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Biomedical subjects

M J Davis

Publications and source records attributed to M J Davis.

At least 145 records · Page 8Linked to original sources
PubMed1988

Comparison of serial synovial fluid cytology in rheumatoid arthritis: delineation of subgroups with prognostic implications.

Serial synovial fluid samples were obtained from patients with rheumatoid arthritis and analysed cytologically. Positive correlations in the serial samples between proportions of polymorphs and ragocytes were found. Based upon the serial synovial fluid cytology, distinct subgroups of rheumatoid joints emerged. Comparison of clinical findings in these subgroups showed that the joints with high ragocyte proportion had a significantly poorer outcome. This study therefore identifies two distinct subgroups of rheumatoid joints on the basis of the nature of the cellular reaction within the joint fluid, which usually holds true during subsequent clinical relapse. Identification of these groups may have prognostic significance.

Adolescent↗
PubMed1988

Microvascular control of capillary pressure during increases in local arterial and venous pressure.

The extent to which capillary hydrostatic pressure might be protected from increases in local arterial and venous pressure was examined in the wing microcirculation of unanesthetized pallid bats (Antrozous pallidus). Arterial inflow and venous outflow pressures to the wing were elevated using a box technique to increase pressure around the body of the animal in steps of 12 mmHg between 0 and +60 mmHg for 3-min periods. During this time, hydrostatic pressure, diameter, and red cell velocity in single microvessels were continuously recorded. All branching orders of arterioles constricted significantly during increases in box pressure (Pb), while capillaries and venules dilated. First-order arteriole and venule pressures increased 1:1 with Pb. Capillary pressures increased by only a fraction of Pb up to +36 mmHg, but at higher Pb, the change in capillary pressure was equivalent to the change in Pb. Calculations of vascular resistance indicate that changes in both pre- and postcapillary resistance in this tissue act to prevent increases in capillary pressure during moderate, but not during large, increases in arterial and venous pressure.

Animals↗
PubMed1988

Control of bat wing capillary pressure and blood flow during reduced perfusion pressure.

Regulation of blood flow depends on changes in the sum of arterial (Ra) and venous (Rv) resistances, whereas regulation of capillary pressure (Pc) depends on the ratio of Rv to Ra. If the myogenic response of the arterial system (i.e., delta Ra) is the primary mechanism for controlling pressure and flow when perfusion pressure is lowered, then Pc and total flow should be regulated to the same degree under these conditions. This hypothesis was tested by making direct measurements of Pc and flow in skin and skeletal muscle in the wings of unanesthetized bats. The box method was used to reduce perfusion pressure to the wing. Pressures were measured with a servo-null system; flows were computed from measurements of vascular diameters and red cell velocities using intravital microscopy. All branching orders of arterioles dilated significantly during decreases in box pressure (Pb). For 0 less than Pb less than or equal to -30 mmHg, total flow (1st-order arteriolar flow) remained nearly constant, whereas Pc was "regulated" only approximately 60%. These results cannot be explained by changes in arteriolar resistance alone and suggest that changes in Rv may be important. The possible consequences of flow redistribution, capillary recruitment, and micropressure sampling procedures are discussed in relationship to local regulation of capillary pressure and flow.

Animals↗
PubMed1988

Myogenic activity in isolated subepicardial and subendocardial coronary arterioles.

The goal of this study was to examine myogenic responses of isolated porcine subepicardial and subendocardial arterioles (80-100 micron in diameter) within physiological ranges of intraluminal pressure. Arterioles were located by perfusion with india ink-gelatin solution then dissected and cannulated with glass micropipettes. Intraluminal pressure was altered in 20-cmH2O steps over the range of 20-140 cmH2O. IN physiological salt solution (36-37 degrees C), the coronary arterioles developed spontaneous tone and exhibited myogenic responses. At the lower pressures (20-60 cmH2O), subendocardial arterioles responded passively (diameter decreased from a control diameter at 60 cmH2O), whereas subepicardial arterioles maintained their diameters. At higher pressures (100-140 cmH2O), both subepicardial and subendocardial arterioles demonstrated myogenic constriction, but subepicardial arterioles demonstrated greater myogenic constriction than subendocardial arterioles. This implies that myogenic autoregulation in subepicardial arterioles is better than that in the subendocardial arterioles at both low and high pressures. In the presence of nitroprusside (10(-4) M), all arterioles responded to pressure changes passively, and there were no differences between subepicardial and subendocardial vessels. The functional integrity of the endothelium was verified by relaxation to substance P (10(-7) M). This is the first in vitro study to demonstrate coronary myogenic activity and transmural differences in these arteriolar responses. Our data support the concept that myogenic mechanisms in 80 to 100-micron arterioles may actively contribute to autoregulation of coronary blood flow.

