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The purpose of this study was to test a variety of microgravity countermeasures and anti-G suit (AGS) in long-term bed-rest and to approve them during 169-days space flight.
In recent years, the use of the MAST suit has become commonplace. While no controlled human studies have shown the device's efficacy, extensive clinical experience suggests that it is practical and useful in combating shock, stabilizing fractures, and promoting hemostasis. Studies indicate that the antishock trousers elevate blood pressure primarily by increasing peripheral vascular resistance. Proper application and removal of the device are crucial. A number of potential complications exist, but are infrequent and rarely should preclude MAST suit use. Further studies are necessary to prove the efficacy of the device and clearly define its role in patient management.
HYPOTHESIS: A newly developed hydrostatic anti-G suit is now commercially available. The suit is said to offer a high level of protection against +Gz acceleration. However, past experience shows that it is difficult to produce a hydrostatic suit with effective high-G protection. Careful testing is, therefore, needed to verify its efficacy. METHODS: The G-protective properties of the hydrostatic anti-G suit (Libelle; L) were compared with those of a pneumatic anti-G ensemble (AGE-39) used in the Swedish JAS 39 Cripen aircraft. Three pilots were studied during vertical (+Gz) acceleration in a centrifuge using the following: 1) the L-suit with varied straining maneuvers; 2) the AGE-39 in combination with full anti-G straining maneuvers (AGSM) throughout each high-G exposure (full maneuver; FM); and 3) the AGE-39 in combination with AGSM during the initial part of each high-G exposure (reduced maneuver; RM). G-intensity tolerance was established during exposures to rapid onset rate (ROR) profiles with G-plateau levels ranging from +6.0 to +9.0 Gz. G-endurance was studied during simulated aerial combat maneuvers (SACM) consisting of 10 cycles of 5.5 to 7.5 G. RESULTS: All three pilots tolerated 9.0 G with the pneumatic system both in the RM and FM conditions; their tolerances averaged 6.3 G (range 6.0 to 7.0 G) for the L suit. Thus, during the ROR exposures only the 6.0 G profile was completed by all subjects in all three conditions. At this G-load both muscle straining (as indicated by electromyographic activity in thigh and abdomen) and heart rate were higher in the L than in the RM condition. Mean arterial pressure at eye level was higher in the FM than in the L and RM conditions. Only one subject was able to complete the SACM profile in the L condition. In the RM condition all subjects completed the SACM profile and in the FM condition two subjects completed the SACM. CONCLUSIONS: Whether the AGE-39 was used in combination with maximal AGSM throughout the duration of each high-G exposure or with AGSM only during the initial part of the high-G exposure, G-intensity tolerance was 9.0 G. While wearing the L-suit, G-tolerance was 6.3 G. Thus, under the conditions tested, the G-protection afforded by the L-suit is not adequate for use in a 9-G aircraft.
OBJECTIVE: To compare cardiovascular function of subjects exposed to positive pressure breathing (PPB) while wearing G-suits with different bladder coverage. METHOD: 6 male healthy subjects (18-20 years) wearing three kinds of G-suit with bladder coverage of 45%, 65% and 90% respectively, were exposed to PPB with counterpressures of 30, 50 or 70 mmHg for up to 3 min continuously. G-suit bladder pressure value was three times as high as that of PPB counterpressure. Cardiovascular function was observed every minute. The interval between PPBs was 10 min. The equipment consists of G-suit, jerkin, helmet and mask. RESULT: All subjects completed the experiment successfully. Mean arterial pressure (MAP) elevated significantly, while stroke volume had no striking change, as compared with control group when wearing G-suit with 65% or 90% bladder coverage G-suit. During PPB for 3 min, cardiovascular function didn't change significantly. The mean value of MAP was proportional to the level of PPB. CONCLUSION: The greater G-suit bladder coverage, the less cardiovascular function effect when PPB was conducted simultaneously.
