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Biomedical subjects

K B Sagar

Publications and source records attributed to K B Sagar.

At least 37 records · Page 2Linked to original sources
PubMed1993

Increased prevalence of abnormal signal-averaged electrocardiograms in older patients who have hypertension with low diastolic blood pressure.

Greater mortality in hypertensive patients with the lowest diastolic blood pressure (DBP) values has been reported and may be partially explained by more fatal arrhythmias. The records of 135 patients were reviewed to determine whether the prevalence of an abnormal signal-averaged electrocardiogram (SAECG+), a risk marker for ventricular arrhythmias, was greater in patients who have hypertension with DBP < 85 mm Hg. SAECG+ was present in 31 (39%) of 80 patients with hypertension and 13 (24%) of 55 subjects with normotension p < 0.05. Hypertensive patients were more likely than normotensive subjects to have left ventricular hypertrophy (LVH, p = 0.01) and LV dysfunction (p < 0.01). In multivariate analysis only age and systolic dysfunction emerged as significant predictors of SAECG+. Among 68 hypertensive patients and for whom recent DBP data were available, SAECG+ was present in 18 of 37 with DBP < 85 mm Hg (group 1), 1 of 12 with DBP 85 to 94 mm Hg (group 2, p < 0.05 vs group 1), and 4 of 19 with DBP > 95 mm Hg (group 3, p < 0.05 vs group 1, p = 0.08 vs group 2). There were no significant differences between the three groups of hypertensive patients for coronary artery disease, LVH, systolic dysfunction, or left-sided cardiac chamber enlargement. Multivariate analysis in hypertensive patients indicated that age and DBP were each independently predictive of SAECG+, whereas the indexes of heart disease were not. Within group 1, those with SAECG+ were significantly older (68 +/- 1 vs 59 +/- 1 years, p < 0.01) and more likely to have LVH (p < 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

Arrhythmias, Cardiac↗
PubMed1993

Improved baroreflex sensitivity in elderly hypertensives on lisinopril is not explained by blood pressure reduction alone.

OBJECTIVE: The major goals of this study were to determine whether lisinopril and nifedipine lowered blood pressure and improved carotid baroreflexes in older hypertensives. DESIGN: The effects of lisinopril at 10-40 mg/day versus nifedipine gastrointestinal therapeutic system (GITS) at 30-90 mg/day on blood pressure and baroreflex sensitivity were studied after 3 weeks each on (1) single-blind placebo, (2) double-blind assignment to either lisinopril or nifedipine, (3) single-blind placebo, and (4) crossover to double-blind lisinopril or nifedipine. Measurements at the end of the four phases included 24-h blood pressure using the Accutracker, laboratory hemodynamics with the Dinamap and impedance cardiography, baroreflex sensitivity with the pneumatic neck chamber, and plasma samples for neurohumoral and metabolic activity. PATIENTS: Thirteen patients aged 55 years or older (mean +/- SEM 65 +/- 1 years) with mild-to-moderate hypertension completed the study. MAIN OUTCOME MEASURES: The primary data for analysis across the four study phases included ambulatory blood pressure values, laboratory hemodynamics, and baroreflex sensitivity. RESULTS: Compared with the preceding placebo, lisinopril and nifedipine lowered 24-h blood pressure significantly. In the laboratory, the effects of both compounds on blood pressure, cardiac output, calculated total systemic resistance, and the stroke volume-pulse pressure relationship, an index of arterial compliance, were similar. Lisinopril was associated with a relative increase in the standing systolic blood pressure compared with nifedipine (P < 0.05). This coincided with an enhanced heart-rate (R-R interval) response to neck pressure, which also decreased carotid transmural pressure, with lisinopril versus nifedipine (P < 0.05). CONCLUSIONS: Lisinopril and nifedipine were both effective as monotherapy for controlling blood pressure in these elderly patients. Despite similar effects on blood pressure and systemic hemodynamics, baroreflex sensitivity in response to a reduction in carotid transmural pressure was greater with lisinopril than with nifedipine.

Aged↗
PubMed1993

The lack of effect of hemodilution, myocardial water content, and increased coronary artery blood flow on integrated myocardial ultrasonic backscatter in the beating canine heart.

