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Biomedical subjects

N C Nanda

Publications and source records attributed to N C Nanda.

At least 73 records · Page 4Linked to original sources
PubMed1993

Comparison of various agents in contrast enhancement of color Doppler flow images: an in vitro study.

The commercially manufactured contrast agents, Echovist and Albunex, were compared with sonicated conventional agents, indocyanine green, 29% renografin-60, 0.9% normal saline and 25% mannitol in their ability to enhance color Doppler flow signals. In a pneumatically regulated pulsatile flow system, a glycerine, saline (0.9%) and sand (5 microns particle size) solution was imaged using a 2.5 MHz phased-array transducer. Four different flow velocities (0.40, 0.35, 0.30 and 0.25 m/s) as measured by color Doppler guided pulse Doppler were utilized. All color Doppler settings were kept constant throughout the study. Utilizing a power injector, four different volumes (1.0, 1.5, 2.0 and 2.5 mL) of each contrast agent were injected into the flow medium at various transducer angles (20, 30, 40 and 60 degrees) and various distances from the transducer (3.38, 5.5, 6.76 cm). For Echovist and Albunex, several concentrations varying from 2% to 100% were used. Keeping instrument settings constant, color flow areas obtained before and after each contrast injection were planimeterized and the percent increase in the color flow area computed and compared. At full (100%) concentration, 20 degrees transducer angle and a flow velocity of 0.40 m/s, the maximum increase in the color flow area was 568%, 251%, 180%, 110%, 71%, and 38% for Echovist, Albunex, sonicated indocyanine green, renografin, normal saline and mannitol, respectively. However, a significant reduction in the degree of color flow enhancement was observed, with decreases in the concentration of these agents, and increases in the Doppler beam incident angle or distance from the transducer. Increasing the flow velocity of the medium into which contrast was injected did not produce significant changes in the contrast enhancement effect for all agents except Echovist. Increasing the injection volume significantly increased the color flow area for sonicated agents but not for Echovist or Albunex. This preliminary in vitro study shows that the commercially manufactured contrast agents, Echovist and Albunex, are much superior to sonicated conventional contrast agents in the enhancement of color Doppler flow signals. Of the sonicated agents, indocyanine green had the best enhancement capability.

Blood Flow Velocity↗
PubMed1993

Quantification of regurgitant flow through bileaflet heart valve prostheses: theoretical and in vitro studies.

A theoretical treatment using turbulent jet theory has yielded a new equation for predicting regurgitant flow through bileaflet heart valve prostheses, the most commonly implanted mechanical valve design. Previously reported techniques assuming an axisymmetric jet are not applicable to the slot-like orifices presented in these valves. The equations were therefore rederived in the context of the prosthetic valve geometry. The purpose of this study was to develop such a method and demonstrate its applicability in principle by using in vitro models. The method was validated under both steady and pulsatile flow conditions. Having derived a method geometrically specific to the orifices presented in bileaflet mechanical heart valves, it should be applicable from patient to patient due to the rigid nature of the valve. These idealized in vitro studies, along with the accompanying theoretical derivation, will guide implementation in the clinical setting.

Echocardiography, Doppler↗
PubMed1993

Recommendations for training in vascular medicine. American College of Cardiology Peripheral Vascular Disease Committee.

Each trainee in vascular medicine must be eligible for the board certification examination of the American Board of Internal Medicine or its equivalent. Training faculty, preferably at least two members, should meet the qualifications and training requirements described in this report. They must be dedicated, effective teachers and should spend most of their time in research, education and patient care related to peripheral vascular diseases. A curriculum of training should be established. Faculty experts in related specialties and in the related basic sciences should be available for teaching. The institution should have a fully equipped noninvasive vascular laboratory and areas where catheter revascularization techniques and vascular surgery are performed. The period of training should not be less than 1 year, preferably continuous.

Cardiology↗
PubMed1993

Influence of left ventricular assist on valvular regurgitation.

BACKGROUND: The effects of mechanical left ventricular assist on the nonassisted right ventricle have not been fully elucidated. Current information indicates that the right ventricle benefits from a lower left atrial pressure; however, ventricular septal shifting and increased venous return caused by left ventricular assist impair right ventricular function. Acute intraoperative alterations in mitral and tricuspid valve regurgitation (MR and TR, respectively) may occur as a result of mechanical left ventricular assist but have not yet been documented. METHODS AND RESULTS: Eight patients undergoing implantation of a left ventricular assist device (LVAD) as a bridge to transplantation were studied during surgery by transesophageal echocardiography. MR was present in seven of eight patients, and TR was present in eight of eight patients before LVAD implant (mean MR jet area, 10.6 +/- 2.4 cm2, mean TR jet area, 4.8 +/- 1.0 cm2). Immediately after LVAD placement, MR was still present in seven of eight patients, and TR was present in eight of eight patients (mean MR jet area, 4.2 +/- 0.9 cm2; mean TR jet area, 8.4 +/- 1.9 cm2) (P < .05 preimplant versus postimplant jet area). These changes in MR and TR were associated with a decrease in left ventricular end-systolic dimension (62 +/- 4 versus 48 +/- 3 mm) and an increase in right ventricular end-systolic dimension (31 +/- 4 versus 40 +/- 5 mm) (P < .05 preimplant versus postimplant end-systolic dimension). No patients developed progressive right ventricular failure during 70 to 279 days of LVAD support. CONCLUSIONS: Mechanical left ventricular assist causes an acute decrease in preexisting MR. However, left ventricular assist may acutely worsen TR, presumably by shifting the ventricular septum leftward and increasing venous return to the right ventricle.

