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At least 595 records · Page 33Linked to original sources
PubMed1994

Effect of hypoxia and hyperoxia on human +Gz duration tolerance.

To determine the effects of varying inspired O2 on positive radial acceleration (+Gz; i.e., head-to-foot inertial load) duration tolerance, seven men were exposed to the +4.5- to +7.0-Gz simulated aerial combat maneuver (SACM) by use of the Armstrong Laboratory (Brooks Air Force Base) centrifuge. Exposures were repeated on different days while subjects breathed gas mixtures of fractional concentration of O2 in inspired air (FIO2) between 0.12 and 0.6. SACM duration tolerance was positively related to inspired O2 of FIO2 between 0.12 and 0.2 but was unchanged at FIO2 between 0.2 and 0.6. SACM exposure decreased arterial O2 saturation and increased heart rates; SACM-induced changes were additive to FIO2 effects. The positive relationship between blood lactate and SACM duration tolerance at all FIO2 indicated an anaerobic component. It is concluded that SACM duration tolerance is limited by reduced FIO2 but not enhanced by hyperoxia. Thus the aerobic component of +4.5- to +7.0-Gz SACM duration tolerance is much greater than previously believed.

Acceleration↗
PubMed1996

Central venous pressure in space.

Gravity affects cardiac filling pressure and intravascular fluid distribution significantly. A major central fluid shift occurs when all hydrostatic gradients are abolished on entry into microgravity (microG). Understanding the dynamics of this shift requires continuous monitoring of cardiac filling pressure; central venous pressure (CVP) measurement is the only feasible means of accomplishing this. We directly measured CVP in three subjects: one aboard the Spacelab Life Sciences-1 space shuttle flight and two aboard the Spacelab Life Sciences-2 space shuttle flight. Continuous CVP measurements, with a 4-Fr catheter, began 4 h before launch and continued into microG. Mean CVP was 8.4 cmH2O seated before flight, 15.0 cmH2O in the supine legs-elevated posture in the shuttle, and 2.5 cmH2O after 10 min in microG. Although CVP decreased, the left ventricular end-diastolic dimension measured by echocardiography increased from a mean of 4.60 cm supine preflight to 4.97 cm within 48 h in microG. These data are consistent with increased cardiac filling early in microG despite a fall in CVP, suggesting that the relationship between CVP and actual transmural left ventricular filling pressure is altered in microG.

Adult↗
PubMed1998

Reflex responses to regional venous pooling during lower body negative pressure in humans.

Lower body negative pressure is frequently used to simulate orthostasis. Prior data suggest that venous pooling in abdominal or pelvic regions may have major hemodynamic consequences. Therefore, we developed a simple paradigm for assessing regional contributions to venous pooling during lower body negative pressure. Sixteen healthy men and women underwent graded lower body negative pressure protocols to 60 mmHg while wearing medical anti-shock trousers to prevent venous pooling under three randomized conditions: 1) no trouser inflation (control), 2) only the trouser legs inflated, and 3) the trouser legs and abdominopelvic region inflated. Without trouser inflation, heart rate increased 28 +/- 4 beats/min, mean arterial pressure fell -3 +/- 2 mmHg, and forearm vascular resistance increased 51 +/- 9 units at 60 mmHg lower body negative pressure. With inflation of either the trouser legs or the trouser legs and abdominopelvic region, heart rate and mean arterial pressure did not change during lower body negative pressure. By contrast, although the forearm vasoconstrictor response to lower body negative pressure was attenuated by inflation of the trouser legs (delta forearm vascular resistance 33 +/- 10 units, P < 0.05 vs. control), attenuation was greater with the inflation of the trouser legs and abdominopelvic region (delta forearm vascular resistance 16 +/- 5 units, P < 0.05 vs. control and trouser legs-only inflation). Thus the hemodynamic consequences of pooling in the abdominal and pelvic regions during lower body negative pressure appear to be less than in the legs in healthy individuals.

