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Biomedical subjects

M J Davis

Publications and source records attributed to M J Davis.

At least 127 records · Page 7Linked to original sources
PubMed1990

Myogenic responses of isolated arterioles: test for a rate-sensitive mechanism.

The arterial myogenic response may consist of both static- and rate-sensitive components. However, in a recent study of bat wing arterioles, we were unable to demonstrate rate-sensitive constrictions when luminal pressure was elevated at rates between 0.06 and 1 mmHg/s. We have now examined this response in isolated arterioles in vitro, where pressure could be elevated more rapidly. Arterioles were dissected from the hamster cheek pouch and cannulated with micropipettes. Diameters were measured using an inverted microscope and video system, while the vessels were pressurized at various rates (up to 120 cmH2O/s) without flow. Most arterioles developed spontaneous tone and vasomotion and showed myogenic responses over the pressure range 40-160 cmH2O. The magnitude and time course of the active diameter response to a rapid pressure change was highly dependent on the amplitude and direction of the pressure step; monophasic constrictions were observed in response to small-amplitude, positive-pressure steps, and biphasic constrictions were consistently observed when box pressure was elevated to values exceeding 120 cmH2O. The time courses of these responses could be partially, but not completely, explained by a myogenic mechanism with static- and rate-sensitive components. The possible mechanism and physiological significance of this behavior in a microvascular network are discussed.

Animals↗
PubMed1990

Coronary arteriolar myogenic response is independent of endothelium.

The purpose of this study was to investigate if myogenic responses of isolated coronary arterioles were dependent on an intact, functional endothelium. Arterioles were located in situ by intracoronary perfusion with india ink-gelatin solution and then dissected and cannulated at both ends with glass micropipettes. Intraluminal pressure was initially set at 60 cm H2O; then the pressure was altered in steps of 20 cm H2O over a range of 20-140 cm H2O. Arterioles developed spontaneous tone and exhibited a significant myogenic response in physiological saline solution (36 degrees -37 degrees C). Arteriolar dilation and constriction were observed at lower (20-60 cm H2O) and higher (60-140 cm H2O) pressures, respectively. The presence of a functional and automatically intact endothelium was confirmed by relaxation to the endothelium-dependent vasodilator bradykinin and by transmission electron microscopy, respectively. After mechanical denudation of the endothelium with a specially designed abrasive micropipette, spontaneous tone and myogenic responses were preserved. Denudation of the endothelium was verified functionally (no response to bradykinin) and with transmission electron microscopy. Moreover, the mechanical denudation technique did not deleteriously affect smooth muscle because vasoconstrictor and vasodilator responses to nonendothelial-dependent drugs were the same before and after denudation. In summary, the present study demonstrates that pressure-dependent responses occur in isolated coronary arterioles and that this response is not dependent on the endothelium. Therefore, pressure-induced changes in coronary arteriolar tone are a true myogenic response in that they originate from smooth muscle.

Acetylcholine↗
PubMed1990

Oral health care in pediatric AIDS.

At the time of this writing, over 1500 cases of HIV infection in children under 13 have been documented. Estimates have been made that ten times that number exist. The oral manifestations of HIV infection in these children, the management of these problems, and access to care pose significant issues for the dentist who treats children. In Washington, D.C., in March of 1989, the Massachusetts Department of Public Health and the Office of Maternal Child Health funded a conference and workshop on oral complications of HIV infection in the pediatric population. This report uses information presented at the workshop and certain recent key papers to provide an overview of current knowledge about pediatric AIDS.

Acquired Immunodeficiency Syndrome↗
PubMed1990

Computed tomography fluid-fluid level in bone metastasis.

Fluid-fluid levels have been reported in a variety of primary bone and soft-tissue tumours, most frequently in aneurysmal bone cysts, but have never been reported in a metastatic bone lesion. To emphasize such a possibility the authors present a case in which serial computed tomography demonstrated a pulmonary nodule, paratracheal adenopathy and a fluid-fluid level within a rib lesion. Further investigation confirmed a rib metastasis from primary carcinoma of the bronchus.

Bone Neoplasms↗
PubMed1989

Safety and convenience of a mechanical injector pump for coronary angiography.

Coronary angiography and left ventriculography was performed in 5,887 consecutive patients over a 5-year period using a mechanical injector pump activated by a foot switch. Five coronary dissections occurred, four of the right coronary artery and one of the left internal mammary artery, which had been grafted to the left anterior descending artery. One patient had angina following an air embolus; there were no significant intramyocardial injections of contrast agent. The pressure generated in the catheter by hand injection of contrast agent was compared with that generated by the injector pump. Contrast agent was injected through a 7F Judkins Right 4 and an 8F Sones catheter by hand at slow, medium, and fast rates by hand and by the injector pump at 2,3, and 4 ml/sec; maximum pressure generated was recorded. Although the pressures generated through a Sones catheter were similar using both methods, pressures with hand injection were much more variable. The pressures generated with hand injection through a Judkins catheter were lower than those with pump injection, but again the pressures showed much greater variability with hand injection. The pump was found to be safe, reliable, predictable, and convenient when used for coronary angiography with Sones and Judkins catheters. It eliminates the need for a trained assistant during the procedure of coronary angiography.