Animals↗
PubMed1988

Variability of serum drug level following a single oral dose of dipyridamole.

Serum dipyridamole levels were measured in 27 patients undergoing planar thallium-201 myocardial perfusion scintigraphy after receiving a 300 mg oral dose. Mean serum dipyridamole level was 2.9 +/- 1.6 mcg/ml (range 0.2-5.7). No correlation was found between serum level and symptoms, heart rate or blood pressure response, peak heart to lung thallium activity ratio, peak heart to liver thallium activity ratio, or peak myocardial thallium washout. Serum level following a single oral dose of dipyridamole is unpredictable and patients with low drug levels cannot be easily identified at the time of study.

Administration, Oral↗
PubMed1987

Histochemical and biochemical observations on the cytotoxicity of paracetamol and its effects on glycogen metabolism in rat liver.

The effects of paracetamol overdose on glycogen metabolism in rat liver have been investigated and related to its cytotoxicity. Paracetamol was administered to male rats by gavaging after a 24-h fast and refeeding was not permitted. An early (9-12-h) increase in histochemically demonstrable glycogen phosphorylase alpha activity in perivenous hepatocytes preceded major loss of membrane integrity as assessed by serum glutamate-pyruvate transaminase (SGPT) activity and uptake of trypan blue during perfusion. These changes occurred only after a decrease in the concentration of reduced glutathione, which is generally observed about 4 h after paracetamol treatment. The activation of glycogen phosphorylase in perivenous hepatocytes occurred concurrently with an increase in glycogen content of periportal hepatocytes, indicating a clear heterogeneity in the response of the two-cell populations to the hepatotoxin. The use of trypan blue perfusion together with histochemical techniques allowed changes in glycogen content and phosphorylase alpha activity of individual hepatocytes to be assessed with reference to the extent of membrane damage evident. The relevance of the results to possible mechanisms of hepatotoxicity is discussed.

Acetaminophen↗
PubMed1987

Determination of volumetric flow in capillary tubes using an optical Doppler velocimeter.

The purpose of this study was to use the optical Doppler velocimeter of Borders and Granger [(1984), Microvasc. Res. 27, 117-127] to determine the ratio of centerline red cell velocity to mean velocity of blood flowing in small glass tubes. Red blood cell suspensions were perfused at different rates through capillary tubes (15-100 microns, id) while measuring centerline velocity (Vmeas). Mean red cell velocity (Vmean) was calculated from measurements of volume flow in the tubes. With the effective slit width (sensor size) of the velocimeter set at 9.0 microns, the ratio of Vmeas/Vmean averaged 1.54 +/- 0.03 (mean +/- SEM), and was essentially independent of tube size. When the slit width was increased, the ratio of Vmeas/Vmean was significantly lower and appeared to vary as a function of tube diameter. These results are compared with previous measurements using other velocimeters, and the relationship between relative sensor size and ratio of Vmeas/Vmean is discussed.

Animals↗
PubMed1987

Incidence and determinants of multiple morphologically distinct sustained ventricular tachycardias.

The incidence and determinants of multiple morphologically distinct ventricular tachycardias were examined prospectively in 71 consecutive patients with at least one documented spontaneous episode of sustained monomorphic ventricular tachycardia. Mean frontal and horizontal QRS axes were determined from the 12 lead electrocardiograms (ECGs) of 190 spontaneous and 352 induced tachycardias. Two or more morphologically distinct spontaneous tachycardias were observed in 19 (43%) of 44 patients who had at least two documented spontaneous episodes. In 43 (61%) of the 71 patients, multiple morphologically distinct tachycardias were induced by programmed ventricular stimulation. Overall, 57 (80%) of the 71 patients had at least two morphologically distinct tachycardias. Predictors of multiple tachycardia configurations were selected by multivariate analysis from clinical and angiographic variables and were similar for both spontaneous and induced ventricular tachycardia: presence of multiple previous myocardial infarctions (p = 0.032 spontaneous, p = 0.005 induced) and number of different antiarrhythmic drug treatments during which ventricular tachycardia was documented (p = 0.0089 spontaneous, p less than 0.0001 induced). These data demonstrate that a large majority of patients with sustained monomorphic ventricular tachycardia exhibit more than one distinct QRS configuration when adequate ECG documentation of multiple episodes is obtained during different antiarrhythmic drug treatments. In individual patients, caution should be used in attributing clinical significance to a single unique QRS configuration.

