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Biomedical subjects

K B Sagar

Publications and source records attributed to K B Sagar.

At least 55 records · Page 3Linked to original sources
PubMed1987

Left ventricular ejection dynamics in hypertrophic cardiomyopathy and aortic stenosis: comparison with the use of Doppler echocardiography.

Left ventricular ejection dynamics of 15 patients with hypertrophic cardiomyopathy (nine obstructive, six nonobstructive) were compared to those in 12 age-matched normal subjects and 10 patients with valvular aortic stenosis by means of combined two-dimensional and Doppler echocardiography. Doppler peak flow velocities in obstructive (HOCM, 2.5 +/- 1.3 m/sec) and nonobstructive (HNCM, 2.6 +/- 0.6 m/sec) hypertrophic cardiomyopathy, as well as in patients with aortic stenosis (AS, 3.6 +/- 1.3 m/sec) were significantly higher than in the normal population (1.0 +/- 0.2 m/sec; p less than 0.001 for all comparisons), but did not differ from each other. The HOCM patients had time to peak velocity (154 +/- 55.7 msec) that was higher than that in both HNCM (86 +/- 8.4 msec) and normal groups (84.5 +/- 8.9 msec; p less than 0.001 for both comparisons), but did not differ from those in AS (117 +/- 52.5 msec). The total ejection time did not differ between HOCM (348.2 +/- 91.1 msec) and AS (328.8 +/- 30.4 msec) groups, but was prolonged in HOCM compared to HNCM (198 +/- 21.0 msec) and normal groups (233 +/- 28.3 msec; p less than 0.001 for both comparisons). The normal and HNCM groups did not differ in time to peak or total ejection time measurements. The percent of flow velocity present in the initial third of the systolic velocity integral for HOCM (44.5% +/- 5.9) and HNCM (49.4% +/- 2.5) groups was greater than for normals (36.2% +/- 5.4; p less than 0.05 for both comparisons), but HOCM values did not differ from HNCM values.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Relationship of left ventricular mass to defibrillation threshold for the implantable defibrillator: a combined clinical and animal study.

Defibrillation results when a critical mass of myocardium is depolarized. The relationship between echocardiographic determinations of left ventricular mass, volume, and cavity radius to wall thickness ratio and defibrillation threshold for the implantable defibrillator was examined. Ten patients with two large patch defibrillating lead systems were studied. Defibrillation threshold was determined intraoperatively as the lowest energy terminating ventricular fibrillation. Left ventricular mass, volume, and radius/posterior wall thickness ratio were calculated from two-dimensional echocardiograms. A significant correlation was found between left ventricular mass and defibrillation threshold (r = 0.78, p less than 0.01). The correlations between defibrillation threshold and left ventricular volume (r = 0.59) and radius/wall thickness ratio (r = 0.55) were not significant. Subsequently, 11 dogs undergoing defibrillation trials with a transvenous catheter and a chest wall patch were studied. Defibrillation threshold was defined as the lowest energy-terminating ventricular fibrillation (four separate attempts). Subsequently, the heart was dissected, and the left ventricle (including the septum) was weighed. The correlation between left ventricular weight and defibrillation threshold (r = 0.76) was significant (p less than 0.01). We conclude that noninvasive assessment of left ventricular mass and direct measurement of left ventricular weight are significantly correlated with defibrillation threshold and consistent with the critical mass hypothesis.

Animals↗
PubMed1987

Detection of exercise induced changes in left ventricular performance by Doppler echocardiography.

