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At least 181 records · Page 10Linked to original sources
PubMed1992

Numerical study of arterial flow during sustained external acceleration.

A computer model of the human arterial tree based upon the one-dimensional flow equations is used to study the effects of sustained acceleration (+Gz) on eye-level arterial pressure and flow. Steady-state physiological compensatory mechanisms are modelled using human centrifuge data found in the literature. Cases investigated include the supine and standing human (+1 Gz), the application of resistive and occlusive anti-G suits, and the occurrence of a stenosis proximal to the carotid bifurcation. Results indicate that the simulated eye-level pressures and flows satisfactorily correspond with those found in the literature.

Acceleration↗
PubMed2006

Pressure-suit combined with pelvic stop-flow: a feasibility study in a bovine model.

BACKGROUND: Isolated pelvic perfusion exposes tissue to high drug doses and may benefit patients with advanced malignancy. However, leakage is a limit to this technique. AIMS: The aim of the study is to increase the perfusion ratio between local and systemic compartments on isolated pelvic perfusion. We hypothesised that an inflated pressure-suit placed above the level of aortic and caval stop flow could decrease leakage from the regional to the systemic blood compartment in a bovine model. METHOD: As the size of the pressure-suit was adapted for use in humans, we performed our experimental study on 6 calves which are big enough to fit into the suit. We used an inflated pressure-suit placed at low (40mmHg) and high pressures (125mmHg) above the level of aortic and caval stop-flow. A pharmacokinetic study with cisplatinum was performed in both compartments. RESULTS: After injection of the drug, the mean ratio of drug concentration in the locoregional/systemic compartment was 43.1. After 30min, this mean ratio was 4 and 9.7 for a pressure-suit pressure of 40mmHg and 125mmHg, respectively. At pressure-suit pressures of 40mmHg and 125mmHg, pelvic perfusion achieved pelvic/systemic exposure ratios of 5.9 and 14.9 at 30min, respectively. Leakage at 30min was higher when the pressure-suit was inflated at low pressure (40mmHg, mean 18%). When the pressure-suit was inflated at high pressure, leakage was lower (125mmHg, mean 7%). CONCLUSIONS: The pressure-suit increased the perfusion ratio between pelvic and systemic compartments in a bovine model.

Animals↗
PubMed1977

Anti-G suit effect of cardiovascular dynamic changes due to +GZ stress.

Lightly anesthetized dogs underwent 1-min exposure to +Gz acceleration without and with a bladder-type anti-G suit. Prior chronic instrumentation permitted through evaluation of cardiac dynamics. During +3 Gz acceleration all recorded dynamic variables were lowered and transient tachycardia occurred. After acceleration ceases, all pressures and dP/dt exceeded control levels. Inflation of the anti-G suit during +3 Gz eliminated the dramatic effects observed during and after acceleration stress. During +6 Gz with the anti-G suit inflated, arterial pressure and dP/dt were maintained whereas left ventricular end-diastolic pressure and total peripheral resistance were much elevated and heart rate was lower. At the onset of G stress, internal diameter of the heart always fell transiently. Otherwise, diameter was not significantly affected by any of the experimental conditions. The results suggest that the anti-G suit maintains perfusion pressure at high sustained G; however, with the anti-G suit inflated at +6 Gz, central venous pressure is dramatically elevated and heart rate depressed. Thus, beneficial effects which provide tolerance to high G are accompanied by potentially detrimental effects.

Animals↗
PubMed1998

[Human tolerance of +Gx loads in anti-G suits during deorbiting of the "Soiuz" space vehicles].

Reported are results of the study of tolerance of the "thorax-back" g-loads (+Gx) during deorbiting of 83 total suited and unsuited cosmonauts in the period of 1997-1997. G-loads averaged 3.7 +/- 0.058 units (from 3.1 up to 5.1 units). Pneumatic gradient G-suits (PGS) Karkas and Centaur had a positive effect on the +Gx tolerance of humans following microgravity. As compared with unsuited crews returning from missions of similar duration, wearing PGS has proven to improve the general health of cosmonauts and to reduce the strain of the leg and abdominal muscles. Tight fitting of PGS abolished visual disorders due to the longitudinal component of G-loads that were registered in 6.6% of observations of unsuited cosmonauts. Sinus tachycardia was significantly weaker (P < 0.05). The authors recommend the use of the standard antiblackout Centaur suit as the efficacy of this PGS was equal to that of Karkas while its ergonomic characteristics were superior.

