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Biomedical subjects

B Sinclair

Publications and source records attributed to B Sinclair.

16 recordsLinked to original sources
PubMed1999

Prenatal features of ductus arteriosus constriction and restrictive foramen ovale in d-transposition of the great arteries.

BACKGROUND: Although most neonates with d-transposition of the great arteries (TGA) have an uncomplicated preoperative course, some with a restrictive foramen ovale (FO), ductus arteriosus (DA) constriction, or pulmonary hypertension may be severely hypoxemic and even die shortly after birth. Our goal was to determine whether prenatal echocardiography can identify these high-risk fetuses with TGA. METHODS AND RESULTS: We reviewed the prenatal and postnatal echocardiograms and outcomes of 16 fetuses with TGA/intact ventricular septum or small ventricular septal defect. Of the 16 fetuses, 6 prenatally had an abnormal FO (fixed position, flat, and/or redundant septum primum). Five of the 6 had restrictive FO at birth. Five fetuses had DA narrowing at the pulmonary artery end in utero, and 6 had a small DA (diameter z score of <-2.0). Of 4 fetuses with the most diminutive DA, 2 also had an abnormal appearance of the FO, and both died immediately after birth. One other fetus had persistent pulmonary hypertension. Eight fetuses had abnormal Doppler flow pattern in the DA (continuous high-velocity flow, n=1; retrograde diastolic flow, n=7). CONCLUSIONS: Abnormal features of the FO, DA, or both are present in fetuses with TGA at high risk for postnatal hypoxemia. These features may result from the abnormal intrauterine hemodynamics in TGA. A combination of restrictive FO and DA constriction in TGA may be associated with early neonatal death.

Constriction, Pathologic↗
PubMed1998

Cerebral blood flow velocities monitored by transcranial Doppler during cardiac catheterizations in children.

Transcranial Doppler (TCD) was used to evaluate brain circulation during cardiac catheterizations in 32 children requiring pulmonary (n=10) or aortic balloon dilatations (n=2), ductus arteriosus coil insertions (n=5), or angiography (n=15). Cerebral blood flow velocity (CBFV) in the middle cerebral artery was measured before (baseline), during, and after each procedure (mean+/-95%ci). High-intensity transient signals (HITS) were also detected during these maneuvers. Balloon angioplasty decreased CBFV by 63+/-11% from baseline (P < 0.01). Shorter durations of the inflation cycle resulted in earlier CBFV recovery (r=0.78). During angiography, CBFV increased by 11+/-4% (P < 0.01) in all except one case that showed retrograde diastolic flow. Mean total HITS count was 44 (95%ci.limits: 27,74). These signals were more frequently found in septal defects or systemic arterial manipulations. Pediatric cardiac catheterization may impose transient fluctuations in brain perfusion as indicated by TCD, but their clinical implications are uncertain. CBFV changes during balloon angioplasty emphasize the importance of rapid inflation/deflation cycles. TCD can monitor such changes and evaluate preventive measures.

Adolescent↗
PubMed1998

Temporal variability of vena contracta and jet areas with color Doppler in aortic regurgitation: a chronic animal model study.

OBJECTIVE: The purpose of our study was to determine the temporal variability of regurgitant color Doppler jet areas and the width of the color Doppler imaged vena contracta for evaluating the severity of aortic regurgitation. METHODS: Twenty-nine hemodynamically different states were obtained pharmacologically in 8 sheep 20 weeks after surgery to produce aortic regurgitation. Aortic regurgitation was quantified by peak and mean regurgitant flow rates, regurgitant stroke volumes, and regurgitant fractions determined using pulmonary and aortic electromagnetic flow probes and meters balanced against each other. The regurgitant jet areas and the widths of color Doppler imaged vena contracta were measured at 4 different times during diastole to determine the temporal variability of this parameter. RESULTS: When measured at 4 different temporal points in diastole, a significant change was observed in the size of the color Doppler imaged regurgitant jet (percent of difference: from 31.1% to 904%; 233% +/- 245%). Simple linear regression analysis between each color jet area at 4 different periods in diastole and flow meter-based severity of the aortic regurgitation showed only weak correlation (0.23 < r < 0.49). In contrast, for most conditions only a slight change was observed in the width of the color Doppler imaged vena contracta during the diastolic regurgitant period (percent of difference, vena contracta: from 2.4% to 12.9%, 5.8% +/- 3.2%). In addition, for each period the width of the color Doppler imaged vena contracta at the 4 different time periods in diastole correlated quite strongly with volumetric measures of the severity of aortic regurgitation (0.81 < r < 0.90) and with the instantaneous flow rate for the corresponding period (0.85 < r < 0.87). CONCLUSIONS: Color Doppler imaged vena contracta may provide a simple, practical, and accurate method for quantifying aortic regurgitation, even when using a single frame color Doppler flow mapping image.