Abdomen↗
PubMed2003

Augmentation of the push-pull effect by terminal aortic occlusion during head-down tilt.

Tolerance to positive vertical acceleration (Gz) gravitational stress is reduced when positive Gz stress is preceded by exposure to hypogravity, which is called the "push-pull effect." The purpose of this study was to test the hypothesis that baroreceptor reflexes contribute to the push-pull effect by augmenting the magnitude of simulated hypogravity and thereby augmenting the stimulus to the baroreceptors. We used eye-level blood pressure as a measure of the effectiveness of the blood pressure regulatory systems. The approach was to augment the magnitude of the carotid hypertension (and the hindbody hypotension) when hypogravity was simulated by head-down tilt by mechanically occluding the terminal aorta and the inferior vena cava. Sixteen anesthetized Sprague-Dawley rats were instrumented with a carotid artery catheter and a pneumatic vascular occluder cuff surrounding the terminal aorta and inferior vena cava. Animals were restrained and subjected to a control gravitational (G) profile that consisted of rotation from 0 Gz to 90 degrees head-up tilt (+1 Gz) for 10 s and a push-pull G profile consisting of rotation from 0 Gz to 90 degrees head-down tilt (-1 Gz) for 2 s immediately preceding 10 s of +1 Gz stress. An augmented push-pull G profile consisted of terminal aortic vascular occlusion during 2 s of head-down tilt followed by 10 s of +1 Gz stress. After the onset of head-up tilt, the magnitude of the fall in eye-level blood pressure from baseline was -20 +/- 1.3, -23 +/- 0.7, and -28 +/- 1.6 mmHg for the control, push-pull, and augmented push-pull conditions, respectively, with all three pairwise comparisons achieving statistically significant differences (P < 0.01). Thus augmentation of negative Gz stress with vascular occlusion increased the magnitude of the push-pull effect in anesthetized rats subjected to tilting.

Acceleration↗
PubMed1994

Lung mechanics, gas exchange and central circulation during treatment of intra-abdominal hemorrhage with pneumatic anti-shock garment and intra-aortic balloon occlusion. An experimental study in pigs.

Standardized intra-abdominal hemorrhage was induced in 7 anesthetized pigs. The resulting hypovolemic shock was treated with pneumatic anti-shock garment (PASG) followed by intra-aortic balloon occlusion. The effects of this treatment on circulation, lung mechanics and gas exchange were studied. Hemorrhage was induced by pulling out sutures introduced in the inferior caval vein. We found that the use of PASG partially restored mean arterial blood pressure from 44 +/- 6 to 66 +/- 6 mm Hg. When intraaortic balloon occlusion was added, the arterial pressure returned to basal levels. Cardiac output fell severely due to the hemorrhage from 3.7 +/- 0.2 to 1.3 +/- 0.2 liters/min and could not be restored during the treatment. A severe fall in total lung compliance was recorded after inflation of the PASG from 18.6 +/- 0.9 to 10 +/- 0.7 ml/cm H2O, this was accompanied by a fall in alveolar ventilation. These findings emphasize the severe restriction in lung function that occurred during treatment with PASG. Both parameters returned to near normal values when the PASG was deflated and the intra-aortic balloon was inflated. Pulmonary vascular resistance increased by more than 400% and remained high during the study period. There was no change in arterial PO2, however the fall in mixed venous PO2 caused by hemorrhage was reversed at the end of the treatment. Indirect monitoring of cerebral function by continuous EEG showed a decreased voltage during the hemorrhage, this was reversed by the combined treatment. We conclude that the outlined treatment makes it possible to restore central hemodynamics and preserve cerebral function at least for a short period of time until definite surgical treatment can be performed. However, severe restriction on lung mechanics, especially when PASG was inflated, makes it probable that ventilatory support can be necessary in such cases.

Abdomen↗
PubMed1984

Renal response to lower body positive pressure produced by military anti-shock trousers.

