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Biomedical subjects

G Davies

Publications and source records attributed to G Davies.

At least 127 records · Page 7Linked to original sources
PubMed1997

Benefit of doubt.

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Disability Evaluation↗
PubMed1997

Basal and flow-mediated nitric oxide production by atheromatous coronary arteries.

OBJECTIVES: This study assessed the effects of inhibition of nitric oxide synthesis on epicardial human coronary arteries and on coronary flow velocity during baseline conditions and during atrial pacing. BACKGROUND: Epicardial coronary artery dilation occurs in response to an increase in heart rate. It is not known whether the dilation of both angiographically normal and diseased epicardial coronary arteries during atrial pacing is nitric oxide dependent in humans. METHODS: The effects of an intracoronary infusion (4 mumol/min for 8 min) of NG-monomethyl-L-arginine (LNMMA), an inhibitor of nitric oxide synthesis, was studied in 16 patients with coronary artery disease and in 6 patients with normal coronary arteriograms. In all patients atrial pacing was performed during normal saline and during LNMMA infusion. the lumen diameter of epicardial coronary arteries was assessed by quantitative angiography, and changes in blood flow velocity were measured with a Doppler catheter. RESULTS: During saline infusion a significant increase in the lumen diameter of the proximal (p < 0.05) and distal (p < 0.01) segments of both normal and diseased arteries occurred during atrial pacing. No significant lumen diameter changes occurred in either group when atrial pacing was performed during LNMMA infusion. Stenosis diameter decreased during LNMMA infusion but did not change with atrial pacing either during saline infusion or during LNMMA infusion. The mean percent change in coronary blood flow with atrial pacing was less (p < 0.05) during LNMMA infusion than during saline infusion in both groups. CONCLUSIONS: These findings confirm that epicardial coronary artery dilation induced by pacing is nitric oxide dependent. Nitric oxide production contributes to the vasomotor tone of coronary resistance vessels. Nitric oxide is produced at the site of atheromatous stenosis but is unaffected by pacing.

Blood Flow Velocity↗
PubMed1997

Structural and sequence-based classification of glycoside hydrolases.

The diversity of oligo- and polysaccharides provides an abundance of biological roles for these carbohydrates. The enzymes hydrolysing these compounds, the glycoside hydrolases, therefore mediate a wealth of biological functions. Glycoside hydrolases fall into a number of sequence-based families. The recent analysis of these families, coupled with the burgeoning number of 3D structures, provides a detailed insight into the structure, function and catalytic mechanism of these enzymes.

Amino Acid Sequence↗
PubMed1997

Cultural factors in the recall of a witnessed event.

Can cultural factors influence testimony? To explore this hypothesis, groups of Spanish and English students (n = 48 per group) observed successively two films showing events specific to Spain (a romeria) and England (a village fete) before giving free recall and a verbal recognition test that contained lures consistent and inconsistent with cultural expectations. In addition, half the subjects were instructed to adopt the role of an observer while the remainder played the role of a participant. Significant interactions between cultural background and type of event reported were found for both recall and recognition. Contrary to expectation (i) recall accuracy was greater for the event that was not from the subject's own country (ii) recall errors were greater for the event from the subject's own country. In line with expectation, recognition accuracy was high for the event from the subject's own country. Results are discussed in terms of the operation of schema-based theories of recall and Johnson's reality-monitoring approach. The practical implications of the current findings for the interviewing of witnesses are briefly discussed.

Adolescent↗
PubMed1997

Gated technetium-99m-tetrofosmin SPECT and cine MRI to assess left ventricular contraction.

UNLABELLED: This study investigates the value of ECG-gated 99mTc-tetrofosmin SPECT in the assessment of resting left ventricular (LV) function by comparison with cine MRI. METHODS: Twenty-eight patients were recruited prospectively from those referred for routine myocardial perfusion scintigraphy. Eight had three-vessel coronary artery disease, two had two-vessel disease, five had single-vessel disease and thirteen had not previously undergone coronary angiography. Twelve patients had previous myocardial infarction. After i.v. injection at rest of 750 MBq 99mTc-tetrofosmin, ECG-gated tomograms (16 frames per cardiac cycle) were acquired after 30 min. A nine-segment model of the LV was used and images were interpreted by two observers independently. Wall motion was assessed using a six-point scale (including unclassified where no judgment was possible), and systolic wall thickening was assessed from count changes through the cycle using a five-point scale. Tracer uptake was scored using a four-point scale. Diastolic wall thickness was assessed using a four-point scale. Cine magnetic resonance images were acquired in the same planes and analyzed in an identical fashion. RESULTS: There was good overall agreement between the techniques for wall motion, thickness and thickening (kappa = 0.55-0.66), although 15 of the 252 (6%) segments were unclassified on radionuclide imaging. While there was absolute agreement in the assessment of all parameters in 10 patients with normal wall motion by MRI, agreement was less good in the 8 patients with three-vessel disease and poor left ventricular function (mean LVEF = 26%, mean LVEDV = 241 ml) (kappa = 0.37-0.48). Where tracer uptake was normal, there was good agreement between imaging, techniques (kappa = 0.64-0.75), but where uptake was absent or nearly absent, agreement was poor (kappa = 0-0.61), and 15 of 22 segments were unclassified on SPECT. CONCLUSION: Gated 99mTc-tetrofosmin imaging provides an accurate assessment of myocardial wall motion, thickening and thickness in normal left ventricles but is less valuable in poorly functioning ventricles. Six percent of segments could not be assessed because of inadequate tracer uptake.

Adult↗
PubMed1996

Origin of BSE.