Astronauts↗
PubMed1983

The medical antigravity suit for management of surgically uncontrollable bleeding associated with abdominal pregnancy.

Three patients with abdominal pregnancy have been treated at Stanford University Hospital in recent years. Common to each was surgically uncontrolled hemorrhage for which circumferential pneumatic compression (supplied by a medical antigravity suit) was used to stop the bleeding. In each patient, the hemostatic effect of treatment was dramatic. In published accounts of the use of the garment in other severely hemorrhaging patients, the effects have been similarly dramatic and equally successful. These observations lead to a compelling consideration in regard to optimum management of patients with abdominal pregnancy. If our experience is confirmed by others, optimum management in abdominal pregnancy hereafter should regularly and routinely include removal of the placenta at the primary operation. This approach would anticipate use of the medical antigravity suit to provide hemostasis if surgically uncontrollable bleeding is encountered. Theoretically, the complications and long-term morbidity associated with retention of the placenta would be eliminated by this means while the previous disadvantage of placental removal, the potential for exsanguinating hemorrhage, would be circumvented.

Adult↗
PubMed1994

The effect of head and body position on +Gz acceleration tolerance.

It has been suggested there is a relationship between acceleration-induced loss of consciousness (G-LOC) and head/body position. A two-part investigation was conducted to determine whether head and body position affects acceleration tolerance. A retrospective analysis of high-G training data (N = 1,914) compared G-LOC occurrence during straight-ahead exposure to a "check-6" exposure [10 s at +9 Gz; 6 G/s onset rate; G-suit inflated; anti-G straining maneuver (AGSM) performed]. A prospective study (N = 12) was conducted with acceleration exposures using light loss criteria with subjects in straight-ahead, above, over-the-right shoulder, or over-the-left shoulder positions. Profiles consisted of 0.1 G/s onset-rate runs (no G-suit inflation; relaxed) to a maximum of +9 Gz and 0.5 G/s onset-rate runs (G-suit inflated; AGSM performed) to +9 Gz for up to 26 s. In the retrospective study, no significant difference existed between G-LOC occurrence during straight-ahead (22/1914) and check-6 (32/1914) positions. During the prospective study with AGSM runs, there was no significant difference in the time at maximum G among any of the positions. During the relaxed runs, several comparisons yielded significant differences in peak G attained. These results indicate there may be an underlying physiologic effect of head and body position on acceleration tolerance; however, the AGSM and the G-suit overcame this effect. Although task saturation and distraction may compromise performance of the AGSM and subsequently predispose acceleration-related hazards, a proper AGSM, combined with effective protective systems, remains essential components of a protection strategy.

Acceleration↗
PubMed1981

Augmentation of systolic blood pressure during external cardiac compression by use of the MAST suit.

External cardiac compression has been shown to circulate blood effectively, but the systolic pressures obtained are less than normal cardiac functioning. This study was undertaken to determine whether applying the military anti-shock trouser (MAST) suit resulted in improving systolic blood pressure while using external cardiac compression during cardiac resuscitation. Individuals admitted to the emergency department in cardiac arrest had external cardiac massage applied at a constant rate and force. Intra-arterial blood pressure monitoring was established and baseline systolic blood pressure obtained. In eight patients, the average increase in systolic blood pressure utilizing the MAST suit was 15 mm Hg. The implications of these findings, as well as other means to increase cardiac output in the cardiac arrest patient, are discussed. These findings will be related to both prehospital and emergency department care of patients in cardiac arrest.

Aged↗
PubMed2000

Effects of inertial load and countermeasures on the distribution of pulmonary blood flow.

