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Biomedical subjects

G Davies

Publications and source records attributed to G Davies.

At least 235 records · Page 13Linked to original sources

Laser recanalisation of coronary arteries by metal-capped optical fibres: early clinical experience in patients with stable angina pectoris.

The delivery of laser energy to the coronary circulation by bare optical fibres may cause perforation of the vessel. Experimental studies have shown that this complication can be avoided if the optical fibre is fitted with a metal cap to prevent the potentially dangerous forward projection of the laser beam. This study was performed to assess the feasibility and short term effects of percutaneous coronary laser recanalisation with these modified fibres. Recanalisation of a severe stenosis of the left anterior descending artery was attempted in six patients who were referred for coronary artery bypass grafting. Although the percutaneous technique was used, the laser procedure was performed during coronary bypass surgery before the start of cardiopulmonary bypass to minimise the effects of potential complications. A 1.5 mm diameter metal-capped fibre coupled to an argon laser was advanced percutaneously over a guide wire positioned across the stenosis. In the first patient the delivery of 152 J resulted in the gradual passage of the fibre through a 3 cm long stenosis. Repeat angiography showed a reduction in the severity of the stenosis. In the second patient the delivery of 112 J failed to allow fibre advancement; a further 80 J pulse caused perforation which was repaired. In the remaining four patients the delivery of laser energy in the attempt to traverse the stenosis was limited to less than 90 J. In two of the four patients the severity of stenosis was reduced. No further complications were seen. Percutaneous coronary laser recanalisation with metal-capped optical fibres is feasible but improvements of currently available technology are needed to increase the primary success rate.

Aged↗

The evaluation of erythrocyte thiamin diphosphate as an indicator of thiamin status in man, and its comparison with erythrocyte transketolase activity measurements.

HPLC measurement of the major physiological form of thiamin, thiamin diphosphate, in erythrocytes (ETDP) has been assessed as an indicator of thiamin status and compared with erythrocyte transketolase activity (ETKA) before and after activation with exogenous thiamin diphosphate (TDP effect). The comparison was made by following the response of the parameters to incubation of erythrocytes with thiamin and by measurements in alcoholic, elderly and student groups. All parameters were responsive to the thiamin content of their environment, but ETDP was at least as sensitive as TDP effect and more sensitive than ETKA in reflecting thiamin uptake and utilisation by erythrocytes. There was a better correlation between ETDP and ETKA than between ETDP and TDP effect. All the groups showed a significant positive correlation between ETDP and ETKA, but only the elderly and the alcoholic groups showed a significant negative correlation between ETDP and TDP effect. The lack of correlation between ETDP and TDP effect in the student group may be due to the relative imprecision of TDP effect measurements at the lower end of the reference range. ETDP is more stable than ETKA in frozen erythrocytes, is easier to standardise and is not affected by various factors which can influence the enzyme assay. Measurement of ETDP is, therefore, recommended for first line assessment of thiamin status.

Adult↗

Intermittent coronary occlusion in acute myocardial infarction. Value of combined thrombolytic and vasodilator therapy.

We performed continuous electrocardiographic ST-segment monitoring and serial coronary arteriography in 45 consecutive patients presenting in the early stages of acute myocardial infarction. During cardiac catheterization, 28 episodes of arteriographically confirmed coronary reopening and subsequent reocclusion were observed in 16 patients before (3 episodes) and during (25 episodes) continuous intracoronary infusion of streptokinase. In addition, ST-segment monitoring demonstrated 12 episodes of spontaneous transient return of the ST segment to the base line in eight patients between the time of admission and the performance of coronary arteriography. During arteriographically documented reocclusion, intracoronary isosorbide dinitrate (2 mg) reestablished the patency of the coronary artery within one to two minutes in 14 of 28 episodes that occurred in 11 of 16 patients. After streptokinase infusion, intracoronary administration of isosorbide dinitrate was followed by dilatation of the infarct-related stenosis from a mean value (+/- SD) of 1.12 +/- 0.3 mm (58.1 +/- 12.1 percent) to 1.33 +/- 0.4 mm (51.6 +/- 12.9 percent; P = 0.004). Spontaneous intermittent coronary recanalization and reocclusion resulting from a variable combination of thrombosis and vasoconstriction are frequent during the early phase of acute myocardial infarction. We propose that the combination of intracoronary streptokinase and isosorbide dinitrate may increase the rate of stable coronary recanalization.

Adult↗

Continuous Fick cardiac output compared to continuous pulmonary artery electromagnetic flow measurement in pigs.

