Search PubMed⌕ Search

Biomedical subjects

R S Meltzer

Publications and source records attributed to R S Meltzer.

At least 37 records · Page 2Linked to original sources
PubMed1992

Myocardial contrast echocardiography: influence of ischaemia and hyperaemia in an animal model.

To evaluate changes in myocardial contrast echocardiography during ischaemia and hyperaemia, contrast studies were performed in 16 open chest dogs. Time-intensity curves were generated using videodensitometry after contrast injections to demonstrate ischaemic and non-ischaemic areas of interest during a wide range of coronary blood flow levels. For each time-intensity curve, the peak contrast intensity (PCI), washout halftime (T1/2) and area under the curve (AUC) were calculated. PCI and AUC decreased significantly only with severe ischaemia (90% or more reduction in flow), and increased significantly with hyperaemia of more than 2.5 times baseline flow. Both ischaemia and hyperaemia were found to prolong the T1/2. There was only a moderate linear correlation between the magnitude of hyperaemia and myocardial contrast echocardiographic parameters. There was significantly less increase in myocardial contrast echocardiographic parameters during hyperaemia in segments supplied by a stenosed coronary artery.

Albumins↗
PubMed1992

Evaluation of coronary flow reserve using myocardial contrast echocardiography in humans.

To evaluate the applicability of myocardial contrast echocardiography for the assessment of coronary blood flow reserve, 21 consecutive patients undergoing coronary angiography were studied. Only patients with a single left anterior descending lesion or normal coronary angiogram were included. Intracoronary injections of sonicated albumin were performed before and after the administration of intracoronary papaverine. Good quality studies at baseline and after the administration of papaverine were obtained in 14 of 21 patients. Ten patients had a significant (greater than 75%) single left anterior descending lesion and four had normal or insignificant lesions (70% or less stenosis) in the left anterior descending coronary artery. Time-intensity curves for the left anterior descending coronary artery region of interest were generated and then the peak contrast intensity (PCI), washout half-time (T1/2) and the area under the curve (AUC) were calculated. The post-papaverine increases in PCI and in the AUC, compared to baseline, were 55 +/- 22% and 102 +/- 14% in the four patients with 70% or less left anterior descending diameter stenosis serving as a control group and 3 +/- 25% and 40 +/- 10%, respectively, in the 10 patients with significant left anterior descending coronary artery disease (mean +/- 1 SD, P less than 0.01). In patients with normal coronary arteriography T1/2 increased after intracoronary injection of papaverine. In patients with severe lesions, either an increase or a decrease in T1/2 was observed. Significant left anterior descending coronary artery stenosis associated with impaired coronary blood flow reserve can be detected by failure of myocardial contrast echocardiographic parameters to increase after injection of papaverine. Mild and transient side effects were noted in three patients.

Aged↗
PubMed1992

Bioeffects in echocardiography.

Two mechanisms have been identified through which ultrasound as it is used clinically could produce biologically significant effects. One is heating that results from the absorption of ultrasonic energy by tissues. The other is cavitation, the ultrasonic activation of gas bodies including the potentially violent collapse of small gas bodies in or near tissue that is sometimes called transient or inertial cavitation. The heart, itself, is well perfused and the likelihood of significant heating of the heart tissues in the most extreme conditions known today is negligible. Lung also appears to be relatively immune to heating under diagnostic exposure conditions. In normal echocardiographic procedures, the only tissues that need serious consideration are the ribs. Under extreme conditions, ultrasonic heating of the bone might be as great as 6 degrees C. Nonthermal action of ultrasound has been demonstrated to cause lung hemorrhage at pressure levels on the order of 1 MPa. Although many diagnostic devices produce focal pressures greater than this amount, it appears unlikely that hemorrhage will occur in normal echocardiographic applications. Under certain conditions, pulsed ultrasound can either stimulate or modify the contraction of the heart but the exposures required are not used in normal echocardiographic applications. Since specific devices have been identified who's outputs approach levels required to produce thermal and nonthermal effects, the user should be aware of potential biological effects, particularly in pediatric or obstetric applications, as output levels increase.