Anti-Arrhythmia Agents↗
PubMed1987

Double-barrel pipette system for microinjection.

A method for constructing double-barrel micropipettes is described. The pipettes are made from theta-tubing, which permits easy beveling of the tips. The two sides of the system operate independently and are suitable for simultaneous microinjection, microperfusion, or servo-null micropressure measurements.

Animals↗
PubMed1987

Wrist arthroplasty: a retrospective study.

A retrospective study was conducted to evaluate the long-term effectiveness of wrist arthroplasties in patients with various arthritic conditions. A total of 39 wrist arthroplasties were performed in 29 patients (average age, 52.5 years) by the orthopedic staff at Tulane University School of Medicine. Rheumatoid arthritis was the major presenting diagnosis in 84.6% of these operative cases and pain was the most common indication for surgery (79.5%). Postoperative relief of pain was reported in all of the cases reviewed, with an average follow up period of 51.2 months (range, 12 to 118 months). A group of 15 patients who were examined clinically had an average grip strength of 19.2 lb (range, 6 lb to 45 lb). Pinch measurements averaged 1.9 lb and arc of motion averaged 59.5 degrees (range, 20 degrees to 100 degrees) for these patients. Postoperative complications included dislocation (3 cases), fracture of the prosthesis (2 cases), and infection (2 cases). No complications were observed in 32 (82.1%) of the 39 cases reviewed. This retrospective study revealed that at an average follow up period of 51.2 months, pain relief was excellent and patient acceptance was good, with 94.9% of the wrists having been improved by the procedure. The majority (82.1%) of the cases were free of complication. It is concluded from this study that wrist arthroplasty is a viable alternative to wrist arthrodesis.

Adult↗
PubMed1987

Pressure profile along the microvascular network and its control.

The distribution of pressures within the arcading microvessels in numerous tissues is described and evaluated relative to potential sites for the control of blood flow and/or pressure. In various tissues a large fraction of the total systemic pressure is dissipated by small arteries and/or large arterioles and by small arterioles, the classical high-resistance vessels. Thus, these sites must be linked to the regulation and distribution of blood flow and pressure within the network as evidenced by the shifts in the profiles of pressures in these vessels after vasoactive stimuli. In fact, there may be some coupling of vasoactivity between these areas of vascular resistance. The vasodilator activity may predominate in small arterioles whereas the neural control may be directed to the small arteries and large arterioles. Thus, physiological, pharmacological, and pathological influences may affect the control of blood flow and/or pressure at one or both of these sites.

Animals↗
PubMed1986

Effect of early anticoagulation on the frequency of left ventricular thrombi after anterior wall acute myocardial infarction.

To determine the effect of early anticoagulation on the incidence of left ventricular thrombi complicating anterior acute myocardial infarction (AMI), 82 consecutive patients admitted within 12 hours of symptom onset and with electrocardiographic changes consistent with anterior AMI were randomly assigned to 1 of 2 treatment groups. Group 1 patients received high-dose intravenous heparin to maintain the whole blood clotting time between 15 and 20 minutes, and commenced warfarin therapy within 48 hours. Group 2 patients received low-dose subcutaneous heparin and warfarin therapy if the peak creatine kinase level was more than 1,000 U/liter. Eighteen group 2 patients received warfarin, but none had a therapeutic prothrombin ratio within 5 days. The presence and morphologic characteristics of thrombus were assessed by serial 2-dimensional echocardiography. Thirty patients were excluded because AMI was not confirmed or because of technically unsatisfactory echocardiograms, death, surgery or, in group 1 patients, inadequate anticoagulation. Thrombi were identified in 29 of 52 patients (56%): in 14 of 25 group 1 patients (56%) and 15 of 27 group 2 patients (56%). Twenty-three thrombi formed within 3 days. Thrombi were protruding rather than mural only in 3 group 2 patients. The groups did not differ in baseline characteristics or in incidence, time of appearance or morphologic characteristics of thrombus (p greater than 0.05, beta for more than 25% reduction in incidence with group 1 treatment less than 0.10). Systemic embolism occurred only in 1 group 2 patient with mural thrombus.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1986

Vascular anatomy and hydrostatic pressure profile in the hamster cheek pouch.