Cardiomyopathy, Dilated↗
PubMed1993

Long-term function of cryopreserved aortic homografts. A ten-year study.

Cryopreserved aortic valve homografts have become an accepted aortic valve substitute, but long-term studies with echocardiographic assessment of valve function are largely unavailable. Between 1981 and January 1, 1991, a total of 178 patients aged 9 months to 80 years (median 46 years) underwent implantation of a cryopreserved aortic valve homograft. Serial two-dimensional Doppler echocardiographic studies were obtained in 149 patients. Overall survival was 91% at 1 year and 85% at 8 years. Survival of patients undergoing isolated primary infracoronary aortic valve replacement was 99% at 1 month and 94% at 8 years. Twelve patients underwent homograft explanation. Freedom from explantation for leaflet degeneration was 95% at 8 years. Freedom from presumed leaflet failure (valve degeneration at explantation or aortic insufficiency grade 3/4 or more without reoperation on echocardiography) was 94% at 5 years and 85% at 8 years. By multivariable analysis younger recipient age was the only risk factor identified for leaflet failure. Ninety-five percent of patients followed up for 4 or more years were in New York Heart Association class I or II.

Actuarial Analysis↗
PubMed1993

Outcomes in neonatal pulmonary atresia with intact ventricular septum. A multiinstitutional study.

A total of 171 neonates with pulmonary atresia and intact ventricular septum were entered into a prospective multiinstitutional study between January 1, 1987, and January 1, 1991. Treatment was not assigned randomly but was selected by the responsible physicians. The Z-value (standard deviation units) of the diameter of the tricuspid valve was less than -2 in 52% of patients and less than -4 in 26%; it was highly correlated with right ventricular cavity size (which was small in 90% of patients and was severely reduced in 54%). Coronary artery-right ventricular fistulas were present in 45% of patients, and right ventricular dependency was severe in 9%; diameter (Z-value) of the tricuspid valve was negatively correlated (P < 0.0001) with the prevalence of both. Survival was 81% at 1 month after the first intervention and 64% at 4 years; the hazard function (instantaneous risk of death) declined rapidly after the initial procedure but remained appreciable for 24 months. Multivariable analysis showed small diameter of the tricuspid valve, severe right ventricular coronary dependency, birth weight, and the date and type of initial procedure to be risk factors for time-related death. Subsequent procedures were performed in 51% of patients. Among patients undergoing an initial procedure that did not include a systemic-pulmonary artery shunt, only 49% did not receive a shunt in the subsequent 1 month; small size of the tricuspid valve was the only risk factor for receiving the subsequent shunt. Ninety-eight percent of living patients whose initial procedure did not include a transannular patch were free of a subsequently placed transannular patch within 1 month, but only 45% were free of it 3 years later; no risk factors were identified. Eighteen percent of living patients had received a one-ventricle repair within 3 years, and 32% had received a two-ventricle repair; the remainder (50%) had incompletely separated pulmonary and systemic circulations. The only patient-specific risk factor for not receiving a two-ventricle repair was the Z-value of the tricuspid valve.

Heart Septum↗
PubMed1992

Usefulness and limitations of transesophageal echocardiography in the assessment of proximal coronary artery stenosis.

To assess the usefulness of transesophageal echocardiography in the evaluation of proximal coronary artery stenosis, 111 consecutive patients (mean age 61 years) who had intraoperative transesophageal echocardiography and coronary angiography within 1 week of surgery were studied. Transesophageal echocardiography visualized the entire length of the left main artery (0.2 to 2.2 cm, mean 0.93), 0.2 to 2.2 cm of the proximal left anterior descending artery and 0.1 to 3.4 cm of the proximal left circumflex artery in 103 patients (93%) and 0.1 to 4.6 cm of the proximal right coronary artery in 55 patients (49%). In the coronary artery segments visualized by echocardiography and compared with the corresponding angiographic segments, transesophageal echocardiography correctly identified 23 (96%) of 24 left main stenoses, 11 (78%) of 14 stenoses involving the left anterior descending artery, 6 (75%) of 8 left circumflex stenoses and all 7 stenoses (100%) of the right coronary artery. In all seven patients with ostial stenosis (left main artery in five and right coronary artery in two), the condition was correctly diagnosed by this technique. The sensitivity and specificity of transesophageal echocardiography in the overall evaluation of proximal coronary artery stenosis as customarily defined by angiography were 96% and 99% for the left main artery, 48% and 99% for the left anterior descending artery, 67% and 100% for the left circumflex artery and 37% and 100% for the right coronary artery, respectively. The distance of the stenotic lesion from the origin of the vessel by transesophageal echocardiography also correlated well with that measured by angiography (r = 0.63 to 0.99).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Nonsurgical closure of femoral pseudoaneurysms complicating cardiac catheterization and percutaneous transluminal coronary angioplasty.

