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Biomedical subjects

S Kaplan

Publications and source records attributed to S Kaplan.

At least 397 records · Page 22Linked to original sources
PubMed1981

Late results of reconstruction of the right ventricular outflow tract with porcine xenografts in children.

Thirty-three children, aged 2.5 to 17.5 years (mean, 8.3 years), having xenograft external conduits placed between the right ventricle and pulmonary artery were followed for 1 to 6 years postoperatively (mean, 3.5 years). There were no late deaths in the study group, and no infection of a valved conduit has been demonstrated. Twenty of these children were catheterized during the follow-up period. The gradients from the right ventricle to pulmonary artery ranged from 8 to 90 mm Hg (average, 31 mm Hg). A total of 8 patients were classified as having hemodynamically documented conduit failure, and an additional 2 patients are clinically expected to have conduit failure. This represents a total incidence of 30% xenograft conduit failure in a 6-year follow-up. Although the etiology of this dysfunction is probably multifactorial, factors such as valve size, conduit angulation, and immunological competence bear special consideration. We conclude that although valved external conduits continue to play an important role in the treatment of complex congenital heart disease, a valved conduit with greater longevity is needed for use in children.

Adolescent↗
PubMed1981

In vivo intermembrane transfer of phospholipids in the photosynthetic bacterium Rhodopseudomonas sphaeroides.

The kinetics of accumulation of phospholipids into the intracytoplasmic membrane of Rhodopseudomonas sphaeroides have been examined. We have previously demonstrated that accumulation of phospholipids in the intracytoplasmic membrane is discontinuous with respect to the cell cycle. In this study we demonstrated a sevenfold increase in the rate of phospholipid incorporation into the intracytoplasmic membrane concurrent with the onset of cell division. Pulse-chase labeling studies revealed that the increase in the rate of phospholipid accumulation into the intracytoplasmic membrane results from the transfer of phospholipid from a site other than the intracytoplasmic membrane, and that the transfer of phospholipid, rather than synthesis of phospholipid, is most likely subject to cell cycle-specific regulation. The rates of synthesis of the individual phospholipid species (phosphatidylethanolamine, phosphatidyglycerol, and an unknown phospholipid) remained constant with respect to one another throughout the cell cycle. Similarly, each of these phospholipid species appeared to be transferred simultaneously to the intracytoplasmic membrane. We also present preliminary kinetic evidence which suggested that phosphatidylethanolamine may be converted to phosphatidycholine within the intracytoplasmic membrane.

Bacterial Chromatophores↗
PubMed1981

Penicillin-binding proteins of Rhodopseudomonas sphaeroides and their membrane localization.

Cytoplasmic membranes (CM) prepared from both chemotrophic and phototrophic cells of Rhodopseudomonas sphaeroides possess penicillin-binding proteins (PBPs), as demonstrated by binding of [125]furazlocillin to isolated membranes, the subsequent separation of the constituent PBPs by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and their detection by autoradiography. The major PBP present in CM from R. sphaeroides corresponds in molecular weight to PBP-5, the predominant PBP present in CM of Escherichia coli. In contrast, the outer membrane of R. sphaeroides shows only low-level furazlocillin-binding activity on a per milligram of protein basis compared with chemotrophic CM. The intracytoplasmic membrane (ICM) derived from phototrophic cells contains less than 5% of the furazlocillin-binding activity of the CM. Based on the specific localization of PBPs in the CM, it is possible to provide quantitative estimates of the extent of CM present in preparations of ICM. This method demonstrates that highly purified preparations of ICM contain less than 5% CM. Additionally, the assay for PBPs demonstrates that during ICM remodeling, which occurs upon a shift from phototrophic to chemotrophic growth, there is no significant insertion of PBPs into the ICM over the first two generations after a shift to chemotrophic growth.

Bacterial Proteins↗
PubMed1981

Exercise testing in children before and after surgical treatment of aortic stenosis.

Twenty-three children with valvar or discrete subvalvar aortic stenosis underwent a controlled, progressive bicycle exercise test within 6 months before and 3-30 months after surgery for left ventricular outflow tract obstruction. The patients were divided into three groups according to the preoperative resting gradient of left ventricular to aortic peak systolic pressure: 30-69 mm Hg (group A), 70-99 mm Hg (group B), and greater than or equal to 100 mm Hg (group C). Preoperatively, 19 of 23 patients (83%) developed significant ST depression (greater than or equal to 1.0 mm) during exercise, whereas only seven (30%) had abnormal ST depression at rest. Postoperatively, mean exercise-induced ST depression regressed to less than 1 mm in all three groups. In the total population the frequency of ST depression greater than 1 mm was significantly reduced after surgical treatment and mean total work and peak exercise systolic blood pressure were significantly increased within 12 months after surgery. Total work increased significantly in group B within 12 months and in group C within 13-24 months after surgery, but remained unchanged on group A. Peak exercise heart rates were similar before and after surgery in each group. Peak exercise systolic pressures increased after surgery in all three groups, but the mean differences were statistically significant only in group C patients tested 13-24 months after surgery. The results of this study show that exercise testing is useful for quantifying the severity of aortic stenosis and documenting the clinical improvement (or lack thereof) after surgical treatment, and that properly supervised exercise testing can be performed at minimal risk to children with significant aortic stenosis.

