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Biomedical subjects

J W Davis

Publications and source records attributed to J W Davis.

At least 235 records · Page 13Linked to original sources
PubMed1984

Evaluation of suture techniques for mitral valve replacement.

Although periprosthetic leak is presently uncommon after mitral valve replacement, suture line disruption still occurs and may be significant in some patients. Suture technique is obviously an important factor in preventing disruption, but few authors have examined this variable. The purpose of this study was to determine which of four suture methods for mitral valve replacement maximized prosthetic stability in the mitral anulus. Horizontal mattress sutures with subannular pledgets, horizontal mattress sutures with supra-annular pledgets, figure-of-eight sutures, and interrupted simple sutures were compared. A Carpentier-Edwards sewing ring was sutured to the mitral anulus of intact canine left ventricles, each technique randomly assigned to eight hearts. Suture size, number of bites, and annular depth were maintained constant in all groups. Progressively increasing force was applied across the suture line until disruption occurred. The yield force at initial suture disruption was measured by a semiconductor strain-gauge transducer and defined the experimental end point. Subannular pledget-supported sutures required the greatest force (38.4 +/- 0.8 N) to produce prosthetic dehiscence and were significantly more secure than supra-annular pledgets (32.7 +/- 0.5 N). The two suture techniques in which pledgets were used were better than the nonsupported sutures, the mean yield force averaging 28.3 +/- 0.3 N for figure-of-eight and 21.3 +/- 0.7 N for interrupted simple sutures. Although clinical techniques may vary with prosthetic valve design, surgical preference, or pathological anatomy, this study suggests that horizontal mattress sutures with subannular pledgets provide the best prosthetic valve stability during mitral valve replacement.

Animals↗
PubMed1983

Protective effects of aspirin against acute myocardial infarction and death in men with unstable angina. Results of a Veterans Administration Cooperative Study.

We conducted a multicenter, double-blind, placebo-controlled randomized trial of aspirin treatment (324 mg in buffered solution daily) for 12 weeks in 1266 men with unstable angina (625 taking aspirin and 641 placebo). The principal end points were death and acute myocardial infarction diagnosed by the presence of creatine kinase MB or pathologic Q-wave changes on electrocardiograms. The incidence of death or acute myocardial infarction was 51 per cent lower in the aspirin group than in the placebo group: 31 patients (5.0 per cent) as compared with 65 (10.1 per cent); P = 0.0005. Nonfatal acute myocardial infarction was 51 per cent lower in the aspirin group: 21 patients (3.4 per cent) as compared with 44 (6.9 per cent); P = 0.005. The reduction in mortality in the aspirin group was also 51 per cent--10 patients (1.6 per cent) as compared with 21 (3.3 per cent)--although it was not statistically significant; P = 0.054. There was no difference in gastrointestinal symptoms or evidence of blood loss between the treatment and control groups. Our data show that aspirin has a protective effect against acute myocardial infarction in men with unstable angina, and they suggest a similar effect on mortality.

Adrenergic beta-Antagonists↗
PubMed1983

Profound neutropenia associated with benzylpenicillin.

A 31-year-old white man with suspected aspiration pneumonia complicated by multiple pulmonary abscesses had profound neutropenia during a course of high-dose benzylpenicillin therapy for suspected bacterial endocarditis. Antigranulocyte antibodies were identified in the patient's serum. Leukopenia is an uncommon but potentially serious complication of therapy with this drug. We recommend weekly monitoring of blood counts during prolonged therapy with any beta-lactam antibiotic.

Adult↗
PubMed1983

Microcosm and experimental pond evaluation of microbial community response to synthetic oil contamination in freshwater sediments.

A multivariate approach was used to evaluate the significance of synthetic oil-induced perturbations in the functional activity of sediment microbial communities. Total viable cell densities, ATP-biomass, alkaline phosphatase and dehydrogenase activity, and mineralization rates of glucose, protein, oleic acid, starch, naphthalene, and phenanthrene were monitored on a periodic basis in microcosms and experimental ponds for 11 months, both before and after exposure to synthetic oil. All variables contributed to significant discrimination between sediment microbial responses in control communities and communities exposed to a gradient of synthetic oil contamination. At high synthetic oil concentrations (4,000 ml/12 m), a transient reduction in sediment ATP concentrations and increased rates of oleic acid mineralization were demonstrated within 1 week of exposure. These transient effects were followed within 1 month by a significant increase in rates of naphthalene and phenanthrene mineralization. After initial construction, both control and synthetic oil-exposed microbial communities demonstrated wide variability in community activity. All experimental microbial communities approached equilibrium and demonstrated good replication. However, synthetic oil perturbation was demonstrated by wide transient variability in community activity. This variability was primarily the result of the stimulation of polyaromatic hydrocarbon mineralization rates. In general, microcosms and pond communities demonstrated sufficient resiliency to recover from the effects of synthetic oil exposure within 3 months, although polyaromatic hydrocarbon mineralization rates remained significantly elevated.

