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INTRODUCTION Earlier research described a linear relationship between the highest 1 min of oxygen consumption (Vo2) during a recurring physical activity and incidence of decompression sickness (DCS) during research chamber exposures to high altitude. The current effort was designed to determine if that relationship holds true at a lower altitude. METHODS Male subjects (20) were exposed without prebreathe to 22,500 ft (6858 m; 314 mmHg; 6.1 psi) for 4 h while seated, nonambulatory the entire time, with echo-imaging at 16-min intervals (Non-Amb Echo), breathing 100% oxygen. Average highest 1 min of Vo2 and level of activity was determined. Results during Non-Amb Echo were compared with earlier research data acquired under identical conditions except for higher levels of activity. RESULTS No DCS was reported or observed and no venous gas emboli were observed. Combined with earlier data, a strong linear relationship (r > 0.99) was observed between DCS incidence and level of activity. DISCUSSION These results suggest physiological envelopes might be expanded or prebreathe time reduced for some high-altitude aircraft operations that involve very low levels of physical activity. They may also help to explain the higher DCS risk for inside observers vs. trainees during altitude chamber training. The data imply potential for update of altitude DCS risk prediction models by adjustment with quantified level of activity during exposure.

UNLABELLED INTRODUCTION, FACILITIES, AND METHODS: Decompression sickness (DCS) occurring in hypobaric environments related to aviation or spaceflight was a major focus of research at Brooks AFB/City-Base, TX, throughout the period 1960-2010. Multiple hypobaric chambers and extensive support facilities were built for research on altitude DCS using both human subjects and animal models. Areas of study included symptomatology, incidence, prediction, and prevention of DCS. High-altitude aviation, spacecraft atmospheres, and pressure suits were evaluated with various decompression and prebreathing schedules to reduce DCS risk. FACTORS AFFECTING DCS INCIDENCE: The results from these efforts were recorded in an extensive Altitude DCS Research Database which served as a resource for developing reports and exploring relationships of various parameters such as altitude, time at altitude, prebreathe time, and mode of activity while decompressed. PREVENTION AND PREDICTION OF DCS: Individual susceptibility to DCS was also evaluated in an effort to tailor preventive measures and predict susceptibility. Completion of the 26 human-use protocols provided information which was incorporated into NASA and USAF operational practices to reduce DCS risk. DOCUMENTATION DCS researchers working at Brooks throughout this period produced 177 papers documenting results of thousands of subject-exposures and other experiments. An Altitude DCS Risk Assessment Computer Model was fielded in 2005. This review centers on the results of research at Brooks and notes questions about operational DCS risk that have not yet been answered.

This article reviews a study in which distal forearm fractures in children were treated with a below elbow semi-rigid cast, with instructions for removal at home. Patient satisfaction surveys established that children and parents were pleased they did not have to return to hospital to have the cast removed, and most patients returned to normal activity immediately or within one week after removing the plaster at home. Although semi-rigid casts are slightly more expensive to apply than standard plaster, the authors believe this is outweighed by the advantages of patients not having to return to the fracture clinic. Hospital clinics were significantly less busy, allowing them to create slots for new referrals.

Future long-duration spaceflights are now being planned to the Moon and Mars as a part of the "Vision for Space Exploration" program initiated by NASA in 2004. This report describes the design reference missions for the International Space Station, Lunar Base, and eventually a Mars Expedition. There is a need to develop more stringent preflight medical screening for crewmembers to minimize risk factors for diseases which cannot be effectively treated in flight. Since funding for space life sciences research and development has been eliminated to fund program development, these missions will be enabled by countermeasures much like those currently in use aboard the International Space Station. Artificial gravity using centrifugation in a rotating spacecraft has been suggested repeatedly as a "universal countermeasure" against deconditioning in microgravity and could be an option if other countermeasures are found to be ineffective. However, the greatest medical unknown in interplanetary flight may be the effects of radiation exposure. In addition, a Mars expedition would lead to a far greater level of isolation and psychological stress than any space mission attempted previously; because of this, psychiatric decompensation remains a risk. Historically, mortality and morbidity related to illness and injury have accounted for more failures and delays in new exploration than have defective transportation systems. The medical care system on a future Mars expedition will need to be autonomous and self-sufficient due to the extremely long separation from definitive medical care. This capability could be expanded by the presence of a physician in the crew and including simple, low-technology surgical capability.

A 10.2 psi staged-decompression schedule or a 4-hour preoxygenation at 14.7 psi is required prior to extravehicular activity (EVA) to reduce decompression sickness (DCS) risk. Results of recent research at the Air Force Research Laboratory (AFRL) showed that a 1-hour resting preoxygenation followed by a 4-hour, 4.3 psi exposure resulted in 77% DCS risk (N=26), while the same profile beginning with 10 min of exercise at 75% of VO2peak during preoxygenation reduced the DCS risk to 42% (P

The Hartnett, Nelson, and Rinn 2004 study indicates that diagnostic confusion between ADD/ADHD and giftedness exists, and that research on medication practices is warranted. Mika disagrees, saying that there is no empirical evidence of misdiagnosis of gifted children as having ADD/ADHD. We disagree with Mika's logic, and describe evidence that suggests that such misdiagnosis does occur, with possible concurrent risks.

