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Biomedical subjects

N C Nanda

Publications and source records attributed to N C Nanda.

At least 55 records · Page 3Linked to original sources
PubMed1997

An improved flow evaluation scheme in orifices of different aspect ratios.

An accurate and reliable method of regurgitant flow calculation is currently unavailable. The goal of this study was to define a new general method of flow calculation for orifices of different aspect ratios. The success of the method relies on matching the imaged flow field distribution obtained by color flow mapping (CFM) to a three-dimensional (3D) numerical flow field distribution of known geometry. The flow field in three orifices of identical cross-sectional area with aspect ratios of 1 (circular), 2 and 4 (elliptical) was evaluated by: (a) CFM, (b) 3D echocardiographic imaging, and (c) 3D finite element modeling (FEM). The orifice shape and size were accurately estimated by 3D echocardiographic imaging. FEM showed that the normalized centerline velocity profile of the flow field depends on the orifice aspect ratio. CFM provided a good description of the centerline profile for each case. For a given distance from the orifice center, the equivelocity contour surface area increases with increasing aspect ratio. A simple flow calculation scheme was developed to calculate regurgitant flow independent of orifice shape. This improved method showed better results than previous studies and may prove to be advantageous when analyzing in vivo flow fields with complex geometries.

Computer Simulation↗
PubMed1996

Transesophageal echocardiographic assessment of papillary muscle rupture.

BACKGROUND: In some patients with papillary muscle rupture, the ruptured head may not prolapse into the left atrium, which makes diagnosis by transthoracic or transesophageal echocardiography difficult. METHODS AND RESULTS: In an attempt to find additional or more definite diagnostic echocardiographic features, we analyzed intraoperative transesophageal echocardiograms of 21 consecutive patients with papillary muscle rupture (20 involved the left ventricle and 1 involved the right ventricle) confirmed at surgery. In 7 (35%) of 20 patients with left ventricular papillary muscle rupture, the ruptured head was not seen to prolapse into the left atrium. In these patients, examination of the left ventricle proved most useful. Abnormal, large-amplitude erratic motion (1 to 5 cm in 17 patients; 0.5 cm in 1 patient) of a large echo density in the left ventricle consistent with the ruptured head was noted in 18 (90%) of these 20 patients. This included all 7 patients with non-prolapse of the ruptured papillary muscle head into the left atrium. Less prominent erratic motion or flutter of the papillary muscle still attached to the left ventricular wall was also noted but was less sensitive in the diagnosis of papillary muscle rupture. The single patient with right ventricular papillary muscle rupture showed erratic motion as well as prolapse of the ruptured head into the right atrium. CONCLUSIONS: Transesophageal echocardiographic examination of the left ventricle is useful in the diagnosis of papillary muscle rupture, especially in those patients in whom the ruptured head does not prolapse into the left atrium. The left ventricle should be scrutinized thoroughly during transesophageal echocardiographic examination for erratic papillary muscle motion in all patients with suspected rupture.

Adult↗
PubMed1996

Accuracy of color doppler velocity in the flow field proximal to a regurgitant orifice: implications for color doppler quantitation of valvular incompetence.

Color Doppler is routinely used in estimates of valvular regurgitation. Velocity and subsequently flow measurements are made at about 7-10 cm from the ultrasonic transducer. Error in velocity measurement may occur due to spatial broadening of the color Doppler beam in the axial, azimuthal and lateral directions. Error in velocity may also occur due to wall filters since the filtering process is not uniform throughout the velocity range indicated by the color bar. An attempt to estimate this error was made using an in vitro orifice model, a numerical finite element model (FEM), and information from the manufacturer. We found that the acoustic beam spatial expansion, wall filter sensitivity and Nyquist limit (NYL) have to be considered simultaneously to account for errors. The combined spatial expansion and wall filter effect on velocity was estimated as a weighted average over the sample volume. The error distributions are not universal but depend on orifice size and flow. For a 3-mm orifice and 100 cm s NYL the overall effect was overestimation of low velocities and significant underestimation of high velocities due to the high velocity gradients inside the sample volume. For the 5- and the 10-mm orifice the effect was less accentuated. Based on this overall error distribution, a correction was incorporated on color Doppler obtained data. The incorporated correction yielded better agreement with numerical velocity data. This correction is important in the application of the proximal isovelocity surface area (PISA) technique and the evaluation of regurgitant flowrates.

