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Biomedical subjects

L S Wann

Publications and source records attributed to L S Wann.

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

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

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

Usefulness of right ventricular diastolic collapse in diagnosing cardiac tamponade and comparison to pulsus paradoxus.

To compare the sensitivity, specificity and predictive value of right ventricular (RV) diastolic collapse and pulsus paradoxus as signs of cardiac tamponade, 21 consecutive patients with pericardial effusion and suspected cardiac tamponade underwent prospective hemodynamic and echocardiographic evaluation. Simultaneous hemodynamic and echocardiographic data were obtained in all patients before and after pericardiocentesis. Cardiac tamponade was considered present when there was diastolic equilibration of the intrapericardial, right atrial and pulmonary capillary wedge pressures and elevation of these pressures to more than 10 mm Hg. RV diastolic collapse was 93% sensitive and 100% specific in diagnosing cardiac tamponade, whereas pulsus paradoxus was only 79% sensitive and 40% specific. The positive and negative predictive values of RV diastolic collapse (100% and 83%) were considerably better than pulsus paradoxus (81% and 40%) and demonstrate that RV diastolic collapse is more sensitive, specific and predictive of cardiac tamponade than is pulsus paradoxus. Serial simultaneous hemodynamic and echocardiographic observations at multiple points during pericardiocentesis in a smaller subgroup (5 patients) also suggest that the hemodynamic effects of RV diastolic collapse in cardiac tamponade are mediated by an increase in intrapericardial pressure.

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 shift in the relationship between intrapericardial fluid pressure and volume induced by acute left ventricular pressure overload during cardiac tamponade.

We hypothesized that a process leading to an acute increase in cardiac size would change the relationship between intrapericardial pressure and fluid volume during cardiac tamponade, resulting in a change in the time of onset of right ventricular diastolic collapse (RVDC) as seen on the two-dimensional echocardiogram. Five spontaneously breathing dogs were instrumented to measure ascending aortic and right atrial blood pressures and intrapericardial pressure (IPP). A hydraulic occluder was placed around the proximal descending thoracic aorta. Each animal underwent six consecutive episodes of cardiac tamponade, three in the presence alternating with three in the absence of aortic constriction. The onset of RVDC was recorded and the volume infused into the pericardial space was measured. In the presence of aortic constriction, the relationship between pericardial pressure and incremental pericardial fluid volume was shifted so that IPP was an average of 3.4 mm Hg higher at any given intrapericardial fluid volume (p less than .001). At the onset of RVDC, the mean IPP was higher and the intrapericardial fluid volume was lower during aortic constriction than under control conditions (p less than .001 for both comparisons). Thus, a rapid increase in left ventricular volume in the presence of an otherwise unimportant pericardial effusion may increase intrapericardial fluid pressure sufficiently to cause RVDC.

Animals↗
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↗
PubMed1985

Diagnostic precision of echocardiography in mitral valve prolapse.

In order to determine the precision with which currently used echocardiographic criteria can be applied for the diagnosis of mitral valve prolapse, three independent observers (A, B, and C) blindly analyzed the separate M-mode and two-dimensional echocardiograms of 50 patients, 27 of whom had previously been identified clinically as having echocardiographic evidence of prolapse. Observer A's intraobserver repeatability for M-mode echocardiography was 92%, Observer B's was 84%, and Observer C's was 90%. For two-dimensional echocardiography, Observer A's intraobserver repeatability was 98%, Observer B's was 80%, and Observer C's was 82%. We believe that the variability in intraobserver repeatability is related to the frequency with which individual observers diagnosed prolapse. The interobserver repeatability for M-mode echocardiography for Observer A versus B was 64%, for Observer A versus C it was 80%, and for Observer B versus C it was 66%. The interobserver repeatability for two-dimensional echocardiography for Observer A versus B was 54%, for Observer A versus C it was 70%, and for Observer B versus C it was 52%. There was no significant difference between the inter- and intraobserver variability of M-mode versus two-dimensional echocardiography. Review of cases in which readings were discrepant revealed that these cases usually had relatively mild changes. Clinicians should be aware of the inherent variability of echocardiographic interpretation when they make a diagnosis of mitral valve prolapse.

Echocardiography↗
PubMed1985

Shape analysis of two-dimensional echocardiograms in mitral valve prolapse.

The inter- and intraobserver variability in applying current diagnostic criteria for mitral valve prolapse as seen on two-dimensional echocardiograms is appreciable. It is therefore proposed that new methods employing computer-based pattern recognition algorithms be developed. The criteria will focus on the shape of the valve throughout systole. Shape analysis is first used to detect prolapsing sections of the valve. These prolapsing segments are fit using spline regression with a minimal number of knots. This mathematical description provides a basis for new shape descriptors.

Computers↗
PubMed1985

Mid-diastolic opening of the pulmonary valve after right ventricular infarction.

