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J D Thomas

Publications and source records attributed to J D Thomas.

At least 307 records · Page 17Linked to original sources
PubMed1989

Studies on bis(crown ether)-based ion-selective electrodes for the potentiometric determination of sodium and potassium in serum.

Bis(crown ether)-based ion-selective electrodes for sodium and potassium are described, based on the bis[(12-crown-4)-2-ylmethyl]-2-dodecyl-2-methyl malonate sensor(I) for sodium and the bis[(benzo-15-crown-5)-15-ylmethyl] pimelate sensor(II) for potassium. The best results were obtained when the sensors were used in association with 2-nitrophenyl octyl ether as plasticising solvent mediator and potassium tetrakis(4-chlorophenyl)borate as anion excluder in poly(vinyl chloride) matrices. Electrode slopes were near-Nernstian, with detection limits of less than 10(-5) M. The electrode features are compared with those of a sodium glass membrane electrode, for sensor I, and with a valinomycin-based potassium electrode, for sensor II. The electrodes are also discussed in relation to others reported for sensors I and II and are shown to be superior. However, although the electrodes described offer promising alternatives to glass electrodes for sodium and valinomycin electrodes for potassium, data for sodium and potassium measurements in blood serum indicate a need for further research in order to improve the correlation with flame photometric measurements.

Chemical Phenomena↗
PubMed1989

Cardiac conduction abnormalities during percutaneous balloon mitral or aortic valvotomy.

To evaluate the electrophysiologic changes in the cardiac conduction system that occur during percutaneous mitral or aortic balloon valvotomy, we prospectively studied the conduction system in 19 patients (10 mitral, 8 aortic, and 1 both) undergoing this procedure. A His bundle electrogram was recorded in all patients, and when sinus rhythm was present, the atrioventricular (AV) node effective refractory period was measured. Holter monitoring was performed during and for 24 hours after the procedure. Follow-up electrocardiograms (ECG) were available in 11 patients 2.3 +/- 1.5 months after the procedure. The AV node effective refractory period before (276 +/- 86 msec) and after valvotomy (298 +/- 85 msec) were not significantly different. The maximum His-Purkinje conduction time (HV interval) observed during valvotomy (66 +/- 20 msec) was significantly longer (p less than 0.01) than that measured before (57 +/- 10 msec) or after (60 +/- 18 msec) valvotomy. The mean HV intervals before and after valvotomy were not significantly different. The mean QRS complex duration increased from 95 +/- 28 to 112 +/- 28 msec during valvotomy and remained significantly prolonged (109 +/- 26 msec) 24 hours after the procedure (p less than 0.01). A new intraventricular conduction defect (QRS complex duration greater than 100 msec) or bundle branch block occurred in five of 13 patients who had normal QRS duration before the procedure. The change in HV interval did not correlate with the change in QRS complex duration. In four patients, the newly acquired intraventricular conduction defect was still present on follow-up ECG tracing. Complete heart block was not observed in any patient.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1988

The C. elegans trans-spliced leader RNA is bound to Sm and has a trimethylguanosine cap.

mRNA splicing in C. elegans is unusual: most introns are very short (approximately 50 bases), and many mRNAs receive a leader by trans-splicing. The donor in trans-splicing is a 94 nucleotide molecule, termed the leader RNA, that contributes its 5' 22 nucleotides to a variety of mRNAs. We show here that C. elegans has the usual snRNAs, which presumably catalyze the splicing reactions. As expected, they are bound to the Sm antigen and have 2,2,7-methylguanosine caps. Remarkably, the trans-spliced leader RNA is also Sm-associated and has this special cap. Hence, a molecule discovered as a substate of splicing has properties of molecules heretofore known only to facilitate splicing of other RNAs. Mature mRNAs that have received the leader evidently lack 2,2,7-methylguanosine caps, suggesting that these caps are removed or altered during processing.

Animals↗
PubMed1988

Echocardiographic evaluation of mitral valve structure and function in patients followed for at least 6 months after percutaneous balloon mitral valvuloplasty.

