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Biomedical subjects

W A Scott

Publications and source records attributed to W A Scott.

At least 55 records · Page 3Linked to original sources
PubMed1992

Evaluation of electrocardiographic leads for detection of atrial activity (P wave) in ambulatory ECG monitoring: a pilot study.

The usual lead systems for ambulatory ECG monitoring (AECG) used in the evaluation of arrhythmias is a modified bipolar V-1 and V-5. A comparison of various lead systems to enhance the detection of atrial activity (p waves) has not been reported. We evaluated various surface lead systems in 12 subjects comparing p waves recorded at 20 mm/mV and 50 mm/sec. We compared p wave area, amplitude, and duration from modified bipolar V1 and V5 as well as seven nonstandard leads recorded on a AECG monitor. Of the seven nonstandard leads, a vertical sternal lead, with the negative pole just below the suprasternal notch and the positive pole at the xiphoid process, had the largest area (1.46 +/- 0.65 mm2), and also had a greater area than the standard V1 (0.88 +/- 0.45 mm) and V5 (1.06 +/- 0.49 mm2) lead system (P less than 0.01). We conclude that the bipolar vertical sternal lead system provides a larger p wave area than seven nonstandard bipolar lead systems and the two standard lead systems currently used in AECG monitoring. Replacement of the modified bipolar V1 lead with a vertical sternal lead should improve the recognition of atrial activity and, therefore, enhance the diagnosis of cardiac arrhythmias.

Adult↗
PubMed1991

Heat loss in an animal experimental model.

Heat loss leading to hypothermia is common during surgery, particularly when a body cavity is exposed. To determine the principal site of heat loss we used heat flux transducers to measure heat loss from the skin and the exposed abdominal cavity of seven pigs. Heat loss from the skin was 74 +/- 15 W/m2, and from the abdominal cavity, 350 +/- 122 W/m2 (p less than 0.002; ratio = 1:4.7). The area of the skin was 0.52 +/- 0.06 m2, and of the abdominal cavity, 0.04 +/- 0.006 m2 (ratio = 13.6:1). For every 13.6 watts lost from the skin, 4.7 watts were lost from the abdominal cavity; i.e. skin heat loss accounted for 74% of total heat loss. Therefore adequate insulation would reduce the incidence of hypothermia. Evaporation accounted for the largest heat loss from the abdominal cavity. Evaporative losses could be minimised by enclosing the bowel in a plastic bag.

Abdomen↗
PubMed1991

Evaluating the child with syncope.

Syncope is a multifactorial disorder; however, most pediatric syncopal episodes result from vasodepressor syndrome or the simple faint. A very detailed history and physical examination should indicate the etiology in the majority of cases. Extensive diagnostic studies are rarely necessary. Tilt table testing is a reliable way of identifying individuals predisposed to vasodepressor syncope, and may provide a means of assessing the efficacy of therapeutic interventions in those who require treatment. Treatment for syncope from etiologies other than vasodepressor syndrome is directed at the underlying cause.

Adolescent↗
PubMed1991

Acoustic analysis of the closing sounds of bileaflet prosthetic valves in a sheep model.

Previous investigations of mechanical valve sounds have shown that (1) frequency spectra of sounds produced by abnormal valves differ from those of properly functioning valves and (2) leaflets of normally functioning bileaflet valves do not close synchronously. This investigation studied effects of mechanical valve size, environment, and hemodynamic state on closing sounds. A single 25 mm bileaflet mitral mechanical valve was implanted in six sheep and a single 27 mm valve in four sheep. With digital signal processing, asynchronous leaflet closure and frequency spectra were assessed after alterations in animal position, respiratory phase, heart rate, afterload, contractility, and preload. Both asynchronous leaflet closure and frequency spectra varied among animals, and, except for a decrease in asynchrony with increasing contractility, were largely independent of valve size and hemodynamics. Baseline asynchrony ranged from 0.5 to 4.2 msec. Frequency spectra were characterized by the first three resonant peaks. Lowest resonant peaks ranged from 2.5 to 3.4 kHz, middle from 4.7 to 6.8 kHz, and highest from 7.2 to 9.6 kHz. These results indicate that accurate assessment of mechanical valve function with acoustic analysis requires baseline studies in all patients by means of a system with a frequency response of more than 10 kHz.