Blood Flow Velocity↗
PubMed1995

A numerical and experimental investigation of the flow acceleration region proximal to an orifice.

Attempts to quantify valvular regurgitation have recently been focused on the proximal orifice flow field. A complete description of the proximal orifice flow field is provided in this investigation. A steady state in vitro model accessible by both color Doppler ultrasound (CDU) and laser Doppler velocimetry (LDV) was utilized. Velocities for varying flow rates and orifices were calculated by finite element modeling (FEM), by LDV and by CDU. The steady flow model was composed of circular orifices of 3, 5 and 10 mm diameters at flow rates from 0.7 to 10 L/min. Regurgitant flow rates were calculated from the proximal CDU data by two separate methods. The first approach utilized angle corrected velocities while the second approach utilized only velocities which did not require angle correction (centerline velocities). Both methods correlated well with known flow rates (y = 0.97x -0.09, r = 0.98, SEE = 0.45, p < 0.0001; and y = 1.0x + 0.07, r = 0.99, SEE = 0.27, p < 0.0001, respectively) and were superior to results obtained by assuming a hemispherical geometry as is done in the aliasing technique. The methodology provides a complete analysis of the proximal flow field and involves fewer geometric assumptions than the aliasing approach. This may prove to be an advantage when analyzing in vivo flow fields with complex, uncertain geometry.

Acceleration↗
PubMed1995

Transesophageal color Doppler evaluation of obstructive lesions using the new "Quasar" technology.

Due to the unavoidable problem of aliasing, color flow signals from high blood flow velocities cannot be measured directly by conventional color Doppler. A new technology termed Quantitative Un-Aliased Speed Algorithm Recognition (Quasar) has been developed to overcome this limitation. Employing this technology, we used transesophageal color Doppler echocardiography to investigate whether the velocities detected by the Quasar would correlate with those obtained by continuous-wave Doppler both in vitro and in vivo. In the in vitro study, a 5.0 MHz transesophageal transducer of a Kontron Sigma 44 color Doppler flow system was used. Fourteen different peak velocities calculated and recorded by color Doppler-guided continuous-wave Doppler were randomly selected. In the clinical study, intraoperative transesophageal echocardiography was performed using the same transducer 18 adults (13 aortic valve stenosis, 2 aortic and 2 mitral stenosis, 2 hypertrophic obstructive cardiomyopathy and 1 mitral valve stenosis). Following each continuous-wave Doppler measurement, the Quasar was activated, and a small Quasar marker was placed in the brightest area of the color flow jet to obtain the maximum mean velocity readout. The maximum mean velocities measured by Quasar closely correlated with maximum peak velocities obtained by color flow guided continuous-wave Doppler in both in vitro (0.53 to 1.65 m/s, r = 0.99) and in vivo studies (1.50 to 6.01 m/s, r = 0.97). We conclude that the new Quasar technology can accurately measure high blood flow velocities during transesophageal color Doppler echocardiography. This technique has the potential of obviating the need for continuous-wave Doppler.

Adult↗
PubMed1995

Intraoperative transesophageal echocardiography in orthotopic liver transplantation in a patient with hypertrophic cardiomyopathy.

With improvements in the surgical technique for orthotopic liver transplantation, patients with significant underlying systemic disease are considered candidates for transplantation, thus increasing the complexity of the medical management of these patients and necessitating additional monitoring in order to minimize the anesthetic risk. We describe the anesthetic management of orthotopic liver transplantation for a patient with severe hypertrophic cardiomyopathy and mitral insufficiency. In this case, transesophageal echocardiography proved useful in the management of the postreperfusion period of the surgical procedure.

Anesthesia↗
PubMed1994

Design of the training levels comparison trial.

The Training Levels Comparison (TLC) trial was a grant-supported, multicenter, randomized, controlled clinical trial designed to determine whether cardiac rehabilitation patients would benefit from supervised exercise for a prolonged period (2 years) and whether subjecting patients to a more vigorous exercise program than currently recommended would provide additional cardiac benefit. If high-intensity exercise does not enhance the cardiac benefit, then physical activity should be limited to low-intensity levels that are safer, easier to implement and more adaptable to a greater number of patients. Patients were randomly assigned to either a low-intensity or high-intensity training program. All patients were to attend three 1-hour supervised exercise sessions per week for a period of 2 years. Attendance at exercise sessions and adherence to assigned treatments were monitored throughout the study. Patients were evaluated for outcome measures at 3, 6, 12, and 24 months. This paper reports the study design and methodology for the TLC trial, and should be useful in providing methodologies to facilitate comparison of data from other studies with different levels of exercise as an intervention.