Animals↗
PubMed1996

Effective regurgitant orifice area by the color Doppler flow convergence method for evaluating the severity of chronic aortic regurgitation. An animal study.

BACKGROUND: The aim of the present study was to evaluate dynamic changes in aortic regurgitant (AR) orifice area with the use of calibrated electromagnetic (EM) flowmeters and to validate a color Doppler flow convergence (FC) method for evaluating effective AR orifice area and regurgitant volume. METHODS AND RESULTS: In 6 sheep, 8 to 20 weeks after surgically induced AR, 22 hemodynamically different states were studied. Instantaneous regurgitant flow rates were obtained by aortic and pulmonary EM flowmeters balanced against each other. Instantaneous AR orifice areas were determined by dividing these actual AR flow rates by the corresponding continuous wave velocities (over 25 to 40 points during each diastole) matched for each steady state. Echo studies were performed to obtain maximal aliasing distances of the FC in a low range (0.20 to 0.32 m/s) and a high range (0.70 to 0.89 m/s) of aliasing velocities; the corresponding maximal AR flow rates were calculated using the hemispheric flow convergence assumption for the FC isovelocity surface. AR orifice areas were derived by dividing the maximal flow rates by the maximal continuous wave Doppler velocities. AR orifice sizes obtained with the use of EM flowmeters showed little change during diastole. Maximal and time-averaged AR orifice areas during diastole obtained by EM flowmeters ranged from 0.06 to 0.44 cm2 (mean, 0.24 +/- 0.11 cm2) and from 0.05 to 0.43 cm2 (mean, 0.21 +/- 0.06 cm2), respectively. Maximal AR orifice areas by FC using low aliasing velocities overestimated reference EM orifice areas; however, at high AV, FC predicted the reference areas more reliably (0.25 +/- 0.16 cm2, r = .82, difference = 0.04 +/- 0.07 cm2). The product of the maximal orifice area obtained by the FC method using high AV and the velocity time integral of the regurgitant orifice velocity showed good agreement with regurgitant volumes per beat (r = .81, difference = 0.9 +/- 7.9 mL/beat). CONCLUSIONS: This study, using strictly quantified AR volume, demonstrated little change in AR orifice size during diastole. When high aliasing velocities are chosen, the FC method can be useful for determining effective AR orifice size and regurgitant volume.

Animals↗
PubMed1996

Evaluation of aortic regurgitation with digitally determined color Doppler-imaged flow convergence acceleration: a quantitative study in sheep.