Although beneficial results have been reported immediately after percutaneous mitral balloon valvuloplasty, little information is available concerning the longer-term outcome of this procedure. The anatomic and functional results of percutaneous mitral valvuloplasty were assessed in 20 patients, in whom two-dimensional and Doppler echocardiographic examination could be obtained both immediately and 6 to 11 months (mean 7.5 +/- 2.0) after balloon dilation. Mean valve area measured by planimetry decreased slightly but significantly from 1.90 +/- 0.59 cm2 immediately after valvuloplasty to 1.62 +/- 0.55 cm2 (p less than 0.001) at follow-up. Individual changes in valve area were variable, and in four patients valve area decreased by greater than 25%. Echocardiographic scores of valvular morphology were obtained by assigning scores of 0 to 4 (with increasing abnormality) to each of four morphologic characteristics of the valve, namely, leaflet mobility, thickening, calcification and subvalvular thickening. This score was higher in the four patients with a decrease in valve area greater than 25% at follow-up than in the other patients (11 +/- 2 versus 7 +/- 2, p less than 0.002). Multiple regression analysis of several hemodynamic and echocardiographic factors identify first the echocardiographic score and second the valve area postvalvuloplasty as the only significant predictors of the percent decrease in valve area (r = 0.70, p less than 0.006). Mitral regurgitation graded by pulsed Doppler ultrasound decreased from 1.9 +/- 1.2 immediately after valvuloplasty to 1.0 +/- 0.9 (p less than 0.003) at follow-up, whereas there was no change in mean transmitral pressure gradient by Doppler echocardiography (5 +/- 2 versus 6 +/- 3 mm Hg, p = NS) and left atrial volume (74 +/- 34 versus 72 +/- 27 cm3, p = NS). Thus, 6 to 11 months after balloon mitral valvuloplasty, mean mitral valve area decreases slightly. Individual changes in valve area, however, are variable. Valvular morphology assessed by two-dimensional echocardiography may be useful for identifying those patients who have an increased likelihood of developing valvular restenosis.

Adult↗
PubMed1988

Improved accuracy of echocardiographic endocardial borders by spatiotemporal filtered Fourier reconstruction: description of the method and optimization of filter cutoffs.

The usefulness of digitized echocardiographic borders in quantitative regional left ventricular function analysis has been limited by the wide reported range for normal wall motion with this technique. We postulated that random error in endocardial border positioning is a major cause of this limitation. To test this hypothesis, we traced the endocardial borders field by field from 17 complete echocardiographic cycles in six dogs. These cycles showed a great deal of random movement, with each endocardial point reversing its motion an average of 18.5 times per cardiac cycle. Spatiotemporal Fourier analysis of these sequences demonstrated that most of the valid information on endocardial motion was contained in the first four temporal harmonics and the first seven spatial harmonics and that beyond these points the Fourier transform has the spectral characteristics of noise. Reconstruction of these 17 cycles eliminating all Fourier components above the sixth temporal and eighth spatial harmonics reduced the mean number of endocardial reversals per cycle to 2.3 (p less than .00001). To derive the optimal temporal and spatial cutoffs, we compared reconstructions of each of the 17 cycles with three M mode echocardiograms obtained simultaneously with the cross-sectional images. Fourier cutoffs were varied between two and 20 harmonics and demonstrated that the optimal temporal cutoff was 5.5 harmonics and optimal spatial cutoff 6.9. With optimal filtering, the correlation between ventricular diameter derived from the M mode and from the cross-sectional images was r = .965, compared with .877 for the M mode vs unfiltered cross-sectional data (p less than .0001). We conclude that two-dimensional filtered Fourier reconstruction significantly improves the accuracy of traced echocardiographic borders. This technique should be useful in the postprocessing of endocardial borders extracted by automated edge detection schemes and should also be applicable to cardiac images derived from modalities other than echocardiography.

Animals↗
PubMed1988

Correlation between echocardiographic endocardial surface mapping of abnormal wall motion and pathologic infarct size in autopsied hearts.

