Biomedical subjects

M Schnall

Publications and source records attributed to M Schnall.

11 recordsLinked to original sources

PubMed1991

Rectal carcinoma: staging at MR imaging with endorectal surface coil. Work in progress.

To increase the accuracy of local staging of rectal carcinomas at magnetic resonance (MR) imaging, the authors placed on endorectal coil mounted on a balloon in a position adjacent to the lesion. Use of such a local coil resulted in increased signal-to-noise ratio compared with use of a body coil; higher-resolution images were obtained because the field of view was decreased. The depth of wall invasion by rectal carcinoma was correctly staged with endorectal MR imaging in 11 of 12 patients. In the detection of perirectal adenopathy, use of MR enabled correct identification of positive perirectal nodes in four of seven patients (57%). There were no false-positive diagnoses of perirectal adenopathy at MR. Endorectal MR imaging is an evolving and promising technique for the local staging of rectal carcinomas, but further studies are needed to demonstrate its efficacy.

Female↗

PubMed1988

Metabolic myopathy in canine muscle-type phosphofructokinase deficiency.

In vivo 31phosphorus nuclear magnetic resonance spectroscopy (P-NMR) of the anterior tibialis muscle was used to investigate the metabolic myopathy of inherited muscle-type phosphofructokinase (PFK) deficiency in four (homozygous) dogs who had mild exercise intolerance, rare muscle cramps, increased serum creatine kinase activity, but no myoglobinuria. During isometric muscle work induced by indirect electrical stimulation, and subsequent recovery, changes in the ratio of phosphocreatine (PCr) and inorganic phosphates (Pi) were comparable in muscle of PFK-deficient and normal dogs and indicated a large capacity for arobic oxidative phosphorylation in canine muscle. The progressive accumulation of sugar phosphates (PME) during graded exercise clearly demonstrated the glycolytic block in PFK-deficient dogs. During a muscle contracture, induced by acute muscle stimulation, PFK-deficient muscle became completely depleted of PCr and ATP, accumulated large amounts of PME, and recovered very slowly. We conclude that PFK-deficient dogs have a metabolic myopathy that demonstrated some but not all the features recognized in the human disorder.

Animals↗

PubMed1987

Cardiac transfer function relating energy metabolism to workload in different species as studied with 31P NMR.

Cardiac metabolism was studied with 31P NMR in 7 dogs and 4 cats to determine whether animals adapted for different life-styles (stalk and sprint vs endurance running) respond to increased work loads (heart rate X blood pressure product) with different high-energy phosphate kinetics. Hearts were exposed via a left lateral thoracotomy under Nembutal anesthesia (40 mg/kg). Two-turned solenoid surface coils were placed on the left ventricles; pacing wires were sutured into the left ventricular apices. The femoral artery and vein were cannulated for blood pressure and arterial blood gas monitoring and fluid and drug infusion, respectively. Animals were placed in a plexiglass holder into a 2.1-T, 31-cm-bore, superconducting magnet. 31P spectra were obtained from the heart using respiratory and electrocardiogram gating. Cardiac work loads were changed by pacing the heart at 4, 4.5, and 5 Hz. Heart rate X blood pressure product "work" was correlated with Pi/PCr ratios. Dog hearts were more resistant than those of cats to changes in Pi/PCr with increasing work load. It is possible that animals adapted to different life-styles may have cardiovascular systems which are metabolically and mechanically adapted for different forms of stress. These differences may be elicited and effectively delineated using in vivo NMR techniques during various physiological interventions, such as pacing. The basis for these differences may be related to cardiac microvasculature or to intrinsic differences in enzyme kinetics. Delineation of these mechanisms may be helpful in the understanding of the physiological basis of cardiac function in health and disease.

Adaptation, Physiological↗

PubMed1987

Simultaneous 31P- and 1H-nuclear magnetic resonance studies of hypoxia and ischemia in the cat brain.

The objective of this study was to evaluate simultaneous 31P/1H nuclear magnetic resonance (NMR) spectroscopy as a technique for monitoring and correlating changes in brain energy metabolism during hypoxia and ischemia. Five cats were studied with a protocol that involved 20 min of hypoxia (PaO2 20 mm), 60 min of recovery, 10 min of hypoxia with relative ischemia (bilateral carotid occlusion, PaO2 20 mm), and 60 min of recovery. Bifrontal and biparietal electrocorticograms (ECoG) were monitored continuously during the entire protocol. The results demonstrate that the degree of metabolic response is different in individual cats, but a number of quantitative relationships between metabolic parameters are consistently observed for all cats. First, there is agreement between increases in lactate and changes in intracellular pH; the observed relationship corresponds to an in vivo cerebral buffer capacity of 29 mumol/g/pH unit. Second, the delayed recovery of PCr is due to the effect of metabolic acidosis on the creatine kinase equilibrium and not to a delayed recovery of the ATP/ADP ratio. Third, the observed rate of lactate clearance from the cell is zero-order (k = 0.36 mumol/g/min) for lactate levels greater than 5 microns/g and may be composed of both lactate efflux from the cell and lactate oxidation.

Adenosine Triphosphate↗

PubMed1986

Myocardial high energy phosphate metabolism in closed chest dog: creation of an animal model.

A chronic closed chest dog model was developed to study myocardial metabolism with NMR spectroscopy. Cardiac windows were surgically created in 10 dogs by removal of two ribs and accompanying skeletal muscle. Marlex mesh was sewn between the two exposed ribs, and fascia and skin were closed. 31P spectra were obtained using a surface coil placed into the surgically created pouch and using routine NMR pulsing techniques.

Adenosine Triphosphate↗

PubMed1972