OBJECTIVES: The aim of the present study was to validate a digital color Doppler-based centerline velocity/distance acceleration profile method for evaluating the severity of aortic regurgitation. BACKGROUND: Clinical and in vivo experimental applications of the flow convergence axial centerline velocity/distance profile method have recently been used to estimate regurgitant flow rates and regurgitant volumes in the presence of mitral regurgitation. METHODS: In six sheep, a total of 19 hemodynamic states were obtained pharmacologically 14 weeks after the original operation in which a portion of the aortic noncoronary (n = 3) or right coronary (n = 3) leaflet was excised to produce aortic regurgitation. Echocardiographic studies were performed to obtain complete proximal axial flow acceleration velocity/distance profiles during the time of peak regurgitant flow (usually early in diastole) for each hemodynamic state. For each steady state, the severity of aortic regurgitation was assessed by measurement of the magnitude of the regurgitant flow volume/beat, regurgitant fraction and instantaneous regurgitant flow rates determined by using both aortic and pulmonary artery electromagnetic flow probes. RESULTS: Grade I regurgitation (regurgitant volume/beat < 15 ml, six conditions), grade II regurgitation (regurgitant volume/beat between 16 ml and 30 ml, five conditions) and grade III-IV regurgitation (regurgitant volume/beat > 30 ml, eight conditions) were clearly separated by using the color Doppler centerline velocity/distance profile domain technique. Additionally, an equation for correlating "a" (the coefficient from the multiplicative curve fit for the velocity/distance relation) with the peak regurgitant flow rates (Q [liters/min]) was derived showing a high correlation between calculated peak flow rates by the color Doppler method and the actual peak flow rates (Q = 13a + 1.0, r = 0.95, p < 0.0001, SEE = 0.76 liters/min). CONCLUSIONS: This study, using quantified aortic regurgitation, demonstrates that the flow convergence axial centerline velocity/distance acceleration profile method can be used to evaluate the severity of aortic regurgitation.

Animals↗
PubMed1996

Three-dimensional reconstruction of color Doppler flow convergence regions and regurgitant jets: an in vitro quantitative study.

OBJECTIVES: This study sought to investigate the applicability of a current implementation of a three-dimensional echocardiographic reconstruction method for color Doppler flow convergence and regurgitant jet imaging. BACKGROUND: Evaluation of regurgitant flow events, such as flow convergences or regurgitant jets, using two-dimensional imaging ultrasound color flow Doppler systems may not be robust enough to characterize these spatially complex events. METHODS: We studied two in vitro models using steady flow to optimize results. In the first constant-flow model, two different orifices were each mounted to produce flow convergences and free jets--a circular orifice and a rectangular orifice with orifice area of 0.24 cm(2). In another flow model, steady flows through a circular orifice were directed toward a curved surrounding wall to produce wall adherent jets. Video composite data of color Doppler flow images from both free jet and wall jet models were reconstructed and analyzed after computer-controlled 180 degrees rotational acquisition using a TomTec computer. RESULTS: For the free jet model there was an excellent relation between actual flow rates and three-dimensional regurgitant jet volumes for both circular and rectangular orifices (r = 0.99 and r = 0.98, respectively). However, the rectangular orifice produced larger jet volumes than the circular orifice, even at the same flow rates (p < 0.0001). Calculated flow rates by the hemispheric model using one axial measurement of the flow convergence isovelocity surface from two-dimensional color flow images underestimated actual flow rate by 35% for the circular orifice and by 44% for the rectangular orifice, whereas a hemielliptic method implemented using three axial measurements of the flow convergence zone derived using three-dimensional reconstruction correlated well with and underestimated actual flow rate to a lesser degree (22% for the circular orifice, 32% for the rectangular orifice). In the wall jet model, the jets were flattened against and spread along the wall and had reduced regurgitant jet volumes compared with free jets (p < 0.01). CONCLUSIONS: Three-dimensional reconstruction of flow imaged by color Doppler may add quantitative spatial information to aid computation methods that have been used for evaluating valvular regurgitation, especially where they related to complex geometric flow events.

Echocardiography, Doppler, Color↗
PubMed1996

Evaluation of eccentric aortic regurgitation by color Doppler jet and color Doppler-imaged vena contracta measurements: an animal study of quantified aortic regurgitation.

