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Biomedical subjects

D H Schmidt

Publications and source records attributed to D H Schmidt.

At least 19 recordsLinked to original sources
PubMed1992

Left ventricular volume calculation using a count-based ratio method applied to first-pass radionuclide angiography.

Most count-based radionuclide methods for calculating left ventricular volume rely on measurement of radioactivity in a peripheral blood sample and a measurement of ventricle to collimator distance. We have developed a method which requires neither a blood sample nor a distance measurement and which is applicable to first-pass radionuclide angiography. The parameters used to calculate volume are the area of pixel, the total counts in the left ventricle and the maximum pixel count. The equation was used to calculate the volumes in 50 patients who had both resting first-pass radionuclide angiography (25 patients with a single crystal and 25 patients with a multicrystal camera) and contrast ventriculography on the same day. Correlation coefficients for end-diastolic and end-systolic volumes showed r ranging 0.93-0.98 and standard error of estimate ranging 23-35 ml for end-diastolic volume (14%-17% of mean end-diastolic volume) and 16-23 ml for end-systolic volume (18%-21% of mean end-systolic volume). Image processing software for extracting the needed values is generally available on most commercial nuclear medicine imaging systems and the additional time for the calculations is short. Although the theory is based on multiple assumptions, the volume calculation appears to be reasonably accurate and clinically applicable.

Adult↗
PubMed1991

Evaluation of transient mitral regurgitation in coronary artery disease.

The pathoanatomy and factors associated with transient mitral regurgitation (MR) induced by myocardial ischemic stress are unknown. Changes in valvular and ventricular parameters during transient, stress-induced MR in patients with coronary artery disease were investigated, and the clinical characteristics of these patients were identified. Color flow Doppler echocardiography was used to quantify the MR color area, the coaptation point of the mitral leaflets, the mitral valve anulus diameter, and left ventricular volumes and wall motion in 42 patients before and immediately after exercise echocardiography (group 1, n = 27), or before and during percutaneous transluminal coronary angioplasty (PTCA) (group 2, n = 15). Of the 27 patients with exercise echocardiography, 4 developed new, transient MR (group 1B) and 9 had MR both at rest and during exercise (group 1C). Of the 15 patients with PTCA, 7 developed new MR (group 2B). New MR (groups 1B and 2B) was associated with more severe stress-induced ventricular dyskinesia (p less than 0.05) than was seen in patients with chronic MR (group 1C) or in patients without MR, and occurred predominantly in patients with left anterior descending or right coronary artery stenoses. Stress-induced MR was not associated with changes in blood pressure or in mitral valve anulus diameter, nor with the development of mitral valve prolapse. It was associated with apical displacement of the mitral leaflets in patients in group 1B and C (p less than 0.05). New MR flow areas were significantly smaller than those in patients with chronic MR (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1990

Technically suboptimal first-pass radionuclide angiographic studies.

First-pass radionuclide angiography (FPRNA) has proven to correctly assess left ventricular function, however, technical difficulties do occur. One hundred and thirty one patients had contrast angiography and resting radionuclide angiography within 24 h. Of the 131 patients, 86 (66%) had adequate studies and 45 (34%) were technically suboptimal studies. In the latter group, low counts affected the quality of the images but did not change the left ventricular ejection fraction (LVEF) or regional wall motion (RWM) scores. Patients with high background activity showed overestimation of LVEF, however, by using a formula that was derived from the linear regression the LVEF could be calculated accurately in most cases. Multiple technical problems were noted in 14 patients in whom the best correlation was between contrast LVEF and background uncorrected LVEF from FPRNA (r = 0.87). In the latter group, FPRNA showed overestimation of RWM in 8 patients (57%), mainly in the inferior wall. We conclude that for most technically compromised first-pass radionuclide angiographic data, accurate LVEF values can be achieved but errors in regional wall motion interpretation will occur, especially when multiple technical problems exist.

Female↗
PubMed1990

Mitral regurgitation: parameters that affect the correlation between Doppler echocardiography and contrast ventriculography.

The correlation between Doppler and contrast angiographic estimation of severity of mitral regurgitation was assessed retrospectively in 60 patients with native mitral valve disease. Results showed r = 0.82. Among 15 parameters (demographic, clinical, echocardiographic and hemodynamic) 3 were found to be associated with overestimation of the severity by Doppler: low left ventricular ejection fraction, low cardiac output, and high mean pulmonary artery capillary wedge pressure. On the other hand, a large left atrium was associated with underestimation of mitral regurgitation by Doppler. Based on that data, Doppler results were adjusted in a prospective group of 30 patients with native mitral valve disease. The correlation between contrast ventriculography and uncorrected Doppler results showed r = 0.83, while the corrected Doppler results showed r = 0.91. The study implies that although a good correlation is found between the two modalities for estimation of mitral regurgitation, a better correlation can be achieved by adjusting the Doppler results according to the above-mentioned parameters.

