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At least 253 records · Page 14Linked to original sources
PubMed2000

The protection against +Gz afforded by pressure breathing with different pressure schedules.

OBJECTIVE: System of pressure breathing for +Gz (PBG) has been incorporated into service in the high performance fighter aircraft, but there were significant differences among PBG pressure schedules used in different countries. The purpose of this study was to define an optimal pressure schedule in PBG system. METHOD: Five male subjects wearing GZ-2 anti-G suit and medium-sized bladder vest, plus PBG with 1.6, 2.4, and 3.2 kPa/G pressure schedules, respectively, were exposed to rapid onset (3.0 G/s) centrifuge +Gz runs. +Gz protection of PBG with each of the three pressure schedules were measured and the subjective ratings were collected. RESULT: The +Gz protection afforded by PBG with 1.60, 2.40, and 3.20 kPa/G pressure schedules were 2.00 +/- 0.31, 2.54 +/- 0.32, and 2.44 +/- 0.31 G, respectively. Subjective ratings showed that the PBG with 2.40 kPa/G pressure schedule was better than the other two. CONCLUSION: Our data suggest that a PBG pressure schedule of 2.4 kPa/G in PBG system is optimal. It not only assures the anti-G performance of PBG, but also reduces its side effects.

Acceleration↗
PubMed1998

Effect of G suit type on cognitive performance.

BACKGROUND: Sustained acceleration protection ensembles are being developed to help pilots of high performance aircraft endure high G exposures for longer periods of time. It has been assumed that better G endurance confers better pilot task performance. This premise was studied on the Armstrong Laboratory Dynamic Environment Simulator centrifuge. METHOD: Human subjects repeatedly endured prolonged high-G simulated aerial combat on a centrifuge to the point of loss of vision or physical exhaustion. Some profiles included over 20 exposures to +9 Gz. While enduring the G exposures, subjects tracked a simulated "bogey" aircraft on a visual display and performed a secondary task. Measures of cognitive function and physiologic status were taken throughout the exposures. G protection ensembles included the standard CSU 13 B/P anti-G suit, the Advanced Technology Anti-G Suit (ATAGS), COMBAT EDGE positive pressure breathing system with the CSU 13 B/P, COMBAT EDGE with ATAGS, and the Northrop Advanced Protection System (APS). RESULTS: More advanced protective systems not only allow longer G endurance, but provide adequate support for maintained cognitive performance throughout the extended exposure. Although measures were affected by the type of protective system the subject was wearing, as well as individual ability and coping strategies, consistent target tracking task performance, rapid choice reaction time, and sufficient arterial oxygen saturation were maintained throughout extended exposures to a point preceding termination by only a second or two. CONCLUSIONS: Those anti-G protection ensembles that cover and protect the body and which employ positive pressure breathing allow longer high G exposures which provide support for maintained cognitive performance.

Adaptation, Psychological↗
PubMed2001

Simulated shuttle egress: comparison of two Space Shuttle protective garments.

BACKGROUND: In a previous study from our laboratory, we observed carbon dioxide (CO2) accumulation in the helmet of the NASA Launch and Entry Suit (LES) during a simulated emergency egress from the Space Shuttle. Of 12 subjects, 8 were unable to complete the egress simulation with a G-suit inflation pressure of 1.5 psi. The purpose of this report was to compare CO2 accumulation and egress walking time in the new Advanced Crew Escape Suit (ACES) with that in the LES. METHODS: Four male subjects who previously were unable to complete the egress in the LES performed a simulated egress while wearing the ACES with the G-suit inflated to 1.5 psi. The egress simulation consisted of 6 min of seated rest, 2 min of standing, and 5 min of walking on a treadmill at 1.56 m x s(-1) (3.5 mph) and 0% grade. The helmet visor was closed with the subjects receiving 100% oxygen throughout the simulation. Inspired CO2 and walking time were measured. RESULTS: The rate of CO2 accumulation was significantly less (ACES: 0.53 +/- 0.03, LES: 1.07 +/- 0.15 %CO2 x min(-1); p = 0.05) and walk time was greater in the ACES (ACES: 5.0 +/- 0.0, LES: 2.7 +/- 0.2 min; p = 0.002). CONCLUSIONS: Changes in the design of the ACES from the LES resulted in a decreased rate of CO2 accumulation and an improved egress walking time compared with the LES.

