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Biomedical subjects

D J Sahn

Publications and source records attributed to D J Sahn.

At least 127 records · Page 7Linked to original sources
PubMed1992

Comparative imaging techniques and models.

The explosion of high-resolution imaging technology in recent years has led to the increasing problem of choosing imaging modalities appropriate to specific clinical questions. In terms of structural information, for example, the relative benefits of ultrasound versus magnetic resonance imaging versus computed tomography scanning are often readily apparent, but in the related area of flow velocity imaging, difficulties may arise. These are perpetuated by the relative lack of information on the fundamental display characteristics of these imaging techniques. Much of this essential information can be acquired from in vitro modeling of the pressure and flow characteristics of a variety of pathologic lesions. The information obtained from such experimental investigation can provide a basis for a more rational approach to the interpretation of these imaging modalities in the clinical setting. We review the recent role of in vitro modeling for enhancing our understanding of the display characteristics of various imaging technologies, with particular emphasis on Doppler ultrasound and color Doppler flow mapping where in vitro modeling has been most extensively studied.

Coronary Circulation↗
PubMed1992

Experimental studies to define the geometry of the flow convergence region. Laser Doppler particle tracking and color Doppler imaging.

The color flow convergence method for calculating volume flow through regurgitant or forward flow restrictive orifices has gained significant interest and a number of in vitro studies have suggested that this method is accurate, even in pulsatile models. Clinical application of the method over a wide range of conditions will require improved understanding of the effect of orifice size, flow geometry, and flow rate on the flow convergence geometry. In this study, we performed laser particle tracking investigations to allow visualization of streamlines into stenotic orifices. These streamlines are theoretically perpendicular to the isovelocity surfaces used for flow convergence calculations. We compared those observations to color flow map, flow convergence images obtained with a Toshiba 160A for orifices 5 to 15 mm 2 with flow rates of 1.5 to 9.7 L/min. Our results show that for large orifices, low flow rates, and/or low pressure gradients, more oblique streamlines in the velocity of the orifice correspond to nonhemispherical, but more elliptical, flow convergence geometries. This can be corrected for by using lower Nyquist limits and calculating flow convergence at greater distances from the orifice. Under high flow and high gradient conditions, increased Nyquist limits and shorter aliasing radii are more suitable. Our studies yield insights into flow convergence geometry and yield corrective procedures to improve volume flow calculation.

Blood Flow Velocity↗
PubMed1992

Influence of the Coanda effect on color Doppler jet area and color encoding. In vitro studies using color Doppler flow mapping.

We studied surface adherence and its effects on color Doppler jet areas and color encoding in an in vitro model with a noncompliant receiving chamber into which a steady flow jet was directed parallel to either a straight or a curved surface adjacent to and 4 mm away from the inflow orifice (1.50 mm2) with the control condition being a free jet matched for flow rates and driving pressures. Jets were imaged perpendicular to the plane of the surface, the plane in which most clinical images of jet-surface interactions are obtained. Ten different flow rates ranging from 0.13 to 0.30 l/min were used. Surface-adherent jet areas were smaller than control jets for every driving pressure-volume combination (paired t test, p less than 0.01). Computer analysis of color Doppler images showed more green and blue (reverse flow) pixels on the surface side of the adherent jets than the control jets (p less than 0.05), suggesting that viscous energy loss and flow deceleration and reversal play a role in the jet-surface interaction. Analysis of variance demonstrated that linear regression slopes of flow rate versus jet area for surface jets were lower (slopes, 11-21 cm2/l/min; r = 0.95-0.97) than those for the control (slope, 33 cm2/l/min; r = 0.97) (p less than 0.0001). Surface adherence (Coanda effect) influences jet size and color encoding, causing smaller color Doppler jet areas and greater variance and reverse velocity encoding.

Coronary Circulation↗
PubMed1992

Intraluminal ultrasound imaging through a balloon dilation catheter in an animal model of coarctation of the aorta.

