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At least 865 records · Page 48Linked to original sources
PubMed1995

Efficacy of subcutaneous heparin in prevention of venous thromboembolic events in trauma patients.

Trauma patients have an incidence of deep venous thrombosis (DVT) of 7% to 65%. Conflicting data exists regarding the impact of prophylactic anticoagulant therapy. The purpose of this study is to assess the efficacy of DVT prophylaxis based upon our data and a meta-analysis of the current literature. Literature review revealed five recent studies that met the following criteria: 1) Adult patients sustaining major trauma (injury severity score (ISS) > 10), 2) prospective surveillance for DVT using lower extremity duplex examinations, 3) clear documentation of method of DVT prophylaxis with particular attention to the use of anticoagulation and the corresponding incidence of DVT or pulmonary embolus (PE). Additionally, 66 trauma patients in our intensive care unit were prospectively identified and followed with duplex examinations. Patients received either anticoagulation DVT prophylaxis or pneumatic compression boots. An unpaired Student t test was used to compare the characteristics of patients with and without DVT. A Mantel-Haenszel chi-square meta-analysis was performed on the five recent studies and our own data to compare the incidence of DVT/PE in patients with and without anticoagulation. Meta-analysis of the literature included 1102 patients and demonstrated no benefit from anticoagulation for DVT prophylaxis in trauma patients (10% DVT/PE with anticoagulation versus 7 per cent DVT/PE without anticoagulation, P = 0.771). Our own population had a mean age of 38 +/- 17 years, ISS of 29 +/- 11 and a length of stay (LOS) of 34 +/- 22 days. Sixteen events occurred with 13 (20%) DVTs and three (4%) pulmonary emboli.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Thermal study of anti-G ensembles aboard F-16 aircraft in hot weather.

Continuing advances in the performance of new fighter aircraft have engendered requirements for more sophisticated protective clothing and life support systems. A major goal is prevention of acceleration-induced loss of consciousness. The USAF's Advanced Technology Enhanced Design G-Ensemble (COMBAT EDGE) increases acceleration tolerance by providing positive pressure to the oxygen mask; the work of pressure breathing is reduced by adding a counter-pressure bladder over the chest. However, the addition of impermeable layers over the chest reduces the area available for evaporation of sweat. This study was designed to determine whether COMBAT EDGE (CE) was demonstrably hotter than standard summer flight clothing (ST) during F-16 sorties in hot weather. Eight male pilots served as volunteer subjects, each flying missions at 1430 and 1745 h on two consecutive days, one day with CE and the other with ST. Data were logged at 1-min intervals for rectal temperature (Tre), skin temperatures at the chest and thigh (Tch and Tth) and air temperatures outside the clothing at the same two sites (Tach and Tath). The weather was stable over the 4 d of data collection with highs of 34-36 degrees C and simultaneous dewpoints of 19-23 degrees C (relative humidity 35-45%). The mean Tach was stable at 28 degrees C in flight, while individual means for Tath ranged from 22 to 25 degrees C. The lower value and greater variability at the thigh reflect its proximity to the air conditioning vent. Despite the differences in air temperature, Tch and Tth remained in the range 34-36 degrees C throughout the flights.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Reciprocity of hemodynamic changes during lower body negative and positive pressure.

Lower body negative pressure (LBNP) and lower body positive pressure (LBPP) are two opposite environments for the lower abdomen and lower extremities. We examined RR interval (RRI), blood pressure, forearm blood flow, cardiac output, plasma atrial natriuretic factor, and plasma catecholamines during sequentially administered LBNP and LBPP in order to define the cardiovascular and neuroendocrine reciprocity of these models of orthostasis (LBNP) and anti-orthostasis (LBPP). Six healthy young men were studied with a ramped onset of LBNP followed by a similarly ramped LBPP, spaced between periods of data acquisition during rest. Forearm blood flow decreased during LBNP and increased during LBPP. However, LBNP and LBPP did not produce reciprocal changes in cardiac output. No reciprocal changes were found in plasma catecholamines and plasma atrial natriuretic factor. The variability of RRI and systolic/diastolic blood pressures were analyzed within two bandwidths of interest: the low bandwidth, corresponding to the frequency of baroreflex-mediated variability (0.04 to 0.12 Hz), and the high bandwidth, representative of parasympathetically mediated variability at the frequency of respiration (0.22 to 0.28 Hz). The ratio of high to low bandwidth RRI variability was reciprocally diminished during LBNP and increased during LBPP, reflecting a relative decrease in the level of parasympathetic tone during LBNP and an increase during LBPP. In addition, the variability of the DBP within the low baroreflex bandwidth increased during LBNP and decreased during LBPP. The phase lag of RRI variability in relation to BP variability did not change reciprocally.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Effects of atrial pacing on right ventricular contractility after coronary artery surgery.