Military anti-shock trousers (MAST) are extensively used in the management of various forms of clinical shock and are presumed to produce their antihypotensive effect by the autotransfusion of blood from the lower extremities. In the present studies we documented the renal response to (1) four hours of recumbency; (2) 4 h of MAST inflation at a pressure of 45 mm Hg over the lower extremities and 15 mm Hg over the abdomen, and (3) 4 h of thermoneutral head-out water immersion in a group of salt replete normal subjects. Similar studies were performed in a group of adults with nephrotic syndrome and edema. In both normal and nephrotic subjects only water immersion produced a natriuresis that was significantly greater than during recumbency. The mean natriuresis following MAST inflation in normal subjects was somewhat greater than that during recumbency but the difference was neither consistent nor statistically significant. We conclude that MAST inflation does not lead to central translocation of more fluid than what would be expected from the assumption of recumbent posture. Thus, MAST are unlikely to be of therapeutic benefit in the relief of edema in patients with nephrotic syndrome and a critical evaluation of their mechanisms of action in the management of hypotension is required.

Adult↗
PubMed1981

Abdominal decompression. An approach towards treating placental insufficiency.

The effects of abdominal decompression applied over a period of several weeks (mean 4 weeks) in late pregnancy on biochemical and haemodynamic parameters as well as fetal growth and cardiotocogram patterns were studied in a group of 64 pregnant women with identified placental insufficiency. A statistically significant improvement was demonstrated in the following findings after treatment: placental perfusion measurements 113mIn and unconjugated oestriol and human placental lactogen, both in serum. A positive influence on antepartum cardiotocogram was observed only immediately after therapy. An acceleration of fetal growth (biparietal diameter) could not be demonstrated. Frequency and severity of EPH gestosis did not change after abdominal decompression. Abdominal decompression seems to be a valuable aid in the still unsatisfactory treatment of placental insufficiency.

Abdomen↗
PubMed1999

Inhibition of tissue factor pathway during intermittent pneumatic compression: A possible mechanism for antithrombotic effect.

Intermittent pneumatic compression (IPC) devices are an effective prophylaxis against lower extremity deep vein thrombosis. Their antithrombotic effect has been attributed to a reduction in venous stasis and enhanced fibrinolysis. The initiating mechanism for blood coagulation is the tissue factor (TF) dependent pathway, which is inhibited by tissue factor pathway inhibitor (TFPI). We have investigated the effect of IPC on the TF pathway in 6 normal subjects and 6 patients with postthrombotic venous disease undergoing IPC for 120 minutes; all subjects were studied with each of 5 IPC devices. In normal subjects and patients, plasma factor VIIa (FVIIa) activity (the activated form of factor VII [FVII]) declined from mean values ranging 51 to 65 and 50 to 53 mU/mL before IPC with different devices to 10 to 13 and 20 to 22 mU/mL at 180 minutes, respectively (P<0.001 for all groups). FVII antigen levels were unchanged. Plasma TFPI (P<0.001) rose from mean baseline values ranging 69 to 79 and 57 to 61 ng/mL to 76 to 123 and 71 to 79 ng/mL at 180 minutes in normal subjects and patients, respectively (P<0. 001 for all groups). Plasma prothrombin fragment F1.2 levels showed minimal changes. There was an inverse relationship between TFPI and FVIIa in normal subjects (r=-0.31, P=0.001) and patients (r=-0.37, P<0.001). IPC results in an increase in plasma TFPI and decline in FVIIa. Inhibition of TF pathway, the initiating mechanism of blood coagulation, is a possible mechanism for the antithrombotic effect of IPC.

Adult↗
PubMed1992

Respiratory responses to chest compression in human subjects.