The relation between age and several critical item sets on the revised Minnesota Multiphasic Personality Inventory (MMPI-2; Butcher, Dahlstrom, Graham, Tellegen, & Kaemmer, 1989) was examined. MMPI-2 protocols from veterans entering a Veterans Affairs domiciliary were obtained, and the number of Grayson critical items, Koss-Butcher critical items. Lachar-Wrobel critical items, and Caldwell critical items were tabulated. Another critical item set consisting of all items of the previously mentioned sets was also tabulated. This composite set was divided into a set that has items scored on Scales 1, 2, and 3, and a second set of items that were not scored on those three scales. The effect of age on Scales L and K was also studied. A one-way analysis of variance confirmed that the number of endorsed critical items was significantly less in older age groups, and L and K increased. The implication is that endorsement of a critical item may have increased clinical significance as a person ages.

Introduction The well-established technique of mask-off hypoxia training in a hypobaric training environment elicits symptoms that are correlated with in-flight symptoms reported by aircrew. Aircrew receive training on recognition of symptoms and response early in their flying career and accomplish refresher training on a 5-yr cycle. The symptoms reported after acute hypoxia represent cognitive and psychomotor impairment. The purpose of this study was to evaluate the correlation of symptoms experienced during hypoxia training and recall of symptoms S from the training sessions 5 yr previously. Methods A survey listing 18 symptoms of hypoxia and severity of condition was presented to 1123 aircrew attending refresher training at 10 U.S. Air Force Aerospace Physiology Training Units prior to and immediately following hypoxia training in the hypobaric chamber. Results The five symptoms most commonly reported following hypoxia training are: lightheaded/dizzy, dizziness, mental confusion, visual impairment, and tingling. The hypoxia symptom "lightheaded/dizzy" recorded the highest frequency of all 18 symptoms. Lightheaded/dizzy frequencies for both previous and current hypoxia training were 67.2% and 72.3%, respectively. This symptom remained consistent throughout all data analysis, retaining the highest frequency in all levels of severity (mild, moderate, and extreme) for both the previous hypoxia training and current hypoxia training. Discussion The similarity of symptoms recalled between hypoxia training events provides strong evidence that hypoxia training is an effective method of establishing recognized decrements that may influence performance in flight.

With the impending termination of USAF operations at Brooks Air Force Base (AFB) in San Antonio, TX, it is time to consider its historic role in Aerospace Medicine. The base was established in 1917 as a flight training center for the U.S. Army Air Service and in 1926 became home to its School of Aviation Medicine. The school moved to San Antonio's Randolph Field in 1931, but in 1959 it returned to Brooks where it occupied new facilities to support its role as a national center for U.S. Air Force aerospace medicine, including teaching, clinical medicine, and research. The mission was then expanded to encompass support of U.S. military and civilian space programs. With the abrupt termination of the military space program in 1969, research at Brooks focused on clinical aviation medicine and support of advanced military aircraft while continuing close cooperation with NASA in support of orbital spaceflight and the journey to the Moon. Reorganization in the 1990s assigned all research functions at Brooks to the Human Systems Division and its successors, leaving to USAFSAM the missions related to clinical work and teaching. In 2002 the USAF and the city of San Antonio implemented shared operation of Brooks as a "City-Base" in the hope of deflecting threatened closure. Nevertheless, under continuing pressure to consolidate military facilities in the United States, the 2005 Base Closure and Realignment Commission ordered Brooks closed by 2011, with its aerospace medicine functions relocated to new facilities at Wright-Patterson AFB in Dayton, OH.

Introduction: The existence of a general influence of exercise on the incidence of decompression sickness (DCS) has been known for more than a half-century. However, quantification of the effect has not been done for several reasons, including isolation of exercise as the only variable.The DCS database at Brooks City-Base, TX, contains detailed physiologic information on over 3000 altitude exposures. The purpose of this study was to measure Vo 2 during the activities performed during those exposures to retrospectively determine if Vo 2 , a quantifiable index of exercise intensity, was related to the level of reported DCS. Methods: Ground-level activity was designed to duplicate the standardized activity during the altitude exposures. Breath-by-breath Vo 2 was determined for each activity using a COSMED® metabolic measurement system. Comparison of the Vo 2 during four levels of activity performed under otherwise comparable conditions allowed a determination of correlation between Vo 2 and DCS risk observed during the altitude exposures. Results and Discussion: Four previous altitude exposure profiles at 8992 m to 9144 m (29,500 to 30,000 ft; 231 to 226 mmHg) for 4 h following a 1-h prebreathe resulted in 38-86% DCS. This study provided the Vo 2 of activities during those studies. The correlation between DCS incidence and the highest 1-min Vo 2 of activity was 0.89. Conclusion: The highest 1-min Vo 2 showed a high correlation with level of DCS risk. Future exposures involving lower levels of activity could provide data that would allow improvement in modeling of DCS risk.