A study was performed to test the hypothesis that Doppler echocardiographic measurement of ascending aortic blood flow can detect exercise induced changes in left ventricular performance during exercise in patients suspected of having ischaemic heart disease. Acceleration and peak velocity of flow and stroke volume were determined by non-imaging Doppler echocardiography in the suprasternal notch in 38 patients as they underwent simultaneous exercise radionuclide ventriculography. The patients were divided into four groups: group 1 had resting ejection fractions greater than or equal to 50% and increased their ejection fractions greater than or equal to 5% during exercise; group 2 had resting ejection fractions of greater than or equal to 50% but the ejection fraction either fell or rose less than 5% during exercise; group 3 had resting ejection fractions less than 50% but the ejection fraction rose greater than or equal to 5% during exercise; and group 4 had resting ejection fractions less than 50% and the exercise ejection fraction either fell or rose less than 5% during exercise. Acceleration, velocity, and stroke volume all rose significantly during exercise in group 1. Acceleration also increased in group 2 but to a lesser extent; velocity and stroke volume did not increase. In group 3 acceleration and velocity increased but to a lesser extent than in group 1; stroke volume did not increase. In group 4 velocity increased slightly during exercise but acceleration and stroke volume were unchanged. Doppler echocardiography thus appears capable of detecting exercise induced changes in left ventricular performance and can identify normal and abnormal responses, as defined by radionuclide ventriculography.

Adult↗
PubMed1987

Intramyocardial variability in integrated backscatter: effects of coronary occlusion and reperfusion.

The present study was undertaken to characterize regional myocardial alterations of reflected ultrasound during the cardiac cycle in normal, ischemic, and postischemic reperfused myocardium. Time-averaged integrated backscatter (IB) and cardiac cycle-dependent amplitude modulation were measured from subepicardial, midmyocardial, and subendocardial regions of the left ventricular apex and the midportion of the right ventricular free wall under normal conditions (n = 5), after 1 hr of 100% acute left anterior descending (LAD) occlusion (n = 8), and after 15 min LAD occlusion plus 120 min reperfusion (n = 5) in anesthetized, ventilated open-chest dogs. A significant increase in time-averaged IB was observed in the subepicardium, the midmyocardium, and the subendocardium during ischemia and reperfusion, but there was no intramyocardial variability. Cardiac cycle-dependent amplitude modulation of IB was significantly higher in the normal subendocardium than in the subepicardium (4.3 +/- 0.6 vs 2.9 +/- 0.8 dB, p less than .01) and midmyocardium (2.8 +/- .05 dB, p less than .01). This transmural gradient in amplitude modulation was abolished during ischemia and reperfusion. We conclude that cardiac cycle-dependent amplitude modulation in IB has a transmural dependence in the normal myocardium and this is abolished during acute myocardial ischemia.

Animals↗
PubMed1987

Determination of stroke volume and cardiac output during exercise: comparison of two-dimensional and Doppler echocardiography, Fick oximetry, and thermodilution.

Simultaneous estimates of cardiac output were made during graded upright maximal exercise in 10 male subjects by means of Doppler velocity spectrum of ascending aortic flow, apical two-dimensional echocardiograms, thermodilution, and Fick oximetry. In 15 subjects, aortic annular and root diameters were measured during similar exercise from parasternal two-dimensional echocardiograms. The linear correlation between Doppler, two-dimensional echocardiography, and the invasive estimates ranged from r = .78 to r = .92. Both echocardiographic techniques were able to predict changes in invasive flow estimates with reasonable accuracy. Two-dimensional echocardiographic flow estimates underestimated invasive values by about 60%. The accuracy of Doppler flow estimates varied with the method of estimating aortic cross-sectional area. Greatest accuracy was obtained with areas calculated from diameters measured at the aortic value anulus with the leading edge-to-leading edge method of measurement. Correlation coefficients comparing Doppler and thermodilution flow estimates were generally higher (r = .75 to .96, mean .86) for individuals than for the group, but accuracy of the Doppler estimates in single subjects was quite variable. Aortic diameters did not increase from rest to moderate levels of upright exercise. A 3% to 5% increase in resting aortic diameter was noted in the upright posture as compared with the supine. Doppler flow estimates were obtained in all subjects to maximal exertion but in only a minority of subjects with two-dimensional echocardiography or thermodilution. Thus two-dimensional and Doppler echocardiography offer a noninvasive means of estimating cardiac output during vigorous exercise. The Doppler technique is technically more suitable to the study of exercise than two-dimensional echocardiography.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Role of exercise Doppler echocardiography in isolated mitral stenosis.

