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Biomedical subjects

D K Stewart

Publications and source records attributed to D K Stewart.

At least 37 records · Page 2Linked to original sources
PubMed1983

Value of partial ejection fraction, volume increment, and regional wall motion in identifying patients with clinically significant coronary artery disease.

Recent studies suggest that the partial ejection fraction (EF) in early systole is a more sensitive index of left ventricular (LV) dysfunction than the holosystolic EF. We examined LV volume, partial EF, and volume increment at each of 12 time points in systole to determine which parameter best distinguishes normal subjects from patients with coronary artery disease (CAD). Contrast ventriculograms, obtained either in the right anterior oblique projection (60 frames/sec) or in the biplane projection (30 frames/sec), of 58 normal subjects and 68 patients with CAD were studied. The endocardial contour in each frame of a sinus beat was traced to derive a volume curve. At each twelfth of systole, LV volume was extrapolated from the curve and the partial EF was calculated. The increment in volume between successive time points was also calculated. Both partial EF and LV volume in patients with CAD became progressively more abnormal with time; peak abnormality occurred at end-systole. In a subgroup of patients with CAD who had normal holosystolic EF, both partial EF and volume were normal throughout systole. The increment in volume with each twelfth of systole in patients with CAD deviated less than 1 SD from normal throughout systole. Thus, maximum abnormality in partial EF and volume occurs at end-systole. Of the parameters of global LV function tested, holosystolic EF best distinguishes patients with CAD from normal subjects. However, regional wall motion measured in the area of interest is more sensitive to localized abnormality, the severity of which may be overestimated or underestimated by the EF due to hyperkinesis or hypokinesis in other regions of the left ventricle.

Cardiac Catheterization↗
PubMed1979

Left ventricular function before and following surgical treatment of mitral valve disease.

Nineteen patients with mitral valve disease were studied before and a mean 11 months +/- 9 months following valve replacement or reconstruction, which resulted in good postoperative valve function. Biplane left ventricular angiography and pressures were utilized to determine end-diastolic volume/M. (EDV), end-systolic volume/M. (ESV), ejection fraction (EF), left ventricular mass/M. (LVM), and stroke work/M. (SW). There were 19 patients--six with mitral stenosis (MS), six with mitral stenosis and regurgitation (MS + MR), and seven with mitral regurgitation (MR). Those with MS and MS + MR preoperatively had no significant change in left ventricular end-diastolic pressure (LVEDP), EDV, ESV, LVM, or EF following surgery. Patients with MR had a significant reduction in LVEDP, EDV, SV, and SW. More importantly, the EF fell in four of these seven patients and LVM did not decrease following surgery. It is concluded that surgical treatment for MS and MS + MR had little effect on left ventricular performance. Following surgical treatment for MR, reduction in EDV is not associated with reduction in LVM, and frequently left ventricular performance deteriorates as judged by the EF.

Angiocardiography↗
PubMed1978

Left ventricular volume during maximal supine exercise: a study using metallic epicardial markers.

Changes in left ventricular (LV) volumes and ejection fraction between rest and maximal supine exercise were evaluated in 11 patients who had had four epicardial markers placed during coronary artery surgery. After calibrating marker distances with respect to volume (r = 0.92--0.99) over one cardiac cycle for each patient, regression equations were used to compute LV volume from marker measurements for beats before and during exercise. The response of the left ventricle to exercise and the extent of revascularization could not be predicted from resting LV volume or ejection fraction. Ten patients had normal resting end-diastolic volumes and eight had normal resting ejection fractions. With exercise, three had a rise in end-diastolic volume and four had a fall in ejection fraction. Graft patency was greater in the group with an unchanged or increased ejection fraction (86 vs 50%, P less than 0.05). Epicardial clip motion can be used to determine LV volumes and ejection fraction during supine maximal exercise in man. The revascularized ventricle with normal or nearly normal performance in studies done at rest responds by decreasing end-diastolic and end-systolic volume and by increasing the ejection fraction. Increases in volumes or decreases in ejection fraction reflect old myocardial damage from infarction, fibrosis or ischemia from incomplete revascularization.

Adult↗
PubMed1977

Nonuniform contraction in the isolated cat papillary muscle.

