Biomedical subjects

J D Thomas

Publications and source records attributed to J D Thomas.

At least 145 records · Page 8Linked to original sources

PubMed1998

Prognostic significance of exercise-induced left bundle-branch block.

CONTEXT: Approximately 0.5% of all patients who undergo exercise testing develop a transient left bundle-branch block (LBBB) during exercise, but its prognostic significance is unclear. OBJECTIVE: To determine whether exercise-induced LBBB is an independent predictor of mortality and cardiac morbidity. DESIGN: Matched control cohort study. Between September 1990 and February 10, 1994, 17277 exercise stress tests were performed on patients. SETTING: Tertiary care, academic medical center. PATIENTS: From the cohort, 70 cases of exercise-induced LBBB were identified. The controls comprised 70 individuals without LBBB at rest or during exercise that matched the 70 cases based on age, test date, sex, prior history of coronary artery disease, hypertension, diabetes, smoking, and beta-blocker use. MAIN OUTCOME MEASURES: All-cause mortality, percutaneous coronary intervention, open heart surgery, nonfatal myocardial infarction, documented symptomatic or sustained ventricular tachydysrhythmia, or implantation of a permanent pacemaker or an implantable cardiac defibrillator. RESULTS: A total of 37 events (28 events from the exercise-induced LBBB cases and 9 from the control cohort) occurred in 25 patients (17 exercise-induced LBBB patients and 8 control patients) during a mean follow-up period of 3.7 (0.9 years) (median, 3.8 years [range, 0.9-5.2 years]). There were 7 deaths, of which 5 occurred among patients with exercise-induced LBBB. Four-year Kaplan-Meier event rates were 19% among exercise-induced LBBB patients and 10% among controls (log-rank chi2, 5.2; P=.02). After further adjusting for small differences in age, exercise-induced LBBB remained associated with a higher risk of primary events (adjusted relative risk, 2.78; 95% confidence interval, 1.16-6.65; P=.02). CONCLUSION: Exercise-induced LBBB independently predicts a higher risk of death and major cardiac events.

Aged↗

PubMed1998

Quantification of intramural calcification in coronary intravascular ultrasound images with automated image analysis.

BACKGROUND: Recent studies have documented the utility of intravascular ultrasonography in quantifying coronary morphologic characteristics and determining an appropriate intervention. Unfortunately, its potential for quantifying lesion calcification is limited by subjective evaluation and manual tracing. The aim of this study was to develop an objective automated method for quantifying calcification in intracoronary images with digital image analysis. METHODS: Images of human coronary arteries acquired with a 30 MHz intracoronary ultrasound catheter were evaluated with digital image analysis and compared with manual tracings. Calcifications were automatically identified as highly echogenic regions detected by global thresholding within sectors of acoustic shadowing defined as regions devoid of texture. RESULTS: The mean percentage agreement, sensitivity, and specificity of detecting calcification in 1-degree sectors of calcified vessels were 82%, 73%, and 87%, respectively. Similar results were obtained in noncalcified images. CONCLUSION: The accuracy of this automated technique was comparable to interoperator and intraoperator variability in manually tracing calcification.

Adult↗

PubMed1998

Three-dimensional echocardiographic planimetry of maximal regurgitant orifice area in myxomatous mitral regurgitation: intraoperative comparison with proximal flow convergence.