BACKGROUND: Controversy still exists over the optimal balloon size, extent of vascular disruption, and long-term results of balloon dilation therapy for coarctation of the aorta. Intravascular ultrasound imaging has been used in patients with coronary artery disease to provide further insight into the anatomy of atherosclerotic lesions and the results of angioplasty and atherectomy. Initial observations of the results of balloon dilation of coarctations with intravascular ultrasound imaging have shown prominent dissections of the inner vascular layers that are often not detected by angiography. The purpose of this study was to test a new transballoon catheter ultrasonic imaging system capable of on-line direct visualization of lumen diameter and vessel wall structure for imaging before, during, and after dilation in an acute animal model of aortic coarctation. METHODS AND RESULTS: Abdominal aortic coarctations were created surgically in three 14-19-kg mongrel dogs by using Teflon gauze ties. The 6.8F ultrasound balloon catheter was placed percutaneously in the right femoral artery through a 9F sheath. Ultrasound imaging allowed measurement of the coarctation diameter, characterization of the vessel wall structure, localization of the stenosis, and placement of the midportion of the balloon at the narrowest area. Imaging through the balloon was performed through several dilations (five to eight per animal), and after balloon deflation, it provided information on postdilation diameter, intimal tears, long-segment dissections, and intramural thrombi, findings that were confirmed at postmortem examination. CONCLUSIONS: The results of this study demonstrate that imaging with a new intraballoon ultrasound device is feasible during inflation to therapeutic dilation pressures; it allows visualization of the changes in diameter and vascular wall structure after serial dilations without having to recross the obstructed area. Adaptation to larger balloon sizes and lower frequencies should make this system applicable to interventional catheterizations in patients with congenital cardiac and vascular lesions.

Animals↗
PubMed1992

Transesophageal echocardiography in infants and children with congenital heart disease.

TEE applications for children and infants with congenital heart disease are now clinically established and TEE is being used in most major pediatric cardiovascular centers. This technology has evolved to the point that it is capable of providing diagnostic quality imaging, even for small infants. With expanding technology and increasing experience, new and more sophisticated applications will be found for pediatric TEE.

Child↗
PubMed1992

Echocardiographic study of the morphology and growth of the aortic arch in the human fetus. Observations related to the prenatal diagnosis of coarctation.

BACKGROUND: In a study of normal and abnormal growth of the aorta before birth, high-resolution echocardiographic imaging of the aortic arch in 92 normal fetuses aged 16-38 weeks was used to establish normal values for aortic arch dimensions at varying gestational ages. METHODS AND RESULTS: From long-axis views of the aortic arch, the internal diameter of the aortic root, ascending aorta, transverse aortic arch, aortic isthmus, proximal descending thoracic aorta, and left common carotid artery were measured. Correlation coefficients for the diameter of each aortic arch segment when related to gestational age varied from r = 0.87 to r = 0.94 (p less than 0.001 for each), and growth curves were derived from the third and 97th percentiles around each linear regression analysis. In most of the fetuses, there was progressive tapering of the aortic arch, with the smallest diameter being at the isthmus. The ratio of the transverse aorta, isthmus, descending aorta, and aortic root to the ascending aorta remained relatively constant with gestational age, with mean values of 0.94, 0.81, 0.96, and 1.13, respectively. In five fetuses in whom a prenatal diagnosis of aortic coarctation was confirmed postnatally, transverse aortic and isthmic measurements fell on or below the third percentile for gestational age from the above data. In each case, the ratio of left common carotid artery to transverse aorta was greater than or equal to 0.73 compared with less than or equal to 0.62 for the 92 normal fetuses (mean ratios, 0.77 +/- 0.05 [SD] for coarctation versus 0.48 +/- 0.08 for normal fetuses; p less than or equal to 0.001). CONCLUSIONS: Use of normal growth curves for the developing aortic arch should facilitate the prenatal diagnosis of left heart and aortic arch abnormalities, particularly aortic coarctation, which until recently has been a difficult prenatal diagnosis to make with certainty.

Aorta, Thoracic↗
PubMed1992

Invasive and noninvasive cardiovascular imaging in the child and fetus.

The imaging technologies available for evaluating congenital cardiac disorders continue to evolve. In noninvasive areas such as color Doppler echocardiography, more sophisticated questions are being asked of the techniques: investigators want not just diagnostic information about the fetus or newborn, but fundamental predictors of prognosis. An improved understanding of the tradeoffs between magnetic resonance imaging and echocardiography for pediatric patients has evolved, and ultrasound technology has invaded invasive areas such as the operating room (with transesophageal echoscopes) and the catheterization laboratory, where it is used to guide therapeutic catheterizations; and angiography. Lastly, the newest technique, intravascular imaging, now appears applicable for pediatric patients and may yield new insights about interventional catheterization procedures, as well as about changes in the circulatory system in preoperative or postoperative congenital heart disease patients.

Cardiac Catheterization↗
PubMed1991

Applications of intravascular scanning and transesophageal echocardiography in congenital heart disease: tradeoffs and the merging of technologies.

