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Biomedical subjects

P C Kahn

Publications and source records attributed to P C Kahn.

At least 37 records · Page 2Linked to original sources
PubMed1984

Equilibrium (gated) radionuclide ejection fraction measurement in the pressure or volume overloaded right ventricle. Comparison of three methods.

Although equilibrium radionuclide angiographic measurement of right ventricular ejection fraction (RVEF) has been validated in patients with coronary artery disease, the accuracy of this technique has not been demonstrated in patients with other cardiac diseases which may result in RV pressure and/or volume overload. The accuracy of three methods of equilibrium radionuclide analysis for measuring RVEF was compared in several subgroups of patients with a variety of cardiac diseases, including congenital and valvular heart disease, cor pulmonale, and cardiomyopathy. It was concluded that RVEF may be accurately derived by equilibrium radionuclide ventriculography in patients with a wide variety of cardiac diseases, including those resulting in RV volume and/or pressure overload. Accuracy varies depending on analysis method and the nature of the hemodynamic derangement.

Adult↗
PubMed1983

Work in progress: the effect of heat on bleomycin cytotoxicity in vitro and on the accumulation of 57Co-bleomycin in heat-treated rat tumors.

The cytotoxic effects of the sequence and timing in combined hyperthermia and bleomycin treatment were tested in vitro using V79 Chinese hamster cells. The order of treatment was important; heat treatment followed by the administration of bleomycin yielded greater cytotoxicity than when the opposite order was used. To determine whether heat-treated tumors have an altered uptake of bleomycin, rat rhabdomyosarcoma (BA 1112) tumors were heated locally with RF current (43 degrees C, 90 min.), injected with 57Co-bleomycin, and imaged on a radioisotope camera. Results of tumor-to-background (T/B) ratio analysis indicate that (a) local hyperthermia (43 degrees C) does not appear to alter tumor uptake patterns of 57Co-bleomycin; and (b) intravenous and intraperitoneal injections produce similar T/B uptake ratios, typically between 2 and 3 at 120 minutes postinjection. In the BA 1112/WAG/Rij tumor system, local hyperthermia treatment does not seem to interfere with the subsequent accumulation of bleomycin in the tumor.

Animals↗
PubMed1982

The absence of volume change in the gelation of hemoglobin-S.

The volume change for the gelation of deoxygenated sickle cell hemoglobin has been measured by dilatometry at 22.0 degrees C and found to be zero. The precision of the result is 0 +/- 1.4 ml/mol of protein present in the sample. When the solubility of the protein is taken into account, the precision is 0 +/- 5.1 ml/mol of gelled hemoglobin. The participation of "hydrophobic interactions" in sickle cell hemoglobin gelation and model compound studies of the volume change associated with transferring hydrophobic solutes from an aqueous to a hydrophobic milieu, as well as the volume changes of other globular protein polymerizations, led us, initially, to expect a large positive delta V. The results are discussed in the context of concentration effects in sickle cell hemoglobin solutions and of recent work on the pressure-induced denaturation of globular proteins, which also gives smaller volume effects than had been anticipated.

Chemical Phenomena↗
PubMed1980

Spectral analysis of allophycocyanin I, II, III and B from Nostoc sp. phycobilisomes.

Low temperature (-196C) and room temperature (25C) absorption spectra of a family of allophycocyanin spectral forms isolated from Nostoc sp. phycobilisomes as well as of the phycobilisomes themselves have been analyzed by Gaussian curve-fitting. Allophycocyanin I and B share long wavelength components at 668 and 679 nm, bands that are absent from allophycocyanin II and III. These long wavelength absorption components are apparently responsible for the 20 nm difference between the 680 nm fluorescence emission maximum of allophycocyanin I and B and the 660 nm maximum of II and III. This indicates that allophycocyanin I and B are the final acceptors of excitation energy in the phycobilisome and the excitation energy transfer bridge linking the phycobilisome with the chlorophyll-containing thylakoid membranes. These Gaussian components are also found in resolved spectra of phycobilisomes, are arguing against this family of allophycocyanin molecules being artifactual products of protein purification procedures.

Cyanobacteria↗
PubMed1980

A primate model for the study of the interaction of 111In-labeled baboon platelets with Dacron arterial prostheses.