Journal Article↗
PubMed1983

Dynamic ventricular interaction in the conscious dog.

In nine conscious, chronically instrumented dogs, ultrasonic dimension transducers measured left ventricular anterior-posterior and septal-free wall minor axis and major axis diameters. Matched micromanometers measured right and left ventricular transmural and transeptal pressures. Ventricular pressures and volumes were varied by inflation of implanted vena caval and pulmonary artery occluders, and the functional significance of the two types of ventricular interaction, i.e., direct and series, was determined. The left ventricle was represented by a modified ellipsoidal geometry. Left ventricular stroke volume calculated from the dimension data correlated well with that measured directly from ascending aortic electromagnetic flow probes during all interventions (r greater than or equal to 0.96). Partial pulmonary artery occlusion significantly increased right ventricular diastolic and systolic pressures as compared to values obtained during control and venal caval occlusion. During pulmonary artery occlusion, latitudinal septal eccentricity was increased throughout the cardiac cycle compared to control and vena caval occlusion (P less than 0.05), indicating leftward interventricular septal shifting and significant alteration of left ventricular shape. The normalized diastolic pressure-volume curve was shifted to the left with pulmonary artery occlusion compared to control and indicated a decrease in left ventricular chamber compliance. However, when selected cardiac cycles with similar end-diastolic volumes from vena caval and pulmonary artery occlusions were compared, parameters of left ventricular systolic function (stroke volume, percent systolic shortening, peak aortic blood flow, peak left ventricular pressure, and its first derivative) remained relatively constant. These data suggest that mean myocardial fiber length is the major preload determinant of left ventricular systolic function independent of chamber pressure and shape, and that direct ventricular interaction mediated by interventricular septal shifting has minimal effects on systolic myocardial performance in this model. Thus, series ventricular interaction during acute imbalances in biventricular loading, where the output of the right ventricle determines the input of the left, seems to be far more important than direct interaction to the regulation of overall cardiac function.

Animals↗
PubMed1983

The role of compartmentalization of epinephrine in the regulation of phenylethanolamine N-methyltransferase synthesis in rat adrenal medulla.

The mechanism of regulation of phenylethanolamine N-methyltransferase (PNMT) in rat adrenal medulla after hypophysectomy and dexamethasone treatment was studied. The activity, amounts, and rates of synthesis and degradation of PNMT were measured in explants of adrenal medullae from sham-operated, hypophysectomized, and hypophysectomized-dexamethasone-treated rats. The storage, uptake, and catabolism of [3H]epinephrine were also measured in these three groups to determine any alteration in the granular vs. extragranular compartmentalization of epinephrine induced by these procedures. In addition, the effect of epinephrine on the rate of the enzyme's synthesis and degradation in cultured explants of medullae was measured. The results indicate that the 40% decrease in the amount of PNMT 1 month after hypophysectomy is due to a 28% decrease in the specific rate of synthesis of this enzyme. Dexamethasone treatment restores both the rate of synthesis of the enzyme and the amount of this enzyme found in the tissue to control levels. Our studies show that there is a 73% increase in uptake of [3H]epinephrine into medullary explants from hypophysectomized rats compared to controls. Fifty-six percent of this [3H]epinephrine was converted to metabolites in both groups, indicating that hypophysectomy produced no change in the rate of catabolism. However, uptake of [3H] epinephrine into medullary storage granules from hypophysectomized rats was decreased by 50%. These studies on the uptake, storage, and catabolism indicate that hypophysectomy favors conditions that increase levels of extragranular epinephrine. This altered compartmentalization is reversed by dexamethasone treatment, which decreases the uptake and increases the binding of epinephrine. Epinephrine added to cultured tissue decreased the rate of biosynthesis of PNMT by 22%, an extent similar to that observed after hypophysectomy. It is concluded that the effect of hypophysectomy on this enzyme is mediated by epinephrine.

Adrenal Medulla↗
PubMed1983

Experimental mitral regurgitation. Physiological effects of correction on left ventricular dynamics.