We assessed the influence of cranial-to-caudal inertial force (+G(z)) and the countermeasures of anti-G suit and positive pressure breathing during G (PBG), specifically during +G(z), on regional pulmonary blood flow distribution. Unanesthetized swine were exposed randomly to 0 G(z) (resting), +3 G(z), +6 G(z), and +9 G(z), with and without anti-G suit and PBG with the use of the Air Force Research Laboratory centrifuge at Brooks Air Force Base (the gravitational force of the Earth, that is, the dorsal-to-ventral inertial force, was present for all runs). Fluorescent microspheres were injected into the pulmonary vasculature as a marker of regional pulmonary blood flow. Lungs were excised, dried, and diced into approximately 2-cm(3) pieces, and the fluorescence of each piece was measured. As +G(z) was increased from 0 to +3 G(z), blood flow shifted from cranial and hilar regions toward caudal and peripheral regions of the lung. This redistribution shifted back toward cranial and hilar regions as anti-G suit inflation pressure increased at +6 and +9 G(z). Perfusion heterogeneity increased with +G(z) stress and decreased at the higher anti-G suit pressures. The distribution of pulmonary blood flow was not affected by PBG. ANOVA indicated anatomic structure as the major determinant of pulmonary blood flow.

Animals↗
PubMed1983

The application of positive pressure breathing for improving +Gz acceleration tolerance.

Investigations on +Gz acceleration tolerance were carried out in pilots using various values of positive pressure breathing (PPB) during centrifugation. The greatest improvement of +Gz tolerance--2.2 +Gz--was achieved while applying PPB=45 mm Hg and using a counterpressure suit. PPB prolonged the time at +5Gz from 2 min 35 s under control conditions to 6 min 53 s at PPB=45 mm Hg. The author discusses the mechanism of the increase in acceleration tolerance at PPB, stressing its protective effect on the circulatory system.

Acceleration↗
PubMed2001

Protection to +12 Gz.

BACKGROUND: The U.S. Air Force has developed +Gz-protective equipment that will provide most pilots protection to +9 Gz with minimal-to-no straining. This equipment includes a pressure breathing system called COMBAT EDGE (CE), which is currently operational, and the Advanced Technology Anti-G Suit (ATAGS), which is not yet operational. For future high-performance aircraft design it is important to know the upper limit of various protective equipment and techniques. METHODS: Six subjects were randomly exposed to a 12-cell matrix composed of +Gz and the following combinations of protective equipment at three seat-back angles (13 degrees, 30 degrees and 55 degrees from the vertical): 1) the standard CSU-13B/P anti-G suit (STD); 2) the STD suit with CE; 3) the ATAGS; and 4) the ATAGS with CE. Relaxed, followed by straining +Gz tolerance was determined using 15-s rapid onset runs to a maximum of +12 Gz. A comprehensive battery of baseline and post-exposure medical surveillance studies was performed to evaluate the medical consequences of these high +Gz exposures. RESULTS: All 6 subjects were able to achieve +12 Gz with various combinations of +Gz-protective equipment, seat-back angle, and various amounts of straining, from none to maximum. When the data were collapsed over all protective equipment there was a significant (p < 0.05) seat effect. Relaxed tolerance to ROR increased with seat-back angle from 13 degrees to 30 degrees to 55 degrees. There was also a significant protective equipment effect when the data were collapsed over all seat-back angles. CONCLUSIONS: These data confirm that effortless protection to +9 Gz is available using ATAGS/CE with the 13 degree and 30 degree seat-back angle (F-15, F-16 and F-22) and to +10.5 Gz with a 55 degree seat-back angle. Moreover, with ATAGS/CE, and a moderate degree of straining, +12 Gz is definitely achievable at 55 degrees, even with reduced anti-G suit pressure at 55 degrees. With additional straining +12 GC is also achievable at the 13 degree and 30 degree seat-back angles.

Acceleration↗
PubMedDate not supplied

[2 autoerotic accidents: fatal nitrous oxide anesthesia and thoracic compression].

Report on 2 fatal autoerotic cases. In the first case a 20-year-old man died due to the use of nitrous oxide (laughing gas) which he had used in a self-constructed breathing-machine. The nitrous oxide came from a cartridge which normally is used for aerosol cans for whipped cream. In the second case a 19-year-old man used a pressure-suit for military-jet pilots and inflated it with a 12-volt-compressor. Additionally the head was covered with 3 masks and a motorcycle helmet. Arms and legs were bound. The cause of death was a massive compression of the thorax.

Accidents↗
PubMed1984

Antishock trousers.

Antishock trousers provide rapid field treatment of hypovolemic shock. This inflatable suit also stabilizes pelvic and lower extremity fractures and compresses bleeding sites. Although widely available, inexpensive and effective, the device is underused. Pulmonary edema is an absolute contraindication. Adverse effects include restriction of ventilation, skin necrosis, and compartment syndromes with prolonged use. Rapid deflation is hazardous.