Increasing heart rate enhances the strength of contraction of cardiac fibers. This has been demonstrated in vitro and recently for the left ventricle. To study this phenomenon on the right ventricle, the effects of increasing heart rate by atrial pacing on right ventricular (RV) contractility were observed after coronary artery surgery in 20 patients. Right ventricular ejection fraction (EF) and stroke volume (SV) were measured by use of a rapid-response thermistor pulmonary artery catheter. Right ventricular volumes were calculated from EF and SV. Right ventricular contractility was assessed by the slope of the end-systolic pressure-volume relationship (ESPVR) before and after increasing RV preload by means of military antishock trousers (MAST) inflation. The dP/dtmax/end-diastolic volume index (EDVI) ratio, which is independent of ventricular preload, was also used as an inotropic index. Results are expressed as mean +/- SEM. Right ventricular preload, as reflected by RVEDVI, was increased by MAST inflation (99 +/- 6 mL/m2 v 106 +/- 7 mL/m2, P < 0.01), but returned to control values when inflation of MAST was combined with pacing (100 +/- 6 mL/m2). The slope of the RV ESPVR significantly increased when heart rate was increased (0.22 +/- 0.03 mmHg/mL/m2 before pacing v 0.77 +/- 0.07 mmHg/mL/m2 during pacing, P < 0.05). The dP/dtmax/EDVI ratio was also increased by pacing (2.32 +/- 0.4 mmHg/min/mL/m2 before pacing v 3.15 +/- 0.5 mmHg/min/mL/m2 during pacing, P < 0.01). Moreover, cardiac index was increased by pacing alone (2.45 +/- 0.2 L/min/m2 v 2.78 +/- 0.2 L/min/m2, P < 0.01), and significantly more when MAST were inflated (2.94 +/- 0.2 mL/m2, P < 0.05 v pacing alone). It is concluded that increasing heart rate by atrial pacing increases RV inotropic status after coronary artery surgery.

Adult↗
PubMed1994

Thermal strain and G protection associated with wearing an enhanced anti-G protection system in a warm climate.

A flight trial was conducted in Cyprus to assess the thermal strain associated with and the G protection provided by the prototype Eurofighter 2000 aircrew equipment assembly (AEA) in a warm climate. Six subjects flew a standardized sortie four times in a Hawk aircraft: two while wearing the Eurofighter 2000 AEA and two wearing standard Hawk summer AEA. The sortie included high-G turns and simulated air combat. Cockpit temperatures, rectal and skin temperatures, heart rate, and sweat rate were recorded. Subjective thermal comfort, fatigue, and G protection were also assessed. Skin temperatures of the back, chest and thighs, mean skin temperatures, and sweat rate were greater when the Eurofighter AEA was worn. Rectal temperature and heart rate did not differ significantly between the two conditions. Superior G protection was provided by the Eurofighter assembly. These findings suggest that wearing the Eurofighter AEA in a warm climate is associated with an increased but not unacceptable level of thermal stress while offering enhanced G protection. These results may not generalize when ambient temperatures are higher or more insulative protective clothing is worn.

Adult↗
PubMed1994

Changes in respiratory resistance to low dose carbachol inhalation and to pneumatic trouser inflation are correlated.

Inflation of the leg compartments of pneumatic trousers increases thoracic blood volume. The resultant response in respiratory impedence was investigated in nine normal volunteers, and compared with the response to increasing doses of inhaled carbachol. Respiratory impedance was measured by the forced oscillation technique (4-32 Hz), and respiratory resistance at zero frequency (R0) was extrapolated from linear regression analysis of resistive impedance versus frequency. The mean increase in R0 was 31% after inhalation of 125 micrograms carbachol, and 21% after inflation of pneumatic trousers. The percentage changes in R0 following pneumatic trouser inflation highly correlated those induced by inhalation of 125 micrograms carbachol (r = 0.98) Our data demonstrate that, even in normal subjects, pneumatic trouser inflation causes an increase in respiratory resistance, which can be predicted by the response to a low dose of carbachol. These results support the assumption that cholinergic agents might not only be bronchoconstrictors but also vasodilators of the bronchial vessels. At a low dose, the vasodilating action of carbachol could be the major factor involved in the respiratory response.