OBJECTIVES: We sought to validate direct planimetry of mitral regurgitant orifice area from three-dimensional echocardiographic reconstructions. BACKGROUND: Regurgitant orifice area (ROA) is an important measure of the severity of mitral regurgitation (MR) that up to now has been calculated from hemodynamic data rather than measured directly. We hypothesized that improved spatial resolution of the mitral valve (MV) with three-dimensional (3D) echo might allow accurate planimetry of ROA. METHODS: We reconstructed the MV using 3D echo with 3 degrees rotational acquisitions (TomTec) using a transesophageal (TEE) multiplane probe in 15 patients undergoing MV repair (age 59 +/- 11 years). One observer reconstructed the prolapsing mitral leaflet in a left atrial plane parallel to the ROA and planimetered the two-dimensional (2D) projection of the maximal ROA. A second observer, blinded to the results of the first, calculated maximal ROA using the proximal convergence method defined as maximal flow rate (2pi(r2)va, where r is the radius of a color alias contour with velocity va) divided by regurgitant peak velocity (obtained by continuous wave [CW] Doppler) and corrected as necessary for proximal flow constraint. RESULTS: Maximal ROA was 0.79 +/- 0.39 (mean +/- SD) cm2 by 3D and 0.86 +/- 0.42 cm2 by proximal convergence (p = NS). Maximal ROA by 3D echo (y) was highly correlated with the corresponding flow measurement (x) (y = 0.87x + 0.03, r = 0.95, p < 0.001) with close agreement seen (AROA (y - x) = 0.07 +/- 0.12 cm2). CONCLUSIONS: 3D echo imaging of the MV allows direct visualization and planimetry of the ROA in patients with severe MR with good agreement to flow-based proximal convergence measurements.

Adult↗

PubMed1998

Quantification of mitral regurgitation by automated cardiac output measurement: experimental and clinical validation.

OBJECTIVES: To develop and validate an automated noninvasive method to quantify mitral regurgitation. BACKGROUND: Automated cardiac output measurement (ACM), which integrates digital color Doppler velocities in space and in time, has been validated for the left ventricular (LV) outflow tract but has not been tested for the LV inflow tract or to assess mitral regurgitation (MR). METHODS: First, to validate ACM against a gold standard (ultrasonic flow meter), 8 dogs were studied at 40 different stages of cardiac output (CO). Second, to compare ACM to the LV outflow (ACMa) and inflow (ACMm) tracts, 50 normal volunteers without MR or aortic regurgitation (44+/-5 years, 31 male) were studied. Third, to compare ACM with the standard pulsed Doppler-two-dimensional echocardiographic (PD-2D) method for quantification of MR, 51 patients (61+/-14 years, 30 male) with MR were studied. RESULTS: In the canine studies, CO by ACM (1.32+/-0.3 liter/min, y) and flow meter (1.35+/-0.3 liter/min, x) showed good correlation (r=0.95, y=0.89x+0.11) and agreement (deltaCO(y-x)=0.03+/-0.08 [mean+/-SD] liter/min). In the normal subjects, CO measured by ACMm agreed with CO by ACMa (r=0.90, p < 0.0001, deltaCO=-0.09+/-0.42 liter/min), PD (r=0.87, p < 0.0001, deltaCO=0.12+/-0.49 liter/min) and 2D (r=0.84, p < 0.0001, deltaCO=-0.16+/-0.48 liter/min). In the patients, mitral regurgitant volume (MRV) by ACMm-ACMa agreed with PD-2D (r= 0.88, y=0.88x+6.6, p < 0.0001, deltaMRV=2.68+/-9.7 ml). CONCLUSIONS: We determined that ACM is a feasible new method for quantifying LV outflow and inflow volume to measure MRV and that ACM automatically performs calculations that are equivalent to more time-consuming Doppler and 2D measurements. Additionally, ACM should improve MR quantification in routine clinical practice.

Adult↗

PubMed1998

New Doppler echocardiographic applications for the study of diastolic function.

Doppler echocardiography is one of the most useful clinical tools for the assessment of left ventricular (LV) diastolic function. Doppler indices of LV filling and pulmonary venous (PV) flow are used not only for diagnostic purposes but also for establishing prognosis and evaluating the effect of therapeutic interventions. The utility of these indices is limited, however, by the confounding effects of different physiologic variables such as LV relaxation, compliance and filling pressure. Since alterations in these variables result in changes in Doppler indices of opposite direction, it is often difficult to determine the status of a given variable when a specific Doppler filling pattern is observed. Recently, color M-mode and tissue Doppler have provided useful insights in the study of diastolic function. These new Doppler applications have been shown to provide an accurate estimate of LV relaxation and appear to be relatively insensitive to the effects of preload compensation. This review will focus on the complementary role of color M-mode and tissue Doppler echocardiography and traditional Doppler indices of LV filling and PV flow in the assessment of diastolic function.

Blood Flow Velocity↗

PubMed1998

Neonatal alcohol exposure produces hyperactivity in high-alcohol-sensitive but not in low-alcohol-sensitive rats.