Animals↗
PubMed1992

Enhancement of fibrinolysis in vitro by ultrasound.

The effect of ultrasound on the rate of fibrinolysis has been investigated using an in vitro system. Plasma or blood clots containing a trace label of 125I fibrin were suspended in plasma containing plasminogen activator and intermittently exposed to continuous wave 1-MHz ultrasound at intensities up to 8 W/cm2. Plasma clot lysis at 1 h with 1 microgram/ml recombinant tissue plasminogen activator (rt-PA) was 12.8 +/- 1.2% without ultrasound and was significantly (P = 0.0001) increased by exposure to ultrasound with greater lysis at 1 W/cm2 (18.0 +/- 1.4%), 2 W/cm2 (19.3 +/- 0.7%), 4 W/cm2 (22.8 +/- 1.8%), and 8 W/cm2 (58.7 +/- 7.1%). Significant increases in lysis were also seen with urokinase at ultrasound intensities of 2 W/cm2 and above. Exposure of clots to ultrasound in the absence of plasminogen activator did not increase lysis. Ultrasound exposure resulted in a marked reduction in the rt-PA concentration required to achieve an equivalent degree of lysis to that seen without ultrasound. For example, 15% lysis occurred in 1 h at 1 microgram/ml rt-PA without ultrasound or with 0.2 microgram/ml with ultrasound, a five-fold reduction in concentration. Ultrasound at 1 W/cm2 and above also potentiated lysis of retracted whole blood clots mediated by rt-PA or urokinase. The maximum temperature increase of plasma clots exposed to 4 W/cm2 ultrasound was only 1.7 degrees C, which could not explain the enhancement of fibrinolysis. Ultrasound exposure did not cause mechanical fragmentation of the clot into sedimentable fragments, nor did it alter the sizes of plasmic derivatives as demonstrated by SDS polyacrylamide gel electrophoresis. We conclude that ultrasound at 1 MHz potentiates enzymatic fibrinolysis by a nonthermal mechanism at energies that can potentially be applied and tolerated in vivo to accelerate therapeutic fibrinolysis.

Fibrinolysis↗
PubMed1992

The acoustic filter: an ultrasonic blood filter for the heart-lung machine.

Cardiopulmonary bypass-associated encephalopathy is thought to be due in part to continuous microembolization of the brain with gas microbubbles more than 40 microns in diameter during bypass. Current barrier filter technology cannot effectively remove such small microbubbles in fragile fluids such as blood. The design concepts for a new nonbarrier ultrasound-based fluid filtration system (an "acoustic filter") capable of filtering small microbubbles from blood are presented. The acoustic filter uses a field of high-intensity ultrasound to push microbubbles down an acoustic gradient, where they can be collected and removed. To test the filtration efficiency of the system, a Doppler ultrasound bubble detector was built. By monitoring the prefilter and postfilter Doppler signal an assessment of filtration efficiency was made. A suspension of stable albumin-encapsulated microbubbles (4 to 32 microns) were used as a model of the microbubble contaminants that might be found in the arterial return line of the heart-lung machine. Inactivated, the acoustic filter neither removed nor added microbubbles to the fluid. Activated, the acoustic filter provided total or near-total clearing of microbubbles. We conclude that the acoustic filter can remove microbubbles from a cardiopulmonary bypass-like apparatus.

Acoustics↗
PubMed1991

Ability of high-intensity ultrasound to ablate human atherosclerotic plaques and minimize debris size.