Adult↗
PubMed1994

Three-dimensional and four-dimensional echocardiography.

Since its introduction in 1974, 3-D reconstruction of the heart has undergone significant technological refinements in image acquisition, processing and display techniques. Image acquisition for transthoracic 3-D reconstruction utilizes the parasternal or apical windows, or combinations of the two. The parasternal approach allows better endocardial border detection, while the apical approach allows a more complete visualization of the left ventricular apex. Computer algorithms are used to process images with various display techniques incorporated into the algorithm. Transesophageal image acquisition overcomes a significant limitation of the transthoracic approach, which is variable and sometimes poor image quality. Both a multiplane approach and a computerized tomographic approach have been successfully used by several investigators. Potential applications of 3-D echocardiography include reconstruction of the mitral annulus, dynamic cardiac anatomy and function and volume calculations. A major limitation is the need for considerable computer time for image processing and display; furthermore, errors may be introduced by the various smoothing and contouring algorithms. Despite these limitations, 3-D echocardiography has considerable potential for clinical utility, particularly in the areas of reconstructive cardiac surgery and congenital heart disease.

Echocardiography↗
PubMed1994

Quantitative assessment of normal and stenotic aortic valve using transesophageal three-dimensional echocardiography.

The present study demonstrates the feasibility of transesophageal three-dimensional reconstruction of normal, sclerotic, and stenotic aortic valves using a computed tomographic ultrasound system. The study also shows the potential clinical usefulness of this technique in delineating aortic valve morphology (extent and severity of valve thickening and calcification and size and number of cusps) and assessing aortic orifice areas by direct planimetry of the three-dimensional images.

Aged↗
PubMed1994

Intramachine and intermachine variability in transesophageal color Doppler images of pulsatile jets. In vitro studies.

BACKGROUND: Color Doppler flow mapping is widely used as a marker of severity of valvular regurgitation, and the transesophageal approach has provided high-quality images in patients with poor acoustic windows. However, different instruments produce significantly variable images. Techniques that use jet spatial information to determine the severity of the lesion may need to be derived specifically for the instrument used. Given a lack of standardization of the many commonly used instruments, the goal of this study was to quantify variability between instruments by imaging well-defined jet flow fields created in vitro. METHODS AND RESULTS: Pulsatile jets were created in vitro using a blood analogue fluid through physiological orifice diameters and imaged from a distal window using six commonly used color Doppler instruments. Transesophageal transducers (5.0 MHz) were used with all instruments studied. Peak jet areas were planimetered and averaged with systematic variations in Nyquist limit, color filter, and sector angle (which produced variations in frame rate). Changes in instrument settings produced significant variation in jet size for all instruments studied. Comparisons within instruments and among instruments were difficult because of preset and ambiguous setting levels. When comparisons were possible between similar settings, variability was dramatic (eg, 57% variability between instruments with very similar Nyquist limits). CONCLUSIONS: A lack of standardized color Doppler instrument settings prohibits translation of jet area techniques from one instrument to another. This should be taken into consideration when using different machines for clinical study.

Algorithms↗
PubMed1994

The Ross operation--early echocardiographic comparison of different operative techniques.

Fifty-four consecutive patients underwent aortic valve replacement with a pulmonary autograft (Ross operation) over an 18-month period. It was inserted as an intra-aortic cylinder in 13 patients and as a total aortic root replacement in 41; unwrapped in 16, partially wrapped with autologous pericardium in 12 and completely wrapped with bovine pericardium in 13. There were two cardiac deaths, one death from mediastinitis, and two early reoperations to replace an incompetent autograft. Comparison of postoperative echocardiographic data showed a higher incidence of moderate and severe autograft incompetence in the intra-aortic cylinder group and also in the subset without previous operation which had a total root replacement without a complete wrap. Autograft function was best in the group which received a total root replacement with a complete wrap and in those with previous cardiac surgery who received an unwrapped autograft. This preliminary information with short follow up supports the use of complete wrapping of the autograft when it is used as a total root replacement particularly in older patients without previous cardiac surgery in whom future autograft growth is not desirable.

Adolescent↗