To reduce the risk of decompression sickness (DCS), current USAF U-2 operations require a 1-h preoxygenation (PreOx). An interruption of oxygen breathing with air breathing currently requires significant extension of the PreOx time. The purpose of this study was to evaluate the relationship between air breaks during PreOx and subsequent DCS and venous gas emboli (VGE) incidence, and to determine safe air break limits for operational activities. Methods: Volunteers performed 30 min of PreOx, followed by either a 10-min, 20-min, or 60-min air break, then completed another 30 min of PreOx, and began a 4-h altitude chamber exposure to 9144 m (30,000 ft). Subjects were monitored for VGE using echocardiography. Altitude exposure was terminated if DCS symptoms developed. Control data (uninterrupted 60-min PreOx) to compare against air break data were taken from the AFRL DCS database. Results: At 1 h of altitude exposure, DCS rates were significantly higher in all three break in prebreathe (BiP) profiles compared to control (40%, 45%, and 47% vs. 24%). At 2 h, the 20-min and 60-min BiP DCS rates remained higher than control (70% and 69% vs. 52%), but no differences were found at 4 h. No differences in VGE rates were found between the BiP profiles and control. Discussion: Increased DCS risk in the BiP profiles is likely due to tissue renitrogenation during air breaks not totally compensated for by the remaining PreOx following the air breaks. Air breaks of 10 min or more occurring in the middle of 1 h of PreOx may significantly cantly increase DCS risk during the first 2 h of exposure to 9144 m when compared to uninterrupted PreOx exposures.

This report is designed to be a reference for Aerospace Researchers and Technicians in the US Air Force who are tasked to perform altitude decompression sickness (DCS) research. It contains information about procedures, records, and equipment used in DCS research at Brooks AFB/City-Base from 1983-2005 involving over 3000 human subject exposures. Although the environmental conditions were different for each profile, the procedures used to gather and record data were standardized. The appendices provide procedural checklists and forms related to the performance of altitude DCS research.

This report is designed to be a reference for Aerospace Researchers and Technicians in the US Air Force who are tasked to perform altitude decompression sickness (DCS) research. It contains information about the development, use, search, reporting, and query capabilities of the USAFSAM Altitude DCS Research Database. The database uses Microsoft(TradeMark) Access 2003 and contains information on over 3000 subject-exposures that includes extensive data on venous gas emboli, symptom development, and, in conjunction with this document, detailed information on the activities performed during decompression.

This report is designed to review the incorporation of methods and procedures for reducing the incidence of decompression sickness (DCS) during U-2 high altitude reconnaissance missions. Exercise During Prebreathe (EDP) during procedures used for some pilots preparing for U-2 high altitude operations is reviewed in detail. The published basis for enhancing prebreathe effectiveness with exercise is summarized along with an operational test with one U-2 pilot and survey results from 2 pilots. Successful incorporation of EDP on the International Space Station prior to extravehicular activity (EVA; space walks) is also reviewed. Procedures for its incorporation and variants in exercise equipment are summarized and equations for calculating individualized exercise parameters are shown. Included are summaries of peer-reviewed publications supporting this information and personal remarks about prebreathe procedures with EDP by National Aeronautic and Space Administration (NASA) Mission Specialists.

Extravehicular activity (EVA) is required from the International Space Station on a regular basis. Because of the weightless environment during EVA, physical activity is performed using mostly upper-body movements since the lower body is anchored for stability. The adynamic model (restricted lower-body activity; non-ambulation) was designed to simulate this environment during earthbound studies of decompression sickness (DCS) risk. DCS symptoms during ambulatory (walking) and non-ambulatory high altitude exposure activity were compared. The objective was to determine if symptom incidences during ambulatory and non-ambulatory exposures are comparable and provide analogous estimates of risk under otherwise identical conditions.A retrospective analysis was accomplished on DCS symptoms from 2010 ambulatory and 330 non-ambulatory exposures.There was no significant difference between the overall incidence of DCS or joint-pain DCS in the ambulatory (49% and 40%) vs. the non-ambulatory exposures (53% and 36%; p0.1). DCS involving joint pain only in the lower body was higher during ambulatory exposures (28%) than non-ambulatory exposures (18%; p0.01). Non-ambulatory exposures terminated more frequently with non-joint-pain DCS (17%) or upper-body-only joint pain (18%) as compared with ambulatory exposures, 9% and 11% (p0.01), respectively.These findings show that lower-body, weight-bearing activity shifts the incidence of joint-pain DCS from the upper body to the lower body without altering the total incidence of DCS or joint-pain DCS.Use of data from previous and future subject exposures involving ambulatory activity while decompressed appears to be a valid analogue of non-ambulatory activity in determining DCS risk during simulated EVA studies.