Animals↗
PubMed1990

Intraoperative awareness due to malfunction of a Siemens 900B ventilator.

A case of intraoperative awareness during a thoracotomy is described. The patient's recall coincided with an intraoperative period during which a Siemens 900B ventilator and a Siemens 952 isoflurane vaporiser were used. Subsequent assessment of this equipment with an anaesthetic agent analyzer revealed that, at the ventilator settings which had been used, the delivered anaesthetic vapour concentration varied greatly from the vaporizer settings. This problem eventually was traced to a malfunctioning inlet control valve on the ventilator. This complication may have been prevented if the end-tidal anaesthetic concentration had been monitored intraoperatively.

Aged↗
PubMed1990

Increased birth prevalence of cardiac defects in Yuma, Arizona.

A systematic study was undertaken to estimate the birth prevalence of congenital heart disease because there was a clinical impression that a disproportionate number of cases occurred in Yuma, Arizona. Control data were obtained from Sierra Vista, Arizona, a region with similar demographic characteristics, and from the Baltimore-Washington Infant Study. Patients with chromosomal or syndromal associations were excluded. In the Baltimore-Washington Infant Study only echocardiographic and invasively documented cases were included. From 1983 to 1988 the birth prevalence was significantly higher in Yuma (10.5/1,000) than in Sierra Vista (5.4/1,000, p less than 0.0001). As assessed only by invasive or echocardiographic diagnosis, there was a higher birth prevalence of congenital heart disease in the study population (6.7/1,000) compared with both the Baltimore-Washington Infant Study (3.7/1,000, p = 0.0008) and Sierra Vista (4.6/1,000, p = 0.04). Families were interviewed to exclude cases in which the mother did not spend the month before conception and the first trimester in Yuma or Sierra Vista. The birth prevalence for Yuma (6.0/1,000) remained significantly greater than that for Sierra Vista (3.8/1,000, p = 0.03). The exclusion of cases in which the mother resided elsewhere suggests, but does not prove, that an environmental influence may have played a role in the increased birth prevalence of congenital heart disease in this community.

Arizona↗
PubMed1990

Conversion of ouabain-induced ventricular tachycardia in dogs with epicardial lidocaine: pharmacodynamics and functional effects.

Epicardial antiarrhythmic drug administration was studied as a therapeutic approach for experimental ventricular tachycardia (VT) in an open-chest dog model. Lidocaine-polyurethane matrices (28%, w/w) were formulated as a model system. Matrices were placed on the left ventricular epicardium in each of 23 anesthetized open-chest dogs with ouabain-induced VT, to evaluate effectiveness in restoring sinus rhythm. Conversion occurred in all animals treated with matrices containing 300 mg or more of lidocaine after 1.5 to 7.0 min. The matrix lidocaine content correlated linearly with the time required for conversion to sinus rhythm (r = 0.75, P = 0.0002); irrespective of matrix size the myocardial/plasma lidocaine ratio was 20.1 +/- 4.2 (mean +/- SD) at the time of conversion. In a separate series of five dogs without ventricular tachycardia, systolic wall thickening measured with sonomicrometers after 5 min of controlled-release lidocaine administration (500- to 1000-mg matrix lidocaine content, 7.48 +/- 3.49-mg/kg dose) was only minimally diminished (-14.1%) and this effect was observed only at the site of matrix placement on the anterior-apical epicardium. In contrast, intracoronary injection of 0.3 or 1.0 mg/kg of lidocaine-HCl resulted in complete elimination of wall thickening or replacement by systolic thinning. Thus epicardial administration of lidocaine from polyurethane matrices was an effective means of treating ouabain-induced ventricular tachycardia. Regional myocardial function in the vicinity of the matrices was modified to a very limited degree, supporting the view that the matrices can be used safely, without serious risk to ventricular contractile performance.