OBJECTIVES: This study was performed to describe the initial experience and follow-up of ultrasound-guided compression of pseudoaneurysms in patients receiving systemic anticoagulant or antiplatelet therapy, or both, after recent cardiac catheterization or percutaneous transluminal coronary angioplasty. BACKGROUND: Femoral artery pseudoaneurysm formation after an interventional procedure is becoming more common as larger caliber catheters and prolonged anticoagulant and antiplatelet therapy are being used. Traditional treatment of this complication has been surgical repair. This study describes a new method of closing femoral pseudoaneurysms by using external compression guided by Doppler color flow imaging. METHODS: Fifteen patients, 3 undergoing cardiac catheterization and 12 undergoing coronary angioplasty, developed an expansile groin mass at the vascular access site diagnosed as a femoral artery pseudoaneurysm by Doppler ultrasound. Seven of the patients had undergone coronary stenting and were receiving postprocedural anticoagulant therapy. These patients underwent progressive graded mechanical (C-clamp) external compression guided by ultrasound. The mechanical compression was titrated to obliterate the vascular tracts to these aneurysms and maintain adequate flow in the femoral artery. RESULTS: After an average compression time of 30 min (range 10 to 120), these tracts remained closed. Follow-up ultrasound examination at 24 h or later confirmed continued closure in all. CONCLUSIONS: This study suggests that nonsurgical closure of femoral pseudoaneurysms is feasible. This technique may be valuable in managing vascular access-related complications after diagnostic and interventional procedures, even in patients requiring prolonged anticoagulant therapy.

Adult↗
PubMed1992

Application of echocardiographic color flow Doppler mitral regurgitation to the diagnosis of acute cardiac transplantation rejection.

Numerous noninvasive techniques have been examined for the detection of acute rejection following cardiac transplantation, but none has proven sufficiently sensitive to replace the endomyocardial biopsy. A prospective study was performed in 92 heart transplant patients in order to test the hypothesis that mitral regurgitant ratio by two-dimensional echocardiography with Doppler flow mapping could detect moderate or severe acute allograft rejection. There were 82 rejection episodes identified, of which 40% were associated with mitral regurgitation by echo-Doppler at the beginning of the episode. With augmentation of immunosuppression during a rejection episode, there was a progressive fall in the degree of mitral incompetence (P = 0.03). The sensitivity of color Doppler studies in identifying rejection was low (60% of all rejection episodes had no associated mitral incompetence at the beginning of the episode), but the likelihood of rejection progressively increased with higher degrees of mitral regurgitation (P less than 0.01), approaching 60% when the echo-Doppler regurgitant ratio exceeded 15%. Echo-Doppler studies do not provide sufficient sensitivity to be useful as a screening technique for acute cardiac rejection, but high or increasing echocardiographic mitral regurgitant ratio is predictive of acute rejection and should indicate prompt endomyocardial biopsy.

Adolescent↗
PubMed1992

Three-dimensional and four-dimensional transesophageal echocardiographic imaging of the heart and aorta in humans using a computed tomographic imaging probe.

We evaluated the clinical applicability of a prototype tomographic transesophageal echocardiographic (TEE) system, which not only provides conventional TEE images but also three-dimensional tissue reconstruction and four-dimensional display capabilities. The probe was used in 16 patients in the echocardiographic laboratory, intensive care unit, and the operating room. The instrument is a 5-MHz, 64-element, phased array unit mounted on a sliding carriage within a casing. After appropriate probe placement within the esophagus, the probe is straightened, a balloon surrounding the probe is inflated, and data acquisition begun with ECG and respiration gating. With computer controlled transducer movement at 1-mm increments, a complete cardiac cycle is recorded at each tomographic level. These are processed using a dedicated four-dimensional software, and displayed as a dynamic three-dimensional tissue image of the heart. We were able to see the dynamic motion of the ventricles and all the valves in the four-dimensional format. In addition to four-dimensional display, we were able to cut and visualize the heart in dynamic mode in any desired plane and also in multiple planes. Patients tolerated the procedure well. We conclude that this tomographic four-dimensional approach, which does not require tedious off-line processing, can easily be performed in patients and has a strong clinical potential.

Aorta↗
PubMed1992

Echocardiography in coronary artery disease.

Echocardiography has come a long way since its beginnings in the early days of M-mode. Today echocardiography is a useful tool in the management and diagnosis of coronary artery disease. It is used in the emergency room to aid in the exclusion or confirmation of acute coronary syndromes and in their management. The spreading use of stress echocardiography has greatly expanded the use of ultrasound in the diagnosis and management of coronary artery disease. Both pharmacologic and nonpharmacologic methods of stress testing have added to the sensitivity and specificity of this technique, making it a viable alternative to thallium imaging for the diagnostic screening of coronary artery disease.

Coronary Disease↗