Many aircraft oxygen systems do not deliver 100% O2. Inert gases can be present at various levels. The purpose of this study was to determine the effect of these inert gas levels on decompression sickness (DCS).Subjects were exposed for 4 h to 5486 m (18,000 ft) with zero prebreathe, using either mild (Test A) or strenuous exercise (Test B), and breathing 60%N2/40%O2. Test C used a breathing mixture of 40%N2/60%O2 at 6858 m (22,500 ft) with zero prebreathe and mild exercise. Test D investigated a breathing mixture of 2.8%N2/4.2%argon/93%O2 with 4 h exposures to 7620 m (25,000 ft), mild exercise, and 90 min of preoxygenation. The controls were from previous studies using similar conditions and 100% O2.The DCS risk for Tests A and B and the Control for B was 7%; the Control for Test A was 0% (n.s.). Breathing the 40%N2/60%O2 mixture (Test C) resulted in 43% DCS compared with 53% DCS with 100% O2 (n.s.). When the 2.8%N2/4.2%argon/93%O2 mixture was used, the results showed 25% DCS compared with 31% DCS with 100% O2 (n.s.).The increased nitrogen and argon levels in the breathing gas while at altitudes of 5486 m to 7620 m did not increase DCS risk. These results support the concept of using the partial pressure gradient of inert gases instead of the percentage of N2 or argon in a breathing gas mixture to determine the risk of DCS during altitude exposure.

There is considerable variability in individual susceptibility to altitude decompression sickness (DCS). The Air Force Research Laboratory Altitude DCS Research Database consists of extensive information on 2980 altitude exposures conducted with consistent procedures and endpoint criteria. We used this database to quantify the variation in susceptibility and determine if anthropometric and/or physiologic variables could be used to predict DCS risk.There were 240 subjects who participated in at least 4 of 70 exposure profiles in which between 5 and 95% of all subjects tested developed DCS symptoms. A subject/study ratio (SSR) was calculated by dividing the DCS experienced by a subject during all their exposures by the DCS incidence for all subjects who participated in the identical exposures. The SSR was used to identify the relative susceptibility of subjects for use in analyzing possible relationships between DCS susceptibility and the variables of height, weight, body mass index, age, percent body fat, and aerobic capacity.The DCS incidence was 46.5% during 1879 subject-exposures by subjects exposed at least 4 times. A significant relationship existed between higher DCS susceptibility and the combination of lower aerobic capacity and greater weight (p0.05).Despite a correlation, less than 13% of the variation in DCS susceptibility was accounted for by the best combination of variables, weight and VO2max.Differences in DCS susceptibility cover a wide range and appear to be related to some anthropometric and physiologic variables. However, there was insufficient correlation to allow prediction of an individual's susceptibility.

Aircraft cabin depressurization is a rare event but one which demands attention because of the grave potential for aircrew incapacity in flight. The purpose of the current study was to determine rates of depressurization incidents for U.S. military aircraft, to examine their causes, and to evaluate the medical importance of these incidents.The U.S. Navy and U.S. Air Force safety center databases were searched for decompression incidents during FY1981-FY2003. A total of 1055 incidents were analyzed as to the cause, speed of onset, and adverse health effects (hypoxia, barotrauma, DCS, or any combination of these). The causes of each incident were identified and classified by aircraft type.The number of incidents per airframe varied from 1 (in many airframes) to 276 in the T-38. The number of total hours flown ranged from 16,332 in the T-6 to 8,101,607 in the C-130. The number of sorties flown ranged from 8800 in the B-2 to 3,543,061 in the C-130. Of 35 common airframes, 30 showed rates between 0 and 20 incidents per million flying hours. Depressurization was "slow" in 83% of incidents. Of the 1055 incidents, only 350 (33.2%) involved adverse health effects. Hypoxia occurred in 221 incidents, DCS in 83, and barotrauma in 71. Only 4 (0.4%) resulted in a fatality. Of the 199 incidents involving hypoxia, 12 (6%) occurred below 4267 m (14,000 ft).Most reported military aircraft depressurization incidents are slow and do not affect aircrew health. Rates have decreased dramatically since the 1980s. Still, this study lends support to continuing hypobaric chamber training for military pilots.

Military aircraft oxygen systems may not always deliver 100% O2. Nitrogen and argon are present to various levels. Determining the effect of these inert gas levels on denitrogenation and decompression sickness (DCS) risk was needed to better manage the operational incidence of DCS. The partial pressure gradient of nitrogen partly determines the extent and rate of denitrogenation during altitude exposure, not the percentage of N2 in the mixture. The degree of denitrogenation influences the extent of bubble formation and DCS incidence. It was found that the increased nitrogen levels in the breathing gas while at altitudes of 18,000 to 25,000 ft did not increase DCS risk. Contrary to the results above 18,000 ft, the use of a high N2 breathing gas at 16,000 ft increased DCS incidence when compared to exposures with 100% O2. It was also found that stage "prebreathing", or in-flight denitrogenation, at 16,000 ft prior to ascent to 25,000 ft is effective in reducing the DCS risk when compared to zero prebreathe exposures.