Children of women who consume high amounts of alcohol during their pregnancies vary greatly in physical and behavioral outcomes. Although many factors, such as dose and timing of exposure, undoubtedly contribute to this variation, one important determinant may be genetic differences in the response to alcohol. The present study examined activity levels in high alcohol sensitivity (HAS) and low alcohol sensitivity (LAS) rats following neonatal alcohol exposure. These lines were selectively bred for extremes in ethanol-induced "sleep times." The HAS and LAS offspring were exposed to alcohol via an artificial rearing procedure using the "pup-in-the-cup" technique. Rat pups were exposed to ethanol (6 g/kg/day) from postnatal day (PD) 4 through 7 and faded to a dose of 3 g/kg/day on PD 8 and 9. An artificially reared gastrostomy control group (GC) and a normally reared suckle control group (SC) were also included. Activity level was measured on PD 18 through PD 21 for 30 min daily in automated activity monitors. Neonatal ethanol exposure produced overactivity in HAS rats, relative to their controls, but the same ethanol treatment had no effect on the LAS rats. Importantly, there were no differences in blood alcohol concentrations (around 420 mg/dl) between the two lines during the treatment period. These data suggest that genetic differences in response to alcohol may be a predictor for some of the behavioral teratogenic effects of alcohol.

Animals↗

PubMed1998

Comparison of transesophageal Doppler methods with angiography for evaluation of the severity of mitral regurgitation.

Doppler evaluation of mitral regurgitation remains difficult; thus, a head-to-head comparison of the diagnostic accuracy of Doppler methods was undertaken. Fifty patients with native mitral regurgitation underwent multiplane transesophageal echocardiography within 5 days of catheterization. Angiographic grade of mitral regurgitation and, in 20 patients with grade II-IV regurgitation, invasively determined regurgitant stroke volume were compared with color Doppler area, regurgitant jet diameter, ratio of systolic to diastolic peak pulmonary venous flow velocities, and (based on the proximal convergence zone) maximal regurgitant flow rate and regurgitant orifice area. Rank correlation coefficients of angiographic grade with Doppler parameters were 0.61 for color jet area, -0.61 for pulmonary venous flow velocity ratio, 0.69 for color jet diameter, 0.79 for maximal regurgitant flow rate, and 0.78 for regurgitant orifice area (all P < .01). Convergence zone-based parameters also correlated best (r=0.73) with invasively determined regurgitant stroke volume. Receiver operating characteristic curve analysis confirmed higher diagnostic accuracy for proximal jet width and proximal convergence zone parameters than for color jet area or pulmonary venous flow velocity ratio. Proximal convergence zone parameters and proximal color jet diameter best distinguished severe from mild forms of mitral regurgitation.

Cardiac Catheterization↗

PubMed1998

Age independence of the difference in duration of pulmonary venous atrial reversal flow and transmitral A-wave flow in normal subjects.

Aging influences pulmonary venous flow and mitral inflow velocities. The duration of pulmonary venous atrial reversal flow exceeds that of the mitral inflow A wave in patients with left ventricular end-diastolic pressures greater than 15 mm Hg. The objective of this study was to investigate the effect of age on the difference between the duration of pulmonary venous atrial reversal flow and that of the mitral inflow A wave in a large number of normal individuals. Pulsed wave Doppler transthoracic echocardiograms of the pulmonary venous flow and the transmitral inflow with respiratory monitoring were made of 72 normal volunteers (40 women) ranging in age between 23 and 84 years. The differences in the durations of pulmonary venous atrial reversal flow and mitral inflow A wave were measured and their correlation with age assessed. Age was not highly correlated with the duration of pulmonary venous atrial reversal flow (r = 0.25) nor the duration of the mitral inflow A wave (r = 0.33). The duration of pulmonary venous atrial reversal flow exceeded the duration of the mitral inflow A-wave flow only in three (4%) of 72 subjects, and age was not related to the index in this group (r = -0.16; p = 0.19). The difference in durations was not significantly affected by the phase of respiration. Men had higher values on all measurements than women. The difference between the pulmonary venous atrial reversal duration and the mitral inflow A-wave duration is independent of age and thus may be used as a reliable index of left ventricular end-diastolic pressure, even in elderly patients.

