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The case presented concerns a patient taking propranolol who developed a severe anaphylactic reaction to pollen extract immunotherapy. Although the hypotension that occurred during the anaphylaxis was refractory to intravenous fluids, epinephrine, and dopamine, the antishock trouser suit was effective in elevating blood pressure.
We have explored the pathophysiological mechanisms of orthostatic hypotension and orthostatic tachycardia, found to be present in 83% and 61% respectively of 18 patients with subsequently proven pheochromocytoma. Orthostatic increases in plasma norepinephrine (NE) concentrations were significantly greater in the patients than in normal control subjects. Intravenous infusions of NE at 1, 2, 4, 8, and 16 micrograms/min induced similar increases in plasma NE levels but smaller increments in systolic and diastolic BP in the pheochromocytoma patients than in normal control subjects. This was reflected by a significantly greater increment in plasma NE concentration required to raise systolic BP by 15 mm Hg and diastolic BP by 7 mm Hg in the pheochromocytoma patients than in the normal subjects (P < .05 and P < .01, respectively). Measurements of venous contractile responses to locally infused NE by the dorsal hand vein (LVDT) technique revealed significantly reduced slopes of the regressions of log NE infusion rate on change in venous diameter in the pheochromocytoma patients compared with normal subjects. The results indicate reduced responsiveness of the vasculature to NE in patients with pheochromocytoma, probably due to down-regulation of alpha-adrenergic receptors resulting from persistent elevation of the physiological agonist NE. This was shown by other authors to be present in circulating platelets. The pathophysiological importance of the subnormal venous responses to the orthostatic hypotension and tachycardia in the patients were supported by the finding that the orthostatic changes were corrected by lower body compression to 45 mm Hg with a MAST pressure suit.
A case of severe symptomatic postprandial hypotension associated with idiopathic autonomic neuropathy and endogenous hyperinsulinaemia is described. The possible mechanisms of the blood pressure changes are discussed. Attempts at treatment included dietary change; the use of vasodilators with salt and fludrocortisone; elastic stockings, antigravity suit; diazoxide and bromocriptine.
The Military Anti-Shock Trouser, or MAST suit, is a controversial device that has been used to support blood pressure in hypotensive trauma patients. Most studies on humans have shown that the device has limited clinical utility. In this study, a telephone survey of all 50 State Emergency Medical Services was conducted to determine the nature and extent of MAST suit usage in the United States. The trend in MAST suit usage in San Diego County over the last 7 years was also analyzed. Thirty (60%) states still require MAST suits to be carried on ambulances. In San Diego County, MAST suit inflations for adult, hypotensive (systolic blood pressure < 90 mmHg,) blunt trauma patients has declined from 37% in 1987, to 2% in 1993. Despite a lack of data supporting efficacy in areas of severe hypotensive shock, blunt trauma, long transport times, and pelvic fractures, states continue to expend resources on the MAST suit. It is for this reason that we believe that the clinical use of the MAST suit should be based upon medical control philosophy rather than legislation.
This study evaluated effects of various anti-G inflation pressures on cardiac volumes and the relationship of these volume changes to mean arterial pressure changes. Ventricular volumes were calculated using two-dimensional echocardiography. An anti-G suit was inflated to 2, 4, and 6 psi in the standing and supine positions for 10 male subjects. In the supine position, mean arterial pressure increased from base line for all three inflation pressures (P = 0.05). The end-diastolic volume increased after 2-psi inflation (P = 0.03). Cardiac output or stroke volume did not change. After standing, mean arterial pressure (P = 0.002), end-diastolic volume (P = 0.002), and stroke volume (P = 0.05) fell after suit deflation. Peripheral vascular resistance fell in the 2- and 4-psi inflation profiles. In the standing protocol, mean arterial pressure, end-diastolic volume, stroke volume, and cardiac output rose with all three inflation pressures (P less than 0.05). After reclining, heart rate increased (P = 0.02) and mean arterial pressure fell (P less than 0.05) in the 4- and 6-psi inflation profiles after suit deflation. Increases in mean arterial pressure are caused by increases in cardiac preload and cardiac output after inflation of the anti-G suit while subjects were standing. Increased cardiac preload was not consistently seen after inflation while subjects were supine. Changes in end-diastolic volume and mean arterial pressure were dependent on the pressure used to inflate the anti-G suit.