To test the hypothesis that respiratory compensation for chest compression in the conscious state is different from that in the unconscious state, a range of chest compression was applied to eight conscious and eight anesthetized subjects. Chest compression was carried out by inflating a pneumatic cuff inserted under a chest corset and placed over the anterior chest wall for 5 min. Cuff inflation pressures were 25, 50, and 100 mm Hg: light, moderate, and heavy chest compression, respectively. In both conscious and anesthetized subjects, chest compression immediately caused a decrease in tidal volume (VT) and a concomitant increase in respiratory frequency (f). These changes stabilized within 2 min and remained nearly steady for the rest of the sustained chest compression. The decrease in VT was more prominent the greater the loads, and the change in f was in reverse proportion to the change in VT. In conscious subjects the increase in f was due to shortening of both inspiratory time (T1) and expiratory time (TE), whereas in anesthetized subjects the increase in f was due solely to shortening of TE. In conscious subjects, the values of minute ventilation (VI) and end-tidal PCO2 (PETCO2) during light and moderate chest compression were not different from the control values, whereas VI increased and PETCO2 decreased during heavy chest compression. In anesthetized subjects, the values of VI and PETCO2 were not different from the control values at any different magnitudes of chest compression.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Effect of synchronized, systolic, lower body, positive pressure on hemodynamics in human septic shock. A pilot study.

The pathophysiologic disturbance observed in volume-resuscitated patients with septic shock is primarily that of hyperdynamic circulation with a markedly reduced systemic vascular resistance. We hypothesized that external, mechanically applied, phasic lower body positive pressure could increase systemic vascular resistance and, thus, blood pressure in patients with refractory septic shock. A total of nine studies were performed on seven patients with septic shock refractory to volume resuscitation and vasopressors. All pre-existing therapies were continued unaltered during the study period. Phasic lower body positive pressure was produced by rapid synchronized inflation of pneumatic fabric cuffs fitted around each lower extremity. The cuffs were inflated for 200 ms to a pressure of 150 mm Hg, and the timing of inflation was adjusted to coincide with the peak systolic arterial pressure. Hemodynamic measurements were obtained at baseline and after 15 min of phasic lower body positive pressure. This off-on cycle was repeated twice for each study. Phasic lower body positive pressure increased mean arterial pressure by 12% and cardiac index by 14% (p = 0.01) over baseline (p < or = 0.001). Heart rate, central venous pressure, pulmonary capillary wedge pressure, arterial pH, arterial pO2, and mixed venous pO2 were unchanged. Synchronized external systolic compression of the lower extremities increased mean arterial pressure and cardiac output in seven patients with refractory septic shock. This hemodynamic improvement was independent of changes in calculated systemic vascular resistance.

Adult↗
PubMed1984

Giant hemangioma in the newborn and infant. Complications and management.

Most hemangiomas do not cause major problems but they may be functionally or emotionally unacceptable. In uncomplicated cases spontaneous involution is frequent and treatment consists of expectant care. We report three newborn babies and two infants with giant hemangiomas in whom acute life-threatening complications required immediate treatment. Complications included cardiac failure, hemorrhage, platelet trapping, and disseminated intravascular coagulation (DIC). Modes of therapy employed were surgical excision, steroids, embolization, radiotherapy, intermittent pneumatic compression (Jobst), and continuous compression treatment (Jobst). Our five cases show that several modalities of treatment may be necessary to control the life-threatening complications of giant hemangiomas.

Adrenal Cortex Hormones↗
PubMedDate not supplied

Functional management of stress fractures in female athletes using a pneumatic leg brace.

Thirteen consecutive female athletes complaining of activity-induced lower extremity pain were evaluated. Ten of the 13 athletes had either an x-ray film or bone scan positive for stress fracture of the tibia or fibula. Three athletes with classic signs and symptoms of tibial stress fractures and negative x-ray films refused the bone scan. Three athletes had bilateral tibial stress fractures. The athletes were treated by the application of a pneumatic leg brace to the affected leg or legs. Following this, all 13 athletes were able to return to their sport and participate at a high level of competition with little or no symptoms.