Angiography↗
PubMed1989

Determination of degree of energy restriction necessary to reduce DMBA-induced mammary tumorigenesis in rats during the promotion phase.

This study was designed to determine the degree of energy restriction necessary to achieve significant inhibition of mammary tumor promotion in rats treated with 7,12-dimethylbenz[a]anthracene (DMBA). A control group of rats was fed a diet containing 5% corn oil ad libitum. Four other groups were pair-fed to the controls; these rats were subjected to energy restriction of 10, 20, 30, or 40%. Weight gains among the groups were proportional to energy intake. The differences in weight were due primarily to reductions in body fat stores. Tumor incidence was reduced slightly by 20% calorie restriction and significantly by 30 and 40% restriction. There were also reductions in number of tumors per tumor-bearing rat and in mean tumor weight. The groups subjected to 30 and 40% energy restriction had significantly reduced serum levels of insulin in the fasting state. These data suggest that body weight, body fat, and fasting serum insulin correlate with susceptibility to mammary tumor promotion and that insulin may be a growth factor for DMBA-induced tumors.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1989

Sulphasalazine therapy in ankylosing spondylitis: its effect on disease activity, immunoglobulin A and the complex immunoglobulin A-alpha-1-antitrypsin.

Serum levels of immunoglobulin A (IgA) and the complex immunoglobulin A-alpha 1 antitrypsin (IgA-alpha 1AT) were measured at the commencement and after 3 months of a double-blind, placebo-controlled trial of sulphasalazine (SAS) in patients with active ankylosing spondylitis (AS). Twenty-eight patients were evaluated, 15 on sulphasalazine, 13 on placebo. Significant falls were seen in both IgA (p less than 0.01) and IgA-alpha 1AT (p less than 0.001) in the actively treated patients. In addition, significant improvement in clinical and laboratory measures of disease were observed. It is concluded that SAS is effective in AS and modulates the immune response.

Adult↗
PubMed1989

Long term efficacy of transvenous catheter ablation of the atrioventricular junction for refractory supraventricular tachycardia.

Twenty-four patients who underwent transvenous catheter ablation of the atrioventricular (A-V) junction between November 1982 and February 1987 were followed from 18-72 months (mean 47.9) to assess the long term efficacy and safety of the procedure. All had severely symptomatic supraventricular tachyarrhythmias refractory to standard treatment. Atrioventricular conduction was abolished in 23 patients, 22 having permanent pacemakers implanted. Conduction has recovered, though it is modified, in one patient who is asymptomatic on digoxin. Four patients have died; one suddenly 20 months following the procedure, one of progressive heart and liver failure due to hemochromatosis, and two of a stroke. Four patients have had complications related to permanent pacing; one patient has required generator replacement and one patient ventricular lead replacement, one patient had asystole and one patient had a pacemaker-related tachycardia. Two patients remain symptomatic but improved by the procedure. Seventeen patients are free of their original symptoms, 11 having no intervening morbid events. These results demonstrate that patients with severely symptomatic supraventricular tachyarrhythmias may gain long term symptomatic relief from the procedure, but permanent pacing is a cause of significant morbidity and there is a small incidence of late sudden cardiac death.

Adult↗
PubMed1989

A rate-sensitive component to the myogenic response is absent from bat wing arterioles.

The responses of three sequential branching orders of arterioles in the bat wing to rapid and slow changes in transmural pressure were studied. Arterial and venous pressures to the wing were elevated simultaneously by pressurizing a box containing the body of the animal, while the wing was exposed to atmospheric pressure. Box pressure was elevated from 0 to +48 mmHg at two rates: 24 and 0.6 mmHg/s. During this time, continuous recordings of hydrostatic pressure and diameter were made in single arterioles using intravital microscopic techniques. Second-order arterioles and arcuate arterioles from skin and skeletal muscle constricted in response to elevated transmural pressure but did not show an enhanced response to rapid pressure changes. There was a trend for terminal arterioles to show a transient peak constriction during rapid stretch, but this response was always associated with a biphasic change in arteriolar pressure. These results suggest that the transient arteriolar resistance changes associated with rapid transmural pressure increases in previous experiments may be primarily a result of transient pressure changes in small arterioles. We find no evidence that arterioles in this preparation exhibit a rate-sensitive component to their myogenic response.