To evaluate the utility of measurements of the color Doppler jet area, jet length, and width of the color Doppler-imaged vena contracta (the smallest flow diameter in any part of the flow acceleration field) as methods for quantifying aortic regurgitation (AR), eight sheep with surgically induced AR were studied. AR was quantified as peak and mean regurgitant flow rates, regurgitant stroke volumes, and regurgitant fractions as determined with pulmonary and aortic electromagnetic flow probes and flowmeters balanced against each other. Simple linear regression analysis between the maximal color jet areas, jet length, and flowmeter data showed only moderately good correlation (jet area: 0.42 < or = r < or = 0.57, SEE = 2.85 cm2; jet length: 0.42 < or = r < or = 0.59, SEE = 1.23 cm). In contrast, the width of color Doppler-imaged vena contracta was a better indicator of the severity of AR on the basis of the electromagnetic flowmeter methods (0.73 < or = r < or = 0.90, SEE = 0.15 cm). Therefore the color Doppler jet length and jet area methods have limited use for determining AR, whereas the width of the color Doppler-imaged vena contracta can be used for quantifying the severity of AR.

Animals↗
PubMed1989

Patterns in the drug treatment of hypertension in Auckland, 1982-7.

This paper examines the pattern of drug treatment of hypertension in Auckland in the period 1982 to 1987 using data from a representative sample of the adult population interviewed in 1982 and followed up in 1987. In 1982 the age standardised prevalence of antihypertensive treatment for people aged 40-64 years was 12.2% (95%Cl 10.4, 14.0) and in 1987 it was 10.2% (95%Cl 8.5, 11.8). Over the five year period of this study, 6% of the sample untreated in 1982 began treatment with antihypertensive medication, while 24% of those on drugs in 1982 had stopped treatment by 1987. The most common medications used in both 1982 and 1987 for hypertension were diuretics and beta blockers. Over the five year period diuretic use fell and beta blocker use remained constant. In 1982 3% of hypertensives were taking a calcium antagonist but in 1987 13% were on these drugs and a further 13% were using ACE inhibitors. This study suggests that the prevalence of drug treatment for hypertension has plateaued in New Zealand; coincidentally there is a trend towards use of more expensive drugs.

Adult↗
PubMed1989

Generalized cortical dysplasia manifested by diffusely thick cerebral cortex.

Unilateral or bilateral rolandic macrogyria has been described as a cause of epilepsy and, in some cases, retardation. Tissue from the periphery of these lesions shows the changes of focal cortical dysplasia. Evidence reported herein suggests that cortical dysplasia may also be generalized. Two patients with intractable epilepsy and mental retardation had diffusely abnormal, thick cortex, shallow gyri, and poor demarcation of gray and white matter. One patient had an anterior callosotomy that led to considerable improvement of the epilepsy. Cortical layers 5 and 6 could not be differentiated on biopsy material. The white matter was poorly myelinated and contained clusters of heterotopic neurons. This syndrome, a congenital disorder of neuronal migration, with prolonged survival, represents a mild form of lissencephaly. It can be diagnosed during life by computed tomography or magnetic resonance scanning.

Adolescent↗
PubMed1988

Surface modeling of craniofacial form in human embryos with a limited graphics terminal.

Three-dimensional morphology of the human embryo typically is visualized through computerized modeling techniques utilizing planar contours as the data base. Through this approach, tissue outlines are digitized, and contour lines are superimposed, providing a depth perspective. However, these techniques represent embryonic tissues as discontinuous surfaces and therefore ignore morphological information between sections. The purpose of this study was to develop a computerized routine for the three-dimensional surface modeling of craniofacial morphology in human embryos. Tissue outlines are digitized, thus converting contour information into x,y,z coordinate data. The three-dimensional reconstruction program BCSURF opens the data file and plots each tissue polygon. A center is determined for each contour, and this value is used to divide each polygon into four segments. Surface patches are generated by mapping each segment onto the corresponding segment of subsequent sections. A face table is constructed representing the surface patches and plane normals are generated for each patch. The normal and depth values are appended to the face table, and these measures determine the color intensity for each patch. Finally, patches are plotted providing a polygon mesh model, and each patch is filled with a dither pattern according to shading values. Three-dimensional reconstructions of the craniofacial region in Carnegie embryos (stages 15-17) are generated, and major morphological features are observed. Although bilevel shading capabilities cause discontinuous shading textures, this simple and inexpensive system can be easily upgraded for high-resolution graphics.

Computer Simulation↗