The zero prebreathe altitude threshold for developing 5% decompression sickness (DCS) symptoms in men has been reported to be 6248 m (20,500 ft). However, such an altitude threshold when 1 h of oxygen prebreathe is used has not been well documented and was the primary purpose of this study.The 51 male human subjects were exposed to 9144 m (30,000 ft), 8382 m (27,500 ft), 7620 m (25,000 ft), and/or 6858 m (22,500 ft) for 8 h. They were monitored for symptoms of DCS and venous gas emboli (VGE).DCS symptom incidence after 4 h of exposure decreased with exposure altitude from 87% at 9144 m to 26% at 6858 m. VGE were lower during the 4-h 6858-m exposures (32%) than at the higher altitudes (76-85%). The symptom incidences during the first 4 h of exposure were lower at 6858 m and 7620 m following a 1-h prebreathe as compared with analogous zero-prebreathe exposures. There were no differences between incidences of VGE or DCS at any of the four altitudes after 8 vs. 4 h of exposure.The altitude threshold for 5% DCS symptoms is below 6858 m after 1 h of prebreathe. However, during 6858-m and 7620-m exposures, a 1-h prebreathe is highly beneficial in reducing DCS incidence and delaying the onset of DCS, keeping the incidence to less than 6% during the first 90 min of exposure. Use of 4-h vs. 8-h exposures does not appear to underestimate DCS risk at or above 7620 m.

Over 80% altitude decompression sickness (DCS) was reported during a 4-h exposure with mild exercise to 7620 m (25,000 ft) without prebreathe. Prebreathe for more than 1 h would be necessary to reduce the DCS risk below 40%. Use of a single period of exercise to enhance prebreathe effectiveness has been successfully tested and used during some U-2 operations. The current tests used multiple exercise sessions to enhance prebreathe (MEEP) as a means of improving denitrogenation efficiency.Two MEEP profiles, 30 or 60 min, preceded 4-h exposures to 7620 m with mild, upper-body exercise while breathing 100% oxygen. Resting prebreathe controls were from published studies at the same laboratory. Both MEEP profiles involved 10 min of strenuous dual-cycle ergometry (75% of maximal oxygen uptake) at the beginning of prebreathe. After a 15-min rest period during the 60-min prebreathe, an additional 5 min of strenuous ergometry was performed. Mild exercise was performed during 15 of the last 20 min of both prebreathe profiles.The 60-min MEEP resulted in 25% DCS and the 30-min MEEP 40% DCS (N.S.). The 25% incidence of DCS following the 60-min MEEP profile was significantly less than the 63% DCS following an equal-time, resting prebreathe control. Following the 30-min MEEP, DCS incidence was not greater than the incidence following a 60-min, resting prebreathe control. There was a lower incidence of venous gas emboli during the MEEP exposures than during resting control exposures.Denitrogenation with multiple periods of exercise provides a shorter alternative to resting prebreathe for reducing DCS risk during exposure to 7620 m.

High altitude exposure has an inherent risk of altitude decompression sickness (DCS). A predictive DCS model was needed to reduce operational risk. To be operationally acceptable, such a theoretical model would need to be validated in the laboratory using human subjects.The Air Force Research Laboratory (AFRL) has conducted numerous studies on human subjects exposed to simulated altitudes in hypobaric chambers. The database from those studies was used to develop a statistical altitude DCS model. In addition, a bubble growth model was developed using a finite difference method to solve for bubble radius as a function of time. The bubble growth model, integrated with the statistical model, constitutes the AFRL DCS Risk Assessment Model. Validation of the model was accomplished by comparing computer predictions of DCS risk with results from subsequent prospective human subject exposures. There were five exposure profiles, not previously found in the database, covering a wide parameter of ranges of altitude (18,000-35,000 ft), exposure time (180-360 min), prebreathe time (0-90 min), and activity level (rest-strenuous) that were used. The subjects were monitored for DCS symptoms and venous gas emboli.There were 30 subjects who were exposed to each of the 5 altitude profiles. The DCS incidence onset curves predicted by the model were not significantly different from the experimental values for all scenarios tested and were generally within +/- 5% of the actual values.A predictive altitude DCS model was successfully developed and validated.

Altitude decompression sickness (DCS) is a health risk associated with the conduct of high altitude airdrop operations, high altitude reconnaissance, future fighter operations, hypobaric chamber training, unpressurized flight, and extravehicular activity (EVA) in space. The treatment for DCS includes the provision of 100% oxygen (O2) at ground level (GLO) and/or hyperbaric oxygen therapy (HBO). In this paper we examine the effect of repressurization to ground level from hypobaric conditions on DCS symptoms. Timely recompression (descent at first recognition of any DCS symptom) may be a safe, effective treatment for the large majority of DCS symptoms.Data from altitude chamber exposures recorded in the Air Force Research Laboratory (AFRL) Altitude DCS Database were reviewed to determine the level of recompression required for complete resolution of 1,699 observed symptoms.Of the 1,699 DCS symptoms reviewed, 66 (3.9%) resolved at altitude, 117 (6.9%) resolved at ground level, and 1,433 (84.3%) resolved during descent. Increasing the pressure by 138 mmHg from the altitude of exposure where symptoms occurred resolved roughly 50% of symptoms. Little resolution of symptoms was noted with recompressions of50 mmHg. The greatest rate of symptom resolution occurred with recompressions of 50-250 mmHg.These findings support the concept that descent and postflight, ground-level oxygen may be sufficient to relieve the majority of altitude DCS symptoms. HBO may be reserved for serious, recurring, delayed, or refractory symptoms. The findings also suggest a need for further study of DCS symptom resolution.