Animals↗
PubMed1989

Length-tension relationship of vascular smooth muscle in single arterioles.

Longitudinal response gradients in the microcirculation may in part be explained in terms of the length-tension relationship of vascular smooth muscle at different points along the vascular tree. To test this hypothesis, four branching orders of arterial vessels (20-80 microns ID) were dissected from the hamster cheek pouch and cannulated with concentric micropipettes. Intraluminal pressure was monitored with a servo-null micropipette, and arteriolar dimensions were measured using a videomicrometer. All arterioles developed spontaneous tone in physiological saline solution. Pressure-diameter curves were recorded for maximally activated vessels and for passive vessels. Maximal active wall tension varied nearly threefold, but maximal active medial wall stress (approximately 4 x 10(6) dyn/cm2) varied only approximately 20% between the different vessel orders. These data support the concept that smooth muscle cells from vessels of different sizes are mechanically similar but do not completely explain the longitudinal response gradients reported in the cheek pouch microcirculation. An analysis of the effect of arteriolar wall buckling suggests that the luminal folds that develop at short vessel radii may broaden the peak of the active stress-length curve and extend the pressure range over which arterioles are most sensitive to physical and chemical stimuli.

Animals↗
PubMed1989

Prone versus supine thallium myocardial SPECT: a method to decrease artifactual inferior wall defects.

Artifactual inferior wall defects as a result of diaphragmatic attenuation of activity are a frequent source of error in thallium myocardial single photon emission computed tomography (SPECT) studies. Thirty-four patients and 11 clinically normal volunteers were studied prospectively to see if specificity of inferior wall defects for right coronary artery disease could be improved by scanning patients prone versus supine. All individuals were scanned both prone and supine, in random order, following symptom limited treadmill exercise. Images were acquired at 3 degrees steps, 25 sec per frame, in a 180 degrees elliptical orbit always beginning in the 45 degrees right anterior oblique position relative to the patient. Polar maps generated from the short axis slices were used to calculate the average regional activity. The prone studies showed consistently higher inferior wall activity compared to the supine studies on both the exercise (182 +/- 22 vs. 160 +/- 23, p less than or equal to 0.001) and 4-hr delay studies (183 +/- 20 vs. 175 +/- 21, p less than or equal to 0.001). Prone imaging resulted in a significantly higher specificity for RCA disease compared to supine imaging (90% vs. 66%, p less than 0.05) with an improvement in accuracy from 71% to 82%. Sensitivity, specificity, and accuracy for left anterior descending and left circumflex artery disease were not significantly affected by patient position during imaging. All patients having SPECT thallium myocardial perfusion studies should be imaged prone to minimize artifactual inferior wall defects and improve accuracy.

Adult↗
PubMed1988

Dual-chamber pacing in the cardiomyopathy of primary amyloidosis.

Cardiac function in a 75-year-old woman with primary amyloidosis and a restrictive cardiomyopathy deteriorated markedly after the occurrence of high-grade atrioventricular block. Atrial synchronous cardiac pacing, which was unreported previously in this setting, produced a marked improvement in cardiac performance.

Aged↗
PubMed1988

Day case cardiac catheterisation--a safe and economic alternative.

Cardiac catheterisation, as a day procedure, has been performed at the Royal Perth Hospital since November 1985. During the 23 month period from November 1985 to September 1987, there have been 1398 day procedures carried out. One hundred and twelve patients (8%) required overnight admission as a consequence of the procedure--39 patients for routine observation, 41 patients for minor hemorrhage from the brachial arteriotomy or femoral artery puncture site; 12 patients for severe angina: three patients with reversible ischemic neurological deficits; two patients with stroke; four patients with transient brachial artery occlusion; two patients with arrhythmias and eight patients for miscellaneous reasons. One patient discharged on the day of the procedure required subsequent re-admission for treatment of an acute myocardial infarction. There were no deaths. The financial cost saving to the hospital in real terms is estimated to be $41.50 per patient and to the community a further saving of $25 per patient due to a reduction in sick leave. The minimum total cost saving to the taxpayer for the 1,285 patients managed as day cases was $85,000. Cardiac catheterisation can be performed as a day procedure with low morbidity, low mortality and modest cost savings to a major hospital.

Ambulatory Care↗
PubMed1988

Radiofrequency catheter ablation of refractory ventricular tachycardia.

Transcatheter radiofrequency ablation of the arrhythmia focus was attempted in a 68-year-old patient with recurrent ventricular tachycardia, both spontaneous and inducible by programmed ventricular stimulation despite treatment with multiple antiarrhythmic drugs. The procedure was performed under local anesthetic without complication. The arrhythmia was not inducible immediately following ablation or 5 days later, and during 5 months follow-up there has been no spontaneous recurrence.

Aged↗