Adolescent↗
PubMed1980

The occurrence of hyperaldosteronism in infants with congestive heart failure.

Serum aldosterone and plasma renin were measured in 20 normal infants and 15 infants with congestive cardiac failure. Serum aldosterone was significantly increased (151 +/- 38 ng/dl mean +/- standard error of the mean) in patients before treatment when compared with aldosterone in normal infants (29 +/- 7 ng/dl). Increasing serum aldosterone was related to increasing plasma renin. The response to furosemide appeared to be inversely related to serum aldosterone concentrations. In four infants, administration of an aldosterone antagonist (spironolactone) resulted in improved diuresis and decreased serum aldosterone. Hyperaldosteronism is an important factor contributing to fluid and sodium retention in infants with heart failure.

Aldosterone↗
PubMed1980

Measurement of the ohmic electrode-tissue contact resistance and the voltage applied to myocardium.

The electrical impedance of a pulse generator-electrode-heart system is a complex one. By analysis of an equivalent circuit developed for the above, a model was derived to describe the output voltage applied to an implanted electrode. On the basis of the dynamic behavior of the equivalent circuit when a pacing pulse was applied, a method for measuring true ohmic electrode-tissue contact resistance was developed, and a device was constructed to provide an instant digital readout of its value. The value of that risestance varied from 179 to 521 omega in 13 patients. When a variable resistance R, was connected in series with an implanted electrode, and a threshold voltage for every value of R was determined the actual voltage applied to the myocardium was computed for 16 patients.

Cardiac Pacing, Artificial↗
PubMed1980

Left atrial size in childhood.

To determine the accuracy of the diagnosis of left atrial enlargement (LAE) by vectorcardiogram (VCG) and electrocardiogram (ECG), we analyzed the magnitude of the P loop on VCG and the P wave duration, amplitude, and deflection on the ECG and compared them with echographic and angiographic data. Twenty-eight children with LAE were selected who had congenital or acquired heart disease. The control population consisted of 24 children with normal left atrial (LA) dimensions. No significant difference in P wave amplitude or duration was found in the two groups on ECG. Negative terminal deflection greater than orequal to - 1 mm in V1 predicted LAE in only 25% of the patients with LAE. P loop magnitudes in all vector planes showed considerable overlap in both groups. When magnitude and direction were considered on VCG, only 29% of the patients with LAE would have been diagnosed as LAE by VCG criteria. Patients with large LA volumes, determined from biplane angiography,were compared with echocardiography, VCG and ECG. All had echocardiographic LAE, 50% had LAE by ECG criteria and only 33% by VCG criteria. It is concluded that more sensitive ECG and VCG criteria for diagnosing LAE by ECG and VCG need to be developed. It must also be determined which of these changes correlate with conduction delay, atrial hypertrophy and/or enlargement.

Adolescent↗
PubMed1980

Doxorubicin cardiotoxicity in children.

To characterize the long-term effects of doxorubicin hydrochloride (Adriamycin) on left ventricular function, a total of 588 echocardiograms were obtained prospectively in 46 children who were treated for malignancy. We found shortening fraction of the left ventricle to be more useful than systolic time intervals for detecting cardiotoxic effects. Abnormal cardiac function occurred in 43% of patients but only 4% developed congestive heart failure which was irreversible. There appeared to be strong individual variation in response to the effects of doxorubicin on the heart unrelated to treatment regimen, age of onset of treatment, or total cumulative dose. If the SF remained normal it was possible to give a dose greater than 550 mg/m2. If cardiac dysfunction occurred following cessation of doxorubicin, it did so within five months in 95% of patients. Discontinuing doxorubicin therapy in patients with SF LEss than 20% who did not have clinical signs of congestive heart failure resulted in improved shortening fraction and administration of digoxin did not further improve the SF. Sequential echographic evaluation of cardiac function at frequent intervals has proven to be useful during and following treatment with doxorubicin.

Adolescent↗
PubMed1980

Vasodilator therapy for congestive heart failure.

Six patients with severe congestive heart failure were treated with nitroprusside intravenously. Four of the six patients showed salutary responses and were successfully weaned from the NP with marked resolution of symptoms. No adverse side effects were observed. These four patients and one additional child (who did not receive NP) were treated with prazosin by mouth in addition to digoxin and diuretics daily. Two of these patients are entirely symptom free, and additional child is moderately improved, and the fourth patient has shown minimal symptomatic improvement. Despite the severity of their pretherapy symptoms, only one patient has died while receiving oral vasodilator therapy. This preliminary study suggests that afterload reduction may be life-saving in children who are virtually moribund because of congestive heart failure. This improvement can be maintained with oral vasodilator therapy and continuation of classic anticongestive therapy. However, afterload reduction has no effect on the underlying disease. Confirmatory studies are essential before this experimental mode of therapy is accepted for routine use in infants and children.

Adolescent↗