Adult↗
PubMed1994

Routine postoperative duplex ultrasonography screening and monitoring for the detection of deep vein thrombosis. A survey of 110 total hip arthroplasties.

The use of duplex ultrasonography for routine noninvasive screening, monitoring, and management of deep venous thrombosis after total hip arthroplasty was evaluated. The reliability of duplex ultrasonography for detection of deep vein thrombosis was confirmed in an initial cohort of 51 total hip arthroplasty patients (102 lower extremities), demonstrating 91% sensitivity, 98% specificity, and 97% accuracy when compared with venography. A second cohort of 110 total hip arthroplasty patients using pneumatic compression stockings and aspirin as deep vein thrombosis prophylaxis underwent screening duplex ultrasonography of both lower extremities on postoperative Day 4. Duplex ultrasonography screening showed 10 (9.1%) patients with proximal deep vein thrombosis and 10 (9.1%) with distal deep vein thrombosis, all of whom were asymptomatic. The 10 patients with proximal deep vein thrombosis on duplex ultrasonography were prescribed therapeutic anticoagulation. Duplex ultrasonography subsequently confirmed resolution of proximal deep vein thrombosis in these patients before discontinuation of anticoagulation; none developed symptomatic pulmonary embolism through 12-month clinical followup. The 10 patients with distal deep vein thrombosis diagnosed by duplex ultrasonography were not treated with anticoagulation, but were monitored by serial duplex ultrasonography through postoperative Day 14 for propagation of distal to proximal deep vein thrombosis; none manifested symptomatic deep vein thrombosis or pulmonary embolism through 12-month clinical followup. The 90 patients with negative duplex ultrasonography results were followed clinically; 3 developed late symptomatic proximal deep vein thrombosis (1 of these later manifested pulmonary embolism). Therefore, duplex ultrasonography was used after total hip arthroplasty for the following: (1) to screen routinely in the hospital for asymptomatic proximal and distal deep vein thrombosis; (2) to monitor for potential propagation of distal to proximal deep vein thrombosis; (3) to minimize exposure to therapeutic anticoagulation by confirming the absence of proximal deep vein thrombosis in 97 of 110 patients; and (4) to demonstrate the effectiveness of mechanical and systemic deep vein thrombosis management by confirming the absence or resolution of deep vein thrombosis in all 110 patients.

Anticoagulants↗
PubMed1994

Reduced pressure in extended coverage anti-G-trousers with assisted pressure breathing.

Six Swedish Air Force pilots and two Armstrong Laboratory subjects volunteered for this study to determine whether reduced pressure in extended coverage anti-G trousers (ECT), in combination with positive pressure breathing for G protection, affected +Gz tolerance. Group mean gradual onset run (GOR) time for the low pressure schedule (0.8 psig.G-1) was significantly different from the other two conditions (1.1, 1.5 psig.G-1)--84.1, 95.6, and 94.1 s, respectively. Group mean simulated aerial combat maneuver (SACM) times statistically differed between the low and middle pressure rates compared to the highest pressure schedule--147.6, 164.8 and 232.3 s, respectively. SACM heart rate (HR) responses for the +9 Gz plateaus were not statistically different among conditions. However, +5 Gz HR's were lower for the highest pressure condition. Similarities were identified between the middle and high pressurization conditions for GOR. However, reducing pressure in the ECT during SACM exposures was not supported by these data.

Gravity Suits↗
PubMed1994

The effect of a new ejection seat headbox and high G garments on head mobility during air combat.