To investigate whether high-intensity ultrasound can destroy atherosclerotic plaques while sparing the normal arterial wall, 279 normal human aortic sites and 119 fibrous and 193 calcified plaques, obtained from 24 necropsies, were insonified in a water tank, at 20 kHz and at 5 different power intensities, ranging from 68 W/cm2 (P1) to 150 W/cm2 (P5). These intensities were associated with a total excursion of the ultrasound irradiation apparatus tip from 90 to 268 microns, respectively. Time to perforate normal aortic sites and fibrous and calcified plaques was recorded at each intensity. There was no difference in perforation time between normal aortic sites and fibrous and calcified plaques when high-power levels (P2 to P5) were used. However, at the lowest power (P1), perforation time for the normal aortic wall was significantly longer than for fibrous and calcified plaques: 30 +/- 18 seconds (166 observations), 14 +/- 7 seconds (p less than 0.001) (78 observations) and 12 +/- 8 seconds (p less than 0.001) (115 observations), respectively. When perforation times for normal vessel wall versus fibrous plaque and normal vessel wall versus calcified plaque from the same necropsy specimen were compared in a pairwise manner, the results were: 29 +/- 13 vs 16 +/- 7 (p less than 0.001) (48 paired observations) and 26 +/- 9 vs 10 +/- 5 seconds (p less than 0.001) (55 paired observations), respectively. Regardless of whether paired or unpaired comparison was applied, no significant difference was found in perforation time between fibrous and calcified plaques. The debris did not differ in size as measured separately for normal sites and fibrous and calcified plaques by a computer-interfaced Channelizer and Coulter Counter system.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Reproducibility of quantitative myocardial contrast echocardiography.

To determine whether myocardial contrast echocardiography is quantitatively reproducible, repeated intracoronary injections of sonicated albumin (5%) were performed in eight open chest dogs. Paired injections were performed at baseline, during ischemia produced by ligation of a coronary artery, and during hyperemia induced by intravenous infusion of 0.75 mg/kg body weight of dipyridamole. Contrast washout curves were generated for the left anterior descending coronary artery territory (ischemic area) and left circumflex coronary artery territory (nonischemic area) by beat per beat analysis of frozen end-diastolic frames of left ventricular short-axis views. Peak contrast intensity, contrast washout half-time and area under the curve were derived from these curves. A total of 75 contrast washout curves were analyzed for the study of interinjection, intraobserver and interobserver reproducibility. The correlation coefficients between measurements obtained from paired injections of the echocardiographic contrast agent (interinjection reproducibility) ranged from 0.78 for peak contrast intensity to 0.87 for area under the curve. Percent error varied between 14.7% and 24.7%. The intraobserver variability in measurements was less than the interinjection variability, with a cumulative mean percent error of 17.8% and correlation coefficients of 0.72 (peak contrast intensity), 0.95 (area under the curve) and 0.96 (washout half-time). Interobserver correlation for all indexes was high (r = 0.92 to 0.96). It is concluded that peak contrast intensity, contrast washout half-time and the area under the curve derived from myocardial contrast washout curves can be measured reproducibly from videotapes. In addition, the variability between two injections attempted under identical conditions is greater than reader variability from videotapes.

Albumins↗
PubMed1990

Intravenous contrast echocardiography with use of sonicated albumin in humans: systolic disappearance of left ventricular contrast after transpulmonary transmission.

The transmission of echocardiographic contrast medium and the cyclic changes in left ventricular videodensity during transpulmonary contrast echocardiography were investigated in nine adult volunteers with the use of intravenous injections of sonicated albumin (microbubble size 5.2 +/- 2.6 microns). Right and left ventricular and myocardial contrast were quantitated by videodensitometric analysis. The injections caused no symptoms, and no hemodynamic or electrocardiographic changes were observed. All injections resulted in right ventricular contrast. Mean peak right ventricular videodensity was 75 +/- 48 at end-diastole and 61 +/- 36 gray scale U/pixel at end-systole (p less than 0.05). Seventy-eight percent of injections resulted in left ventricular contrast with a mean peak videodensity of 21 +/- 33 gray scale U/pixel. Early systole was associated with a rapid decrease in left ventricular contrast intensity with near total disappearance of contrast by end-systole (from 23 +/- 33 and 17 +/- 23 U/pixel at end-diastole to 6 +/- 10 and 3 +/- 2 at end-systole at the left ventricular base and apex, respectively; p less than 0.05). None of the injections resulted in myocardial contrast enhancement by visual or quantitative analysis. Thus, left ventricular contrast echocardiography can be achieved after intravenous injections of sonicated albumin. Transpulmonary left ventricular contrast echocardiography is associated with near total disappearance of contrast during systole. This may be secondary to the destruction of microbubbles by the high left ventricular systolic pressure. These findings may help explain the limited success of this technique thus far for myocardial perfusion imaging.