Adult↗
PubMedDate not supplied

[+Gx-tolerance by the Cosmonauts of ISS crews 1, 6-9 and visiting crews 1-7 aboard Soyuz vehicles].

Analysis of +Gx tolerance of 15 members of short-term ISS missions and 9 members of long-term ISS missions aboard the Soyuz vehicles showed good tolerance during insertion and satisfactory during descent provided the use of in-flight countermeasures and anti-g suit Kentaur inside the vehicle. Objective data about the tolerance of off-nominal +Gx (6.26 and 8.1 G) pointed to a more pronounced sinus tachycardia and tachypnea in a ballistic descent following long-duration weightlessness as compared with nominal. Physiological deviations were transient, functional by character. Cardiac arrhythmia was largely observed during return to Earth. Two cosmonauts were found to develop prognostically unfavorable ECG indications during off-nominal descent. Main factors in these deviations could be age (above 45) and existence of some individual specifics of cardiac rhythm regulation. These results emphasize the necessity of more careful screening of candidates older than 45 years, as weightlessness may impact their general condition and tolerance of g-loads during return to Earth.

Adult↗
PubMed1986

Decompression sickness and intravenous bubble formation using a 7.8 psia simulated pressure-suit environment.

The purpose of this study was to determine the minimum spacesuit pressure required to prevent decompression sickness (DCS) during operational conditions in a 50% oxygen/50% nitrogen environment. In this study, 30 male volunteer subjects were exposed in groups of three, to three consecutive daily extravehicular activity (EVA) simulations at 7.8 psia (5,031 m altitude equivalent) for a continuous period of 6 h. During each altitude exposure, the subjects participated in similar exercise workloads expected to be experienced by astronauts during a typical EVA scenario. Precordial Doppler monitoring revealed that 73.3% of the subjects had intravenous bubbling during at least 1 d of the 3 d of exposure, with 26.7% remaining bubble-free during the entire study. No correlation was found between either body fat or age and incidence of bubble formation. One case of DCS occurred during the study indicating that 7.8 psia is not sufficient pressure to totally preclude DCS in a 50% oxygen/50% nitrogen environment. The necessary pressure awaits further study.

Adult↗
PubMedDate not supplied

[Study of mechanisms of the antihypotensive effects of antishock suits in injured with traumatic shock].

The mechanisms of antihypotensive action of antishock overalls (ASO) were studied on the basis of comparison of 30 patients with traumatic shock at the prehospital stage of medical care; in 15 of these ASO was used, in the other 15 traditional antishock intensive care. Use of a portable device for noninvasive measurement of cardiac stroke volume at the prehospital stage permitted us detect the principal mechanisms of liquidation of shock-induced arterial hypotension with the use of ASO: increase of cardiac output at the expense of autohemotransfusion from the lower part of the body to the upper vital organs with increase in the volume of venous blood restitution to the heart, the increase of total peripheral vascular resistance being negligible. Use of ASO in a complex of intensive care measures for the treatment of traumatic shock at the prehospital stage is physiological and conducive to optimization of medical care rendered to victims at the early stages of treatment.

Adolescent↗
PubMed1985

Factors affecting human tolerance to sustained acceleration.