Full coverage anti-G trousers, a chest counter pressure garment for positive pressure breathing for G tolerance, and a smaller ejection seat headbox have been developed for future agile aircraft. The hypotheses that the new headbox might improve, and that the more restrictive high G garments might compromise, pilot head mobility were tested. The RAF institute of Aviation Medicine Hawk aircraft was equipped with a wide angle video camera facing the front seat pilot. Two experimental conditions were compared to the control air combat sortie: 1. standard garments and the smaller headbox; 2. high G garments and the smaller headbox. Data were recorded from five instructor pilots during three scheduled air combat training sorties. Their helmets were marked with 10-mm white dots in a standardized pattern. Software for recording helmet dot positions from single frame video images, and a trigonometric method for calculating head rotation and translation from changes in the helmet dot positions were devised. No differences were found between headboxes or garments at the three extremes of head movements analyzed. Observed neck rotations were similar to maximal seated norms. Optimal head and neck extension is impeded by the ejection seat headbox. Pilots' head movements are not restricted during air combat at moderate G levels.

Aerospace Medicine↗
PubMed1994

The effect of lower body positive pressure on the exercise capacity of individuals with spinal cord injury.

The purpose of this study was to determine the effect lower body positive pressure (LBPP) has on the cardiovascular/exercise capacities of individuals with spinal cord injury (SCI) during both arm crank exercise (ACE) and wheelchair exercise performed on a treadmill (WCTM). Ten male adults (age = 31.1 +/- 10 yr) with SCI and five male nondisabled (ND) adults (31.2 +/- 10 yr) participated in this study. The ND subjects performed ACE only. For subjects with SCI, significantly higher (P < 0.025) peak VO2 (1042 +/- 212 vs 839 +/- 218 ml.min-1), peak VE (46 +/- 17 vs 35 +/- 9 l.min-1), and work rate (50 +/- 15 vs 40 +/- 13 W) were seen during ACE with LBPP. No significant differences for peak VO2, VE, or work rate were seen for the ND subjects with LBPP during ACE. In addition, significantly higher peak VO2 (960 +/- 322 vs 828 +/- 312 ml.min-1) was recorded with LBPP for the subjects with SCI during WCTM. Cardiac output (Q, l.min-1; CO2 rebreathing method) was measured at 50% peak VO2 for both ND subjects and subjects with SCI during ACE. Subjects with SCI demonstrated significantly higher SV (94 +/- 20 vs 84 +/- 20 ml) with LBPP. No differences were observed in SV at 50% peak VO2 during ACE for the ND subjects with LBPP. The results of this study suggest that for individuals with SCI, LBPP augments exercise capacity by preventing the redistribution of blood to the lower extremities.

Adolescent↗
PubMed1993

Hemodynamic alterations in venous blood flow produced by external pneumatic compression.

Venous stasis associated with prolonged bed rest can enhance the risk of deep venous thrombosis (DVT). Pneumatic compression of the lower extremities can reduce this risk by preventing venous stasis. When selecting a method of leg compression for their patients, physicians must chose between two distinctly different types of compression devices. One device applies pressure with a single-chambered sleeve to the below knee region while the other applies pressure in a sequential gradient fashion from the ankle to the thigh. The current prospective study was designed to evaluated the ability of two such devices to increase blood flow in the profunda femoral vein. Venous blood flow velocity, compression time, and vein diameter were measured in nine normal experimental subjects using an Accuson duplex-Doppler before, during and after leg compression. Compression with the single-chambered device produced a significant rise in venous blood flow velocity; however, this could not be maintained and our results indicate a higher average velocity was achieved with the sequential gradient device. The sequential gradient device also moved a greater volume of blood and achieved a higher average blood flow rate. The time between deflation of the sleeve and return of a phasic respiratory signal was greater after compression with the sequential gradient device. These results suggest that sequential gradient compression produces the type of hemodynamic alterations needed to reduce the risk of DVT by achieving a sustained increase in venous blood flow and more completely emptying of the veins in the leg.

Analysis of Variance↗
PubMed1993

Individual differences and subgroups within populations: the shopping bag approach.

The aerospace medical research community needs to consider the individual as something other than a statistical entity. The cumulative effects of performance enhancers that are collectively ignored, secondary to statistical analysis of populations, can be significant for individuals. By considering the individual, all aspects of whatever makes humans unique need to be integrated into research. One suggested remedy to the problem of subordination of the individual to the population mean/standard deviation is the use of a "shopping bag" approach. In this approach, each individual may select those performance enhancers that work best for him or her (based on controlled studies). Acceleration protection devices are used as an example. The impact of this philosophy can be readily seen in human factor design strategy as well as in the interpretation of human research data.

Aerospace Medicine↗