Pelvic fractures, which are most often caused by blunt abdominal trauma in our motor vehicle-oriented society, continue to be associated with significant mortality and morbidity. Hemorrhage is the cause of death in nearly 60 per cent of those patients who die of pelvic fractures. With increasing awareness of the problem and improved methods of management, the mortality rate of acute hemorrhage secondary to pelvic fracture should decrease. Four cases of vascular injuries associated with severe pelvic fractures are discussed. One patient presented with bleeding from a false aneurysm of the superior gluteal artery 3 months after his pelvic fracture. This complication was successfully managed by selective arteriographic embolization. The other three patients required early angiography with embolization of hypogastric vessels to control acute hemorrhage after pelvic fracture. Pelvic arteriography with selective embolization of injured vessels is recommended in the management of hemorrhage secondary to severe pelvic fractures. Application of the Military Antishock Trousers (MAST) suit may also be a useful maneuver. These principles of management and a pertinent review of the literature are presented.
The purpose of this study was to determine the changes in thoracic volume and pattern of breathing during partial anti-G suit (PAGS) inflation by respiratory inductive plethysmography (RIP). Nine normal subjects donned the PAGS, with bladders over legs and thighs, and rested for about 10 min in 60 degrees head-up tilt position. The subjects breathed with closed glottis at functional residual capacity while PAGS was suddenly inflated to 140 mmHg using a calves to thighs sequence. The increase in thoracic volume, as measured from deflection of RIP baseline was 252 ml (S.D. 43 ml), which reflected displacement of blood from the lower extremities into the thorax. On resuming normal breathing, thoracic volume returned to baseline level. Breathing pattern was then monitored for a 15 min baseline period, PAGS was inflated, expiratory reserve volume (ERV) was measured by spirometry, and breathing pattern was monitored another 15 min. ERV decreased 227 ml (+/- 60) after PAGS inflation, which did not differ from the change in thoracic volume expected from displacement of blood into the thorax. Breathing pattern was monitored for another 15 min after PAGS was deflated. No changes took place in minute ventilation, tidal volume, frequency, inspiratory time, fractional inspiratory time, and mean inspiratory flow from deflation to PAGS inflation. Thus, 1) increase in thoracic volume produced by displacement of blood from the calves and thighs is balanced by a decrease in gas volume and, 2) no changes in breathing pattern occur after partial anti-G suit inflation, probably because the pulmonary blood vessels and heart are sufficiently distensible to accept a 250 ml volume increment without leakage of fluid into pulmonary tissues.
INTRODUCTION: To test the hypothesis that G-suit inflation could increase cardiac chronotropic responses to baroreceptor stimulation and enhance baroreflex buffering of BP, the carotid-cardiac baroreflex response of 12 subjects was measured across two levels of lower body negative pressure (LBNP = 0 and 50 mm Hg) and two levels of G-suit inflation (0 and 50 mm Hg) in random order. METHODS: Carotid-cardiac baroreflex stimulation was delivered via a silastic neck pressure cuff and responsiveness quantified by determination of the maximum slope of the stimulus-response function between R-R intervals (ms) and their respective carotid distending pressures (mmHg). RESULTS: Mean +/- SE baseline control baroreflex responsiveness was 3.8+/-0.4 ms x mm Hg(-1). LBNP reduced the baroreflex response to 2.7+/-0.4 ms x mm Hg(-1), but G-suit inflation with LBNP restored the baroreflex response to 4.3+/-0.6 ms x mm Hg(-1). CONCLUSIONS: These results suggest that, in addition to increased venous return and elevated peripheral resistance, G-suit inflation may provide protection against the debilitating effects of blood distribution to the lower extremities during orthostatic challenges such as standing or high +Gz acceleration by increasing cardiovascular responsiveness to carotid baroreceptor stimulation.
To ensure safety of cosmonauts impacted by +Gx loads during insertion into orbit of a Soyuz-type space vehicle, it is critical to conduct appropriate medical selection of candidates to space flights, to give them proper complete physical and specialized centrifuge training, and to make it sure that at the moment of actual injection the cosmonaut's posture is optimal relative to the g-vector and that the body is tight fitting the custom-molded couch. No AGS is needed. For the purposes of protection of cosmonauts descending in the Soyuz vehicles, vital are countermeasures applied in the course of flight, water-salt supplements on the descent day, and the optimal posture, an anti-g suit, and a custom-molded couch with an additional body-restraint system and dampers used on the phase of reentry.