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Animals↗
PubMed1996

Amniotic fluid culture failure: clinical significance and association with aneuploidy.

OBJECTIVE: To characterize clinical aspects associated with second-trimester amniotic fluid (AF) culture failure. METHODS: The reports of all amniocentesis samples received in our cytogenetic laboratory over a 9-year period were reviewed to identify cases in which culture failure of amniocytes occurred. Medical records were then reviewed for the prenatal ultrasonographic findings, karyotype when available, and clinical outcome. RESULTS: During the study period, 4134 second-trimester AF samples were processed, of which 42 (1%) failed to yield a result. Complete information was available in 41 pregnancies, which are the basis of this report. Karyotyping was done ultimately in 32 of the 41 cases (78%). The frequency of an abnormal karyotype was greater in those pregnancies in which AF culture failure occurred in comparison with those in which a cytogenetic result was obtained (six of 32 [19%] versus 149 of 4092 [4%], P < .001). There was also a greater prevalence of fetal abnormalities detected on prenatal ultrasonography, mainly oligohydramnios, hydrops, and fetal growth restriction, in the AF culture failure group compared with the successful AF culture group (17 of 41 [41%] versus 351 of 4092 [9%1, P < .001). All chromosomally abnormal fetuses had anomalies detected at ultrasonography. CONCLUSION: Our findings confirm the previously reported association between karyotype abnormality and AF culture failure, but suggest that this association is probably due to fetal anomalies, detectable on prenatal ultrasonography, that lead to decreased fetal cell shedding.

Amniocentesis↗
PubMed1996

High failure rate of postmortem karyotyping after termination for fetal abnormality.

OBJECTIVE: To determine the failure rate of karyotyping from samples taken after termination of pregnancy for fetal abnormality. METHODS: Perinatal autopsy reports over a 12-month period were reviewed to identify those with cytogenetic studies performed after termination of pregnancy for fetal abnormality. RESULTS: During the audit period, there were 104 terminations for fetal abnormality. In 89 fetuses, fetal skin (n = 85), placenta (n = 62), or other samples (n = 8) were obtained for postmortem cytogenetic analysis. In 24 (27%) fetuses, postmortem tissues did not yield a karyotype result. The failure rate of post-termination karyotyping was significantly influenced by delivery-sampling interval, but not by gestational age, type of tissue sampled, use of potassium chloride, or aneuploidy. Of the 24 cases for which no post-termination karyotype was obtained, 16 had had successful pre-termination karyotyping, resulting in only eight of 89 (9%) cases in the overall series not having a final karyotype. CONCLUSION: The high failure rate for post-termination karyotyping suggests that a pre-termination procedure is necessary if parents wish to have almost 100% certainty that cytogenetic information will be available for later genetic counseling.

Abortion, Induced↗
PubMed1996

The effect of a rigid collar on intracranial pressure.

Spinal immobilization and the application of a rigid collar to protect the neck forms an integral part of care of the injured. The very nature of collar design predisposes to vascular obstruction of blood draining from the brain and theoretically may raise intracranial pressure (ICP). We analysed this effect prospectively in a series of injured patients using the Stifneck rigid collar, the most popular collar used in the UK. Comparison of the ICP before, during and after collar application showed a significant rise (P < 0.001), a mean rise in ICP of 4.5 mmHg, with a standard deviation of 4.1 mmHg. Insignificant changes in mean arterial pressure suggested that this effect is a response to distortion of venous drainage rather than cutaneous stimulation alone. Since head-injured patients with lowered level of consciousness form a key group who require cervical spinal immobilization it is essential that secondary insults producing raised ICP are minimized. Alternative forms of cervical spinal immobilization should be considered if collars impede venous drainage through the neck.

Catheterization, Central Venous↗
PubMed1996

Variable coronary vasomotor responses to acetylcholine in patients with normal coronary arteriograms: evidence for localised endothelial dysfunction.

OBJECTIVE: The vasomotor responses of the epicardial coronary arteries to acetylcholine were examined in patients with normal coronary arteries and chest pain. DESIGN: Quantitative angiography was used to measure minimum lumen diameter of proximal and distal coronary artery segments at baseline, during intracoronary infusion of acetylcholine (10(-7) - 10(-3) mol/l), and following an intracoronary bolus (2 mg) of isosorbide dinitrate. PATIENTS: Coronary arteriograms were obtained in 15 patients (mean (SEM) age 48 (10) years) with normal coronary arteries and chest pain. MAIN RESULTS: In response to the low concentrations of acetylcholine (10(-7) - 10(-6) mol/1) 20 (61%) distal and 11 (41%) proximal segments showed dilatation (group 1), whereas 13 (39%) distal segments and 14 (52%) proximal segments showed constriction (group 2) (P < 0.05 v group 1). In group 1, the maximum dilatation induced by acetylcholine in the proximal and distal segments was 7.83 (1.19)% and 11.6 (2.2)% respectively. In group 2, the maximum constriction at higher concentration was 16.55 (3.3)% and 33.11 (11.63)% in the proximal and distal segments respectively. The two different patterns of the vasomotor response coexisted in eight (53%) of the 15 patients. Intracoronary isosorbide dinitrate caused a greater increase in the coronary luminal diameter of distal segments than in proximal segments in group 1 (25.63 (5.16)% v 12.43 (3.48)%, P < 0.01) but not in group 2 (12.65 (2.53)% v 10.82 (3.33)%. CONCLUSIONS: Constriction and dilatation may occur in proximal and distal coronary artery segments, suggesting local areas of endothelial dysfunction, in response to acetylcholine in patients with chest pain and angiographically normal coronary arteries.

Acetylcholine↗