The purpose of this study was to describe the vascular architecture and blood supply to the hamster cheek pouch and to measure the intravascular pressure distribution in the entire pouch. Previous anatomic descriptions have focused either on the vasculature of the facial region or on the microcirculation of the cheek pouch tip. Micropressures in cheek pouch capillaries, terminal arterioles, and small venules have not previously been measured. Cheek pouches were prepared for examination under an intravital microscope using both everted and noneverted methods. Microvessel diameters were measured through a video system using a video micrometer, and intravascular hydrostatic pressures were measured with a servo null micropressure system. Blood vessels in the face and pouch were traced after injection of Microfil into the external maxillary artery. The results indicate that the pouch is supplied directly or indirectly by six small arteries in the neck and face. Fifty percent of the total pressure drop across the cheek pouch vasculature occurs in the small cheek pouch arteries, suggesting that these vessels are potentially important in controlling cheek pouch blood flow. The measurements of microvascular pressures and diameters in this study help clarify apparent discrepancies in similar measurements from previous studies.

Adenosine↗
PubMed1985

Initial experience with physiological pacing.

Fifty patients, aged 23 to 88 years, with permanent rate-responsive dual chamber pacemakers were studied prospectively for 14.1 +/- 11.4 (S.D.) months after implantation to assess the benefits and complications associated with this technique. In 12 patients the device replaced a ventricular demand pacemaker. Minor complications associated with implantation occurred in one case. Atrial leads required repositioning because of increase in threshold and/or problems of sensing in five cases and ventricular leads in five. There were two patients with symptomatic pacemaker-related arrhythmias necessitating reprogramming; one patient with pacemaker-mediated tachycardia and one with pacemaker autoinhibition. Seven patients have died; one suddenly and possibly related to a pacemaker-triggered arrhythmia. Of 43 living patients, five are now programmed to the ventricular demand mode; two with atrial fibrillation, one with failed atrial lead repositioning, one with persistent sinus tachycardia, and one because of angina pectoris. Thirty-six of the 43 living patients are asymptomatic and a further six are symptomatically improved. All 12 patients changed from ventricular demand pacing have less symptoms. Rate-responsive dual chamber pacing is safe and appears to improve symptoms in most cases. Complications are infrequent and usually easily overcome. This mode of pacing should be considered in all patients with normal sinoatrial function in whom a permanent pacemaker is indicated.

Adult↗
PubMed1985

A new preparation for microcirculatory studies of the hamster cheek pouch.

Existing methods of preparing the hamster cheek pouch for observation under an intravital microscope have several disadvantages. The everted method, described by Duling (Microvasc. Res. 5: 423-429, 1973), appears to restrict blood flow by placing unnatural tension on the retractor muscle and by requiring an incision in the tip of the pouch. The method of Yamaki et al. (Microvasc. Res. 21: 299-301, 1981) requires an incision in the tip of the pouch and complete disconnection of the retractor muscle. The chamber method of Greenblatt et al. (Microvasc. Res. 1: 420-432, 1969) has a limited optical resolution because the tissue cannot easily be transilluminated with properly condensed light. We have devised a less traumatic method of preparing the pouch, which eliminates these disadvantages. The hamster is anesthetized, and a thin, glass support plate is inserted into the left cheek pouch. The plate is constructed and positioned so that it does not restrict flow to any part of the pouch. The free end of the plate is secured to the animal stage. An incision is made in the skin to expose the cheek pouch, and the loose, avascular connective tissue investing the pouch and the retractor muscle is removed. The pouch is positioned at an angle of 20 degrees from the hamster's body in a temperature-controlled chamber over a standard microscope condensor system. Throughout both surgical and experimental procedures, the pouch is superfused with Ringer-bicarbonate solution at 37.5 degrees C. This preparation minimizes surgical trauma and allows the entire vascular supply to the cheek pouch to be studied.

Animals↗