Adult↗

PubMed1998

Tissue harmonic imaging: why does it work?

The recent utilization of harmonic frequencies in the imaging of both tissue and contrast agents has dramatically improved echocardiographic image quality. In contrast harmonics, the harmonic frequency energy is generated on reflection from the microbubble contrast agent. In tissue harmonics, the harmonic frequency energy is generated gradually as the ultrasonic wave propagates through the tissue. Critical to the utility of tissue-generated harmonic frequencies is their origin beyond the chest wall and their nonlinear relation to the fundamental frequency energy strength. These two characteristics of tissue-generated harmonics ensure that the echoes most likely to produce artifact are least likely to produce harmonic waves. Armed with an understanding of how these images are produced and with data emerging as to their clinical utility, we anticipate that harmonic imaging will become the standard for assessing regional and global left ventricular function in technically difficult studies.

Artifacts↗

PubMed1998

Comparison of MPEG digital video with super VHS tape for diagnostic echocardiographic readings.

BACKGROUND: Digital recording of echocardiographic studies is on the clinical horizon. However, full digital capture of complete echocardiographic studies in traditional video format is impractical, given current storage capacity and network bandwidth. To overcome these constraints, we evaluated the diagnostic image quality of digital video by using MPEG (Motion Picture Experts Group) compression. METHODS AND RESULTS: Fifty-eight complete, consecutive studies were recorded simultaneously with the use of MPEG-1 and sVHS videotape. Each matched MPEG and sVHS study pair was reviewed by two from a total of six readers, and findings were recorded with the use of a detailed, computerized reporting tool. Intrareader and interreader discrepancies were characterized as major or minor and analyzed in total and for specific subgroups of findings (left and right ventricular parameters, valvular insufficiency, and left ventricular regional wall motion). Intrareader discrepancies were reviewed by a consensus panel for agreement with either MPEG or sVHS findings. There was an exact concordance between MPEG and sVHS readings in 83% of findings. The majority of discrepancies were minor, with major discrepancies in only 2.7% of findings. There was no difference in the rate of consensus panel agreement with MPEG or sVHS for instances of intrareader discrepancy, either in total or for any subgroup of findings. Interreader discrepancy rates were nearly identical for both MPEG and sVHS. CONCLUSIONS: MPEG-1 digital video is equivalent to sVHS videotape for diagnostic echocardiography. MPEG increases the range of practical options for digital echocardiography and offers, for the first time, the advantages of digital recording in a familiar video format.

Echocardiography↗

PubMed1998

Digital echocardiographic laboratory: where do we stand?

The transition to an all-digital echocardiographic laboratory has been slow despite the advantages of digital echocardiography, the dramatic improvement in computer technology, and the acceptance by all major vendors and professional organizations of the Digital Imaging and Communications in Medicine image-formatting standard. This review article examines some current issues in digital echocardiography, including types of digital output, disk versus network exchange, digital and clinical compression techniques, and the choice of image storage format. Although specific exceptions exist, we conclude that the optimal solution will be one based on a network exchange of formatted images that follow the Digital Imaging and Communications in Medicine standard, now available from several manufacturers. For a clinical interpretation, modest compression with the Joint Photography Expert Group algorithm appears acceptable, though possible enhancements to this compression standard are also discussed. We hope this review will enable the echocardiographic community to make more intelligent choices as digital storage and transmission products become available in the marketplace.

Algorithms↗

PubMed1998

The origins, fate, and ecological significance of free amino compounds released by freshwater pulmonate snails.