We previously developed a cross-sectional echocardiographic technique for quantitatively mapping the endocardial surface of the left ventricle and on which regions of abnormal wall motion can be superimposed in their correct spatial distribution. This endocardial mapping technique (EMT) provides a measure of the left ventricular endocardial surface area (ESA in cm2), the area of abnormal wall motion (AWM in cm2), and the overall percent dysfunction (%AWM) as a measure of the functional "infarct size." To test this approach, we compared the EMT measurements with the actual endocardial surface area (in cm2) and pathologic infarct size (both percent infarct by volume and percent endocardial surface overlying infarct) measured at later autopsy in 20 adults (14 men, six women) ranging in age from 47 to 76 years (mean 64 +/- 9.6 years). The median interval from echocardiographic study to death was 19 days (range 1 to 269 days). Patients were divided into two groups based on the age of their infarcts at the time of death: (1) recent (infarct age less than 14 days; mean age 5.3 +/- 4.6 days) and (2) old (infarct age greater than 6 months; mean age 3.6 +/- 3 years). When the left ventricular endocardial surface area at autopsy was compared with the EMT-derived ESA, a close correlation was found (EMT area = 1.17 X autopsy area + 20.4; r = .94, p = .0001), with the systematic difference in the measurements accounted for by systolic arrest, loss of distending pressure, and specimen shrinkage. The echocardiographic measure of infarct size (%AWM) correlated well with the autopsy percent infarction by volume (%AWM = 1.1 X infarct volume + 5.5; r = .82, p = .0001). Similarly, a good correlation was found for the percent abnormal wall motion and the autopsy percent endocardial surface area overlying infarction (%AWM = 0.89 X infarct area - 0.9; r = .89, p = .0001). When the data were examined in relation to the age of the myocardial infarct, the echocardiographic %AWM appeared to overestimate the autopsy infarct size (by percent infarct volume) in the recent infarct group (n = 6), and underestimate the extent in the old infarct group (n = 13). The findings suggest that the EMT will provide a useful quantitative measure of left ventricular endocardial surface area and the extent of ischemic/infarct-related dysfunction.

Aged↗
PubMed1988

Combined influence of ventricular loading and relaxation on the transmitral flow velocity profile in dogs measured by Doppler echocardiography.

The relation of the Doppler transmitral flow velocity profile to left ventricular loading conditions and diastolic properties remains poorly described. We studied seven adult mongrel dogs with an open-chest right heart bypass model in which left atrial pressure, representing preload, was varied by controlling blood flow into the pulmonary artery and left ventricular systolic pressure, representing afterload, was controlled independently by pumping blood into or from the femoral arteries. Heart rate was kept constant by crushing the sinus node and pacing the right atrium. Mitral inflow velocity profiles were measured by pulsed-wave Doppler echocardiography at multiple left atrial and left ventricular systolic pressures. In individual dogs, the peak E-wave velocity increased linearly with increasing left atrial V-wave pressure at constant left ventricular systolic pressure and decreased with increasing left ventricular systolic pressure at constant left atrial pressure. Stepwise multiple linear regression analysis of data pooled from all experimental stages in all dogs identified left atrial V-wave pressure, the time constant of relaxation (TL), and left ventricular systolic pressure, in order of decreasing significance, as predictors of the peak E-wave velocity (n = 82, multiple r = 0.87, p less than 0.0001). Multivariate analysis with the same three factors in individual dogs yielded higher r values (mean r = 0.89; range, 0.85-0.97), suggesting the presence of important interdog differences that were not accounted for by these three factors alone. When the values of codeterminant hemodynamic factors were kept within narrower limits, correlations between peak E-wave velocity and left atrial V-wave pressure (n = 35, multiple r = 0.83, p less than 0.0001), TL (n = 76, multiple r = -0.54, p less than 0.0001) and left ventricular systolic pressure (n = 20, multiple r = -0.59, p less than 0.005) improved substantially. In the pooled data, the relation of the peak E-wave velocity to left atrial V-wave pressure was shifted downward by an increase in TL (reduced relaxation rate), and the relation of the peak E-wave velocity to TL was shifted upward by an increase in left atrial V-wave pressure. Multivariate analysis also selected left atrial V-wave pressure and TL as the two most significant correlates of the velocity-time integral and deceleration rate of the E wave.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Inaccuracy of mitral pressure half-time immediately after percutaneous mitral valvotomy. Dependence on transmitral gradient and left atrial and ventricular compliance.