The effects of coronary blood flow, tissue water content and hematocrit variation on the Integrated Myocardial Backscatter Rayleigh 5 (IBR5) and Fourier coefficient of amplitude modulation (FAM, an index of cardiac cycle-dependent variation in IBR5) were measured in five open chest dogs. Data were obtained at baseline, during adenosine infusion and after two hours of crystalloid hemodilution (Hct 15%). IBR5 of -46.4 +/- .94 dB at baseline did not change significantly during adenosine infusion (-45 +/- .85 dB) and after hemodilution (-46.4 +/- 2.0 dB). FAM at baseline was (4.0 +/- 1.0 dB) (3.8 +/- -1.0 dB) during adenosine infusion and after hemodilution (5.0 +/- 1.8 dB). Myocardial water content increased significantly (p < .05) from 78 +/- .20% at baseline to 80.7 +/- .17% after hemodilution. Coronary blood flow demonstrated a three-fold increase with adenosine and two-fold increase with hemodilution. Electronmicroscopy demonstrated an increase in intracellular and extracellular water content. In conclusion, IBR5 and FAM did not change significantly despite significant increases in coronary blood flow and myocardial water content. Myocardial cellular derangements seen with nonischemic cell swelling, increased blood flow and a fall in hematocrit are insufficient to affect integrated backscatter.

Animals↗
PubMed1991

Static versus dynamic exercise: effects on Doppler echocardiographic indices of left ventricular performance.

In order to compare the effects of static exercise with those of dynamic exercise on the Doppler echocardiographic measurements of ascending aortic blood flow velocity and acceleration, Doppler echocardiography was performed with sustained handgrip exercise and with supine bicycle exercise in 12 normal subjects, 12 patients with coronary artery disease, and 7 patients with heart failure. In normal subjects: peak velocity decreased by 16 +/- 11% with handgrip from the resting value and increased by 49 +/- 19% with bicycle exercise (p less than 0.01); mean acceleration decreased by 6 +/- 30% with handgrip and increased by 162 +/- 83% with bicycle exercise (p less than 0.01). In patients with coronary artery disease: peak velocity declined by 9 +/- 14% with handgrip and increased by 19 +/- 18% with bicycle exercise (p less than 0.01); mean acceleration increased by 13 +/- 27% with handgrip and by 41 +/- 33% with bicycle exercise (NS). In patients with congestive heart failure: peak velocity decreased by 19 +/- 13% with handgrip and increased by 5 +/- 17% with bicycle exercise (p less than 0.01); mean acceleration decreased by 12 +/- 23% with handgrip and by 4 +/- 37% with bicycle exercise. A marked increase in afterload stress induced by static exercise presumably offsets the moderately increased contractility and accounts for the decline of peak velocity and mean acceleration with static exercise both in normals and cardiac patients. In contrast, marked increase in contractile state along with little change in afterload with dynamic exercise results in markedly increased peak velocity and mean acceleration in normal subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1991

Acute, reversible tricuspid insufficiency: creation in canine model.

Relatively few methods have been described for the creation of valvular insufficiency in an animal model. Those presented involve limitations such as permanent destruction of the valves or lack of control over the degree of regurgitation produced. We describe a method of acute reversible tricuspid insufficiency that can be easily created and controlled in anesthetized dogs. The model employs a wire spiral that is advanced through the atrioventricular canal from the right atrium. The spiral causes regurgitation by preventing complete apposition of the valve leaflets while permitting retrograde flow to occur through the spiral lumen. The degree of regurgitation can be controlled by the use of spirals of different sizes. Creation of tricuspid insufficiency is demonstrated by the onset of right atrial pressure V waves, a "ballooning" of the right atrium during ventricular systole, palpation of an atrial thrill, or by color Doppler echocardiography. In 14 dogs, right atrial pressure increased from a control value of 9 +/- 3 (mean +/- SD) mmHg to 10 +/- 3 and 12 +/- 3 mmHg, respectively, with spirals of 1.5 and 2.2 cm in diameter (both P less than 0.05). With the 2.2-cm spiral, aortic blood pressure decreased from a control value of 104 +/- 20 to 83 +/- 17 mmHg (P less than 0.05), and cardiac output decreased from 73 +/- 26 to 59 +/- 19 ml.min-1.kg-1 (P less than 0.05). This model is reversible, allows repeated trials of various grades of regurgitation, does not require ventriculotomy, and is relatively nonarrhythmogenic.

