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Biomedical subjects

J W Davis

Publications and source records attributed to J W Davis.

At least 181 records · Page 10Linked to original sources
PubMed1990

Effects of the left ventricular assist device on right ventricular function.

Right ventricular failure is a leading cause of death in patients who require the left ventricular assist device. Previous reports suggested right ventricular functional deterioration during left ventricular assist but lacked a method by which right ventricular function could be quantified adequately. This study examined the effects of left ventricular volume unloading on right ventricular systolic function by means of the stroke work/end-diastolic volume relationship, a load-insensitive index of myocardial performance. In 12 anesthetized open-chested dogs, right ventricular and left ventricular pressures were measured with micromanometers while ultrasonic dimension transducers measured left and right ventricular orthogonal diameters. Left ventricular unloading was accomplished with left atrial-to-femoral artery bypass with a centrifugal pump. Data were recorded during transient vena caval occlusion in the control state and with maximal left ventricular unloading by full support by the left ventricular assist device. Modified ellipsoidal geometry was used to calculate simultaneous biventricular volumes, and linear regression analysis of right ventricular stroke work versus end-diastolic volume was used to quantify right ventricular systolic function. Average slope and x intercept of this relationship under control conditions were 2.2 +/- 0.3 X 10(4) erg/ml and 10.7 +/- 5.0 ml, respectively. During full support by the left ventricular assist device (mean flow rate, 2.4 +/- 0.3 L/min), left ventricular end-diastolic volume decreased by 31% (p less than 0.01), left ventricular septal-free wall diameter decreased by 7% (p less than 0.001), and rate of rise of right ventricular peak positive pressure declined by 13% (p less than 0.05). The corresponding slope and x intercept of the right ventricular stroke work/end-diastolic volume relationship during full unloading of left ventricular assist device were 2.3 +/- 0.3 X 0.3 X 10(4) erg/ml and 14.3 +/- 4.8 ml, respectively; these values were not significantly different from control values (p greater than 0.5). Additionally, analysis of right ventricular end-diastolic pressure-volume relationships suggested improved right ventricular chamber compliance, although the effects were small and did not reach statistical significance (p = 0.10). These data imply that marked alterations in biventricular geometry accompanying left ventricular volume unloading by the left ventricular assist device in a normal heart do not significantly alter right ventricular performance characteristics.

Animals↗
PubMed1989

A trial of dipyridamole and aspirin in the prevention of smoking-induced changes in platelets and endothelium in men with coronary artery disease.

A random-order, double-blind crossover study compared the effects of placebo, dipyridamole and dipyridamole plus aspirin on smoking-induced changes in endothelium and platelets. Each of 12 male habitual smokers with coronary artery disease was given dipyridamole (75 mg) and aspirin (324 mg), dipyridamole (75 mg) and placebo for aspirin, or a placebo for each drug 3 times daily for 1 week before each of three 20-minute periods (separated by 2 weeks) of smoking 2 cigarettes after a 12-hour period of abstinence. During each period of smoking there were increases in the mean values of the plasma concentrations of beta-thromboglobulin, platelet factor 4 and nicotine, the endothelial cell count and the blood level of carboxyhemoglobin. In addition, the mean platelet aggregate ratio decreased during each period. After administration of placebos for both dipyridamole and aspirin, the respective mean values +/- standard deviations before and after smoking were 28 +/- 8 and 30 +/- 7 ng/ml (beta-thromboglobulin), 7.4 +/- 1.0 and 8.2 +/- 1.4 ng/ml (platelet factor 4), 3.7 +/- 0.6 and 15.7 +/- 3.5 ng/ml (nicotine), 4.2 +/- 1.4 and 5.4 +/- 1.7/counting chamber (endothelial cell count), 5.0 +/- 2.2 and 6.6 +/- 2.2% (carboxyhemoglobin) and 0.80 +/- 0.07 and 0.68 +/- 0.10 (platelet aggregate ratio). Each of the differences between the means before and after smoking was statistically significant (p less than or equal to 0.02). Neither dipyridamole alone nor in combination with aspiring significantly affected the mean smoking-induced change in any of these variables.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1989

Comparison of cross-sectional and longitudinal measurements of age-related changes in bone mineral content.