Adolescent↗
PubMedDate not supplied

Anterior tibial compartment pressures during intermittent sequential pneumatic compression therapy.

We studied the anterior tibial compartment pressures during the application of a JOBST sequential intermittent pneumatic compression device on 5 healthy human volunteers (10 legs). Intracompartmental pressures were measured using a slit catheter. The measurements of interstitial pressures were highest at maximal calf inflation, and pressures were increased for approximately 120 seconds during each cycle. Pressure measurements in the inflated pressure sleeve varied less than 10% with the measured anterior tibial compartment pressures during intermittent pneumatic compression therapy. This intermittent pneumatic compression device may elevate intramuscular pressure significantly above that necessary to render muscle ischemic. However, these periods of pressure elevation are not long enough to produce any significant adverse effects, and the beneficial effects of decreased edema fluid may be safely realized.

Adult↗
PubMed1998

Pneumatic sequential compression reduces the risk of deep vein thrombosis in stroke patients.

OBJECTIVE: To determine if pneumatic sequential compression devices (SCDs) combined with subcutaneous heparin and antiembolic hose reduce the risk of deep vein thrombosis (DVT) and pulmonary embolism (PE) in stroke patients. BACKGROUND: DVTs and PEs are serious complications among hospitalized stroke patients. Subcutaneous heparin and SCDs have both been used to prevent DVT. It is not known if SCDs combined with subcutaneous heparin can improve the protection afforded by heparin alone. METHODS: The study group was comprised of nonhemorrhagic stroke patients admitted to the neurology service from October 1988 through June 1996. From October 1988 through April 1991 (233 patients), and during February 1993 (16 patients), patients received 5,000 U subcutaneous heparin twice daily and antiembolic hose. From June 1991 through January 1993 and from March 1993 through June 1996 (432 patients) all nonambulatory stroke patients had SCDs applied to both legs in addition to subcutaneous heparin and antiembolic hose. RESULTS: Twenty-three of 249 patients (9.2%; 21 of 233 and two of 16 patients) treated with heparin alone developed DVT and six patients (2.4%) developed PE (six of 233 and zero of 16). Half the PE cases (three of six) were fatal and all PEs were in patients with DVT. Eighty-three of the 249 patients were nonambulatory. Twenty-two of the 23 DVTs and all the PEs developed in nonambulatory patients. Only one DVT (0.23%) and no PEs occurred among the 432 patients (148 nonambulatory) treated with SCDs as well as heparin. The addition of SCDs resulted in more than a 40-fold reduction in the risk of DVT. CONCLUSIONS: Nonambulatory stroke patients have an increased risk for DVT and PE. Adding SCDs to treatment with subcutaneous heparin and antiembolic hose reduced the risks of DVTs and PEs. SCDs should be considered for adjunctive DVT prophylaxis in nonambulatory stroke patients.

Aged↗
PubMed2002

A randomised comparison of a foot pump and low-molecular-weight heparin in the prevention of deep-vein thrombosis after total knee replacement.

Patients who undergo total knee replacement (TKR) are at high risk of venous thromboembolism. Low-molecular-weight heparins (LMWH) are the most suitable chemical prophylactic agents but there are some uncertainties about their safety and effectiveness. The foot pump offers an alternative. We randomised 229 patients undergoing primary, unilateral TKR to receive either the A-V Impulse foot pump or enoxaparin, a LMWH. Ascending venography was undertaken between the sixth and eighth postoperative day in 188 patients without knowledge of the randomisation category. The prevalence of venographic deep-vein thrombosis was 58% (57/99) in the foot-pump group and 54% (48/89) in the LMWH group which was not statistically significant. There were four cases of proximal thrombi and two of fatal pulmonary emboli in the foot-pump group and none in the LMWH group. There were fewer haemorrhagic complications and soft-tissue effects in the foot-pump group. We conclude that the neither method provides superior prophylaxis.

Aged↗