Animals↗
PubMed1991

Estimation of myocardial infarct size with ultrasonic tissue characterization.

BACKGROUND: Ultrasonic tissue characterization (UTC) can distinguish normal from infarcted myocardium. Infarcted myocardium shows an increase in integrated backscatter and loss of cardiac cycle-dependent variation in backscatter. The cyclic variation of backscatter is closely related to regional myocardial contractile function; the latter is a marker of myocardial ischemia. The present study was designed to test the hypothesis that intramural cyclic variation of backscatter can map and estimate infarct size. METHODS AND RESULTS: Transmural myocardial infarction was produced in 12 anesthetized, open-chest dogs by total occlusion of the left anterior descending coronary artery for 4 hours. A real-time ultrasonic tissue characterization instrument, which graphically displays integrated backscatter Rayleigh 5, cardiac cycle-dependent variation, and patterns of cyclic variation in backscatter, was used to map infarct size and area at risk of infarction. Staining with 2,3,4-triphenyltetrazolium chloride (TTC) and Patent Blue Dye was used to estimate infarct size and the area at risk, respectively. The ratio of infarct size to area at risk of infarction determined with UTC correlated well with that determined with TCC (r = 0.862, y = 23.7 +/- 0.792x). Correlation coefficients for infarct size and area at risk were also good (r = 0.736, y = 12.3 +/- 737x for infarct size and r = 0.714, y = 5.80 +/- 1.012x for area at risk). However, UTC underestimated both infarct size and area at risk. CONCLUSIONS: Ultrasonic tissue characterization may provide a reliable, noninvasive method to estimate myocardial infarct size.

Animals↗
PubMed1990

Long-term therapy with benazepril in patients with congestive heart failure: effects on clinical status and exercise tolerance.

Benazepril hydrochloride (CGS 14824A) is an orally active, nonsulfhydryl compound that is transformed in vivo to a long-acting inhibitor of angiotensin-converting enzyme (ACE). Previous studies have shown benazepril to lower blood pressure in hypertensive patients and to confer acute hemodynamic benefits in patients with congestive heart failure (CHF). In the current multicenter investigation, 16 patients with chronic CHF due to left ventricular systolic dysfunction (ejection fraction less than 0.40 at rest) whose symptoms corresponded to New York Heart Association classes II to IV were given open-label benazepril once daily in ascending doses of 2 to 20 mg and followed biweekly for 12 weeks. Evaluation of the 15 subjects who completed the trial showed a progressive increase in treadmill exercise duration (from 7.65 +/- 3.64 [SD] minutes at baseline to 9.74 +/- 3.66 minutes at 12 weeks, P less than .001); augmentation of the mean left ventricular ejection fraction (from 0.266 +/- 0.133 at baseline to 0.292 +/- 0.136 at 12 weeks, P less than .025); relief of exertional dyspnea in 7 of the 15 patients (P less than .02); and improvement in global symptomatic status in 10 of the patients (P less than .01). These responses were accompanied by a reduction in serum ACE activity of 75% (from 27.2 +/- 10.5 IU/L at baseline to 6.7 +/- 1.9 IU/L at 12 weeks, P less than .001), which was independent of dose and duration of treatment. The magnitude of ACE inhibition did not correlate with changes in the efficacy variables. Aside from two instances of symptomatic hypotension (one of which was complicated by volume depletion), the drug was well tolerated.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1990

Quantitative ultrasonic assessment of normal and ischaemic myocardium with an acoustic microscope: relationship to integrated backscatter.