A system for continuous Fick cardiac output measurement (CFCO) is described and compared to continuous electromagnetic pulmonary artery flow (EMCO) and intermittent thermodilution (TDCO) measurements. Oxygen consumption was determined from continuous respiratory gas exchange analysis and arterio-venous oxygen difference from fiberoptic oximetry. A computer calculated cardiac output and other variables every 20 s. Seven pigs were monitored for a total of 10 h, during which cardiac output was manipulated by obstructing venous return or infusing epinephrine. 1748 pairs of EMCO and CFCO values were compared. The best correlation was obtained when CFCO was advanced 20 s with respect to EMCO (R = .89, CFCO = .99 EMCO + .16). TDCO was compared to EMCO during periods of steady state (R = .85, TDCO = .89 EMCO + 1.25, N = 139). TDCO was also compared with simultaneous CFCO (R = .87, TDCO = .89 CFCO + 1.01, N = 251). CFCO is recommended as a reliable standard of continuous cardiac output measurement. It is not a real time measurement; the technique has a time lag of approximately 20 s which is the result of the time constant of the VO2 measurement. Sources for error are discussed with suggestions for improving quality control.

Animals↗

Phaeochromocytoma as a cause of pulmonary oedema.

Phaeochromocytoma can mimic many serious disease entities. This report describes a 43-year-old man who presented with pulmonary oedema due to a phaeochromocytoma. Predominantly adrenaline-secreting tumours seem to predispose to this complication. Labetalol, a combined alpha- and beta-receptor blocker, should be considered as the initial treatment in these cases and continued during surgery.

Adrenal Gland Neoplasms↗

Preoperative myocardial ischaemia: its relation to perioperative infarction.

One hundred consecutive patients undergoing coronary artery bypass surgery were randomly allocated to a preoperative (24 h) intravenous infusion of isosorbide dinitrate (1.5-15 mg/hr) (50 patients) or to placebo (50 patients). The characteristics of the two groups were similar. Evidence of acute myocardial ischaemia was sought by continuous electrocardiographic Holter recordings and acute myocardial infarction by the appearance of new Q waves and increased activity of the creatine kinase MB isoenzyme. Episodes of acute myocardial ischaemia were found in 18% of patients in the control group and in none of those who received isosorbide dinitrate. None the less, the frequency of perioperative myocardial infarction was similar (22% and 18% respectively) in the two groups. Perioperative infarction was significantly more common in women, in patients with unstable angina or poor left ventricular function, in those who had coronary endarterectomy, and in those in whom the aortic clamping time was greater than 50 minutes. These factors may have obscured any effect that prevention of preoperative ischaemia had on perioperative infarction. Preoperative infusion of isosorbide dinitrate eliminated preoperative ischaemia but did not influence the occurrence of perioperative infarction. The probable benefits of prevention of preoperative ischaemia on postoperative left ventricular function, which is a determinant of long term survival, remain to be established.

Acute Disease↗

Induction of coronary artery spasm by a direct local action of ergonovine.

To investigate whether ergonovine acts directly on coronary arteries or via remote neurohumoral reflexes, we administered small titrated increments of intracoronary ergonovine up to a maximum cumulative dose of 50 micrograms to 15 patients. In six patients with variant angina (group 1), ischemic electrocardiographic ST changes, angina, and localized coronary spasm (local coronary diameter reduction of 87.8 +/- 18.9% [mean +/- SD]) followed after 6 to 50 micrograms (mean 20.7) cumulative intracoronary ergonovine. In nine patients with atypical chest pain, normal baseline coronary arteriograms, and no evidence of variant angina (group 2), there was no ischemic ST segment change or localized coronary spasm after 6 to 50 micrograms (mean 31.6) intracoronary ergonovine. Coronary diameter of proximal vessels of patients in group 2 was reduced by 16.2 +/- 6.5% and did not differ from the response of nonspastic vessels of comparable size of group 1 (20.5 +/- 13.8%; p = .7). There was no significant difference in the median effective dose values in the dose-response curves of the spastic and nonspastic segments between groups 1 and 2. Ergonovine causes coronary spasm by a direct local effect, which seems to be caused by localized arterial hyperreactivity rather than supersensitivity. Intracoronary delivery may be safer than intravenous administration because negligible drug recirculation may prevent perpetuation of spasm and selective coronary administration can avoid branches with critical stenoses.

Coronary Vasospasm↗

Retinal pigment epithelial cells secrete substances that are chemotactic for monocytes.