The mass-specific accumulation rates (MSAR) of both total (TFAC) and individual free amino compounds (FAC) in conditioned media were measured by HPLC, using the orthophthaldialdehyde (OPA) methods, in the following cases: (a) laboratory-reared freshwater snails (B. glabrata) with chemosterilized shells; (b) Biomphalaria glabrata with non-chemosterilized shells; (c) B. glabrata faeces; (d) isolated shells of B. glabrata; and (e) 10 other species of freshwater gastropods from the Lewes Brooks, East Sussex, U.K. The MSAR values for B. glabrata show that 95% of the TFAC's (predominantly ethanolamine, phosphoserine, and the amino acids leucine, isoleucine, valine, aspartic acid, and glycine/threonine) originated from the snails themselves as the faeces and shells contributed only 5.0 and 0%, respectively. In contrast, epizootic organisms on the shells of all 10 snail species from the Lewes Brooks released significant amounts of FAC with the two smallest species (Planorbis vortex and Planorbis contortus) having the highest MSAR values. The MSAR for isolated B. glabrata mucus was 42.45 micromol x g(-1)h(-1). As 500 mg snails can release 16.67 mg of mucus daily, this could potentially result in the daily loss of 707.5 micromol of FAC. The cost/benefits of mucus secretion and the various anatomical, physiological, biochemical, and ecological mechanisms which allow freshwater snails to recover FAC's lost as a result of a high rate of urine production in their hypotonic environment, are discussed.

Amines↗

PubMed1998

The DICOM image formatting standard: its role in echocardiography and angiography.

Both echocardiography and angiography have traditionally used analog media for long-term storage, but increasingly there is the desire to develop digital storage and exchange methodology. Before digital storage can become a reality, though, standards must be agreed to by the vendor and user community to ensure global intra operability of medical instrumentation. To this end, the National Electrical Manufacturers' Association and various professional organizations from around the world have collaborated to develop the DICOM (Digital Imaging and Communications in Medicine) image formatting standard. This standard specifies the exact way in which digital images are exchanged between instruments, either using a network or storage medium, and distinct standards have been developed for angiography and echocardiography. In angiography, only gray scale images are considered, whereas in echocardiography several different types of image formats are allowed to account for color Doppler echocardiography. Distinct standards have also evolved for disk-based storage. For angiography, only storage on the writable CD-ROM is allowed, whereas echocardiograms may be stored on re-writable magneto-optical disks, floppy disks, and CD-ROMs. Only lossless compression is allowed in the angiographic standard, whereas echocardiography allows the use of the JPEG (Joint Photographic Expert Group) lossy compression algorithm. Currently, all major angiographic and echocardiographic vendors have agreed to support the DICOM standard, and products are beginning to appear, first with disk-based storage but increasingly with network-based exchange of image data.

Coronary Angiography↗

PubMed1998

Digital echocardiography.

Continued improvement in the computer price-to-performance ratio and the adoption of international standards have enhanced the feasibility of completely digital echocardiographic laboratories that were initially described more than a decade ago. Digital archival has distinct advantages over analog recording, including improved laboratory efficiency, capability of side-by-side comparison of current and historical studies, streamlined image storage, and enhanced interinstitution image transfer. Studies have demonstrated that clinical and electronic image compression allows efficient storage of data, without affecting diagnostic accuracy. Finally, digital echocardiography has important telemedicine applications.

Echocardiography↗

PubMed1998

Age-related development of atherosclerotic plaque stress: a population-based finite-element analysis.

BACKGROUND: In order to identify those age-related factors in the development of coronary atherosclerosis that would affect the stability of the plaque system, we have developed idealized, finite-element, cross-sectional models of the arterial wall and associated lesions, derived from population-based data. METHODS: The physical development and morphology of coronary plaques was documented in the Pathobiological Determinants of Atherosclerosis in Youth histological study. Using this database, finite-element analysis models were created for five age groups (15-19, 20-24, 25-29 and 30-34 years) and for the 25 largest lesions. Cosmos (Structural Research, Inc., Los Angeles, California, USA) was used to create and analyze the models. RESULTS: The area of greatest stress shifted from the intima opposite the lesion in the 15-19 years age group to the edge of the cap and adjacent healthy tissue in the later age groups. Increasing age had a strong positive correlation with the shoulder stress level (r = 0.95) and the per cent stenosis correlated well with shoulder stress (r = 0.99, P < 0.002). Increasing the cap stiffness from a soft cap to a fibrous cap in the 30-34 year age group model resulted in a localized increase in shoulder surface stress by 10%. A calcified cap increased this shoulder surface stress by 30%. CONCLUSIONS: This finite-element analysis of the population-based data shows that the increase in stress appears to be closely related to the impaired load-bearing capability of the lipid pool that develops with age. The shoulder area of the lesion has been shown to be the location of most of the plaque fractures.