The purpose of this study was to determine the influence of altered chest wall compliance, chest wall shape, and G-suit abdominal bladder inflation on regional intrapleural pressure (Ppl) during +Gz stress. Experiments were conducted in two species (9 dogs, 10 pigs) so that data relating to a spectrum of chest wall characteristics could be obtained. Anesthetized animals were exposed to +Gz levels ranging from 1 to + 5 Gz. Regional Ppl was monitored at 2-4 sites during spontaneous breathing with and without G-suit abdominal bladder inflation and after removal of active chest wall muscular tone by sacrificing the animal. In the dog, Ppl became more negative in the upper and middle thoracic regions with +Gz stress (-1.63 and -1.66 cm H2O.G-1, respectively), but, in the lower thorax, Ppl increased slightly (0.05 cm H2O.G-1). When active muscular tone was removed, the rate of Ppl change increased in the upper thorax (-2.55 cm H2O.G-1), but not in more dependent regions. In the pig, Ppl became more negative with +Gz stress (upper = -3.3; middle = -1.99; lower = -2.16 cm H2O.G-1), and without active muscular tone, the rate of Ppl change tended to increase in all regions (upper = -4.3; middle = -3.47; lower = -2.97 cm H2O.G-1). With G-suit application in both species, Ppl increased toward or exceeded control values at all levels. Results indicate that chest wall characteristics play a significant role in determining regional Ppl during +Gz stress.
U-2 pilots are at an increased risk of decompression sickness compared with other aviators in the U.S. Air Force. This is due to the extreme altitudes at which the missions take place. Presented here is a case of decompression sickness that occurred in a U-2 pilot who was wearing a full-pressure suit while flying at an altitude greater than 70,000 ft, with a pressurized cabin altitude of 29,200 ft. This case demonstrates the continued need for pilot education and awareness of DCS risk factors and symptoms.
Initial anti-G suits were based on the belief that decreased venous return was the critical effect of increased weight of blood during acceleration. Cumbersome water filled, pneumatic gradient or pulsatile pressure suits resulted. Subsequent centrifuge studies implicated arterial pressure, rather than venous return, as the major determinant of G tolerance in the sitting position. Consequently, methods of increasing arterial pressure were developed. Findings that the hypertensive, associated anti-blackout and discomfort effects of suit inflation all increase with bladder system pressure up to arterial occlusive levels resulted in the simplified G-suit used in W.W.II to the present. Recent +Gz loss of consciousness crashes indicate current straining maneuvers plus this suit are inadequate. Furthermore, because of very high pressures to maintain cerebral circulation in the sitting position, very high G suit protection is hazardous. If piloting is essential for full use of super performance fighters, the prone position with counter-weighted head support plus omni-directional surveilance is the surest strategem to obtain this advantage.
The degree of protection afforded by three jerkin G-suit systems (British, Canadian and Swedish) using different pressures against the adverse physiological effects produced by high levels (50 mm Hg and 70 mm Hg) of positive pressure breathing (PPB) was investigated at ground level in 10 male subjects. The British and Canadian systems were evaluated with G-suit pressure equal to breathing pressure and 3.2 times breathing pressure, whereas the Swedish system was studied only with 3.2 times breathing pressure in the G suit. The experimental design was a 10 X 10 Latin swuare. PPB produced significant increases in heart rate, peripheral resistance, and systolic, diastolic and mean arterial blood pressures, and significant decreases in stroke volume and cardiac output. These effects were directly related to the level of PPB. Our results show that the British system provides the highestdegree of protection against PPB, followed by the Swedish and the Canadian systems. It was also found that a G-suit pressure of 3.2 times breathing pressure significantly increases the degree of protection afforded by the British and Canadian systems.
A case of anterior tibial compartment syndrome following the use of the military antishock trousers (MAST) suit is reported. Early recognition of this complication is necessary to ensure a good outcome. Monitoring of the MAST pressure and use of the lowest pressure that is effective may decrease the likelihood of this complication.