This chapter will review the evolving role of intravascular ultrasound imaging and transesophageal echo in the care of children, infants and adults with congenital heart disease. The technologies relevant to congenital heart disease applications differ from those involving coronary disease since the intravascular structures imaged often involve visualization of large vessels and cardiac chambers. On the other hand, the requirements for transesophageal echo in children with congenital heart disease involve intraoperative (surgical) and imaging procedures in the catheterization laboratory which are performed for monitoring interventional catheterization therapy. As such, whereas the intravascular devices needed for pediatric cases involve lower frequency and sometimes larger catheters, the requirements for transesophageal echocardiography require higher frequency and smaller esophagoscopes. Applications of intravascular imaging including sizing of congenital stenoses, dilation of coarctation and valvular stenoses, imaging of intrapulmonary thrombi and monitoring of placement of ASD 'button' devices in the heart will be reviewed. The intraoperative transesophageal uses for monitoring infant surgery include procedures for tetralogy repair, transposition repair and repair of AV septal defects and other complex congenital heart disorders. Both of these 'invasive' methods of echocardiography have an important and evolving role in the management of congenital heart disease in children and infants.

Adult↗
PubMed1991

Tricuspid valve disease with significant tricuspid insufficiency in the fetus: diagnosis and outcome.

The echocardiographic studies and clinical course of 27 fetuses (mean gestational age 26.9 weeks) diagnosed in utero with tricuspid valve disease and significant tricuspid regurgitation were reviewed. The diagnosis of Ebstein's anomaly was made in 17 of the fetuses, 7 had tricuspid valve dysplasia with poorly developed but normally attached leaflets and 2 had an unguarded tricuspid valve orifice with little or no identifiable tricuspid tissue. One fetus was excluded from data analysis because a more complex heart lesion was documented at autopsy. All fetuses had massive right atrial dilation and most who were serially studied had progressive right-sided cardiomegaly. Hydrops fetalis was found in six cases and atrial flutter in five. Associated cardiac lesions included pulmonary stenosis in five cases and pulmonary atresia in six. Four fetuses with normal forward pulmonary artery flow at the initial examination were found at subsequent study to have retrograde pulmonary artery and ductal flow in association with the development of pulmonary stenosis (n = 1) and pulmonary atresia (n = 3). On review of the clinical course of the 23 fetuses (excluding 3 with elective abortion), 48% of the fetuses died in utero and 35% who were liveborn died despite vigorous medical and, when necessary, surgical management, many of whom had severe congestive heart failure. Of the four infants who survived the neonatal period, three had a benign neonatal course, all of whom were diagnosed with mild to moderate Ebstein's anomaly; only one had pulmonary outflow obstruction. An additional finding at autopsy was significant lung hypoplasia documented in 10 of 19 autopsy reports.(ABSTRACT TRUNCATED AT 250 WORDS)

Ebstein Anomaly↗
PubMed1991

A new method for noninvasive estimation of ventricular septal defect shunt flow by Doppler color flow mapping: imaging of the laminar flow convergence region on the left septal surface.

An accurate but simple and noninvasive method for quantifying flow across a ventricular septal defect has yet to be implemented for routine clinical use. A region of flow convergence is commonly imaged by Doppler color flow mapping on the left septal surface of the ventricular septal defect, appearing as a narrowed region of laminar flow with aliased flow velocities entering the orifice. If the first aliasing region represents a hemispheric isovelocity boundary of a surface of flow convergence and all flow at this surface crosses the ventricular septal defect, the flow through the defect can be estimated by using the radius (R), measured from the first alias to the orifice, and the Nyquist limit (NL) velocity (the flow velocity at the first alias). Doppler color flow imaging was performed in 18 children with a single membranous ventricular septal defect undergoing cardiac catheterization at a mean age of 29.8 months (Group I). Indexes of maximal flow rate across the defect were developed from either the radius or the area, obtained by planimetry, of the first alias, based on Doppler color flow images. All indexes were corrected for body surface area and compared with shunt flow (Qp-Qs) and pulmonary to systemic flow ratio (Qp/Qs) determined at cardiac catheterization. Doppler color flow indexes derived from images of flow convergence in both the long-axis (n = 15) and oblique four-chamber (n = 10) views correlated closely with Qp/Qs (r = 0.71 to 0.92) and Qp - Qs (r = 0.69 to 0.97).(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Flow Velocity↗
PubMed1991

Effects of pressure and volume of the receiving chamber on the spatial distribution of regurgitant jets as imaged by color Doppler flow mapping. An in vitro study.