Adolescent↗

PubMed1998

Segmentation and tracking in echocardiographic sequences: active contours guided by optical flow estimates.

This paper presents a method for segmentation and tracking of cardiac structures in ultrasound image sequences. The developed algorithm is based on the active contour framework. This approach requires initial placement of the contour close to the desired position in the image, usually an object outline. Best contour shape and position are then calculated, assuming that at this configuration a global energy function, associated with a contour, attains its minimum. Active contours can be used for tracking by selecting a solution from a previous frame as an initial position in a present frame. Such an approach, however, fails for large displacements of the object of interest. This paper presents a technique that incorporates the information on pixel velocities (optical flow) into the estimate of initial contour to enable tracking of fast-moving objects. The algorithm was tested on several ultrasound image sequences, each covering one complete cardiac cycle. The contour successfully tracked boundaries of mitral valve leaflets, aortic root and endocardial borders of the left ventricle. The algorithm-generated outlines were compared against manual tracings by expert physicians. The automated method resulted in contours that were within the boundaries of intraobserver variability.

Algorithms↗

PubMed1998

Fetal alcohol syndrome: does alcohol withdrawal play a role?

Alcohol use by a pregnant woman may interfere with the development of her fetus. Newborns whose mothers are intoxicated during delivery can experience withdrawal symptoms, such as tremors and even seizures. It is likely that withdrawal also can occur during fetal development. Thus, the possibility exists that withdrawal by the pregnant woman may exacerbate alcohol's adverse effects on her fetus. One potential mechanism through which alcohol withdrawal might damage the fetus involves the receptor for the neurotransmitter glutamate (i.e., the N-methyl-D-aspartate [NMDA] receptor). This receptor plays a crucial role during neuronal development. Excessive activation of the NMDA receptor, which occurs during withdrawal, may lead to neuronal cell death. Animal studies suggest that these effects may contribute to behavioral deficits following prenatal exposure to alcohol.

Animals↗

PubMed1997

Comparison of mortality rates and progression of left ventricular dysfunction in patients with idiopathic dilated cardiomyopathy and dilated versus nondilated right ventricular cavities.

This study assesses the influence of right ventricular (RV) dilation on the progression of left ventricular (LV) dysfunction and survival in patients with idiopathic dilated cardiomyopathy (IDC). Using transthoracic echocardiography, we studied 100 patients with IDC aged 20 to 80 years (mean 55 +/- 14); 67% were men. In the apical 4-chamber view, diastolic LV and RV chamber area measurements classified patients into 2 groups: group RV enlargement+ (RV area/LV area > 0.5) included 54 patients; group RV enlargement- (no RV enlargement) had RV area/LV area < or = 0.5. Echocardiographic studies were repeated in all patients after a mean of 33 +/- 16 months. At the time of the initial study, the 2 groups did not differ in age, gender, incidence of atrial fibrillation and diabetes, left ventricular mass, and LV ejection fraction, but the RV enlargement+ group had more severe tricuspid regurgitation and less LV enlargement. After 47 +/- 22 months (range 12 to 96), patients in group RV enlargement+ had lower LV ejection fraction (29% vs 34%, p = 0.006) than patients with initial RV enlargement-. At clinical follow-up, mortality was higher (43%) in patients with initial RV enlargement+ than the RV enlargement- patients (15%), p = 0.002. For survivors, the mitral deceleration time averaged 157 +/- 36 ms; for nonsurvivors or patients who required transplant, the mitral deceleration time averaged 97 +/- 12 ms (p < 0.0001). With use of a multivariate Cox model adjusting for LV ejection fraction, LV size, and age, the relative risk ratio of mortality from initial RV enlargement+ was 4.4 (95% confidence limits 1.7 to 11.1) (p = 0.002). Thus, patients with significant RV dilation had nearly triple the mortality over 4 years and more rapidly deteriorating LV function than patients with less initial RV dilation. In IDC, RV enlargement is a strong marker for adverse prognosis that may represent a different morphologic subset.

Adult↗