Animals↗
PubMed1990

Efficacy of epicardial controlled-release lidocaine for ventricular tachycardia induced by rapid ventricular pacing in dogs.

The effects of epicardial lidocaine on ventricular tachycardia (VT) induced by rapid ventricular pacing (50 Hz) were studied in dogs. Lidocaine-polyurethane (28% wt/wt) matrixes (40-50 mg, 5 x 5 mm) were placed proximal to bipolar left ventricular epicardial electrodes in open-chest anesthetized dogs (n = 9) after VT was established by rapid ventricular pacing. In the first set of experiments, matrices were removed immediately after VT had converted to sinus rhythm. Control animals underwent VT induction protocol with a nondrug-containing matrix positioned next to the epicardial electrode. In the lidocaine-treated animals, VT conversion was noted in all animals and occurred after 51.7 +/- 8.9 s (mean +/- SE), with a VT threshold current elevation of 73.5 +/- 11.2% above baseline at the time of conversion which progressed to 259 +/- 44% of the initial value by 5.4 +/- 0.5 min post-matrix placement. Lidocaine 1.4 +/- 0.1 mg was delivered to the myocardium at the time of VT conversion (0.11 +/- 0.01 mg/kg). In comparison, accelerated VT persisted for 5 min in three of five control animals, and progressed to ventricular fibrillation (VF) in the other two animals. In a separate series of eight dogs, the lidocaine-polyurethane matrixes were left in palce for 4 h so that we could study the sustained antiarrhythmic action of controlled-release lidocaine on VT induction. The results of these experiments demonstrated a maintenance of the VT threshold elevation at a level of 53.9 +/- 10.8% after 4 h, with a net lidocaine dose of 0.52 +/- 0.06 mg/kg after 4 h of controlled release.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Alignment of P waves for signal averaging.

Signal averaged atrial activity recorded from the body surface is finding increased use in assessing atrial arrhythmias. The process of signal averaging is critically dependent upon precise alignment of the waveform of interest. The alignment accuracy of wide (0.01-300 Hz) and narrow (10-300 Hz) bandpass filtered P waves recorded from the body surface were compared to atrial electrograms recorded from temporary pacing wires. The locations of the filtered P waves relative to the atrial electrogram were calculated beat-by-beat for 100 beats in 15 patients aged 1 month to 71 years. The standard deviation of the alignment error for the wide filtered surface P wave averaged 1.7 +/- 0.8 msec and for the narrow filtered P waves was 0.8 +/- 0.4 ms. These results demonstrate that high pass filtering will improve alignment accuracy, and therefore, improve frequency resolution for the analysis of signal averaged P waves.

Arrhythmias, Cardiac↗
PubMed1990

Heat loss in exposed volunteers.

Hypothermia is a common complication of major surgery and trauma. We studied this problem using Heat Flux Transducers to directly measure heat exchange between seven exposed volunteers and the environment. Heat exchange by radiation and convection was measured from the anterior chest wall and by conduction, between the back and a thermal mattress (CSZ, Blanketrol II). We determined the coefficients for: radiation = 6.6; convection = 8.3 square root of v; combined radiation and convection = 9.7; conductance = 41, all expressed in W/m2.degrees C. The clinical significance of these results is that heat loss, by radiation and convection alone, is 10 W/m2.degrees C. However, heat production under anaesthesia is only 40 W/m2, so a temperature gradient of greater than 4 degrees C between the skin and environment will cause more heat to be lost than is produced. The thermal mattress can supply 41 W/m2.degrees C, effectively doubling heat production.

Body Temperature Regulation↗
PubMed1989

Recombinant bovine alpha-lactalbumin obtained by limited proteolysis of a fusion protein expressed at high levels in Escherichia coli.