This study reports the role of Doppler ultrasound during exercise for assessment of patients with mitral stenosis. Doppler echocardiography was performed at rest and during symptom-limited supine bicycle exercise in ten patients with isolated mitral stenosis. The mean mitral valvular gradient was calculated using modified Bernoulli's equation, and the mitral valvular area was estimated from the equation, 220/pressure half-time. During exercise the heart rate increased from 74 +/- 14 beats per minute (mean +/- SD) at rest to 110 +/- 8 beats per minute (p less than 0.001) during exercise. The mean mitral gradient increased from 9 +/- 5 mm Hg at rest to 18 +/- 7 mm Hg (p less than 0.01) during exercise. The mitral pressure half-time decreased from 225 +/- 62 msec at rest to 190 +/- 42 msec during peak exercise (p less than 0.005). This corresponded to a reduction of 15 percent. The estimated mitral valvular area increased from 1.0 +/- 0.4 sq cm at rest to 1.2 +/- 0.3 sq cm at peak exercise (p less than 0.005). In conclusion, Doppler echocardiography can be used to evaluate patients with mitral stenosis, with the response of the mitral valvular gradient being the index of obstruction; however, caution should be used in applying the mitral pressure half-time for estimation of the mitral valvular area at high heart rates and flows.

Adult↗
PubMed1986

Echocardiographic left ventricular mass to differentiate chronic hypertension from preeclampsia during pregnancy.

In order to differentiate pregnancy-induced hypertension from chronic systemic hypertension, we measured left ventricular mass for comparison in each trimester of pregnancy in 11 normotensive patients and 14 patients with chronic hypertension and in the third trimester in 10 patients with pregnancy-induced hypertension. The mean left ventricular mass was comparably increased above normal in the patients with chronic hypertension in all three trimesters. In the third trimester in the normotensive women, left ventricular mass (147 +/- 12 gm) was similar to that of the group with pregnancy-induced hypertension (157 +/- 16 gm), whereas the group with chronic hypertension had an elevated left ventricular mass (238 +/- 39 gm) (p less than 0.01). However, three patients with chronic hypertension developed superimposed pregnancy-induced hypertension. We concluded that an elevated left ventricular mass during pregnancy is consistent with underlying chronic hypertension but does not rule out superimposed pregnancy-induced hypertension. A normal left ventricular mass in the third trimester of a hypertensive pregnancy is most consistent with pregnancy-induced hypertension.

Adult↗
PubMed1986

Doppler echocardiographic evaluation of Hancock and Björk-Shiley prosthetic values.

Doppler echocardiographic characteristics of normally functioning Hancock and Björk-Shiley prostheses in the mitral and aortic positions were studied in 50 patients whose valvular function was considered normal by clinical evaluation. Doppler studies were also performed in 46 patients with suspected malfunction of Hancock and Björk-Shiley valves and who subsequently underwent cardiac catheterization. Mean gradients were estimated for both mitral and aortic valve prostheses and valve area was calculated for the mitral prostheses. Doppler prosthetic mitral valve gradient and valve area showed good correlation with values obtained with cardiac catheterization (r = 0.93 and 0.97, respectively) for both types of prosthetic valves. The correlation coefficient (r = 0.93) for mean prosthetic aortic valve gradient was also good, although Doppler echocardiography overestimated the mean gradient at lower degrees of obstruction. Regurgitation of Hancock and Björk-Shiley prostheses in the mitral and aortic positions was correctly diagnosed. These results suggest that Doppler echocardiography is a reliable method for the characterization of normal and abnormal prosthetic valve function.

Adult↗
PubMed1986

The influence of preload and heart rate on Doppler echocardiographic indexes of left ventricular performance: comparison with invasive indexes in an experimental preparation.