Adult↗
PubMed1990

Statistics of the physiologic phase of integrated backscatter from canine myocardium with normal and reduced coronary circulation.

The phase, relative to the arterial pressure, of cyclically varying integrated backscatter from canine myocardium was measured at normal and reduced coronary blood flow levels and was found to become more randomized with decreasing flow. The phase, modeled as a von Mises distribution on a unit circle which is very similar to the normal distribution on the line, is characterized by a mean (mu 0) and a concentration or width parameter (kappa). kappa is used to characterize the degree of randomization. The von Mises distribution provides an excellent fit to measured data (p less than 0.01). Hypothesis tests performed on the data for various coronary flow levels indicate that the phase distribution for normal coronary flow level is significantly different from the distributions at other flow levels (p less than 0.05). The results suggest that the parameter kappa may be used for differentiating normal and ischemic myocardium.

Animals↗
PubMed1989

Quantitative assessment of the immediate results of coronary angioplasty by myocardial contrast echocardiography.

A low pressure gradient across the residual lesion and a minimal percent residual stenosis are markers of a successful coronary angioplasty. A more physiologic method of assessing the results of coronary angioplasty would involve assessment of myocardial perfusion in the affected coronary bed. Contrast two-dimensional echocardiography provides information about regional myocardial perfusion. To assess the correlation between pre- to postcoronary angioplasty changes in gradient or percent stenosis and the increase in peak contrast intensity, 23 consecutive patients were studied during coronary angioplasty. In 19 of the 23 patients, the coronary angioplasty was successful and in 15 (79%) of the 19, an adequate echocardiographic study was obtained. Mild and transient side effects of echo contrast were observed in 3 of the 15 patients. The gradient across the residual lesions decreased from 52 +/- 12 to 11 +/- 4 mm Hg (mean +/- SD), the diameter of the stenotic lesion decreased from 89 +/- 10 to 25 +/- 16% and corrected peak contrast intensity (peak contrast - baseline contrast in gray level U/pixel) increased from 15 +/- 16 to 50 +/- 26. All these differences were significant at the p less than 0.001 level. Corrected peak contrast intensity correlated exponentially with the decrease in pressure gradient (r = 0.82, p less than 0.001). The correlation curve had a greater increase in peak contrast intensity at gradient decreases greater than 45 mm Hg. Corrected peak contrast intensity did not correlate with decrease in diameter of the stenotic lesion (r = 0.19).

Adult↗
PubMed1989

Superiority of visual versus computerized echocardiographic estimation of radionuclide left ventricular ejection fraction.