Inflatable suits were constructed for lower body compression in pigs and dogs. The suit for pigs encompassed hindquarters and part of the abdomen, and the smaller suit for dogs compressed only the hindquarters, leaving free the abdominal cavity. In conscious, diazepam-pretreated pigs, the compression lasted 30 minutes; during that period the blood pressure increased 50/38 mm Hg over the baseline. In chloralose-anesthetized dogs, the compression was extended to 3 hours; the blood pressure increase was 44/53 mm Hg. Blood pressure fell to the baseline immediately after decompression in both animals. In both species the substantial blood pressure increase was due to an increase of vascular resistance; this did not induced the expected baroreceptor-mediated bradycardia. In dogs, the blood pressure increase was accompanied by a large increase of plasma norepinephrine (from 179 to 975 pg/ml). To test whether the increase of vascular resistance reflected the mechanical compression of the vessels under the suit, animals were pretreated with trimethaphan. In pigs the trimethaphan substantially decreased the vascular resistance and the blood pressure response. This indicated that a portion of the vasoconstriction occurred in areas outside the suit. Lower body compression is a new model to cause prolonged blood pressure elevation by noninvasive and nonpharmacologic means. The mechanism of the blood pressure elevation requires further investigation.
The state of the sympathico-adrenal system (SAS) before and during three days of suited immersion was investigated in six male subjects on the basis of renal excretion of adrenaline (A), noradrenaline (NA), dopamine (DA) and DOPA according to Vasilyev. Computer-aided analysis of the experimental data by the method of principal components showed that the SAS was functionally stressed in all subjects. Suited immersion that simulated hemodynamic, metabolic and vestibulo-motor effects of microgravity helped to distinguish between men with sustained and lowered capabilities of the SAS which are largely determined by the A-, NA-, and mixed type of its function. Clinical manifestations of A-crises in all subjects pointed to central genesis of SAS reactions to simulated microgravity. A correlation between the decline of SAS reserve capabilities and the level of the vestibulo-autonomic syndrome during suited immersion as well as drastic decrease of physical work capacity after immersion was established. It is emphasized that correction of unstable states of the SAS functional activity acquires special importance.
A miniaturized nuclear probe (MNP) and multiple gated cardiac blood pool imaging (RCBI) were used to measure left ventricular function during positive pressure breathing (PPB) while wearing an extended-coverage (EC) vs. standard-coverage (SC) anti-G-suit. Seven subjects were exposed to 4.0 and 9.3 kPa PPB wearing each anti-G-suit during 3 min of PPB at ground level. Ejection fraction was unchanged using both techniques. The atrial component to diastolic filling was greater with the SC suit (p < 0.02). Using the MNP, end-diastolic and end-systolic volumes declined non-linearly over time at both PPB levels; these declines were greater with the SC G-suit (p < 0.001). Left ventricular preload declines during PPB. This is attenuated with increased G-suit coverage, confirming prior results using impedance cardiography. RCBI is less sensitive than MNP's for measuring non-steady-state cardiac physiology such as PPB.
The majority of the environmental factors which comprise the spacecraft and space suit environments can be controlled at "Earth normal" values, at optimum values, or at other values decided upon by spacecraft designers. Factors which are considered in arriving at control values and control ranges of these parameters include physiological, engineering, operational cost, and safety considerations. Several of the physiological considerations, including hypoxia and hyperoxia, hypercapnia, temperature regulation, and decompression sickness are identified and their impact on spacecraft and space suit atmosphere selection are considered. The past experience in controlling these parameters in U.S. and Soviet spacecraft and space suits and the associated physiological responses are reviewed. Current areas of physiological investigation relating to environmental factors in spacecraft are discussed, particularly decompression sickness which can occur as a result of change in pressure from Earth to spacecraft or spacecraft to space suit. Physiological considerations for long-term lunar or Martian missions will have different impacts on atmosphere selection and may result in the selection of atmospheres different than those currently in use.
OBJECTIVE: To observe cardiovascular responses to positive pressure breathing (PPB) using different counter pressures. METHOD: Cardiovascular responses of 7 male healthy subjects (aged 18-20 years) wearing two kinds of Jerkin-G-suit were observed under three levels of ground-level PPB (30, 50, 70 mmHg) for 3 min. RESULT: All subjects completed the experiment successfully. While during PPB at 50, 70 mmHg levels within 3 min, HR, MAP, TPR elevated significantly, while SV declined significantly. At all 3 PPB levels Q-Z time was not significantly changed. There were significant difference (P<0.05) between delta SV and delta TPR with the two Jerkin-G-suits under PPB of 70 mmHg. CONCLUSION: PPB resulted in elevation of MAP, TPR, HR and decline of SV significantly using two kinds of Jerkin-G-suit. PPB had no effect on contractile function of cardiac muscle. Under PPB, SV increased significantly when chest counter pressure was equal to the mask pressure.