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Biomedical subjects

D H Schmidt

Publications and source records attributed to D H Schmidt.

At least 73 records · Page 4Linked to original sources
PubMed1980

Improvement in left ventricular function after myocardial revascularization: assessment by first-pass rest and exercise nuclear angiography.

Thirty-six patients with coronary artery disease were studied by first-pass radionuclide angiography to assess the effects of myocardial revascularization on exercise-induced myocardial ischemia. The radionuclide studies were performed in the 30 degree right anterior ablique position, at rest and during exercise, 1 to 3 days preoperatively and 10 to 14 days postoperatively. The mean population age was 53 years; the mean number of grafts placed was 4.0 per patient. Fifteen normal male volunteers were tested by rest and exercise radionuclide angiography to serve as normal control subjects. In all exercise radionuclide studies, progressive upright bicycle exercise was performed to symptoms of fatigue, dyspnea, or chest pain. The parameters of ejection fraction (EF), end-diastolic volume (EDV), and regional wall motion (RWM) were determined. Twenty-nine of the 36 patients had postoperative coronary arteriography that was correlated with radionuclide determinations. The results showed that in the normal subjects with maximal exercise the mean EF rose, the mean EDV increased 19%, and there was no exercise-induced regional wall motion dysfunction (ERWMD). In the patients with coronary artery disease prior to operation, the mean EF fell significantly, the mean EDV rose 24%, and 26 of 36 patients had ERWMD. After operation, the mean EF of the group rose, the EDV increased only 15%, and only two of 36 patients continued to show ERWMD. Of the eight patients who demonstrated on abnormal response postoperatively, seven had what was considered to be inadequate revascularization, and in one there was no explanation. The data demonstrate that myocardial revascularization does improve ventricular function by abolishing exercise-induced evidence of ischemia (decreased EF, increased EDV, and ERWMD) as assessed by radionuclide angiography. Failure to abolish the exercise-induced functional instability suggests incomplete revascularization.

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↗
PubMed1976

Myocardial blood flow in congestive and hypertrophic cardiomyopathy: relationship to peak wall stress and mean velocity of circumferential fiber shortening.

Myocardial blood flow/unit mass (MBF) and the determinants of myocardial oxygen consumption were measured in seven control subjects (group I) and 15 patients (pts) with cardiomyopathy (CM), group II (group IIa-congestive CM: 10 pts; group IIb-hypertrophic CM: 5 pts). In group I left ventricular (LV) MBF was 64 +/- 8 (SD) ml/100g-min; it was significantly lower in IIa (45 +/- 15 ml/100g-min, P less than 0.01) and IIb (39 +/- 7 ml/100g-min, P less than 0.01). However, calculated total LV flow (LV mass X MBF) was increased in the two CM groups. In nine CM pts, LV MBF increased in response to atrial pacing from 41 +/- 7 to 63 +/- 13 ml/100g-min. In group IIa, calculated peak wall stress was normal (4.39 +/hortening (MVcf) was significantly reduced (0.53 +/- 0;18 vs 1.26 +/- 0.12 circum/sec, P less than 0.01). In IIb, MVcf was normal but peak stress was significantly reduced (2.80 +/- 0.75 vs 4.51 +/- 1.10 dynes/cm2 X 10(5), P less than 0.05). Multiple regression analysis based on all pts yielded, MBF - 16.9 MVcf + 9.30 Stress + 0.26 Heart Rate - 26.4 (r=0.79). The data indicate that MBF is reduced in CM patients and the regression analysis suggests that MBF in these 22 pts with normal coronary arteriograms was determined largely by heart rate, peak stress, and ventricular performance.

Blood Flow Velocity↗
PubMed1975

Superior bioavailability of digoxin solution in capsules.

The bioavailability of various formulations of digoxin was assessed after single and multiple doses in a series of crossover studies in human volunteers. Digoxin tablets that were 97% dissolved in 1 hr in vitro were not significantly better absorbed than tablets with a dissolution rate of 78%. A solution given in capsule form had greater bioavailability than tablets of 97% dissolution rate; serum and urinary glycoside levels after 0.4 mg doses of the encapsulated solution were similar to those attained after 0.5 mg doses of tablets with dissolution rates of 78% and 97%. The bioavailability of the solution in capsule form exceeded that of equal doses of the same solution given as a liquid or that of a standard elixir. No increase in gastrointestinal or cardiac toxicity was detected. Inter- and intrasubject variation in bioavailability was not decreased. Above a certain level, dissolution rate is no longer the limiting factor in digoxin absorption. The mechanism of the enhanced bioavailability of concentrated liquid digoxin in capsule form remains to be determined. Such a preparation deserves further consideration as a possible replacement for digoxin tablets.

Adult↗
PubMed1975

Measurement of regional myocardial blood flow in man: description and critique of the method using xenon-133 and a scintillation camera.

A method has been devised to measure regional myocardial blood flow in man. The approach consists of selective injection of xenon-133 into a coronary artery and the external monitoring of radioisotope washout curves from multiple areas of the myocardium with a multiple crystal scintillation camera. Rate constants of isotope washout are calculated using a monoexponential model, and the capillary blood flow rates in multiple regions of the heart are calculated by the Kety formula. The pattern of perfusion rates is related to the coronary arteriogram obtained in the same study. Myocardial perfusion patterns obtained in patients with and without coronary artery disease and during atrial pacing are given, as well as examples of results obtained in myocardial aneurysms, in regions of ischemic myocardium supplied by collateral vessels and after tracer injection into an aortocoronary bypass graft. Advantages of the method are discussed along with limitations related to the tracer, the scintillation camera, the form of mathematical analysis and the three dimensional nature of the heart.