Contrast Media↗
PubMed1990

Regional myocardial blood flow with a reperfusion catheter and an autoperfusion balloon catheter during total coronary occlusion.

We investigated the ability of two new coronary perfusion catheters to maintain regional myocardial blood flow throughout a 90-minute period of occlusion. In 21 dogs (group I = total occlusion control; group II = reperfusion catheter; group III = autoperfusion balloon catheter) we studied regional blood flow, distal coronary perfusion pressure, infarct size, and red blood cell hemolysis after placement of either catheter into the left anterior descending coronary artery. Regional (microsphere) blood flow showed a reduction in transmural blood flow during occlusion in comparison to baseline values (1.07 +/- 0.12 to 0.81 +/- 0.11 and 1.01 +/- 0.16 to 0.73 +/- 0.08 ml/min subendocardial perfusion for groups II and III, respectively). Comparable changes in blood flow were observed in the subepicardial and midmyocardial regions. Distal coronary perfusion pressures were reduced by 26% and 28% for groups II and III, respectively. Both catheters prevented significant infarction and maintained adequate regional myocardial blood flow throughout the 90-minute period of occlusion without significant complications of clotting or destruction of erythrocytes.

Angioplasty, Balloon, Coronary↗
PubMed1990

Left ventricular volume calculation using a count-based ratio method applied to multigated radionuclide angiography.

The purpose of this study was to investigate the accuracy of a new count-proportional method for the measurement of left ventricular volume when applied to gated equilibrium blood-pool imaging. An equation is developed that relates total chamber volume, Vt, to the area of a pixel (M) and the ratio (R) of total counts within the chamber to the counts within the hottest pixel in the chamber such that Vt = 1.38 M3R3/2. The value of M is a constant for the particular scintillation camera-collimator system and R is obtained from observed count rates. All calculated volumes were compared to volumes measured using biplane contrast ventriculography. In 25 patients, the method for ventricular volumes gave an r of 0.95 and an s.e.e. of 23 ml [Volume (nuclear) = 0.94 Volume (cath) + 1.3]. Endsystolic volume was best calculated from end-diastolic volume and ejection fraction. Manual regions of interest were more accurate than automated regions of interest. This method appears to be as accurate as more complex approaches and has the advantage of not requiring attenuation correction or blood sampling.

Angiography↗
PubMed1988

Inadequate subendocardial oxygen delivery during perfluorocarbon perfusion in a canine model of ischemia.

Perfusion of the coronary artery distal to an occlusion was performed in 16 canine preparations to compare the mechanical perfusion of autologous blood to the perfluorocarbon fluosol DA, 20% emulsion (FDA-20). Both substances were perfused under similar conditions (30, 60, and 80 ml/min) and regional electrograms, contractility, and coronary perfusion were measured relative to native coronary perfusion. Autologous blood (60 and 80 ml/min) produced a significant increase in regional (epicardial, midmyocardial, and endocardial) and transmural flow, but not in the endocardial/epicardial perfusion ratio. No other significant changes were observed during autologous blood perfusion. In contrast, FDA-20 perfusion resulted in significant ST depression (-1.8 +/- 0.2, -1.7 +/- 0.2, and -1.3 +/- 0.3 mm) at 30, 60, and 80 ml/min, respectively. FDA-20 also induced a significant decrease in distal diastolic coronary pressure and resistance, a significant decrease in the endocardial/epicardial perfusion ratio at all three perfusion rates, and a significant reduction in delivery of O2 to the subendocardium. These results indicate that autologous blood perfusion of the distal coronary artery during occlusion preserves myocardial function to a better degree than does FDA-20.

Animals↗
PubMed1987

Effect of age and training on aerobic capacity and body composition of master athletes.