Microspheres infused into the coronary microcirculation were used as markers to define segments within isolated cat papillary muscles. Video recording and analysis provided measurements of the variations of segment lengths as the muscles contracted at lengths of 76-100% Lmax. In all muscles, segments in the center region were found to shorten during muscle isometric contraction while those in the end regions lengthened. Central shortening was typically 10-15%. In the passive state, segment lengths varied directly with muscle length over a broad range characterized by low force. Segments in the center region, however, displayed an abrupt transition to high stiffness at a certain length while end regions continued to stretch. Force-length relationships obtained for the presumably healthy center segment are significantly different from those obtained for the whole muscle. These results suggest that there may be major difficulties with the interpretation of mechanical measurements on papillary muscles unless contractile inhomogeneity is eliminated or taken into account.

Animals↗
PubMed1977

Immediate effect of contrast medium injection on left ventricular volumes and ejection fraction. A study using metallic epicardial markers.

The immediate effect of contrast medium injection on left ventricular (LV) volume, stroke volume (SV) and ejection fraction (EF) was evaluated from postoperative LV biplane cineangiograms of 10 patients with 4-6 epicardial markers placed at the time of coronary artery surgery. After calibrating marker distances with respect to volume (r = 0.97-0.99) over one cardiac cycle for each patient, regression equations were used to compute LV volume from marker measurements for beats prior to, during and following injection. End-diastolic volumes (EDV) prior to injection ranged from 93-263 ml and did not change significantly with injection. End-systolic volumes (ESV) showed a mean decrease of 7.3 ml by beat 7 following injection; this was of borderline significance. Similarly, there was no significant change of SV or EF until beat 7 when there were small but significant increases of 6.4 ml and 0.04, respectively. The injection of moderate amounts of contrast in man does not cause significant changes in LV volume or EF through the sixth post-injection beat.

Cardiac Output↗
PubMed1977

Left ventricular function before and following aortic valve replacement.

Twenty-four patients with aortic valve disease were studied before and 19+/-12 months following valve replacement with a well functioning prosthesis. Biplane left ventricular angiography and pressures were utilized to determine end-diastolic volume/m2 (EDV), end-systolic volume/m2 (ESV), ejection fraction (EF), left ventricular mass/m2 (LVM) and stroke work (SW). There were nine patients with aortic stenosis (AS), ten patients with combined stenosis and regurgitation (AS-AR), and five patients with aortic regurgitation (AR). Following surgery, patients with regurgitation preoperatively showed marked regression in EDV and ESV. All groups demonstrated regression in LVM. Fifteen patients with a normal EF preoperatively (65+/-11%) had no change after surgery; the nine patients with a low EF before surgery (38+/-8%) had a normal EF after surgery (60+/-16%). We conclude that left ventricular dilatation, hypertrophy, and reduced left ventricular pump function are largely reversible after successful aortic valve replacement.

Angiography↗
PubMed1977

Length-dependent calcium inotropism in cat papillary muscle.

We studied changes in the relationship of isometric developed force to muscle length when extracellular calcium concentration was altered in isolated cat papillary muscles. In two series of experiments at temperatures of 30 degrees C and 32 degrees C, and rates of 12 and 30 beats/min, 21 muscles were exposed to calcium concentrations of 1.125, 2.25 and 4.5 mM. Muscle lengths were varied between 80% and 100% of the length at which maximum developed force occurred (Lmax). Peak developed force and the time from stimulus to peak were measured. The data indicate that force is not altered proportionately at all lengths when calcium concentration is changed. Rather, we found that a substantially greater modification of force occurs at short lengths than at long lengths. Similarly, the time to peak force increases with length at a rate which is more than 4 times greater at the low calcium concentration than it is at the high concentration. Small but consistent shifts of Lmax also are seen. We observed that Lmax is longer when inotropic changes reduce force and shorter when force is increased. These results indicate that the inotropic effect of extracellular calcium concentration changes is dependent on muscle length.

Animals↗
PubMed1976

Quantitative measurement of left ventricular volumes in man from radiopaque epicardial markers.

The distances between three or four radiopaque markers located on the left ventricular epicardial surface at the apex and in the region of the minor axes in 22 subjects showed close correlations with left ventricular chamber radii, length, volume and wall thickness determined from biplane angiograms over the range of stroke volume. The markers were previously placed during heart surgery. Regression equations relating the distances between epicardial markers and chamber volumes were used to predict volumes for other beats. There was close agreement of end-diastolic, end-systolic, and stroke volumes as determined by the angiographic and epicardial marker methods for premature atrial contraction beats and post premature contraction beats, and in studies performed during rest and exercise. Time-volume curves determined by the epicardial marker and angiographic methods were similar. It is concluded that epicardial marker measurements can be used to quantitate beat-to-beat left ventricular chamber volume and dimension changes.

Angiocardiography↗