This paper presents early experience with a primate model for the noninvasive study of the interaction of circulating platelets with healing arterial prostheses. These experiments demonstrate that baboon platelets can be isolated and labeled with 111Indium with high efficiency using a sterile technique. Platelets subjected to this process have a linear life span similar to that of 51Chromium-labeled baboon platelets. The high energy gamma emission of 111Indium oxine allows for external scanning using a standard gamma camera. The small quantity of 111Indium-labeled platelets in the region of the graft can be discriminated from the surrounding blood vessel and quantitated by gamma camera imaging and computer analysis. There was a significant increase in the platelet deposition on prosthetic surfaces observed 5--48 hours after graft implantation and injection of 111Indium-labeled autologous platelets.

Animals↗
PubMed1979

Coupling between oxidation state and hydrogen bond conformation in heme proteins.

In all heme proteins for which crystal structures are available, the N(epsilon) of a histidyl residue is bonded to the heme iron and N(delta) is hydrogen bonded to a carbonyl oxygen of the peptide backbone. We investigate here the possibility that a change in oxidation state of the iron or a change in the geometry of this hydrogen bond might change the hydrogen bond strength in a functionally significant way. Dimerization energies obtained from ab initio molecular orbital calculations on the hydrogen-bonded dimer of imidazole and planar formamide are used to represent the strength of this hydrogen bond in heme proteins. The effect of a change in iron oxidation state is modeled by varying the positive charge on imidazole. The effect of a change in hydrogen bond geometry is studied by employing x-ray coordinates for reduced and oxidized cytochrome c, deoxy- and metmyoglobin, and deoxy- and methemoglobin. Our conclusions are that the strength of this hydrogen bond in heme proteins is sensitive to both the oxidation state of the iron atom and to geometry changes on the order of those obtained from the x-ray coordinates. We speculate that the changes in oxidation state may be functionally coupled with changes in hydrogen bond geometry and that this hydrogen bond represents a feasible pathway to link protein conformation with redox potential or reactivity of the iron atom.

Animals↗
PubMed1978

Ventilation-perfusion scans in neonatal regional pulmonary emphysema complicating ventilatory assistance.

Two cases of ventilator-related neonatal lobar overexpansion with similar radiographic appearance, but probably different pathogenesis, are presented. In one infant, persistent interstitial lobar emphysema was confirmed by markedly decreased perfusion shown on scintigraphy; this information was of great value in predicting the beneficial effect of lobectomy. In the other case, ventilation and perfusion scans indicated functional value of the emphysematous lobe and correctly suggested conservative management. Radioisotope lung scans may provide valuable information regarding lung function in regional pulmonary emphysema associated with assisted ventilation in neonatal respiratory distress syndrome, and thus determine patient management.

Humans↗
PubMed1977

The relative roles of gallium-67-citrate scanning and lymphangiography in the current management of malignant lymphoma.

The usefulness of gallium-67-citrate scanning and lymphangiography in the detection of iliac and paraaortic lymph node involvement was evaluated in 53 patients with Hodgkin's disease and non-Hodgkin's lymphomas who subsequently underwent laparotomy. Our data suggest that the overall accuracies of the two procedures in this regard are comparable. Although in this anatomic area the gallium scan tends to underestimate the presence of disease (higher false-negative rate), the false-negative rate is quite low. The false-negative rate with lymphangiography is lower than with scanning but it tends to overestimate the presence of disease (higher false-positive rate). It was concluded that gallium scanning should be an integral part of the staging of lymphomas and a schema for their clinical staging based on the use of gallium scanning early in the diagnostic sequence is proposed.

Adult↗
PubMed1977

Osteochondritis of the tarsal navicula: radioisotopic appearances.

A case of Köhler's disease of the tarsal navicula is described as presenting with swelling, tenderness, and hyperthermia of the right foot. Scintigraphy revealed decreased uptake in the right midtarsal area. The ability of the pinhole collimator to image these tiny bones is demonstrated.

Child, Preschool↗
PubMed1977

The place of 57Co-bleomycin scanning in the evaluation of tumors.

The clinical records and imaging studies of 140 patients who had 57Co-bleomycin scans were reviewed. In 53% of the patients with known tumor at the time of examination, all clinically demonstrable lesions picked up cobalt. The success rate was particularly high in carcinoma of the lung (15 of 17) and gastrointestinal tract (12 of 17). The major role of cobalt bleomycin seems to be as an early screening test for metastases in patients with carcinoma of the lung, gastrointestinal tract, and uterus. The scan is most useful in demonstrating spread to the brain, liver, and adrenals.

Adolescent↗
PubMed1976

Clinical usefulness of 67gallium scanning in the malignant lymphomas.