Monocyte/macrophages play a prominent role in several forms of retinal pathology including proliferative vitreoretinopathy, senile macular degeneration, and retinal wound healing. In each of these entities, the retinal pigment epithelium (RPE) is characteristically involved as well. Since RPE cells are known to secrete chemoattractants for astrocytes, we considered the possibility that they might secrete chemotactic factors for monocytes in addition. We have found in in vitro assays that a 5% concentration of medium from 6 different well-established RPE culture lines each consistently induced monocyte migration greater than that elicited by either buffer or unconditioned medium. "Checkerboard" analysis indicated that RPE culture supernatants induced optimal migration with a stimulus gradient (chemotaxis as opposed to chemokinesis alone). Chemotactic activity could be detected in eluates from ion exchange high performance liquid chromatography or gel filtration columns. Several peaks of activity suggested that more than one factor may be responsible for the ability to induce cell migration. The chemotactic activity was largely heat stable. The chemotactic factor induced only minimal migration of polymorphonuclear leukocytes. The secretion of chemotactic factors for monocytes could contribute significantly to the pathogenesis of several retinal diseases.

Cell Line↗

Detection of spread of malignant lymphoma to the liver by low field strength magnetic resonance imaging.

The accuracy of spin lattice relaxation time (T1) measurement obtained with a low field strength magnetic resonance imager for the detection of spread of malignant lymphoma to the liver was assessed. The results of histological examination obtained at open liver biopsy were compared with liver T1 values in 27 patients with lymphoma. The normal range for T1 was established by scanning 61 healthy volunteers. Magnetic resonance imaging was highly sensitive in detecting hepatic lymphoma, all seven patients with liver lymphoma proved by biopsy having considerably higher T1 values. Specificity was less good. Five out of 20 patients with no histological evidence of hepatic lymphoma had abnormal T1 values. this level of sensitivity is considerably better than that reported for other imaging methods and contrasts with the results of one previous study using a different magnetic resonance system. Low field strength magnetic resonance imaging may prove to be a useful screening test in patients with lymphoma. The presence of a normal liver T1 seems to be a reliable guide to the absence of hepatic disease.

Adolescent↗

Variability of results during repeat exercise stress testing in patients with stable angina pectoris: role of dynamic coronary flow reserve.

In some patients with stable angina, the variability of results during repeated exercise tests is higher than in others with similar symptoms. The aim of the study was to assess whether this difference can be explained by a different susceptibility of the coronary arteries to vasoconstrictor stimuli. Ten patients (group A) with stable angina, who developed myocardial ischemia (angina and ST segment depression greater than 0.1 mV) following ergonovine-induced coronary constriction, and 10 other patients (group B) with stable angina, but a negative ergonovine test result, were subjected to two treadmill exercise tests. The variability of heart rate and heart rate-blood pressure product at 0.1 mV ST segment depression was significantly higher in group A than in group B (12 +/- 4 vs 4 +/- 4 bpm, respectively, p less than 0.001 and 3366 +/- 1900 vs 930 +/- 960 bpm X mm Hg, respectively, p less than 0.005), such as the variability of heart rate-blood pressure product at the onset of angina (3887 +/- 2400 vs 1428 +/- 1800 bpm X mm Hg, respectively, p less than 0.04). The remaining exercise parameters were always more variable in group A than in group B, but these differences did not achieve statistical significance. Thus patients with stable angina who develop myocardial ischemia in response to ergonovine have a larger variability of results during repeat exercise testing. Such findings could be explained by an enhanced susceptibility to the coronary constrictor effects of exercise resulting in dynamic changes in coronary flow reserve.

Aged↗

Differential transmyocardial platelet behavior in response to pacing and ergonovine-induced myocardial ischemia.

In 17 anginal patients with critical narrowing of the left anterior descending artery, we studied the effects of acute ischemia, either induced by atrial pacing or by ergonovine, on transmyocardial platelet behavior. Six other patients with atypical chest pain and normal coronary arteries served as controls. Simultaneous arterial and great cardiac vein samples were drawn during control and ischemia to measure the levels of platelet factor four (PF4) and beta-thromboglobulin (BTG). During pacing-induced ischemia the great cardiac vein-arterial differences of PF4 and BTG decreased significantly, indicating a reduced platelet aggregability; no significant changes were observed in the control patients. By contrast, when ischemia resulted from ergonovine-induced spasm of the left anterior descending artery (five patients), the great cardiac vein-arterial differences increased, indicating enhanced platelet aggregability. Again no differences were observed in the patients with a negative ergonovine test. The results of our study suggest that the transcardiac platelet behavior may vary during different ischemic conditions. When ischemia is due to increased myocardial demands and flow is normal or increased, myocardial metabolites released from the ischemic area may oppose platelet aggregation. By contrast, spasm and the stagnant flow resulting from it may enhance platelet aggregation.

Adult↗