Age-related, postmenopausal bone loss was examined among a cohort of Japanese-American women living in Hawaii. None of the women were using estrogens or thiazides. Cross-sectional and longitudinal measurements of bone mineral content were compared at the calcaneus, the proximal radius, and the distal radius. Cross-sectional measurements were also available for the lumbar spine. The longitudinal data showed a slowing rate of bone loss with increasing age at the radius sites. By contrast, the cross-sectional data suggested constant rates of bone loss for all ages at both radius sites and the spine. The calcaneus demonstrated a complex pattern of bone loss in both cross-sectional and longitudinal analyses. The loss rates among women in their fifties were greater than for those in their sixties. From the middle sixties onward calcaneal bone loss remained essentially constant. Because of the sustained bone loss, however, women in their seventies were actually losing greater percentages of their calcaneal bone mineral than they had in their sixties.

Aged↗
PubMed1989

Perspectives: methodologic issues in evaluating risk factors for osteoporotic fractures.

Techniques for measuring bone mineral content (BMC) were developed for the purpose of providing an objective and noninvasive indication of bone strength (or lack thereof) and fracture risk, to the extent that strength relates to bone mass. As such, BMC measurements could help to (1) identify those who are most likely to experience nonviolent fractures in the future and who would therefore benefit most from preventive measures, (2) improve their treatment compliance, and (3) monitor the efficacy of treatments intended to reduce bone loss. All these potential uses require that the measurement provide an indication of fracture risk (probability of fractures). During the past 10-15 years there have been conflicting reports regarding the association of reduced BMC with nonviolent fractures. Some authors have criticized the usefulness of BMC measurements, whereas others have questioned the value of one or more techniques. However, the epidemiology of osteoporosis has only recently been subjected to rigorous study. The use of appropriate statistical methods for relating fracture risk to bone mass may be no more widely practiced in osteoporosis epidemiology today than it was for studying risk factors (e.g., blood pressure) in cardiovascular epidemiology during the 1960s. The intent of this article is to explore three areas that may have contributed to controversy in the study of bone mass and fracture occurrence: (1) perspective of the investigators, (2) study design, and (3) analytic methodology. Although the focus of this paper is on bone mass, these considerations are equally applicable to some investigations of other risk factors for osteoporotic fractures (e.g., bone architecture, bone turnover and loss rate, or biochemical markers of bone loss).

Bone Density↗
PubMed1989

Quantitative fluorimetric effects of leeching on a replanted ear.

Leeching is used to relieve venous congestion in microscopically replanted tissues. A quantitative description of the effects of leech application on tissue perfusion has not been reported. We report a case of an ear replantation in which venous congestion was consistently improved with leeching. In four instances, quantitative fluorimetry, which indicated impaired circulation and prompted leech application, showed restoration of normal circulation patterns following leech application. The fluorometric studies suggested that arterial inflow improved and venous congestion was relieved.

Adult↗
PubMed1989

Comparison of bone mineral content between Japan-born and US-born Japanese subjects in Hawaii.

The bone mineral content (BMC) of the calcaneus, and distal and proximal radius was measured by the single photon absorptiometric technique for 2307 US-born and 172 Japan-born subjects of Japanese ancestry living in Hawaii. The bone mineral content of the US-born subjects was greater than that of their Japan-born counterparts, on the average, by 8.8% at the calcaneus, 3.5% at the distal radius and 4.5% at the proximal radius. Differences between the two groups in height, weight, thiazide use, exercise (in men), estrogen therapy (in women), and calcium and vitamin D intake accounted for much of the difference in BMC between the US-born and Japan-born women, but less so for the men. Additional studies of BMC in migrant populations are needed to characterize further the environmental factors affecting bone mineral content.