Regurgitant jet dimensions imaged by color Doppler flow mapping have been used to evaluate the severity of valvular insufficiency in clinical studies. To study the effect of pressure and volume within the receiving chamber on the magnitude of spatial distribution of regurgitant jets assessed by color Doppler techniques, we designed a simple constant-flow model in which a jet was driven through a known orifice (1.5 mm2) into a compliant receiving chamber by a steady-flow pump. A distal tube at the outflow closed the system and maintained the volume of the chamber constant during pump operation. We varied flow rate from 60 to 270 ml/min into elastic balloons with different static compliances of 1, 2, 4.5, and 9 ml/mm Hg (pressures of 57, 28, 18, and 8 mm Hg, respectively); the balloons served as receiving chambers at the constant volume of 150 ml. We also evaluated the effect of different volumes of a receiving chamber (110, 130, and 150 ml and pressures of 5, 15, and 24 mm Hg) with a static compliance of 2 ml/mm Hg over the same range of flow rates. For each of the different balloons, jet area correlated linearly with the jet velocity across the orifice (r = 0.98, 0.99, 0.98, and 0.97) and also with flow rate (r = 0.97, 0.99, 0.98, and 0.99). At the same flow rate and volume of receiving chamber, however, the jet area imaged by color Doppler decreased as the pressure in the receiving chamber increased, although receiving-chamber volume was constant.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Flow Velocity↗
PubMed1991

Transvascular intracardiac applications of a miniaturized phased-array ultrasonic endoscope. Initial experience with intracardiac imaging in piglets.

BACKGROUND: Recent advances in miniaturization of phased-array and mechanical ultrasound devices have resulted in exploration of alternative approaches to cardiac and vascular imaging in the form of transesophageal or intravascular imaging. Preliminary efforts in adapting phased-array endoscopes designed for transesophageal use to a transvascular approach have used full-sized phased-array devices introduced directly into the right atrium in open-chested animals. The purpose of this study was to assess the feasibility of using a custom-made, very small phased-array endoscope for intracardiac imaging introduced intravascularly through a jugular venous approach in young piglets. METHODS AND RESULTS: Experimental atrial septal defects created in four piglets (3-4 weeks old) had been closed with a buttoned atrial septal defect closure device consisting of an occluder in the left atrium and a counteroccluder in the right atrium. Five to 15 days after atrial septal defect closure, the piglets were returned to the experimental laboratory, where a 6.3-mm, 17-element, 5-MHz phased-array probe mounted on a 4-mm endoscope was introduced through a cutdown incision of the external jugular vein and advanced to the right atrium. From the right atrium all four cardiac chambers, their inflows and outflows, and all four valves were well imaged with minimal superior and inferior rotation. High-resolution imaging of the atrial septum defined with anatomical accuracy, later verified by autopsy, the exact placement of both the occluder and counteroccluder in the left and right sides of the atrial septal defects and the absence of any shunting across the atrial septum in any of the four animals. CONCLUSIONS: Our efforts indicate that transvascular passage of small phased-array probes can be easily accomplished and is a promising technique for detailed visualization of cardiac structures. This approach may provide an alternative to transesophageal echocardiography, particularly for guiding interventional procedures such as placement of transcatheter closure devices in pediatric patients.

Animals↗
PubMed1991

A new method for quantitation of mitral regurgitation based on color flow Doppler imaging of flow convergence proximal to regurgitant orifice.

BACKGROUND: Imaging of the flow convergence region (FCR) proximal to a regurgitant orifice has been shown to provide a method for quantifying the regurgitant flow rate. According to the continuity principle, the FCR is constituted by concentric hemispheric isovelocity surfaces centered at the orifice. The flow rate is constant across all isovelocity surfaces and equals the flow rate through the orifice. For any isovelocity surface the flow rate (Q) is given by: Q = 2 pi r2 Vr, where 2 pi r2 is the area of the hemisphere and Vr is the velocity at the radial distance (r) from the orifice. METHODS AND RESULTS: We studied 52 consecutive patients with mitral regurgitation (mean age, 49 years; age range, 21-66 years) verified by left ventricular angiography using color flow mapping. The FCR r was measured as the distance between the first aliasing limit--at a Nyquist limit obtained by zero-shifting the velocity cutoff to 38 cm/sec--and the regurgitant orifice. Seven patients without evidence of an FCR had only grade 1+ mitral regurgitation angiographically. There was a significant relation between the Doppler-derived maximal instantaneous regurgitant flow rate and the angiographic degree of mitral regurgitation in the other patients (rs = 0.91, p less than 0.001). The regurgitant flow rate by Doppler also correlated with the angiographic regurgitant volume (r = 0.93, SEE = 123 ml/sec) in the 15 patients in normal sinus rhythm and without other regurgitant lesions in whom it could be measured. The correlation between regurgitant jet area within the left atrium and the angiographic grade was only fair (rs = 0.75, p less than 0.001). CONCLUSIONS: Color flow Doppler provides new velocity information about the proximal FCR in patients with mitral regurgitation. According to the continuity principle, the maximal instantaneous regurgitant flow rate, obtained with the FCR method, may provide a quantitative estimate of the severity of mitral regurgitation, which is relatively independent of technical factors.