Linear increases in G tolerance with increases in anti-G suit (AGS) bladder inflation pressure occurred when relaxed subjects were exposed to acceleration plateaus while riding a centrifuge and were either seated upright, (15 degrees seat back angle or SBA) or supine (60 degrees SBA). Supine G tolerance with AGS bladder inflation decreased as G onset time was increased by factors of two and four. Changing the mode of operation of a new servo-controlled anti-G valve regulating AGS bladder pressure had no effect on G tolerance nor on AGS comfort scores. Comfort was unaffected by G onset time and reduced with high AGS bladder pressures. Results support the hypotheses that G protection provided by simultaneously applied anti-G techniques is additive and that the simple hydrostatic model of the circulatory system can adequately account for AGS bladder pressure changes required for G protection when body position is changed.

Acceleration↗
PubMed2003

[Effects of extended flight factors on +Gz tolerance].

Tolerance of single-seat fighter pilots to +Gz loads in long missions was evaluated. In centrifuge experiments, after 5-hr flight simulation 6 test-subjects were exposed to +Gz with a growth rate of 0.1 u/s using muscular relaxation but not anti-G suit (AGS), and to complex-profile ultimate +Gz (2.0 to 9.0 units) with a growth rate of 1.0 u/s with AGS-3 and anti-G straining maneuvers. Pre-experimental data about the subjects' tolerance to +Gz by similar protocols were used as control. Hemodynamic parameters were measured during and immediately after centrifugation. Strength of the leg muscular effort was determined during the centrifuge runs. External respiration and gas exchange parameters were evaluated immediately after centrifugation. Results of the experiments made it evident that 5-hr flight simulation impairs pilot's functional state and tolerance of high +Gz loads, as incidence and severity of visual disorders and cardiac arrhythmias rose and energy expenditure and cervical muscles fatigue increased pointing to the necessity to develop a special purpose preventive system.

Acceleration↗
PubMed1988

Effect of longitudinal physical training and water immersion on orthostatic tolerance in men.

To test the hypothesis that moderately intense physical training has no effect on orthostasis, orthostatic and fluid-electrolyte-endocrine responses to 60 degrees head-up tilt were compared before and after 6 h of water immersion (34.5 +/- 0.1 degrees C) up to the neck following 6 months of exercise training. During the tilt test the five male subjects (27-42 years) each wore a lower-body positive-pressure suit (MAST-111A antishock trousers). The tilt procedure consisted of a 40-min supine control period (suit deflated), followed by a maximum 90-min tilt period (suit inflated to 50 +/- 5 mm Hg for 30 min, then deflated for 60 min or until presyncope). The mean +/- S.E. pretraining cycle ergometer peak VO2 was 3.20 +/- 0.14 L.min-1 (39 +/- 2 ml.min-1.kg-1), 3.36 +/- 0.27 L.min-1 (42 +/- 4 ml.min-1.kg-1) after 3 months (N.S.), and increased by 18% to 3.78 +/- 0.36 L.min-1 (48 +/- 5 ml.min-1.kg-1, +22%, p less than 0.05) posttraining. During pretraining, water immersion tilt tolerance decreased from 74 +/- 16 min before to 34 +/- 9 min (delta = 40 min, p less than 0.05) after immersion. During posttraining, water immersion tilt tolerance decreased similarly from 74 +/- 16 min preimmersion to 44 +/- 13 min (delta = 30 min, p less than 0.05) postimmersion (74 vs. 74 min, N.S.; 34 vs. 44 min, N.S.).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1984

Effect of circumferential pneumatic compression devices on digital flow.

We reviewed the effects of circumferential pneumatic compression suits (CPCS) when applied to normal and ischemic limbs without prior application of prehospital orthopedic traction devices beneath the garment. The digital arterial toe pressures of 11 normal and six claudicating limbs were measured with the trouser applied and the limbs pressurized to 40, 60, 80, and 100 mm Hg. In addition, normal limbs had the Hare traction device and the Sager splint applied prior to application of the trouser and retesting of the digital arterial flow. We conclude that CPCS prevents flow into the limbs, and this may potentiate the development of compartment syndromes in the previously traumatized or ischemic limbs. Normal limbs with traction devices already applied may be at a higher risk for compartment syndromes, and we suggest that patients with fractured limbs who are in need of CPCS not have the traction device applied.