Maximum oxygen uptake (VO2max) and body composition have been shown to deteriorate with age. How much of the decline is attributable to aging and how much is affected by reduced physical activity is not known. The purpose of this investigation was to determine the aerobic capacity and body composition of 24 master track athletes and to evaluate the relationship to age and maintenance of training over a 10-yr period. The subjects (50-82 yr of age) were retested after a 10.1-yr follow-up (T2). All continued their aerobic training, but only 11 were still highly competitive (COMP) and continued to train at the same intensity. The other 13 athletes studied became noncompetitive (post-COMP) and reduced their training intensity. The results showed the COMP group to maintain its VO2max and maximum O2 pulse while the post-COMP group showed a significant decline (54.2-53.3 vs. 52.5-45.9 ml X kg-1 X min-1; 20.7-20.8 vs. 22.4-20.0 ml/beat from test one (T1) to T2 for the COMP vs. post-COMP groups, respectively). Maximum heart rate declined 7 beats/min for both groups. Body composition showed no difference between groups from T1 to T2. For both groups body weight declined slightly (70.0-68.9 kg), percent fat increased significantly (13.1-15.1%), and fat-free weight decreased significantly (61.0-59.0 kg). Thus, when training was maintained, aerobic capacity remained unchanged over the follow-up period. Body composition changed for both groups and may have been related to aging and/or the type of training performed.

Aged↗
PubMed1986

High count rate first-pass radionuclide angiography using a digital gamma camera.

In this study, first-pass radionuclide angiography (FPRNA) was performed using a digital single-crystal gamma camera. Twenty-nine men and six women (ages 43-80, mean 61 yr) underwent FPRNA in the supine position immediately prior to cardiac catheterization. Total counts/sec in the whole field-of-view in the right ventricular phase were 150,352 +/- 26,006. Background uncorrected counts in the representative cycle were 7,651 +/- 2,527 at end-diastolie and 4,904 +/- 2,314 at end-systolie. A linear correlation between FPRNA left ventricular (LV) ejection fraction and contrast LV ejection fraction gave an r = 0.95 with an s.e.e. of 0.05. Analyses of intra- and interobserver variability gave r = 0.99 and 0.98 and an s.e.e. of 0.02 and 0.03, respectively. Spearman-Rank correlation coefficients between FPRNA and contrast angiographic wall-motion scores were greater than 0.8 for all walls, while sensitivity/specificity were 0.86/0.90, 0.76/1.00, 0.76/1.00 for anterior, apical, and inferior wall-motion abnormalities, respectively. We conclude that satisfactory counting statistics for FPRNA can be obtained with a digital gamma camera, and that accurate and reproducible measurements of global and regional left ventricular function can be obtained with this technique.

Adult↗
PubMed1986

Background correction in first-pass radionuclide angiography: comparison of several approaches.

This study was designed to test the comparative accuracy of several commonly used background correction techniques in first-pass radionuclide angiography (FPRNA). Thirty patients underwent FPRNA and single plane contrast angiography (CA) within 1 hr of each other. The left ventricular ejection fractions (LVEF) calculated from the different background subtraction approaches to FPRNA were compared to the CA LVEF. When applied to a representative cycle, a horseshoe-shaped background region of interest (BKROI) underestimated LVEF (p less than 0.005, r = 0.91, s.e.e. = 0.06) while a ring shaped BKROI adjusted at end-systole for aortic valve motion insignificantly overestimated LVEF (p = NS, r = 0.91, s.e.e. = 0.07). A lung background approach applied to a representative cycle gave the best correlation with CA (p = NS, r = 0.96, s.e.e. = 0.04). Without using a representative cycle, time-activity curves from a horseshoe-shaped BKROI and the LV ROI were created and the LV curve was normalized to the peak counts in the BKROI curve. LVEF calculated from the normalized curve correlated favorably with CA LVEF (p = NS, r = 0.91, s.e.e. = 0.08). The influence of some recently described improvements in representative cycle generation are also documented.

Aged↗
PubMed1985

Sequential internal mammary artery grafts. Expanded utilization of an ideal conduit.

The internal mammary artery, when used as a conduit for coronary artery bypass, offers a better long-term patency rate and survival rate than the saphenous vein; however, its utility has been limited. Among other factors, the availability of only two internal mammary arteries for anastomosis has been a major limitation. In an attempt to overcome this limitation, we constructed sequential internal mammary artery grafts in 87 patients. In 49 patients (Group I), only one internal mammary artery was used for sequential anastomosis. In another 31 patients (Group II), one internal mammary artery was used for sequential anastomosis and the other was used for single end-to-side anastomosis. Both internal mammary arteries were used in seven patients (Group III) for the construction of sequential anastomoses. Postoperatively, 64 patients were evaluated by exercise stress tests. None of these patients had a positive stress test although seven patients (11%) had electrocardiographic changes that were considered equivocal. Coronary angiography was performed in 35 of the 87 patients, with 92 vein grafts and 90 internal mammary artery anastomotic sites evaluated within 1 year of operation. A total of 83 vein grafts and 84 internal mammary artery anastomotic sites evaluated within 1 year of operation. A total of 83 vein grafts and 84 internal mammary artery anastomoses were found to be patent. Thus the patency rate for vein grafts was 90% and for internal mammary artery grafts, 93%. During the follow-up period (8 to 52 months), three patients died and one was lost to follow-up. Among the remaining patients, 79 had complete relief from symptoms, three had minimal symptoms, and one patient obtained no relief from symptoms. Based on these results, we have concluded that the extended use of internal mammary artery, constructing sequential anastomoses, is technically feasible and provides adequate perfusion to the area of myocardium supplied by such grafts.