Premature opening of the pulmonary valve in mid-diastole before atrial systole was observed during inspiration in a patient with extensive right ventricular infarction. Transient inspiratory elevation of right ventricular diastolic pressure to a level exceeding pulmonary artery pressure was documented. Although forward flow into the pulmonary artery was seen on Doppler echocardiography after atrial systole, most of the flow continued to be in response to right ventricular contraction, despite extensive infarction.

Cardiac Catheterization↗
PubMed1985

Alterations in intravascular volume affect the relation between right ventricular diastolic collapse and the hemodynamic severity of cardiac tamponade.

Right ventricular diastolic collapse has been demonstrated to be a sensitive and specific sign of cardiac tamponade. Because the shape and position of the right ventricular wall are related to the relative pressures within the pericardial space and the right ventricular chamber, the usefulness of right ventricular diastolic collapse as a marker of cardiac tamponade may be influenced by intravascular volume and right heart filling pressures. This study was undertaken to determine the effects of volume loading and hemorrhage on the point within the hemodynamic progression of cardiac tamponade at which right ventricular diastolic collapse first appears. Five unanesthetized, chronically instrumented dogs were studied with two-dimensional echocardiography during 41 episodes of cardiac tamponade induced by the intrapericardial infusion of warm saline solution. Intravascular volume was adjusted before cardiac tamponade to a hypovolemic, euvolemic or hypervolemic state using saline solution and dextran infusion or hemorrhaging to achieve the prescribed mean right atrial blood pressure. The measurements recorded during each episode of cardiac tamponade were right atrial blood pressure, aortic blood pressure, cardiac output (by electromagnetic flow meter), heart rate and intrapericardial pressure. When compared with the euvolemic state, the onset of right ventricular diastolic collapse in volume contraction occurred at a lower intrapericardial pressure (with a lower aortic blood pressure and cardiac output), whereas in volume expansion it occurred at a higher intrapericardial pressure (with a higher aortic blood pressure and cardiac output). Volume expansion delayed the decrease in hemodynamic variables during cardiac tamponade in this canine model.

Animals↗
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↗
PubMed1985

The relative merits of pulsus paradoxus and right ventricular diastolic collapse in the early detection of cardiac tamponade: an experimental echocardiographic study.

An inspiratory decline in systolic arterial blood pressure exceeding 10 mm Hg has been used clinically to identify hemodynamically significant pericardial effusions. Recently, the echocardiographic sign of right ventricular diastolic collapse (RVDC) has been shown to occur early in the course of cardiac tamponade in association with a hemodynamically important decline in cardiac output. This study was undertaken to compare the relative merits of pulsus paradoxus and the onset of RVDC in the early detection of cardiac tamponade in an unanesthetized canine preparation. We studied six chronically instrumented, conscious dogs with two-dimensional echocardiography during cardiac tamponade induced by continuous infusion of saline into the pericardial space. We recorded intrapericardial pressure, cardiac output (electromagnetic flowmeter), aortic (catheter-tip transducer) and right atrial blood pressures, heart rate, and respiration. None of the dogs had RVDC when the pericardial space was empty, but all dogs showed RVDC during cardiac tamponade. We found that RVDC was strongly related to all of the cardiac parameters evaluated (intrapericardial pressure, cardiac output, aortic blood pressure, heart rate, and stroke volume) and provided information on each that was independent of that provided by pulsus paradoxus. Furthermore, RVDC appeared to be more strongly related to most cardiac parameters than was pulsus paradoxus and to be more sensitive and specific than pulsus paradoxus in detecting changes in intrapericardial pressure early in cardiac tamponade.

Animals↗
PubMed1985

Effects of intravascular volume state on the value of pulsus paradoxus and right ventricular diastolic collapse in predicting cardiac tamponade.

Both pulsus paradoxus and right ventricular diastolic collapse detected by two-dimensional echocardiography are noninvasive markers of impaired cardiac function in cardiac tamponade, yet the reliability of each may vary with the patient's state of hydration. To examine the relative value of these noninvasive markers at various states of hydration, we studied five chronically prepared, conscious mongrel dogs during 37 episodes of cardiac tamponade at three different intravascular volumes. We continuously measured cardiac output (electromagnetic flowmeter), aortic blood pressure, right atrial blood pressure, intrapericardial pressure, and respirations. Intravascular volume was varied by adjusting the mean right atrial blood pressure to hypovolemic (-2 to -6 mm Hg), euvolemic (0 to 4 mm Hg), or hypervolemic (6 to 10 mm Hg) levels. The sensitivity and specificity of right ventricular diastolic collapse in predicting increases in intrapericardial pressure remained high at all levels of hydration. Pulsus paradoxus showed good sensitivity and specificity at low intravascular volumes, but both sensitivity and specificity declined at higher intravascular volumes. Thus right ventricular diastolic collapse was more sensitive and more specific than pulsus paradoxus in detecting increases in intrapericardial pressure during euvolemia and hypervolemia whereas the two tests were equally valuable in hypovolemic states.

Animals↗