It has been suggested that mitral valve replacement for mitral regurgitation can precipitate acute myocardial failure by increasing left ventricular afterload. However, most studies of this problem have involved anesthesia, acute surgical trauma, or ischemic cardioplegia, each of which can influence myocardial function. The pure hemodynamic consequences of mitral valve replacement were investigated by surgically instrumenting eight dogs with ultrasonic transducers to measure left ventricular diameter, electromagnetic flow probes to measure ascending aortic blood flow, and micromanometers to measure left ventricular and pleural pressures. At the time of implantation, an 8 mm stainless steel shunt was inserted through the left ventricular myocardium at the base of the anterior wall and sutured to the left atrial appendage, producing simulated mitral regurgitation of 20% to 40% of total ventricular output. Balloon occluders were placed around the left atrial shunt and both venae cavae. One to 7 days after implantation, each dog was studied in the conscious state, and data were recorded during acute occlusion of the shunt. After shunt occlusion, left ventricular mean ejection pressure increased significantly in all studies. Systolic wall tension also increased by an average of 8%, diameter shortening decreased by 21%, and forward cardiac output increased by 17%. Thus the higher afterload associated with elimination of mitral regurgitation produced an acute fall in stroke shortening and total left ventricular output. However, forward cardiac output increased in all studies, implying improved pump efficiency and overall cardiac performance. Thus the improvement in pump efficiency associated with restoration of mitral valve competence uniformly increases forward cardiac output despite an increased ventricular afterload and a decreased total stroke volume. Although there may be differences between this relatively acute model and chronic forms of mitral regurgitation encountered clinically, these data suggest that forward cardiac output should increase with correction of mitral regurgitation and that the associated augmentation in afterload is probably not a major factor causing low cardiac output after correction.

Animals↗
PubMed1983

The effect of smoking on the stressed template bleeding time.

Tobacco cigarette smoking is known to affect platelet function. The purpose of this study was to determine whether cigarette smoking acutely shortens the bleeding time of healthy men. The mean initial stressed template bleeding time of 12 nonsmokers (9.0 minutes) was not significantly different from that of nine habitual smokers (9.2 minutes) who were asked to abstain from smoking for 12 hours before determination of the bleeding time. The mean bleeding time was the same immediately before and after the 21 men smoked two filtered tobacco cigarettes in 20 minutes. Separate analyses showed that the mean bleeding time of neither the nonsmokers nor the habitual smokers changed significantly after experimental smoking. We conclude that smoking two cigarettes has no effect on the stressed template bleeding time of healthy men.

Adult↗
PubMed1982

In healthy habitual smokers acetylsalicylic acid abolishes the effects of tobacco smoke on the platelet aggregate ratio.

After abstinence for at least 8 hours, 20 healthy habitual smokers smoked two unfiltered cigarettes during each of two 20-minute periods separated by 48 hours. They had taken one 0.32-g tablet of acetylsalicylic acid (ASA) the night before the second period. The mean platelet aggregate ratios in venous blood taken immediately before and after each period of smoking were 0.79 and 0.70 respectively when ASA had not been taken beforehand and 0.89 and 0.91 when it had. The mean after smoking was significantly higher when ASA had been taken beforehand. In conjunction with the previous finding that in nonsmokers ASA prevented a lowering of the platelet aggregate ratio by experimental smoking without affecting the ratio before smoking, the data from the present study suggest that ASA abolishes both acute and longer-lasting effects of tobacco smoke on the platelet aggregate ratio in healthy habitual smokers.

Adolescent↗
PubMed1982

Incidence of Vibrio species associated with blue crabs (Callinectes sapidus) collected from Galveston Bay, Texas.

Bacteria were readily isolated from the hemolymph of a majority (88%) of the blue crabs collected from Galveston Bay, Texas. The hemolymph of most crabs contained moderate (greater than 10(3) bacteria/ml) to heavy (greater than (10(5) bacteria/ml) infections. Large variances were observed in the bacterial number associated with individual crabs, but no significant difference was observed between the mean bacterial levels in the hemolymph of crabs collected during different seasons of the sampling year. Vibrio spp. were the predominant bacterial types in the hemolymph of infected crabs and increased in number significantly during the summer season. Warmer water temperatures were thought to be responsible for this increase. Bacterial numbers and the percentage of Vibrio spp. were highest in the interior of the crab bodies, especially in the digestive tract. The exterior of the crabs did not appear to be the source of the hemolymph's bacterial flora. Bacteria taxonomically identical to Vibrio cholerae. V. vulnificus, and V. parahaemolyticus were routinely isolated from the crab hemolymph and external carapace. V. parahaemolyticus was the most prevalent of the pathogenic Vibrio spp. and was isolated from 23% of the hemolymph samples. V. vulnificus (7%) and V. cholerae (2%) occurred less commonly in the hemolymph. The incidences of V. parachaemolyticus and V. vulnificus were related and increased in the summer months. Both organisms were frequently isolated from the same crab.

Animals↗
PubMed1982

The effects of airway pressure on cardiac function in intact dogs and man.