Adult↗
PubMed2006

G-induced loss of consciousness: retrospective survey results from 2259 military aircrew.

INTRODUCTION: Prevalence of G-induced loss of consciousness (G-LOC) in the United Kingdom Royal Air Force (RAF) was found to be 19.3% in 1987. With the introduction of the Typhoon, a fourth generation aircraft, the prevalence of G-LOC has been re-assessed to determine the effectiveness of current G tolerance training. METHOD: A survey was sent to 4018 RAF aircrew, irrespective of their current role. Information was requested on G-LOC, role and aircraft type, experience, and attitudes toward G-LOC prevention. RESULTS: Responses were received from 2259 (56.2%) individuals, 882 (39%) of whom were current fast jet aircrew. At least one episode of G-LOC was reported by 20.1% of all respondents. In front line aircraft, prevalence of G-LOC among the 882 fast jet aircrew who responded was 6%. In the whole group, G-LOC was reported most commonly in aircrew under training (70.9%), and was most prevalent in training aircraft (77.4% of G-LOC events). At the time of the G-LOC, 64% of aircrew had less than 100 h total flying time. G-LOC was reported most frequently between +5 to +5.9 Gz, and "push-pull" maneuvers were associated with 31.3% of G-LOC events. Pulling G was not considered a problem by 50.6% of respondents, although over 80% recognized the value of flying currency, use of an anti-G suit, and physical fitness, and 55.6% felt that centrifuge training would be valuable. DISCUSSION: The prevalence of G-LOC in the RAF has changed little since 1987, and there remains considerable scope for aircrew education, particularly with the introduction of the Typhoon.

Adult↗
PubMed1997

Influence of a reduced G-suit pressure schedule on G-duration tolerance using enhanced G-protection ensembles.

BACKGROUND: Reducing pressure to enhanced G-protection ensembles may diminish potential undesirable physiologic effects, as well as improve wear comfort and garment durability. HYPOTHESIS: G-duration tolerance will not be affected by reducing pressure to the Swedish tactical flight combat suit (TFCS). A second objective tested the similarity in G-duration tolerance between the TFCS and Combined Advanced Technology Enhanced Design G-Ensemble (COMBAT EDGE) combined with a prototype enhanced coverage G-suit. METHODS: There were 12 Swedish pilots (mean = 30 yr) who experienced gradual onset (+0.1 G.s-1) runs (GOR) to +9 Gz, rapid (+6 G.s-1) onset runs (ROR) and simulated aerial combat maneuvers (SACM) with +5 to +9 Gz cycles. The GOR and ROR profiles had a sustained times of 60 s after reaching +9 Gz. RESULTS: GOR duration tolerance was statistically decreased (p < 0.01) by the lower pressure (1.1 psig.G-1) when compared to standard pressure (1.5 psig.G-1). No statistical difference between TFCS and COMBAT EDGE was observed during the GOR trials. For all conditions, during the RORs, 90% of the subjects completed at least 30 s at +9 Gz. Many technical or medical difficulties during SACM trials limited statistical treatment of these data. However, no obvious among-condition differences were observed. Noteworthy among SACM trials were those of 3 subjects enduring more than 9 min before stopping; one completing 12.5 min (35 cycles). Neither heart rate, blood pressure, nor perceived exertion data revealed a condition-effect difference. CONCLUSION: Moderately reduced pressure to the extended coverage anti-G suit, combined with positive pressure breathing, may yield decreased G-tolerance results during laboratory evaluation; however, observed differences are sufficiently small they are likely operationally insignificant.

Adult↗
PubMed1983

Cardiac function monitored by impedance cardiography during changing seatback angles and anti-G suit inflation.

Impedance cardiography (IC) appears to be a promising noninvasive technique for monitoring small changes in pilot cardiovascular status during conditions simulating flight. Heart rate (HR), stroke volume (SV), cardiac output (CO), ventricular ejection time (VET), and thoracic impedance (Zo) were monitored in ten volunteers for 5 min at each of four seatback angles from vertical: 12 degrees, 30 degrees, 45 degrees, and 60 degrees. Data were also obtained at three seatback angles (12 degrees, 30 degrees, 60 degrees) for 6 min each before, during, and after inflation of the standard USAF anti-G suit to 1.5 psi. Significant differences (p less than 0.05) in HR, SV, CO, VET and Zo were observed among the four positions. Inflation of the standard anti-G suit to 1.5 psi at 1.0 +Gz did not significantly alter HR, SV, or CO; whereas, 1 min of deflation of the anti-G suit significantly altered HR, SV, CO compared to inflation values. The results suggest IC can detect small differences in HR, SV, CO, VET, and Zo within subjects as a function of minor changes in body position.