The current extravehicular activity (EVA) space suit at 4.3 psia causes hand and arm fatigue and is too heavy for Martian EVA. A 3.5 psia EVA pressure suit requires increased preoxygenation time but would reduce structural complexity, leak rate, and weight while increasing mobility, comfort, and maintainability. On Mars, nitrogen and argon are available to provide the inert gas necessary for a fire-resistant habitat atmosphere, eliminating need for transport. This study investigated breathing argon/oxygen and 100% oxygen gas mixtures during staged decompression prior to exposure to 3.5 psia.During this study, 40 subjects each completed 3 hypobaric exposures to 3.5 psia for 3 h in a reclined position: (A) a 4-h 25-min 14.7-psia (ground level) denitrogenation (100% oxygen breathing) prior to exposure to 3.5 psia; (B) the same as A, utilizing a 7.3-psia stage denitrogenation; and (C) the same as B, with 62% argon-38% oxygen (ARGOX) during the stage. Venous gas emboli (VGE) were monitored with echocardiography.Decompression sickness (DCS) incidence at 3.5 psia with ARGOX at 7.3 psia (C) was significantly higher than with oxygen breathing with or without staged decompression: there was 78% DCS for C compared with 33% and 55% DCS, respectively, for A and B. The corresponding VGE incidences were 73% (C) compared with 33% (A) and 45% (B).Preoxygenation at a 7.3-psia stage resulted in a higher DCS risk at 3.5 psia than ground level preoxygenation. It is suggested that an 8.0-psia stage pressure could eliminate this difference. Unfavorable results after preoxygenation with ARGOX indicate argon on-gassing was significant.

Loss of aircraft cabin pressurization can result in very rapid decompression rates. The literature contains reports of increased or unchanged levels of altitude decompression sickness (DCS) resulting from increasing the rate of decompression. We conducted two prospective exposure profiles to quantify the DCS risk at 12,192 m (40,000 ft), and to determine if there was a greater DCS hazard associated with a much higher rate of decompression than typically used during past DCS studies.The 63 human subjects participated in 80 altitude chamber decompression exposures to a simulated altitude of 12,192 m (2.72 psia; 18.75 kPa) for 90 min, following preoxygenation with 100% oxygen for 90 min. Half of the subject-exposures involved an 8-min decompression (1,524 mpm; 5,000 fpm) and the other half experienced a 30-s decompression (mean of 24,384 mpm; 80,000 fpm). Throughout each ascent and exposure, subjects were seated at rest and breathed 100% oxygen. At altitude, they were monitored for precordial venous gas emboli (VGE) and DCS symptoms.The higher decompression rate yielded 55.0% DCS and 72.5% VGE and the lower rate produced 47.5% DCS and 65.0% VGE. Chi square and log rank tests based on the Kaplan-Meier analyses indicated no difference in the incidence or onset rate of DCS or VGE observed during the two profiles.Decompression rate to altitude up to 24,384 mpm was found not to have an effect on DCS risk at altitude. However, research is needed to define the DCS risk with decompression rates greater than 24,384 mpm. It was also found that the onset time to DCS symptoms decreases as altitude increases.

Early, retrospective reports of the incidence of altitude decompression sickness (DCS) during altitude chamber training exposures indicated that women were more susceptible than men. We hypothesized that a controlled, prospective study would show no significant difference.We conducted 25 altitude chamber decompression exposure profiles. A total of 291 human subjects, 197 men and 94 women, underwent 961 exposures to simulated altitude for up to 8 h, using zero to 4 h of preoxygenation. Throughout the exposures, subjects breathed 100% oxygen, rested or performed mild or strenuous exercise, and were monitored for precordial venous gas emboli (VGE) and DCS symptoms.No significant differences in DCS incidence were observed between men (49.5%) and women (45.3%). However, VGE occurred at significantly higher rates among men than women under the same exposure conditions, 69.3% and 55.0% respectively. Women using hormonal contraception showed significantly greater susceptibility to DCS than those not using hormonal contraception during the latter two weeks of the menstrual cycle. Significantly higher DCS incidence was observed in the heaviest men, in women with the highest body fat, and in subjects with the highest body mass indices and lowest levels of fitness.No differences in altitude DCS incidence were observed between the sexes under our test conditions, although men developed VGE more often than women. Age and height showed no significant influence on DCS incidence, but persons of either sex with higher body mass index and lower physical fitness developed DCS more frequently.