Blood Pressure↗
PubMed1988

Optimum sampling times for maximum blood lactate levels after exposures to sustained +Gz.

Six male subjects wearing anti-G suits were exposed to +4.5 Gz and +4.5-7 Gz simulated aerial combat maneuvers (SACM), sustained until terminated because of fatigue. Before and after each G exposure, venous blood was withdrawn (using the finger-prick method) and analyzed for lactate concentration. Five samples were taken serially, at 1, 3, 6, 10, and 20 min after each G exposure to determine the maximum (peak) level of blood lactate. Individual lactate levels varied, with peaks at 1, 3, and 6 min; however, group levels were maximum at 3 min after the G exposure. Maximum lactate levels (mean +/- S.D.) of 27.8 +/- 11.3 mg% and 42.7 +/- 19.4 mg% were found for the 4.5-G and SACM exposures, respectively. Lactate recoveries were a simple exponential function, with a half life of approximately 10 min. The relationship between these data, following G exposure, and those measured after aerobic physical activities, is discussed.

Gravitation↗
PubMed1994

G-LOC recovery with and without G-suit inflation.

During acceleration (+Gz) training in the human centrifuge, the anti-G suit (AGS) is usually deflated as acceleration decreases upon termination of the exposure, regardless of the reason for termination, including +Gz-induced loss of consciousness (G-LOC). This is when the trainee most needs the support provided by the AGS. A method to reduce the time of incapacitation resulting from G-LOC was evaluated. The standard CSU15-P suit worn by 30 aircrew while undergoing +Gz tolerance training was inflated to 10 psi immediately upon G-LOC (GS group). Incapacitation times and flailing activity were recorded and compared with 51 aircrew whose AGS was not abruptly inflated upon G-LOC (NGS group). Absolute incapacitation was significantly different between both groups (p = 0.024). The GS group exhibited flailing behavior for a longer period of time during relative incapacitation than the NGS group (p = 0.0003). Total incapacitation remained unaffected. A brief period of confusion occasionally accompanied by mimic or myoclonic convulsions was observed more often in the GS group. Inflation of the AGS upon G-LOC seems to reduce absolute incapacitation by approximately 2 s, thereby causing the trainee to be aware of his environment and G-LOC more quickly, even though his motor function has not yet been fully restored.

Acceleration↗
PubMed1992

G-endurance during heat stress and balanced pressure breathing.

The effect of heat stress and balanced pressure breathing during G (PBG) on G-endurance was investigated. Ten fighter pilots wearing anti-G-suits with increased bladder coverage were warmed to 38.2 degrees C and exposed to 15-s periods at 4.5 and 7 G in a heated human centrifuge gondola until exhaustion during PBG and normal breathing (NB). During both NB and PBG, the rectal temperature rose to a mean of 38.3 degrees C, and the dehydration was about 1.2 kg. With NB the endurance was a mean of 254 s, while it was 300 s with PBG (n.s.). Oxygen saturation and ratings of perceived exertion were mainly unchanged, while the maximum heart rate decreased by a mean of 13 bpm during PBG. In conclusion, the G-endurance was not deteriorated with PBG, in comparison with NB, during heat stress. In conjunction with experiences from other studies, however, it emphasizes the importance of avoiding heat stress and dehydration during G-loads, even with PBG.

Adult↗
PubMed1988

High-G stress and orientational stress: physiologic effects of aerial maneuvering.