Cardiac Output↗
PubMed1982

Regional distribution of cardiac output in unanesthetized baboons during +Gz stress with and without an anti-G suit.

The radiolabeled (46Sc, 85Sr, 141Ce, and 125I) microsphere (15 mu diameter) technique was used to measure blood flow to most major organs of eight chronically instrumented, unanesthetized baboons during exposure to +5 Gz and +7 Gz stress. Exposure to +5 Gz with anti-G suit support resulted in tachycardia, increased total peripheral resistance, increased aortic pressure, decreased aortic flow velocity, decreased blood flow to visceral beds, and no change in cerebral or coronary blood flows. Exposure to +7 Gz with anti-G suit support, in most animals, caused tachycardia, small increases in coronary blood flow, increased arterial pressure, decreased aortic flow velocity, and decreased blood flow to the retina, kidney, liver, spleen, pancreas, and no change in cerebral blood flow. When the animals were exposed to +Gz without anti-G suit inflation, the reductions in aortic flow velocity were more dramatic and heart-level arterial pressure was decreased below baseline values. Coronary blood flow was still increased during +Gz without anti-G suit support. Brain blood flow decreased and the regional blood flows throughout the body were decreased further than during similar +Gz exposures with a G suit. These results indicate that the baboon compensates for the +Gz-induced decrease in cardiac output by a redistribution of blood flow away from the renal and splanchnic beds in an apparent effort to maintain blood flow to the brain and heart.

Acceleration↗
PubMed1989

Interventions in the therapy of electromechanical dissociation.

Electromechanical dissociation (EMD) is a major arrest rhythm for which there is often inadequate treatment. The purpose of this study was to evaluate the different pharmacological and non-pharmacological interventions considered in the treatment of EMD. During the 6-year period, January 1st, 1980 to December 31st, 1985, 503 evaluable adult patients presented in a non-traumatic, non-poisoning cardiopulmonary arrest with the initial rhythm of EMD. One hundred nineteen patients obtained a pulse during resuscitation efforts following drug administration. The average time to obtaining pulses after the last drug administration was 1.97 +/- 2.21 min. The following drugs were last administered prior to transient pulses: bicarbonate, 31/119 (26%); epinephrine, 26/119 (22%); atropine, 26/119 (22%); dopamine, 13/119 (11%); calcium, 11/119 (9%); isoproterenol, 7/119 (6%); other drugs, 5/119 (4%). Ninety-five percent of the successful resuscitations received eight or less drug interventions and all saves received three or less drug interventions. Two hundred twenty-four patients (44.5%) had 288 non-pharmacological interventions. Twenty-three patients developed a pulse after intervention in the following distribution: MAST suit (N = 9), pericardiocentesis (N = 6), fluid challenge (N = 5), needle thoracostomy (N = 1), and intervention combinations (N = 2). The time interval between intervention and the onset of pulse was as follows: MAST suit, 4 +/- 2.8 min; pericardiocentesis, 3.7 +/- 3.6 min; fluid challenge, 4.8 +/- 4.1 min; needle thoracostomy, 6 min. The overall save rate for intervention patients was 0.9% whereas for those not having intervention it was 7.2% (P less than or equal to 0.0003).(ABSTRACT TRUNCATED AT 250 WORDS)

Atropine↗
PubMed1983

Thigh compartment syndrome without lower extremity trauma following application of pneumatic antishock trousers.

Reported are two cases of thigh compartment syndrome following application of a pneumatic antishock trouser suit. Both patients developed compartment syndromes after prolonged antishock suit use in the absence of any apparent leg trauma. We recommend that suit compartment pressures be no more than required to restore adequate blood pressure. The duration of application should be no longer than is clinically necessary. Patients with prolonged application (greater than 120 minutes) should be closely monitored for the development of compartment syndromes.

Adult↗