Objective recordings of respiratory and cardiovascular parameters at heart and head levels on human centrifuges and in flight provided the physiologic insights which led to development, during and shortly after World War II, of very effective anti-G suits and simultaneous use of positive pressure respiratory straining maneuvers. The high sustained Gz capabilities of current and future fighter planes have forced recourse to these techniques with minimal awareness of their origins. Possible catastrophic limitations of very effective full coverage anti-G suits, including water immersion to the apex of the thorax, especially when used without positive pressure breathing, were also documented at that time.
The purpose of this study was to compare cardiovascular responses of subjects exposed to long-duration positive pressure breathing (PPB) while wearing a standard (Combat Edge; CE) vs. extended coverage (Tactical Life Support System; TLSS) G-suit. Twelve experienced subjects, wearing TLSS and CE, were separately exposed to counterbalanced 60, 70, 80, and 88 mm Hg PPB for up to 10 min continuously. Termination resulted if presyncopal symptoms arose. G-suit inflation was 4 x mask/jerkin pressure. Using TLSS, all subjects completed 10 min of PPB at all levels, vs. 7 and 5 subjects completing 10 min at 80 and 88 mm Hg, respectively, using the CE ensemble (p < 0.001). Heart rate was significantly elevated at all PPB levels using CE (p < 0.0001) vs. TLSS. Stroke and Cardiac Indexes were significantly lower with CE at all levels vs. TLSS (p < 0.0001), and mean arterial blood pressure failed to be maintained at the 80 and 88 PPB mm Hg levels using CE (p < 0.0001). Extended G-suits afford superior protection against PPB-induced cardiovascular dysfunction vs. standard ensembles and consequently permit use of higher levels of PPB. This is due to the larger and more uniform application of pressure in the leg G-suit bladders, augmenting venous return and stroke volume.
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The performance of a suited operator was studied. The experiments were carried out in a trainer consisting of a cockpit and electronic model of the plane attitude realized by an Electron analogue computer. The experiments showed that a special suit may decrease the performance. The main cause for that is that under positive pressure the influx of afferent signals impoverishes due to a reduction of proprioceptive feedback. This disturbs the interaction of the optic and motor analyzers. In order to increase the performance of a suited pilot, it is necessary to build the construction maintaining the optic-proprioceptive relation.
Acceleration (+Gz) research and aircrew training using human centrifuges involves considerable stress that can alter normal cardiovascular and neurologic function even in completely healthy individuals. It is clear that electrocardiographic rate, rhythm, and conduction disturbances are frequently associated with +Gz exposures. These cardiac changes can result in altered perfusion of the central nervous system (CNS) to an extent which exceeds that induced by the +Gz stress alone. Although centrifuge-based research and training have a proven record of overall safety, there is finite risk associated with such stressful exposures, and adverse events have been observed. It is, therefore, extremely important to continually develop improved avenues to enhance human safety during centrifuge exposure. We have implemented techniques that can be immediately employed by centrifuge medical personnel to reduce the potential for significant CNS embarrassment and possible injury. These include techniques to 1) reduce excessive parasympathetic tone that may result in marked bradycardia and transient asystole post +Gz stress, and 2) manually controlled inflation and pulsation of the anti-G suit to enhance CNS perfusion post +Gz stress.
The effect of acceleration on central hemodynamics was investigated in centrifugation experiments. Also examined was the protective effect of muscle tension, anti-G suit, and of an altered acceleration vector. It was demonstrated that visual disorders were caused by a decrease in cardiac output. The countermeasures diminished the rate with which cardiac output declined due to the higher values of stroke volume that were produced by the anti-G suit and a changed body position. Arbitrary muscle tension ensured the effect only as a result of increased heart rate.
Although balanced positive pressure breathing increases protection by G suits and reduces fatigue during sustained high Gz exposures, it does not prevent dependent pulmonary right-to-left shunts (arterial hypoxemia) and potentially dangerous distention of nondependent alveoli. An incident of acute incapacitating mediastinal emphysema in a healthy young man during a sustained exposure to 5.5 Gx documents this possibility. This, plus neurogenic bradycardia during sustained high Gz exposures without pressure breathing, suggests that testing of full counterpressure to neck level suits at sustained > 9 Gz exposures may be hazardous. Fully instrumented studies of animal surrogates with comparable thoracic dimensions are indicated.