Since strenuous exercise for 10 min during preoxygenation was shown to provide better protection from decompression sickness (DCS) incidence than resting preoxygenation, a logical question was: would a longer period of strenuous exercise improve protection even further?Increased strenuous exercise duration during preoxygenation increases DCS protection.There were 60 subjects, 30 men and 30 women, who were exposed to 9,144 m (4.3 psia) for 4 h while performing mild, upper body exercise. Before the exposures, each subject performed three preoxygenation profiles on different days in balanced order: a 90-min resting preoxygenation control; a 240-min resting preoxygenation control; and a 90-min preoxygenation including exercise during the first 15 min. The subjects were monitored at altitude for venous gas emboli (VGE) with an echo-imaging system and observed for signs and symptoms of DCS.There were no significant differences in occurrence of DCS following any of the three preoxygenation procedures. Results were also comparable to an earlier report of 42% DCS with a 60-min preoxygenation including a 10-min exercise. There was no difference between VGE incidence in the comparison of protection offered by a 90-min preoxygenation with or without 13 min of strenuous exercise. The DCS incidence following a 240-min resting preoxygenation, 40%, was higher than observed during NASA studies and nearly identical with the earlier 42% DCS after a 60-min preoxygenation including exercise during the first 10 min.The protection offered by a 10 min exercise in a 60-min preoxygenation was not increased with extension of the preoxygenation exercise period to 15 min in a 90-min preoxygenation, indicating an upper time limit to the beneficial effects of strenuous exercise.

INTRODUCTION: Early, retrospective reports of the incidence of altitude decompression sickness (DCS) during altitude chamber training exposures indicated that women were more susceptible than men. We hypothesized that a controlled, prospective study would show no significant difference. METHODS: We conducted 25 altitude chamber decompression exposure profiles. A total of 291 human subjects, 197 men and 94 women, underwent 961 exposures to simulated altitude for up to 8 h, using zero to 4 h of preoxygenation. Throughout the exposures, subjects breathed 100% oxygen, rested or performed mild or strenuous exercise, and were monitored for precordial venous gas emboli (VGE) and DCS symptoms. RESULTS: No significant differences in DCS incidence were observed between men (49.5%) and women (45.3%). However, VGE occurred at significantly higher rates among men than women under the same exposure conditions, 69.3% and 55.0% respectively. Women using hormonal contraception showed significantly greater susceptibility to DCS than those not using hormonal contraception during the latter two weeks of the menstrual cycle. Significantly higher DCS incidence was observed in the heaviest men, in women with the highest body fat, and in subjects with the highest body mass indices and lowest levels of fitness. CONCLUSION: No differences in altitude DCS incidence were observed between the sexes under our test conditions, although men developed VGE more often than women. Age and height showed no significant influence on DCS incidence, but persons of either sex with higher body mass index and lower physical fitness developed DCS more frequently.

The objective of this study was to determine the effect of exercise after altitude exposure (post-exposure exercise) on subsequent altitude decompression sickness (DCS) incidence. Existing USAF prohibition of exercise following altitude chamber training exposures and interest from operational personnel prompted our evaluation of post-exposure exercise as a DCS-inducing stressor.After a 1-h resting preoxygenation, 67 subjects were exposed to 30,000 ft for 2-h while performing mild, upper body exercise. The subjects were monitored for venous gas emboli (VGE) with an echo-imaging system and observed for signs and symptoms of DCS. Subjects without DCS (n = 31) or with DCS which resolved during recompression (n = 29) were randomly assigned to post-exposure rest (control, n = 29) or moderate exercise (50% of peak oxygen uptake, dual-cycle ergometry; n = 31) and both groups were monitored for delayed or recurring DCS.The altitude exposure resulted in 48.3% DCS in the 60 volunteers serving as test or control subjects. Of 31 subjects assigned to the post-exposure exercise group, 15 had developed DCS which resolved during descent. No cases of DCS were observed or reported during or following post-exposure exercise.The results show that moderate exercise after exposure did not result in either delayed-onset or recurring DCS.

Repeated altitude exposures in a single day occur during special operations parachute training, hypobaric chamber training, unpressurized flight, and extravehicular space activity. Inconsistent and contradictory information exists regarding the risk of decompression sickness (DCS) during such hypobaric exposures.We hypothesized that four short exposures to altitude with and without ground intervals would result in a lower incidence of DCS than a single exposure of equal duration.The 32 subjects were exposed to 3 different hypobaric exposures--condition A: 2 h continuous exposure (control); condition B: four 30-min exposures with descent/ascent but no ground interval between the exposures; condition C: four 30-min exposures with descent/ascent and 60 min of ground interval breathing air between exposures. All exposures were to 25,000 ft with 100% oxygen breathing. Subjects were observed for symptoms of DCS, and precordial monitoring of venous gas emboli (VGE) was accomplished with a SONOS 1000 echo-imaging system.DCS occurred in 19 subjects during A (mean onset 70+/-29 min), 7 subjects in B (60+/-34 min), and 2 subjects in C (40+/-18 min). There was a significant difference in DCS incidence between B and A (p = 0.0015) and C and A (p = 0.0002), but no significant difference between B and C. There were 28 cases of VGE in A (mean onset 30+/-23 min), 21 in B (41+/-35 min), and 21 in C (41+/-32 min) with a significant onset curve difference between B and A and between C and A, but not between B and C. Exposure A resulted in four cases of serious respiratory/neurological symptoms, while B had one and C had none. All symptoms resolved during recompression to ground level.Data indicate that repeated simulated altitude exposures to 25,000 ft significantly reduce DCS and VGE incidence compared with a single continuous altitude exposure.