We evaluated the ability of Doppler echocardiography to assess left ventricular performance in six open-chest dogs studied under various conditions. Intravenous infusions of nitroglycerin were used to vary preload, atrial pacing was used to control heart rate, and changes in inotropic state were induced by two different doses of dobutamine (5 and 10 micrograms/kg/min iv) and by administration of propranolol (1 mg/kg iv). Left ventricular anterior wall myocardial segment length was used as an index of preload. Maximum aortic blood flow, peak acceleration of aortic blood flow, and dP/dt were measured with an electromagnetic flow probe around the ascending aorta and a high-fidelity pressure transducer in the left ventricle. A continuous-wave Doppler transducer applied to the aortic arch was used to measure peak aortic blood velocity, mean acceleration, time to peak velocity, and the systolic velocity integral. The differences between mean values obtained under different inotropic conditions were significant at the p less than .01 level for peak velocity and at the p less than .05 level for mean acceleration. Within a given animal, Doppler measurements of peak velocity correlated very closely with maximum aortic flow (r = .96), maximum acceleration of aortic flow (r = .95), and with maximum dP/dt (r = .92). Mean acceleration measured by Doppler echocardiography also correlated very closely with conventional indexes, but was subject to greater interobserver variability. Doppler measurements of time to peak and the systolic velocity integral correlated less well with conventional hemodynamic indexes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

The myocardial signature: absolute backscatter, cyclical variation, frequency variation, and statistics.

This paper studies the absolute myocardial backscatter as a function of the frequency and phase of the cardiac cycle. This was achieved by calibration of the ultrasonic instrumentation and the random diffraction process. We have discovered a first-order model in which the scattering from the myocardium is Rayleigh scattering with a cardiac cycle variation in the scattering cross section. Furthermore, the statistics are approximately those of a radio frequency waveform with two independent Gaussian components (Rayleigh envelope). Deviations from the first-order model suggest measurable fine structure related to myocardial ultrastructure. This model has profound effects on the choice of optimal radiation patterns and signal processing schemes for preparing diagnostic parameters (e.g., integrated backscatter).

Animals↗
PubMed1985

Univentricular heart in adults: report of nine cases with review of the literature.

Nine patients with univentricular heart 17 years of age or older were followed up for a mean duration of 13 years (range 5 to 26 years). Five patients had type A and four patients had type C univentricular heart. Pulmonary stenosis was present in eight of nine patients. Palliative shunt surgery was performed in seven patients, ventricular septation was performed in one patient, and no surgical intervention was performed in one patient. Eight patients were in New York Heart Association functional class II and one patient was in New York Heart Association functional class III. Long term follow-up of these patients suggests that a selected group of adults with univentricular heart may achieve a relatively long survival and good functional class with conservative management.

Adolescent↗
PubMed1985

Doppler echocardiographic measurement of flow velocity in the ascending aorta during supine and upright exercise.

Doppler echocardiography was used to measure stroke volume, peak flow velocity, and acceleration of flow in the ascending aorta in 10 healthy young volunteers during unlimited supine bicycle exercise and upright treadmill exercise. High quality studies were obtained in all subjects through the suprasternal notch acoustic window; there was no appreciable degradation in Doppler signal caused by interference by increased respiration or chest wall motion. Stroke volume index increased from 54 ml/m2 at rest to 63.5 ml/m2 at peak supine exercise and from 38 ml/m2 standing at rest to 63.3 ml/m2 during peak upright exercise. Mean peak flow velocity rose from 0.91 m/s at supine rest to 1.36 m/s during maximum supine exercise. In the upright position mean peak flow velocity increased from 0.75 m/s at rest to 1.39 m/s during maximum exercise. Mean peak velocities were lower in the upright position at rest but were not significantly different at peak exercise. Mean acceleration of flow in the ascending aorta increased from 12.02 m/s2 during supine rest to 21.6 m/s2 during supine exercise and from 10.8 m/s2 at rest on the treadmill to 21.9 m/s2 during peak upright exercise. This study shows that echocardiographic measurement of ascending aortic blood flow by the Doppler technique is feasible even during vigorous exercise; that stroke volume and peak flow velocity at rest are lower in the upright position than in the supine position but equalise at peak exercise; and that acceleration of flow in the ascending aorta is the same in both the supine and upright positions and increases equally at peak exercise in both positions.