Mitral pressure half-time (T1/2) is widely used as an independent measure of mitral valve area in patients undergoing percutaneous mitral valvotomy. However, fluid dynamics theory predicts T1/2 to be strongly dependent on chamber compliance and the peak transmitral gradient, which are variables that change dramatically with valvotomy. These theoretical predictions were tested in an in vitro model of the left heart where valve area, chamber compliance, and initial gradient were independently adjusted. Measured T1/2 was observed to vary inversely with orifice area and directly with net chamber compliance and the square root of the initial pressure gradient. Theoretical predictions of T1/2 agreed with observed values with r = 0.998. To test this theory in vivo, the hemodynamic tracings of 18 patients undergoing mitral valvotomy were reviewed. Predictions were made for T1/2 assuming dependence only on valve area; these showed some correlations before valvotomy (r = 0.48-0.64, p less than 0.05) but none after valvotomy (r = 0.05-0.28, p = NS). Predictions for T1/2 based on the theoretical derivation (and thus including compliance and pressure in their calculation) were much better: before valvotomy, r = 0.93-0.96, p less than 0.0001; after valvotomy, r = 0.52-0.66, p less than 0.05. These data indicate that T1/2 is not an independent inverse measure of mitral valve area but is also directly proportional to net chamber compliance and the square root of the initial transmitral gradient. These other factors render T1/2 an unreliable measure of mitral valve area in the setting of acute mitral valvotomy.

Catheterization↗
PubMed1987

Effect of metoprolol on the submaximal stress test performed early after acute myocardial infarction.

To determine the effect of beta-adrenergic blockade on the submaximal stress test after acute myocardial infarction (AMI), 36 post-AMI patients performed their treadmill test on 2 separate days, with and without metoprolol, in a double-blind, placebo-controlled, crossover design study. Rest and peak submaximal exercise heart rate was diminished by 100 mg of metoprolol administered twice daily (from 84 +/- 3 to 68 +/- 2 beats/min, p less than 0.001, and from 126 +/- 3 to 97 +/- 2 beats/min, p less than 0.001, respectively) compared with placebo. Rest and peak submaximal systolic blood pressure was also decreased (from 121 +/- 3 to 108 +/- 2 mm Hg, p less than 0.001, and from 151 +/- 4 to 124 +/- 3 mm Hg, p less than 0.001). Exercise-induced ST-segment depression of 1 mm or more from baseline occurred in 12 patients taking placebo. However, only 4 of these patients had ST depression when they exercised while taking metoprolol (p less than 0.05). Angina pectoris occurred in 4 patients taking placebo but in only 1 of these taking a beta-blocking drug. It is concluded that beta-blocking therapy renders the post-AMI submaximal stress test less sensitive for markers of exercise-induced ischemia than if the test is performed without the drug. Therefore, when using the prognostic information of published studies, it is important to define the conditions surrounding the exercise test.

Adult↗
PubMed1987

Disease, lifestyle, and consanguinity in 58 American Gypsies.

Medical data on 58 Gypsies in the area of Boston, Massachusetts, were analysed together with a pedigree linking 39 of them in a large extended kindred. Hypertension was found in 73%, diabetes in 46%, hypertriglyceridaemia in 80%, hypercholesterolaemia in 67%, occlusive vascular disease in 39%, and chronic renal insufficiency in 20%. 86% smoked cigarettes and 84% were obese. Thirteen of twenty-one marriages were consanguineous, yielding an inbreeding coefficient of 0.017. The analysis suggests that both heredity and environment influence the striking pattern of vascular disease in American Gypsies.

Adolescent↗