Adult↗
PubMed1989

Methodological issues in comparing genetic and environmental influences on bone mass.

Measurements of bone mineral content (BMC), bone width (BW) and BMC/BW (BMA) at the proximal radius were compared for both Japanese and Japanese-American men and women, after adjusting for measurement technique differences. Within each nationality, men had greater values than women at all ages. Japanese-Americans had substantially greater values of BMC (6-10%) and BMA (16-17%), but lower BW (-12 to -15%), relative to Japanese. Adjustment for body size (height and weight) reduced the magnitude of these differences by approximately one-half for BMC, but had a smaller effect on BMA, and slightly increased the difference in BW. Comparison of these results to published data suggests that environmental factors may have influences on bone mass that are similar in magnitude to the effects of race. The need for additional studies to address potential methodological problems is discussed, using this and other reports as examples.

Adult↗
PubMed1989

Prospective, randomized trial of hypertonic sodium lactate versus lactated Ringer's solution for burn shock resuscitation.

We prospectively randomized 51 adult burned patients on admission to study fluid, electrolyte, and physiologic parameters during burn resuscitation with the use of hypertonic saline (HSL, Na 250 mEq/L, 514 mOsm) or lactated Ringer's solution (LR, Na 130 mEq/L, 268 mOsm). Patients suffered at least 20% total body surface area burns (BSA); the mean BSA injury was 36.7% BSA, with a range of 20 to 74% BSA. All patients were admitted to our Burn Center within at least 12 hours of injury. Laboratory studies included frequent determinations of serum chemistries including osmolalities, and continuous 24-hour urine collections for electrolytes and osmolality determinations. Fluid requirements (cc/kg/% BSA), urine output (cc/kg/hr), sodium intake and excretion (mEq/kg/% BSA), serum and urine osmolality (mOsm/kg), serum creatinine (mg/dl), body weight (kg), and enteral intake (cc/24 hrs and calories/24 hrs) were analyzed for comparison at 24-hour intervals following burn injury. Using Student's t-test, significance was attributed to a p less than 0.05. Nonparametric methods were used to compare non-normalized data. Regression analysis was used to compare sodium intake (mEq/kg) and fluid intake (cc/kg) between the HSL and the LR groups in relation to % BSA. Our data show no advantage of HSL over conventional therapy with LR for burn resuscitation. We were not able to demonstrate decreased fluid requirements, improved tolerance of feedings, or decrease in per cent weight gain.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Thoracotomy during trauma resuscitations--an appraisal by board-certified general surgeons.

As trauma systems have developed and board-certified in-house surgeons are now immediately available, enthusiasm has returned for thoracotomy as part of initial resuscitation. This study evaluated the impact of thoracotomy by board-certified surgeons during the resuscitative phase of treatment. Resuscitative thoracotomy, performed on patients in cardiac arrest within 20 minutes of arrival in the hospital, was undertaken in 113 of 4,752 patients over a 4 1/2-year period. Resuscitative thoracotomy added nothing to beneficial survival in patients with a blunt mechanism despite the addition of a board-certified surgeon. Survivors of penetrating injury had a probability of survival (Ps) of 0.48. Most patients suffering penetrating deaths had severe and advanced physiologic derangements at the time of admission despite similar anatomic injuries to survivors.

Attitude of Health Personnel↗
PubMed1989

Epidemiology and pathology of traumatic deaths occurring at a Level I Trauma Center in a regionalized system: the importance of secondary brain injury.

