 90-percent complete at 150 min. Postflight increases were 87-percent complete at 1.5 h postlanding. Mass measurements during and after Skylab 4 showed a loss of 2.5 kg over the first 4 d on orbit, with a gain of 2.7 kg over the first 4 d of recovery. These changes are assumed to be tissue fluids secondary to changes in hydrostatic pressures and are much greater than those seen in bed rest. Rate and magnitude of inflight and postflight changes have significant operational impact.
Beginning with the fourth flight of the Space Transport System (STS-4), objective measurements of inner ear function were conducted in near-zero G conditions in earth orbit. The problem of space motion sickness (SMS) was approached much like any disequilibrium problem encountered clinically. However, objective testing techniques had built-in limitations superimposed by the strict parameters inherent in each mission. An attempt was made to objectively characterize SMS, and to first ascertain whether the objective measurements indicated that this disorder was of peripheral or central origin. Electronystagmography and auditory brain stem response recordings were the primary investigative tools. One of the authors (W.E.T.) was a mission specialist on board the orbiter Challenger on the eighth shuttle mission (STS-8) and had the opportunity to make direct and personal observations regarding SMS, an opportunity which has added immeasurably to our understanding of this disorder. Except for two abnormal ENG records, which remain to be explained, the remaining ENG records and all the ABR records made in the weightless environment of space were normal.