The effects of +GZ acceleration stress on renal blood flow were studied in chronically instrumented, conscious miniature swine. Renal blood flow was determined using the radiolabeled (46Sc, 85Sr, 141Ce, and 125I) microsphere technique (29 animals) and Doppler-principle flow probes (1 animal). The results obtained with the microsphere technique indicate that +GZ exposure with anti-G suit support caused decreases in renal blood flow throughout the kidney, and that renal blood flow remains decreased for 1-10 min after +GZ stress. Medullary blood flow appeared to recover after +GZ exposure more rapidly than cortical blood flow. The flow probe data also indicate that +GZ stress with or without anti-G suit support results in decreases in renal blood flow, and that anti-G suit inflation in the absence of +GZ can also cause significant decreases. We conclude that the reductions in renal blood flow observed in miniature swine, during +GZ stress with anti-G suit support, may be due to a combination of direct anti-G suit interference and +GZ-induced reflex increases in alpha-constrictor sympathetic tone to the renal vascular bed.
The energy metabolism of men in full pressure suit with additional pressure and without additional pressure were measured during rest and exercise. Results show that the rates of energy metabolism of men in full pressure suit with additional 28 kPa pressure and without additional pressure increased as the exercise load increased. The rates of energy metabolism of men in full pressure suit with additional 28kPa pressure had no significant difference during rest and 0.9W exercise, but significantly increased during 8.5 W exercise, as compared with that without additional pressure. It suggested that full pressure suit with 28 kPa did not affect human energy metabolism during rest, but affected during exercise.
Computer simulation studies using our newly developed mathematical model of human cardiovascular (CV) system were performed to investigate the effect of bladder coverage and inflation schedule of anti-G suit on G protection and CV response. The simulation results agree well with centrifuge experiments. The study demonstrates that additional +Gz protection provided by the extension of the bladder coverage depends mainly upon the pressure transmission efficiency to the underlying tissues and vessels. Although G tolerance increases clearly with the increase of suit inflation schedule, the tendency of increase seems slower when inflation schedule becomes higher than 10 kPa/G.
The purpose of this study was to measure the effect of enhanced venous return on atrial natriuretic factor (ANF) secretion during exercise and upright posture and the consequences on renin angiotensin aldosterone system (RAAS) activity. Six healthy male subjects were submitted to four different procedures. All procedures were performed in the same position, i.e. riding on a support with legs hanging. Two procedures were performed at rest: the subjects were studied after a 25-min rest in this position, with and without the lower limb fitted with an anti-G suit inflated to 60 mmHg. Two procedures were carried out with physical exercise; arm-cranking was performed in the same position with and without the anti-G suit inflated to 60 mmHg. Venous blood was collected before and after each procedure in order to measure plasma ANF, plasma aldosterone concentration (PAC), plasma renin activity (PRA), corticotrophin (ACTH) and catecholamine level. The data mean +/- SEM showed that the ANF plasma level decreased significantly (p less than 0.05) from 32.5 +/- 4 to 28 +/- 6 pg.ml-1 after a 20-min rest in the upright posture, whereas this effect was absolished with anti-G suit inflation. Physical exercise with and without the anti-G suit increased the ANF level above control values (60 +/- 13.6 pg.ml-1 and 53 +/- 13 pg.ml-1): anti-G suit inflation had no significant effect. PRA increased after rest in an upright posture and during physical exercise; anti-G suit inflation abolished this increase in both conditions.(ABSTRACT TRUNCATED AT 250 WORDS)
The effects of pneumatic antishock trousers on central venous pressure (CVP) and mean arterial pressure (MAP) were compared with those of volume expansion with normal saline in a group of healthy young men. CVP increased from 4.8 +/- 1.9 to 7.3 +/- 2.5 mm Hg (P less than .001) with the suit and from 4.7 +/- 1.9 to 7.3 +/- 2.2 mm Hg (P less than .001) with volume expansion. During suit use, MAP increased from 85 +/- 6.7 to 93 +/- 6.8 mm Hg (P less than .001), while during volume expansion it did not change. Therefore, despite equivalent increases in CVP, the pneumatic antishock suit significantly increased MAP while volume expansion did not. The data suggest that the increased blood pressure produced by the suit may be at least in part dependent on mechanisms other than increased preload from an "auto transfusion" of blood into the central circulation.
Uncontrollable hemorrhage can occur during any surgical procedure, and only an organized approach to its control will minimize morbidity and mortality. When routine hemostatic measures fail, extraordinary methods must be used. The use of intraabdominal packs with a MAST (medical antishock trousers) suit successfully controlled a life-threatening hemorrhage in one such patient.