To determine the clinical usefulness of 67 gallium (Ga) scanning in the evaluation of patients with lymphomas, we reviewed 142 total body Ga scans performed on 44 patients with Hodgkin's disease and 53 patients with non-Hodgkin's lymphoma. Fifty-two per cent (123 of 236) of known disease sites were detected on scan. The false-positive rate was less than 5 per cent. The accuracy of detecting lymphoma varied in individual anatomic areas from 33 per cent in the axilla to 73 per cent in the thorax. In eight patients with bone involvement, all bone lesions were detected on scan. The size of the lesion appeared to influence accuracy, since tumors greater than 3 cm in diameter were more often positive.

Adolescent↗
PubMed1976

Unusual pelvic masses: a comparison of computed tomographic scanning and ultrasonography.

Four unusual pelvic masses, studied by CT and gray scale ultrasonography, demonstrate the comparative values of these modalities for this area of the body. In each instance a significant contribution to the diagnosis was made by one or both techniques. The ultrasound study provides a somewhat better differentiation of solid from cystic lesions, but the CT scan denotes to best advantage the anatomy of the area, and provides a means of viewing bone as well as soft tissue detail.

Adult↗
PubMed1976

Mechanism of localization of 99mTc-labeled pyrophosphate and tetracycline in infarcted myocardium.

The gross and subcellular localizations of 99mTc-labeled pyrophosphate and tetracycline in myocardial infarcts were studied in a rabbit model. Experiments utilizing double-nuclide labeling were carried out using a useful mapping technique. Concentration of the various chelates decreases in an expected manner from the center of the infarcted area toward its periphery, but it is higher near the epicardial surface than toward the endocardium. Technetium-99m-pyrophosphate is concentrated in the same infarcted areas as 45Ca ion or 32P-pyrophosphate, but to a much greater degree. The uptake is dependent on both the degree of necrosis and residual blood flow. Gel filtration experiments with rabbit serum indicate that 99mTc-tagged pyrophosphate, tetracycline, and diphosphonate are mainly protein-bound, whereas 32P-pyrophosphate is not. Subcellular localization studies show that 99mTc-tetracycline and 99mTc-pyrophosphate are bound primarily to soluble protein, and only a small fraction is associated with nuclei, mitochondria, and microsomes. The uptake of technetium chelates in myocardial infarcts may be due to the formation of polynuclear complexes with denatured macromolecules rather than to the deposition of calcium in mitochrondria.

Animals↗
PubMed1976

Routine renal imaging after 99mTc-glucoheptonate brain scans.

Immediately after brain scanning with 99mTc-glucoheptonate, the kidneys were imaged in 200 prospectively studied cases. Abnormalities were found in 22 cases (11%); they included renal metastases, renal cysts, and kidney displacement or obstruction by masses. In five instances, significant previously unknown abnormalities were found. The renal contours were usually better seen than on intravenous urograms or bone scans. Most kidney studies could be completed in less than 2 min, making renal imaging worthwhile as a low-cost high-yield routine addition to brain scanning.

Adolescent↗
PubMed1975

Ultrasonic and radionuclide scanning in pancreatic disease.

Ultrasonic examination of the pancreas is rendered difficult by the echogenic characteristics of the organ, by its depth, by the overlying gas, and by bony structures and anatomic variations. The reintroduction of gray-scale imaging promises to simplify the technique and expand its usefulness. The 75Se-/-selenomethionine scan is a reliable test when performed after effective pancreatic stimulation with a scintillation camera that permits the angulation required to separate pancreas from liver. Gallium-67-citrate may be important for both mapping inflammatory processes and imaging some tumors. Retrograde pancreatography has developed into a rather reliable and sensitive method of visualizing pancreatic duct abnormalities. Angiography remains the most reliable technique for finding small lesions, while computerized axial tomography appears a promising modality in the near future. In acute pancreatitis, gallium scanning may find a place alongside plain films, GI series, and echography. Chronic pancreatitis appears best studied by pancreatography, possibly with selenomethionine scanning as a function study and echography to find associated mass lesions. Pseudocysts are most easily located by ultrasound examination. Screening for pancreatic carcinoma is done most effectively with selenomethionine scanning when the index of suspicion is low and with pancreatography or arteriography when it is high. Echography is useful for localization for aspiration biopsy and for sequential evaluation of therapeutic response. Islet-cell tumors are best found by angiographic studies.

Acute Disease↗