G stress can readily incapacitate pilots of modern fighter aircraft and result in mishaps due to G-induced loss of consciousness (GLC). The physiologic effects of high-G stress, including decreased head-level blood pressure due to hydrostatic pressure drop and decreased cardiac output due to inadequate venous return, result in the symptoms of visual loss and GLC. The body's primary natural defenses against the effects of G stress in flight, i.e., the neural tissue energy reserve and the cardiovascular baroceptor reflexes, determine the characteristic shape of the G-time tolerance curve, which is presented. Means of raising G tolerance fall into three categories: mechanical, physiological, and educational. Mechanical means include anti-G suits and valves, assisted positive-pressure breathing (APPB) systems, and special seats in which the seatback is reclined and/or the pilot's legs are elevated. Physiological means include frequent exposure to G stress, physical conditioning (weight training and moderate aerobic conditioning), selection of pilots for high natural tolerance, and performance of a vigorous and efficient anti-G straining maneuver. Educational means include briefings on methods of enhancing tolerance, and high-G training in a centrifuge to allow the pilot to perfect his anti-G straining maneuver. An improved anti-G valve, physical conditioning, high-G awareness briefings, and centrifuge training are now being applied in efforts to prevent GLC in current fighter aircraft. Future generations of even more maneuverable aircraft will probably necessitate the use of APPB, pilot selection, and high-G seats for protection of pilots from the effect of sustained high G forces.

Aerospace Medicine↗
PubMed2000

Mathematical models for predicting G-duration tolerances.

Mathematical models that predict fatigue-based G-duration tolerances for relaxed and straining subjects are developed and validated using published data. These models are based on regression analysis calculations using published G-duration tolerance data of relaxed subjects exposed to 3-5 G and subjects exposed to 6-9 G using an anti-G suit and performing the anti-G straining maneuver. These G-duration models are derived from published G-level tolerance models based on intravascular hydrostatic pressures and physiologic responses to maximum voluntary contractions (MVC%). Included in the validation of these models are the baroreceptor and muscle contraction cardiovascular reflexes that support arterial BP. A basic energy pool that supports a G-duration of 140 s for G exposures > 5 G is theorized. Because of the long duration of sustained G exposures in these models, the physiologic dynamics involved in predicting straining G-duration tolerances, are identified and validated using different time periods, i.e., Phases I and II. These models, based on sustained G exposures to a constant G level are also applicable to exposures of variable G levels known as simulated aerial combat maneuver (SACM) G-profile tolerances. G-duration tolerances > 9 G are predicted using these models for subjects using reclined-seat backs and positive pressure breathing.

Aerospace Medicine↗
PubMed1998

Female exposure to high G: effects of simulated combat sorties on cerebral and arterial O2 saturation.

BACKGROUND: One of the key factors in maintaining optimal cognitive performance in the high-G environment is the adequate delivery of oxygen to the cerebral tissue. As eye-level blood pressure is compromised at 22 mmHg x G(-1), perfusion to the peripheral cerebral tissues (cerebral cortex) may not be adequate to support the mental demands of flight. This study measured the effect of closed-loop flight simulations (3 min) on cerebral oxygen saturation changes (rSO2), arterial oxygen saturation (SAO2), and heart rate (HR), in both rested (8 h of rest) and sleepless (24 h without sleep) conditions. METHODS: Subjects (16; 8 males and 8 females) were subjected to G-exposures via closed-loop flight simulations in a series of four 3-min sorties flown by subjects on the Dynamic Environment Simulator (centrifuge) in either a rested or a sleepless state. Prior to the centrifuge flight, subjects were instrumented with sensors for measurement of arterial oxygen saturation (SAO2) and regional cerebral tissue oxygenation (rSO2). Subjects wore the standard flight suit, boots, CSU-13B/P anti-G suit, and the COMBAT EDGE positive-pressure breathing for G-protection system. RESULTS: Significant changes in cerebral and arterial oxygen saturation were observed within groups when comparing pretest baselines and minimum values during the test and pre- and post-G rSO2, SAO2, and HR in both the rested and sleepless state, (p # 0.01), respectively, for each group. Comparisons between groups showed women to have significantly smaller regional cerebral cortex oxygen decreases than men (p # 0.01). No significant changes in SAO2, however, were observed between groups. Both men and women showed a slow recovery of rSO2 values to the prebaseline levels. CONCLUSIONS: Sleeplessness had no effect on the rSO2, SAO2, and HR compared with the rested condition. During acceleration, regional cerebral tissue oxygen decreased 13% in men compared with 9% in women. The recovery of cerebral tissue oxygen levels to prebaseline values was retarded somewhat when compared with the recovery response of arterial oxygen saturation.