Inclusion of females in combat roles places some of them in cockpits where decompression sickness (DCS) in their male counterparts occurs on a routine basis. A retrospective review of data from 765,216 training chamber exposures indicated females are 4.6 times more susceptible to DCS than males (0.224% in females versus 0.049% in males). Relevant published data from research chamber human subject protocols are scarce and equivocal. A research chamber study comparing female and male susceptibility to DCS was initiated at the Armstrong Laboratory at Brooks AF03, TX. The six-h, zero-preoxygenation exposures used a breathing gas of 100% oxygen during exposure and subjects performed mild exercises while decompressed. Altitude of exposure in It, number of subjects and gender (M or F), and % DCS incidence were, respectively: 15,000, lOM, 0%; 16,500, 8M, 0%; 18,100, lOM, 0%, lOF, 0%; 19,800, lOM, 0%, lOF, 10%; 21,200, 17M, 6%; 22,500, 18M, 50%, 2F, 0%; 23,800, lOM, 50%. No statistical comparison could be made of DCS susceptibility due to the low number of female subjects exposed at the altitudes where DCS was common in male subjects. Further research is needed at higher altitudes under identical conditions with both genders to enable comparisons of DCS susceptibility.

Howard's teachers say he just isn't working up to his ability. He doesn't finish his assignments, or just puts down answers without showing his work; his handwriting and spelling are poor. He sits and fidgets in class, talks to others, and often disrupts class by interrupting others. He used to shout out the answers to the teachers' questions (they were usually right), but now he daydreams a lot and seems distracted. Does Howard have attention deficit hyperactivity disorder (ADHD), is he gifted, or both? Frequently, bright children have been referred to psychologists or pediatricians because they exhibited certain behaviors (e.g., restlessness, inattention, impulsivity, high activity level, daydreaming) commonly associated with a diagnosis of ADHD. Formally, the Diagnostic and Statistical Manual of Mental Disorders (DSM-III-R) (American Psychiatric Association) lists 14 characteristics that may be found in children diagnosed as having ADHD. Almost all of these behaviors, however, might be found in bright, talented, creative, gifted children. Until now, little attention has been given to the similarities and differences between the two groups. Sometimes, professionals have diagnosed ADHD by simply listening to parent or teacher descriptions of the child's behaviors along with a brief observation of the child. Other times, brief screening questionnaires are used, although these questionnaires only quantify the parents' or teachers' descriptions of the behaviors (Parker, 1992). Children who are fortunate enough to have a thorough physical evaluation (which includes screening for allergies and other metabolic disorders) and extensive psychological evaluations, which include assessment of intelligence, achievement, and emotional status, have a better chance of being accurately identified. How Can Parents or Teachers Distinguish Between ADHD and Giftedness? Seeing the difference between behaviors that are sometimes associated with giftedness but also characteristic of ADHD is not easy. Consider the Situation and Setting It is important to examine the situations in which a child's behaviors are problematic. Gifted children typically do not exhibit problems in all situations. For example, they may be seen as ADHD-like by one classroom teacher, but not by another; or they may be seen as ADHD at school, but not by the scout leader or music teacher. Close examination of the troublesome situation generally reveals other factors which are prompting the problem behaviors. By contrast, children with ADHD typically exhibit the problem behaviors in virtually all settings--including at home and at school--though the extent of their problem behaviors may fluctuate significantly from setting to setting (Barkley, 1990), depending largely on the structure of that situation. That is, the behaviors exist in all settings, but are more of a problem in some settings than in others. In the classroom, a gifted child's perceived inability to stay on task might be related to boredom, curriculum, mismatched learning style, or other environmental factors. Gifted children may spend from one fourth to one half of their regular classroom time waiting for others to catch up--even more if they are in a heterogeneously grouped class. Their specific level of academic achievement is often two to four grade levels above their actual grade placement. Such children often respond to nonchallenging or slow-moving classroom situations by "off-task" behavior, disruptions, or other attempts at self-amusement. This use of extra time is often the cause of the referral for an ADHD evaluation. Hyperactive is a word often used to describe gifted children as well as children with ADHD. As with attention span, children with ADHD have a high activity level, but this activity level is often found across situations (Barkley, 1990). A large proportion of gifted children are highly active too. …