Ventilation with positive end-expiratory pressure (PEEP) is associated with reduced cardiac output, but the mechanisms involved are controversial. Possible explanations include increased intrathoracic pressure, reflex changes in myocardial inotropism, pulmonary vascular obstruction and abnormal ventricular interaction. Three types of conscious canine preparations were developed to examine simultaneously each of these factors during ventilation with PEEP. In addition, similar measurements were obtained in patients after cardiac surgical procedures and compared with the results of animal experiments. The primary cause of reduced cardiac output during PEEP appeared to be a diminished end-diastolic volume of the left ventricle, and this appeared to be the result of elevated intrathoracic pressure and increased impedance to blood flow through the lungs. Abnormal interventricular septal shifting and reflex autonomic alterations did not appear to be significant in the normal cardiovascular system. These data provide insight into the cardiac effects of PEEP and emphasize the importance of simultaneous quantification of biventricular performance when assessing cardiopulmonary function.

Animals↗
PubMed1982

Failure of low temperature to arrest degradation of 14C-adenosine 5'-diphosphate by human plasma in the presence of EDTA.

Degradation of 14C-ADP in human platelet-rich and platelet-poor plasmas was studied. Three procedures were tested to determine which method was most effective in "stopping" enzyme reactions. One involved the immediate addition of perchloric acid to the reaction mixture at the end of the incubation period. Another involved "stopping" enzyme reactions at 0 degree C for about 20 min before the addition of perchloric acid. The third involved adding EDTA (10 mM final concentration) to "stop" the reactions at the end of incubation. The protein-free extracts from the plasmas were processed for adenine nucleotide assays by thin-layer chromatography. Addition of perchoric acid was most effective. Low temperature did not stop degradation of 14C-ADP in plasma even in the presence of EDTA. 14C-ADP was converted primarily to 14C-AMP. ADPase activity was the same in platelet-rich and platelet-poor plasmas. We conclude that the addition of EDTA and the cooling of plasma did not completely stop the enzymic degradation of ADP.

Adenosine Diphosphate↗
PubMed1982

Dimensional characteristics of left ventricular function after coronary artery bypass grafting.

During coronary artery bypass grafting, 20 patients underwent epicardial placement of miniature ultrasonic dimension transducers across the minor-axis diameter of the left ventricle to monitor cardiac function postoperatively. Left atrial or left ventricular pressure was measured in all patients, and thermodilution cardiac outputs were obtained routinely. Data from 1, 6, 12 and 20 hours postoperatively were analyzed. Directional changes in systolic shortening of the left ventricular diameter correlated well with stroke volume measured by thermodilution techniques and could be used as an on-line index of cardiac output. In five patients who had preoperative abnormalities in wall motion, systolic bulging of the minor-axis diameter was seen initially after revascularization and then gradually resolved over the next 12 hours. Systolic bulging that did not resolve was the earliest indication of a perioperative myocardial infarction in another patient. The end-diastolic diameter increased progressively in all patients in the first 12 hours postoperatively and was associated with stabilization of cardiac function. This improvement in diastolic left ventricular filling was not reflected (p greater than 0.2) by changes in mean left atrial pressure. Therefore, ultrasonic assessment of left ventricular diameter is a simple, precise and safe method of monitoring systolic and diastolic ventricular function postoperatively.

Adult↗
PubMed1982

Rape mythology.

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Adolescent↗
PubMed1981

Hemodynamic effects of military anti-shock trousers (MAST) in experimental cardiac tamponade.

The ability of military anti-shock trousers (MAST) to increase central venous pressure and improve cardiac filling pressure suggests that they might be useful in the prehospital treatment of pericardial tamponade. This study utilizes a canine model to examine the hemodynamic effects of MAST inflation on experimentally induced pericardial tamponade. Use of the MAST garment improved cardiac filling, mean arterial pressure, and cardiac output in the decompensated tamponade state. It should be realized that animal data may not correlate with human clinical response.

Animals↗
PubMed1981

Effects of pneumatic antishock trousers on canine intracranial pressure.

The military antishock trouser (MAST) has become an accepted prehospital treatment modality for hypovolemic shock. Our interest in the effect of MAST on intracranial pressure (ICP) was aroused by the manufacturer's written warning that use of the device was contraindicated in patients with suspected head injury. This study was undertaken to determine the effect of MAST device inflation on intracranial pressure in dogs with normal and artificially elevated ICP in both normovolemic and hypovolemic states. The largest increase in hemodynamic parameters was seen in mean arterial pressure (MAP) in hypovolemic animals. Although the ICP did increase with MAST inflation, it never reached levels of clinical significance. Furthermore, the cerebral perfusion pressure (MAP--ICP) was calculated and shown to be improved in all groups when the MAST device was inflated. Data from this study support clinical use of the MAST garment in hypovolemic patients even in the presence of suspected head injury.

Animals↗