PURPOSE OF INVESTIGATION: The aim was to study ultrasonic propagation properties of normal and ischaemic myocardium with a scanning laser acoustic microscope and to correlate these changes with ultrasonic backscatter. DESIGN: Myocardial ischaemia was produced by total occlusion of left anterior descending coronary artery in anaesthetised open chest dogs. Myocardium supplied by left circumflex coronary artery served as normal control. IBR5, an optimum weighted frequency average (4-6.8 MHz) of the squared envelope of diffraction corrected backscatter, was measured in vivo. Ultrasonic attenuation coefficient, an index of loss per unit distance, the propagation speed and heterogeneity index were measured from normal and ischaemic regions with a scanning laser acoustic microscope which operates at 100MHz in vitro. Myocardial water content of normal and ischaemic myocardium was also estimated. SUBJECTS: Were five anaesthetised mongrel dogs. RESULTS: Attenuation coefficient of 33.8(SD4.2) dB.mm-1 in the ischaemic tissue was lower than 63.8(17.2) dB.mm-1 in the normal tissue (p less than 0.01). Ultrasonic speed was lower in ischaemic than normal myocardium at 1584(25) v 1612(35) m.s-1 (p less than 0.05). Heterogeneity index of 11(7) m.s-1 in the ischaemic region was lower than 14(8) m.s-1 in the normal region (27% reduction, p less than 0.05). IBR5 and myocardial water content were higher in the ischaemic than the normal myocardium: -37.2(SEM1.8) dB v -46.6(0.6) dB, (p less than 0.01) and 80.9(0.0)% v 78(0.2)%, (p less than 0.05) respectively. CONCLUSION: Ultrasonic properties of the myocardium are significantly altered during acute ischaemia.

Animals↗
PubMed1990

Ultrasonic tissue characterization of normal and ischemic myocardium.

Cardiac ultrasonic tissue characterization is designed to use the alterations in acoustic signals from the myocardium to differentiate normal from ischemic or infarcted tissue due to their characteristic backscatter attenuation. Various approaches such as use of a gray scale, color display, or quantitative image analysis have been used for tissue characterization, but all depend on subjective assessments and are not necessarily reproducible. The most promising method has been the use of "raw" radiofrequency signals and measure changes in the ultrasonic attenuation with an index of backscatter to distinguish normal from abnormal myocardium called "integrated backscatter" (IB). Various studies have demonstrated the changes in the ultrasonic backscatter with ischemia or infarction. In this review we summarize our experience with a research prototype instrument in tissue characterization and differentiation of normal, ischemic, infarcted, and post ischemic reperfused myocardium in anesthetized open chest dogs. Currently we are investigating the role of ultrasonic tissue characterization to estimate infarct size and plan to apply these observations to patients in order to detect viable myocardium and quantitate infarct size.

Animals↗
PubMed1990

Doppler echocardiographic evaluation of left ventricular function.

Invasive measurements of maximum acceleration of aortic blood flow are sensitive indicators of left ventricular function. Doppler echocardiography provides noninvasive measurements of aortic blood flow acceleration. Our studies establish the accuracy of Doppler-derived indices of aortic blood flow velocity for evaluation of left ventricular function. Doppler-derived peak velocity and mean acceleration showed excellent correlation with invasively measured peak left ventricular dP/dt and maximum aortic blood flow (dQ/dt) under varying heart rate, preload, afterload, and inotropic states. Similar correlations were observed between Doppler-derived peak velocity and mean acceleration and invasively measured left ventricular dP/dt and dQ/dt under conditions of varying degrees of myocardial ischemia. Thus, Doppler echocardiography provides an accurate noninvasive method to evaluate left ventricular performance.

Animals↗
PubMed1990

Cardiovascular regulation during head-out water immersion exercise.

Head-out water immersion is known to increase cardiac filling pressure and volume in humans at rest. The purpose of the present study was to assess whether these alterations persist during dynamic exercise. Ten men performed upright cycling exercise on land and in water to the suprasternal notch at work loads corresponding to 40, 60, 80, and 100% maximal O2 consumption (VO2max). A Swan-Ganz catheter was used to measure right atrial pressure (PAP), pulmonary arterial pressure (PAP), and cardiac index (CI). Left ventricular end-diastolic (LVED) and end-systolic (LVES) volume indexes were assessed with echocardiography. VO2max did not differ between land and water. RAP, PAP, CI, stroke index, and LVED and LVES volume indexes were significantly greater (P less than 0.05) during exercise in water than on land. Stroke index did not change significantly from rest to exercise in water but increased (P less than 0.05) on land. Arterial systolic blood pressure did not differ between land and water at rest or during exercise. Heart rates were significantly lower (P less than 0.05) in water only during the two highest work intensities. The results indicate that indexes of cardiac preload are greater during exercise in water than on land.