A cDNA clone containing the entire coding region for bovine pre-alpha-lactalbumin (LA) together with 27 base pairs of 5'-noncoding and 268 base pairs of 3'-noncoding sequences was isolated from a bovine mammary cDNA plasmid library in the Okayama-Berg vector system using a synthetic oligonucleotide probe and sequenced. The coding segment for mature LA was subcloned into the T7 expression system of Studier and co-workers (Studier, F.W., and Moffatt, B.A. (1986) J. Mol. Biol. 189, 113-130; Rosenberg, A.H., Lade, B.N., Chui, D.S., Lin, S.W., Dunn, J.J., and Studier, F.W. (1987) Gene (Amst.) 56, 125-135) and expressed as a 21-kDa fusion protein that consisted of the mature bovine LA sequence connected to the NH2-terminal 50 residues of human cathepsin D by a linker sequence containing protease cleavage sites. This fusion protein was expressed in an insoluble form and accumulated to about 50% of the total bacterial protein within 3 h after induction of T7 RNA polymerase synthesis. The protein was solubilized, purified by gel filtration, and converted to an active form by treatment with mixtures of reduced and oxidized glutathione in the presence of Ca2+. The maximum specific activity of the fusion protein was about 25% of that of native LA, suggesting that the attachment of an NH2-terminal extension sterically hinders but does not prevent the interaction with galactosyltransferase. The extension also does not block the binding of the regulatory Ca2+ ion that is required for folding from the reduced denatured state. Trypsin cleaved the folded fusion protein specifically at a Lys-Glu bond at the junction with the mature LA sequence to give a product indistinguishable in structure and activity from native LA.

Amino Acid Sequence↗
PubMed1989

Epitopes on the major capsid protein of simian virus 40.

Thirteen monoclonal antibodies which react with the major capsid protein (VP1) of simian virus 40 (SV40) have been isolated. Of these, five neutralized viral infectivity when added in sufficient concentration. Seven of the antibodies reacted with denatured VP1 and also recognized fragments generated by protease or cyanogen bromide cleavage. The region of VP1 recognized by all seven antibodies was mapped within a nine-amino-acid segment located in the carboxyl portion of the protein (from amino acid positions 312 to 321). This region is likely to protrude from the surface of the protein as judged by high hydrophilicity and low hydropathy predicted from the amino acid sequence and lack of secondary structure by contrast with the rest of the protein for which predominantly beta-sheet structure is predicted. Competition between these antibodies and synthetic peptides for binding to virus particles confirmed that the continuous epitope is contained within the nine-amino-acid sequence. Competition between the different monoclonal antibodies suggested that the continuous epitope was also part of more complex discontinuous epitopes recognized by some of the other antibodies. These results support a model in which a segment of the carboxyl-terminal portion of VP1 protrudes from the surface of the virus to form an antigenic structure.

Algorithms↗
PubMed1989

Transcatheter electrical ablation of accessory pathways in children.

Supraventricular tachycardia (SVT), the most common sustained symptomatic arrhythmia of childhood, is often supported by a manifest or concealed accessory pathway. Permanent interruption of the accessory pathway usually requires surgical division. Recent experience with electrical ablation of posterior septal pathways in adults prompted us to apply the technique to children. Six children, ages 8 to 15 years, underwent a complete electrophysiological study followed by transcatheter electrical ablation. Five of the 6 children, 3 with a right posterior septal and 2 with a left posterior septal pathway, were approached with the ablation catheter at the os of the coronary sinus. In the remaining patient, a left lateral pathway was mapped with an electrode catheter in the coronary sinus and then approached with the ablation catheter through the patent foramen into the left atrium. Two patients are asymptomatic 18-24 months postablation; one patient had return of anomalous conduction between 7 and 21 days after ablation. Two patients had transient interruption of anomalous conduction, whereas one patient experienced no effect. We conclude that in carefully selected patients, transcatheter electrical ablation offers an alternative to surgery for permanent interruption of an accessory pathway.

Adolescent↗