Adult↗
PubMed1984

Analysis of random backscatter in the presence of static reflection components.

The problem of analysis of random ultrasonic backscatter is treated using linear time-varying channel theory. The backscatter is modeled to have random and deterministic echo components, where the emphasis is on the estimation of the random component in the presence of the deterministic component. A tissue characterizing mechanism is modeled as the range correlation of the random backscatter component, which gives rise to a frequency signature function. Finally, the statistics of the resulting backscatter are given as non-central Chi Squared.

Humans↗
PubMed1983

Aspergillus fumigatus endocarditis on a normal heart valve.

We have described an elderly man with no known underlying predisposing systemic or valvular disease who had mitral valve infection and endophthalmitis due to Aspergillus fumigatus. Two-dimensional echocardiography was valuable in detecting fungal vegetations.

Aged↗
PubMed1983

Echocardiographic tissue characterization and range-gated Doppler ultrasound for the diagnosis of pulmonary embolism.

We evaluated reflection and absorption indexes of ultrasound as well as Doppler estimates of intrapulmonary blood flow for diagnosing pulmonary embolism. The pulmonary reflection coefficient (PRC), coefficient of tissue attenuation (alpha R) and range-gated blood Doppler signals were studied in 25 patients with pulmonary embolism, 19 with pneumonia, nine with atelectasis, 20 with congestive heart failure, 20 with chronic obstructive lung disease and 10 normal subjects. The PRC was significantly diminished in pulmonary embolism, pneumonia and atelectasis, but was not altered by underlying chronic obstructive lung disease or congestive heart failure. The alpha R in pulmonary embolism was 1.03 +/- 0.04 db/MHz cm, significantly lower than that for pneumonia, 1.48 +/- 0.03 db/MHz cm (p less than 0.001), but not significantly different from that for atelectasis, 0.95 +/- 0.05 db/MHz cm. Doppler signals indicating blood flow in the affected area of lung were present in only two of 25 patients with pulmonary embolism, compared with seven of nine with atelectasis and 17 of 19 with pneumonia. The combined use of PRC, alpha R and blood Doppler signals correctly diagnosed pulmonary embolism in 23 of 25 patients. Thus, ultrasound offers a reliable noninvasive method for diagnosis of pulmonary embolism.

Echocardiography↗
PubMed1982

Prevalence and significance of arrhythmias in long-term survivors of cardiac transplantation.

The prevalence and significance of arrhythmias after cardiac transplantation were evaluated in the absence of acute rejection in 13 long-term survivors (greater than 3 months). ECGs were obtained daily for the first 70 days 8- and 24-hour ambulatory electrocardiographic monitoring was performed 3 months after the transplantation and every 6 months thereafter. Junctional rhythm occurred during the early transplant period (less than 70 days) in nine of 13 patients. Complex premature ventricular depolarizations (Lown grade III or higher) were present in the late transplant period (greater than 70 days) in all five patients in whom severe coronary artery disease was found in the donor heart at postmortem, compared with two of the eight remaining patients (six survivors and two patients who died but did not have coronary artery disease at postmortem) (p less than 0.05). The high prevalence of junctional rhythm in the early transplant period appeared to be due to sympathetic denervation and reversible surgical damage to and ischemia of the sinus node region of the donor heart. Routine ambulatory electrocardiographic monitoring detected complex premature ventricular depolarizations, which were a sensitive marker for the subsequent mortality related to accelerated atherosclerosis of chronic rejection in the donor heart.

Adult↗