An optimal method for determining left ventricular ejection fraction (LVEF) by echocardiography should be rapid, reliable, and widely applicable in order to be utilized routinely in a busy clinical laboratory. Most methods reported in the literature are reliable in selected, high-quality echocardiograms. Most require off-line computer analysis and are time-consuming and poorly suited to the routine of a busy laboratory. We compared in a blinded manner several echocardiographic methods of LVEF determination with the ejection fraction obtained by equilibrium radionuclide angiography (ERNA) in 44 patients unselected for image quality. Echocardiographic methods included: [1] cubed M-mode formula; [2] Teichholz M-mode formula; [3] subjective estimation of LVEF from two-dimensional echocardiographic videotape; [4] area-length method in one four-chamber view; [5] average of area-length method in three four-chamber views; [6] average of area-length method in four-chamber and two-chamber views (one beat each); [7] subjective estimation from stored videoloop of four-chamber and two-chamber view. In 30 cases M-mode tracings were available for analysis. In only 23 of the 44 patients were the apical views suitable for quantitative analysis. The ERNA ejection fraction was 44 +/- 17% (mean +/- 1 SD). The best echocardiographic correlation with ERNA ejection fraction in each patient subgroup studied was obtained by method 3. We concluded that subjective analysis of the videotaped study by an experienced cardiologist/echocardiographer provided the best estimation of ERNA ejection fraction. More time-consuming and costly computer techniques yielded a worse estimate.

Adult↗
PubMed1989

Exercise Doppler echocardiography in patients with mitral prosthetic valves.

Submaximal supine exercise was done by 17 patients with mitral prostheses. Eleven had Björk-Shiley (BS) and six had Starr-Edwards (SE) valves. In 15 patients with normally functioning prostheses, valve area at rest was 2.4 +/- 0.25 cm2 in the BS patients and 1.8 +/- 0.35 cm2 in the SE group (p less than 0.01). In the SE group, peak and mean gradients increased from 8 +/- 1 and 5 +/- 1 mm Hg, respectively, at rest to 22 +/- 5 and 13 +/- 4 mm Hg at peak exercise (mean +/- 1 SD). In the BS group, peak and mean gradients increased from 10 +/- 3 and 5 +/- 2 mm Hg, respectively, at rest to 16 +/- 3 and 10 +/- 3 mm Hg at peak exercise. Peak pressure gradient at peak exercise and the increase in peak gradient with exercise (exercise-resting gradient) were significantly higher in the SE group (p less than 0.05). By plotting the heart rate versus the transmitral gradient during the recovery period, a heart rate-gradient curve was obtained for each type of prosthesis. Doppler echocardiography with moderate supine exercise can be performed in most patients with mechanical prosthesis. Hemodynamic properties (the occlusive character of the SE prosthesis) were brought out by exercise. Doppler echocardiographic measurements during exercise can provide important information, particularly in patients with borderline measurements at rest.

Adult↗
PubMed1989

Myocardial perfusion imaging by contrast echocardiography with use of intracoronary sonicated albumin in humans.

Sonicated albumin has been proposed as a near ideal echocardiographic contrast agent with little myocardial toxicity or hemodynamic effect. Its use has not yet been reported in humans, partly because of difficulties in preparation. With use of the newly modified sonication method, 10 ml of 5% albumin was sonicated for 75 s with a 5.0 ml slow infusion of air. This resulted in microbubbles with a mean diameter (+/- SD) of 5 +/- microns). Fourteen patients undergoing routine coronary angiography were studied. One patient had normal coronary arteries; the other 13 had significant coronary artery disease. In a subgroup of nine patients, sonicated albumin and sonicated diatrizoate meglumine sodium (microbubble diameter 9 +/- 3 microns) were injected several minutes apart, using the same technique. Videodensity-time curves were obtained from a region of interest in the myocardium. Corrected peak contrast intensity (baseline contrast intensity subtracted from peak contrast intensity, gray scale U/pixel) for sonicated albumin and for sonicated diatrizoate meglumine sodium was 51 +/- 26 and 52 +/- 19, respectively (p = 0.89). Washout half-time (T1/2) for the two agents was 5.5 +/- 4.5 and 16.0 +/- 12.2 s, respectively (p = 0.01). One patient with unstable angina experienced transient chest pain after repeated albumin injections. No electrocardiographic changes, blood pressure changes or wall motion abnormalities were observed. Administered by intracoronary injection, sonicated 5% albumin is a safe and effective echocardiographic contrast agent for myocardial perfusion imaging, yielding excellent myocardial contrast with physiologic washout time.

Adult↗