Adult↗
PubMed1978

Reentry within the His-Purkinje system. Elucidation of reentrant circuit using right bundle branch and His bundle recordings.

Routes of impulse propagation during reentry in the His-Purkinje system (Re-HPS) in 13 patients were studied using the right ventricular extra stimulus (V2) method and right bundle branch (RBB) recordings in addition to the conventional His (H) bundle recordings. The H-V and RB-V intervals during sinus rhythm averaged 44.2 and 27.6 msec respectively, with the average antegrade H-RB interval 16.6 msec. All 13 patients demonstrated Re-HPS in the form of V3 showing a left bundle branch block (LBBB) pattern, and two of the 13 patients also manifested V3 with a right bundle branch block (RBBB) pattern. During Re-HPS showing a LBBB pattern, the retrograde activation of the His bundle (H2) in response to V2 occurred via the left bundle branch (LBB), as indicated by inscription of retrograde H2 prior to RB2 in nine of 13 cases (average H2-RB2 = 9.4 msec), and simultaneous incription of retrograde H2 and RB2 in the remaining four. When V3 showed a RBBB pattern the retrograde RB2 preceded H2, suggesting H2 activation via the RBB. These findings suggest that circuit of Re-HPS incorporates both bundle branches and the bundle of His. The H-RB recordings were also useful in distinguishing sustained Re-HPS from atrioventricular nodal reentry when in both instances the QRS complex showed a LBBB pattern.

Adult↗
PubMed1977

Effects of sheep digoxin-specific antibodies and their Fab fragments on digoxin pharmacokinetics in dogs.

Intact sheep antidigoxin antibodies and their Fab fragments have both been found to exert profound effects on digoxin pharmacokinetics in [3H] digoxin-treated dogs. Both classes of molecule remove digoxin from the extravascular space and sequester it in the circulation in protein-bound form, a form in which the digoxin is presumably inactive. These two classes of molecule differ, however, in that the intact antibody molecules interfere with digoxin excretion, thereby promoting the retention of the glycoside; this retained digoxin is eventually released in free, active form when the administered antibody is metabolically degraded. In contrast, urinary excretion of digoxin continues in Fab-treated dogs, with significant quantities of digoxin being excreted promptly in the urine in complex with Fab fragments. These differences in urinary excretion, together with the probable decreased immunogenicity of sheep antidigoxin Fab fragments, suggest that such fragments possess potential advantages over intact antibody molecules for use in the therapy of life-threatening digoxin intoxication in man.

Animals↗
PubMed1976

Regional myocardial perfusion during atrial pacing in patients with coronary artery disease.

Regional myocardial perfusion (RMP) was measured with 133xenon and a multiple-crystal scintillation camera at rest and during atrial pacing in 24 patients with normal coronary arteriograms or less than 50% lesions, Group I, and in 24 with significant (greater than 50% lesions) left coronary artery disease (CAD), Group II. Pacing induced increases in the double product (DP) of heart rate and systolic blood pressure, an index of myocardial oxygen consumption, were not different for Groups I and II. In Group I average mean LV perfusion rate was subnormal at rest but rose from 49 to 73 ml/100 g-min during pacing to 150/min without angina. A response index (RI), (deltaMP X 10(3)/deltaDP), averaged 2.93. Twenty patients in Group II developed angina during pacing. The average mean LV perfusion rose less than in Group I, from 48 to 64 ml/100 g-min (P less than 0.05) and the average RI, 1.76, was lower (P less than 0.01). In 19 of these patients, average RMP distal to the major coronary lesion increased from 46 to 58 ml/100 g-min; this increase during pacing was significantly less than in the remainder of the LV of 48 to 66 ml/100 g-min (P less than 0.05). Average regional RIs were 1.39 and 2.18, respectively. In three patients the presence of collaterals termed adequate by radiological criteria was not associated with preferential decreases in the distal regional RI. The data support the hypothesis that in some patients with CAD, angina pectoris results when an obstructive coronary lesion restricts the total or regional myocardial blood flow response to an increased rate of myocardial oxygen consumption.

Angina Pectoris↗