We reviewed the hospital records and autopsy data of all deaths occurring at a Level I Trauma Center during a 1-year interval to determine the epidemiology of traumatic death in a regionalized system of care: 1,581 patients were admitted and 106 died (6.6%). Nonsurvivors (NS) differed significantly from survivors (S) in age, Trauma Score, Injury Severity Score, and probability of survival, but there was no difference between NS and S in scene time or transport time. Of the NS 91.4% died within 7 days; only 8.6% died after 7 days. Central nervous system (CNS) injury was responsible for 48.1% of deaths, followed by hemorrhage (36.8%) and cardiovascular disease (5.7%). Sepsis was responsible for 5.5% of deaths. Secondary brain injury was found at autopsy in 66% of patients dying of CNS injury. The relatively small number of septic deaths may be due, in part, to improvements in treatment associated with regionalization of trauma care. The frequency of secondary brain injury, despite rapid transport and evacuation of mass lesions, suggests that it may play a major role in the pathophysiology of CNS death occurring in a trauma system.

Adult↗
PubMed1989

Granulocytic sarcoma presenting as an epidural mass with cord compression.

Granulocytic sarcoma (GS) usually occurs during the course of, or as a presenting sign of myelogenous leukemia. Rarely it is found before peripheral blood or bone marrow evidence of leukemia is present. We describe a man who presented with low back pain and lower extremity weakness. He had spinal cord compression due to GS without evidence of leukemia. Only four such instances have been previously reported. Such aleukemic presentations of GS are frequently misdiagnosed. The chloroacetate esterase stain and electron microscopy are useful in demonstrating the myeloid origin of GS cells. GS lesions are probably best treated by localized radiation therapy and systemic chemotherapy.

Humans↗
PubMed1989

A comparison of single and multi-site BMC measurements for assessment of spine fracture probability.

In a prospective study of 699 women, 39 new spine fracture cases were observed during a mean follow-up of 3.6 yr. Spine fracture incidence was compared to initial bone mineral content (BMC) of the calcaneus, distal radius, proximal radius, and the lumbar spine. BMC at all four sites was significantly related to spine fracture incidence. Women at -1 s.d. for calcaneal BMC had a sevenfold greater probability of spine fracture than women at +1 s.d.; women at -2 s.d. had a 50-fold greater probability than women at +2 s.d., even after adjustment for the effects of age. Combinations of BMC at two sites further strengthened the relationship to spine fracture; the best two-site combination is calcaneus and distal radius BMC. Thus women can be categorized and stratified according to future fracture risk, and the selection of postmenopausal women for preventive treatments can be guided by measurements of BMC.

Adult↗
PubMed1989

Cervical injuries--perils of the swimmer's view: case report.

A subluxation of an unstable cervical spine injury occurring during swimmer's positioning is described. Based on this experience, it is recommended that the initial radiographs be obtained and reviewed without traction or swimmer's positioning. With clinical or radiographic evidence of cervical injury, bilateral oblique views, plain lateral tomography, or computerized axial tomography may be required to evaluate the C7-T1 junction.

Accidents, Traffic↗
PubMed1989

Passive smoking affects endothelium and platelets.

Blood was obtained before and after ten healthy male nonsmokers sat for 20 minutes in open hospital corridors beside men who were already there smoking by their own initiative. Mean values before and after passive smoking were 0.87 and 0.78 for the platelet aggregate ratio, 2.8 and 3.7 per counting chamber for the endothelial cell count, 0 and 2.8 ng/mL for the plasma nicotine concentration, and 0.9% and 1.3% for the carboxyhemoglobin level. No variable changed significantly during control periods in which the subjects sat in a room where smoking was prohibited. Passive exposure to tobacco smoke affected the endothelial cell count and platelet aggregate ratio in a manner similar to that previously observed with active smoking.

Adult↗
PubMed1988

Symptomatic mediastinal thymic cysts.

The case of a symptomatic, hemorrhagic mediastinal thymic cyst associated with idiopathic thrombocytopenic purpura is reported and the literature reviewed. Contrary to previous reports, mediastinal thymic cysts are frequently symptomatic (39%), presenting with complaints of tracheal and esophageal compression. The age distribution is the same in symptomatic and asymptomatic patients. Complete excision remains the treatment of choice.

Adolescent↗