Adult↗
PubMed1990

IBR5: an optimal measurement of integrated backscatter and cyclic variation of integrated backscatter.

Various methods have been developed to measure the coefficient of volume backscatter. For these measures, correction has made for signal energy, instrumentation/transducer filtration, diffraction and bulk loss, while using various square law or log magnitude detectors. Also, tissue backscatter has been measured as a function of frequency and the statistics of the backscatter has been examined. This paper unites methods of measuring a properly scaled (unbiased) estimate of the backscatter coefficient with knowledge of the scattering statistics and frequency response using statistical communications techniques. The maximum likelihood, minimum variance, unbiased estimator for wideband measurement of backscatter is developed together with its performance. The measurement technique has strong implications for system design for measuring cyclic myocardial backscatter.

Coronary Disease↗
PubMed1988

The effect of regional myocardial ischemia on Doppler echocardiographic indexes of left ventricular performance: influence of heart rate, aortic blood pressure, and the size of the ischemic zone.

Doppler echocardiographic indexes of ascending aortic blood flow velocity have been found to be an effective method of assessing changes in left ventricular performance induced by myocardial ischemia in both experimental animal preparations and in patients. In eight opened-chest anesthetized dogs, we investigated the influence of heart rate, aortic blood pressure, and size of the ischemic zone on Doppler indexes during regional myocardial ischemia. With control of mean aortic blood pressure and heart rate, transient coronary artery occlusion resulted in a statistically significant decline in peak velocity and mean velocity when as little as 24% of left ventricular myocardium was rendered ischemic. However, when heart rate and mean aortic blood pressure were not controlled, significant declines in peak velocity and mean velocity occurred only with simultaneous two-vessel occlusions involving greater than 47% of left ventricular myocardium. Although transient coronary artery occlusions generally produced no significant change in heart rate in the absence of atrial pacing, significant declines in aortic blood pressure were observed. We conclude that Doppler indexes of left ventricular performance obtained during myocardial ischemia are influenced not only by the extent of myocardium rendered ischemic, but also by changes in mean aortic blood pressure.

Animals↗
PubMed1988

Influence of heart rate, preload, afterload, and inotropic state on myocardial ultrasonic backscatter.

Ultrasonic backscatter is substantially modified by pathologic changes in myocardium. Influence of physiologic changes in heart rate, mean arterial pressure, preload, and inotropic state were studied in 17 anesthetized open-chest dogs. Heart rate was changed with atrial pacing/ULFS'49 (a selective bradycardiac agent). Mean arterial pressure was varied with aortic constriction/nitroprusside, preload was altered with nitroglycerin/volume infusion, and inotropic states were altered with dobutamine (10 microns/kg)/esmolol (100 microns/kg). IBR5, an optimum weighted frequency average (4 to 6.8 MHz) of the squared envelope of diffraction corrected for absolute backscatter, and the Fourier coefficient of amplitude modulation (FAM), an index of cardiac cycle-dependent variation, were measured from six sequential electrocardiographically gated intervals throughout the cardiac cycle. Heart rate, mean arterial pressure, preload, and inotropic state did not significantly affect IBR5. FAM increased from 3.5 +/- 0.3 dB (mean +/- SEM) to 7.0 +/- 0.4 dB (p less than .01) at a heart rate of 120 beats/min, and decreased to 3.9 +/- 0.4 at a heart rate of 160 beats/min. No change in FAM was noted with a rise (70 +/- 12 to 45 +/- 10 mmHg) in mean arterial pressure or preload (an increase or decrease in diastolic segment length of +/- 10% from the baseline). Dobutamine produced a significant increase in left ventricular dP/dt (2600 +/- 200 to 3475 +/- 275 mm Hg) and FAM (3.4 +/- 0.1 to 6.4; p less than .01). Esmolol significantly reduced left ventricular dP/dt (2600 +/- 200 to 2000 +/- 175 mm Hg, p less than .05) and FAM (3.4 +/- 0.01 to 6.4 +/- 0.1; p less than .01). We conclude that IBR5 is independent of heart rate, mean arterial pressure, preload, and inotropic state. Cardiac cycle-dependent amplitude modulation follows changes in cardiac contraction.

Animals↗