Adult↗
PubMed1999

Premature ventricular contractions during +Gz with and without pressure breathing and extended coverage anti-G suit.

BACKGROUND: High +Gz is known to provoke cardiac dysrhythmias. Pressure breathing during G (PBG) and extended coverage anti-G suits (ECGS) are used to enhance +Gz-endurance and reduce fatigue during high +Gz flying. It is not known whether PBG in combination with ECGS increases the risk for premature ventricular contractions (PVC). HYPOTHESIS: PBG in combination with ECGS increases the risk of PVCs during high +Gz-loads. METHODS: Retrospective data were obtained from 14 subjects exposed to three different simulated aerial combat sorties each, in the centrifuge with a standard anti-G suit ensemble or with PBG in combination with ECGS. Each sortie consisted of a gradual onset G-exposure (GOR) and three simulated aerial combat maneuvers (SACM) containing four cycles of a +4.5 to +7 GzSACM; four cycles of +4 to +9 Gz tactical aerial combat maneuver (TACM) with several rapid transitions from +4 or +5 Gz to +8 or +9 Gz; and four cycles of +5 to +9 Gz SACM (5-9 SACM) with four cycles. ECG was recorded during the +Gz exposures to reveal any cardiac dysrhythmias. RESULTS AND CONCLUSIONS: No PVCs occurred during the GORs. During 4.5-7 SACMs, TACMs, and 5-9 SACMs there were 83, 50, and 24 PVCs with standard equipment, respectively, and 63, 54, and 39 PVCs with PBG and ECGS, respectively. There was no statistically significant difference between the equipment in any of the different types of +Gz exposures. No episodes of supraventricular tachycardia or relative bradycardia were found with either equipment.

Adult↗
PubMed1988

Abnormal orthostatic changes in blood pressure and heart rate in subjects with intact sympathetic nervous function: evidence for excessive venous pooling.

The normal ranges of orthostatic changes in blood pressure and heart rate have been defined in 92 individuals aged 18 to 64 years. In 34 individuals whose symptoms (especially orthostatic light-headedness) suggested cerebral ischemia, but in whom none of the known causes of orthostatic hypotension could be identified, we have found one or more of five theoretically possible orthostatic circulatory derangements: systolic hypotension, diastolic hypotension, diastolic hypertension, excessive narrowing of the pulse pressure, and tachycardia after standing for at least 3 minutes. The orthostatic disorders of blood pressure and heart rate identified in the 34 patients were significantly reduced, almost always into the normal range, by external pressure of 45 to 50 mm Hg applied through an inflatable pressure suit. After labeling with sodium pertechnetate Tc 99m and reinjecting the erythrocytes contained in 3 to 6 ml blood, external gamma counting over a fixed site in the calf, both in the recumbent and in the standing posture, showed excessive gravitational pooling of blood in the legs of five patients with orthostatic diastolic hypertension, of four with orthostatic narrowing of the pulse pressure, and of 10 with orthostatic tachycardia alone. Plasma norepinephrine concentrations were usually normal in recumbency and elevated above normal limits during standing for 15 to 30 minutes in the 18 patients so observed. Red cell mass, plasma volume, and circulating blood volume were subnormal in more than half the seven patients in whom these measurements were made. We conclude that most of the patients with idiopathic sympathicotonic abnormalities of orthostatic blood pressure control have a venous pooling syndrome often aggravated by hypovolemia, the cause(s) of which remains to be determined.

Adolescent↗