Angiocardiography↗
PubMed1991

Quantification of valvular regurgitation by Doppler echocardiography.

One of the widest uses of color Doppler echocardiography is for the quantification of valvular regurgitation. In this article we review the physics and instrumentation factors related to the most commonly applied method, that of planimetering areas of regurgitant jet spray within the receiving chamber, and relate features such as instrument gain, pulse repetition frequency, and important physical parameters such as receiving chamber compliance and driving pressure to the application of this method for precordial as well as transesophageal echocardiography. New approaches to the quantification of valvular insufficiency, such as measurement of the momentum of the jet and study of the acceleration flow in the proximal flow convergence region within the chamber of origin of an insufficiency jet and proximal to the orifice, are described and preliminary results given for a new method of quantification of volume flow across regurgitant orifices.

Compliance↗
PubMed1990

Color Doppler diagnosis of mechanical prosthetic mitral regurgitation: usefulness of the flow convergence region proximal to the regurgitant orifice.

In prosthetic or paravalvular prosthetic mitral regurgitation, transthoracic color Doppler flow mapping can sometimes fail to detect the regurgitant jet within the left atrium because of the shadowing by the prosthetic valve. To overcome this limitation, we assessed the utility of color Doppler visualization of the flow convergence region (FCR) proximal to the regurgitant orifice in 20 consecutive patients with mechanical prosthetic mitral regurgitation documented by surgery and cardiac catheterization (13 of 20 patients). In addition, we studied 33 patients with normally functioning mitral prostheses. Doppler studies were performed in the apical, subcostal, and parasternal long-axis views. An FCR was detected in 95% (19 of 20) of patients with prosthetic mitral regurgitation. A jet area in the left atrium was detected in 60% (12 of 20) of patients. In 18 of 19 patients with Doppler-detected FCR, the site of the leak was correctly identified by observing the location of the FCR. A trivial jet area was detected in eight patients with a normally functioning mitral prosthesis; in none was an FCR identified. Thus color Doppler visualization of the FCR proximal to the regurgitant orifice is superior to the jet area in the diagnosis of mechanical prosthetic mitral regurgitation. Moreover, FCR permits localization of the site of the leak with good accuracy.

Adult↗
PubMed1990

Directions for the use of intracardiac high-frequency ultrasound scanning for monitoring pediatric interventional catheterization procedures.

Intravascular and intracardiac ultrasound imaging using high-frequency ultrasound catheters has a number of potential applications in pediatric cardiology. This article reviews the current difficulties associated with interventional procedures for congenital heart lesions, the feasibility of intravascular ultrasound imaging in children, and its potential applications.

Angioplasty, Balloon, Coronary↗
PubMed1990

Doppler studies of vena cava flows in human fetuses. Insights into normal and abnormal cardiac physiology.

We examined vena cava Doppler flow velocity tracings from 69 fetuses between 22 and 40 weeks' gestation. Twenty-three fetuses had arrhythmias. Fifteen fetuses had absent end-diastolic Doppler velocities in the umbilical artery, a condition associated with intrauterine growth retardation, and 15 normal fetuses with normal umbilical artery Doppler velocity ratios were matched by gestational age. In studies in 16 additional fetuses, inferior vena cava Doppler velocity waveforms were compared with superior vena cava Doppler velocity waveforms. Peak velocities and time-velocity integrals of forward or reverse flow during systole, early diastole, and atrial contraction were measured. In addition, the time-velocity integral during flow coincident with atrial contraction (a wave) was expressed as a percent of the time-velocity integral of total forward flow during both systole and early diastole. Systolic-to-diastolic ratios of inferior vena cava forward time-velocity integrals were not significantly different from systolic-to-diastolic ratios of superior vena cava forward time-velocity integrals (p = 0.86), but the percent of blood moving in a reverse direction during atrial contraction in the inferior vena cava was greater than the percent of blood moving in a reverse direction in the superior vena cava (p less than 0.05). Relative forward flow in early diastole in the group of normal fetuses increased with advancing gestational age (r = 0.60, p less than 0.05). During premature atrial contractions flow in the inferior vena cava was reversed, and the percent of reverse flow during atrial systole increased significantly from 4.5 +/- 0.3% to 28.3 +/- 3.7% (mean +/- SEM, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Arrhythmias, Cardiac↗