Angina Pectoris↗
PubMed1975

The relationship between regional myocardial perfusion at rest and arteriographic lesions in patients with coronary atherosclerosis.

Measurements of mean left ventricular (LV) and regional myocardial blood flow rates were made at rest in 161 patients with 133Xe and a multiplecrystal scintillation camera. Myocardial perfusion rates were correlated with assessments of the degree of coronary artery disease made from the arteriograms obtained during the same studies. In patients with normal coronary arteries without heart failure, the presence of hypertension, aortic stenosis, or aortic insufficiency was not associated with changes in mean LV perfusion from the control value of 61+/-7 ml/100 g-min. However, mean LV perfusion was significantly reduced in patients with normal coronary arteries who had cariomyopathy and impaired ventricular performance. Mean LV perfusion was not significantly different from control values in patients with "mild" coronary artery disease (less than 50% obstruction) or in patients with significant isolated disease (greater than 50% obstruction) of the left anterior descending (lad) artery. Significant reductions in mean LV perfusion were found in patients with greater than 50% obstruction of two coronary arteries (LAD + right or LAD + circumflex) and in patients with triple-vessel disease. The average perfusion rate for regions distal to LAD obstructions in patients with isolated LAD disease was not lower than the LAD perfusion in control patients, but was significantly reduced in patients with LAD + right coronary artery disease (43+/-14 ml/100 g-min). In the latter group average perfusion distal to the LAD lesion was significantly lower than the average regional perfusion rate for the remainder of the LV. However, the mean blood flow rate for the remainder of the LV was also significantly lower than control values despite the lack of significant circumflex disease. The data demonstrate that the presence of radiographically "mild" or significant isolated LAD coronary disease is not associated with reductions in mean LV perfusion at rest, but that mean LV perfusion is reduced in the presence of significant disease of two or three coronary artieries. None of the patients experienced angina during the resting studies and most had clinical evidence of ventricular failure. The observation of depressed LV perfusion in this group, as in the patients with cardiomyopathy, raises the possibility that a lowered resting blood supply may be adequate for a reduced level of performance of a diseased ventricle. The lack of selective reductions of regional perfusion at rest in the majority of the patients with LAD lesions suggests that regional myocardial blood flow must be measured during an intervention which increases myocardial oxygen consumption in order to assess the physiological significance of lesions which are observed at coronary arteriography.

Adult↗
PubMed1975

Studies of regional myocardial perfusion in patients with coronary atherosclerosis, using xenon-133 and a multiple crystal scintillation camera.

Regional myocardial perfusion was measured in 164 patients at coronary arteriography. Washout of xenon-133 from multiple areas of the heart was monitored with a multiple crystal scintoooillation camera after tracer injection int the left or right coronary artery. Rate constants of radioisotope clearance were computed by monoexponential analysis of the initial portion of each washout curve. Regional myocardial blood flow rates in ml/100 g.min were calculated by the Kety formula. The pattern of local myocardial perfusion rates was compared to the coronary arteriogram obtained during the same study. In patients with normal coronary arteriograms, the average mean myocardial perfusion rate in the left ventricle (LV) significantly exceeded that of the right ventricle and the right atrial area. Mild heterogeneity of local myocardial flow rates in the LV was observed. In patients with essential hypertension, aortic stenosis, and aortic insufficiency, the average LV perfusion rates were similar to those of subjects with normal coronary arteriograms, pressures, and ventriculograms. The mean LV perfusion rates were significantly reduced in patients without coronary disease who had cardiomyopathy and cardiac failure.

Collateral Circulation↗
PubMed1974

Persistence of hapten-antibody complexes in the circulation of immunized animals after a single intravenous injection of hapten.

To study the fate of a low molecular weight antigen (hapten) in the circulation of animals whose sera contain antibodies specific for that low molecular weight antigen, a single injection of digoxin-(3)H (0.4 mg/kg) was administered intravenously to 18 rabbits. Thirteen animals (nine nonimmunized and four immunized with bovine serum albumin) served as control animals. In five rabbits which had been immunized with a digoxin-bovine serum albumin conjugate and whose sera contained digoxin-specific antibodies, the mean 12-h serum digoxin concentration was 8,300 ng/ml (control: 92 ng/ml) and the mean serum concentration 12 mo after the single injection of digoxin-(3)H was 85 ng/ml. In digoxin-immunized rabbits, less than 10% of the digoxin-(3)H was excreted in the first 10 days (control: 77% recovered in urine and feces) and the mean biological half-life of digoxin, as calculated from serum digoxin-(3)H disappearance curves, was 72 days (control: 3.4 days). In sera of digoxin-immunized rabbits, more than 90% of the circulating digoxin-(3)H was immunoglobulin bound, as determined by the double-antibody and dextran-coated charcoal methods. The serum disappearance rate of (125)I-antidigoxin antibodies was similar in nonimmunized and in immunized animals and in the presence or absence of digoxin. It is concluded that the biological half-life of a hapten may be markedly prolonged when the hapten is bound to specific antibody. The persistence of antibody-hapten complexes in the circulation suggests that these complexes may not be deposited in tissues and raises the possibility that low molecular weight determinants may be capable of preventing or reversing the deposition of immune complexes, containing macromolecular antigens, in the tissues of experimental animals and man.

Animals↗