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Biomedical subjects

T Sheffield

Publications and source records attributed to T Sheffield.

5 recordsLinked to original sources
PubMed1981

Inhibition of gonadotropin-releasing hormone-stimulated luteinizing hormone release by pimozide: evidence for a site of action after calcium mobilization.

In the present work, we show that pimozide is a noncompetitive antagonist of gonadotropin-releasing hormone (GnRH)-stimulated LH release from pituitary cell cultures. For several other neurotropic agents, the concentration needed to inhibit 50% of LH release in response to GnRH correlates well with the ability to inhibit enzyme activation by calmodulin in vitro. Pimozide does not alter the affinity or amount of releasing hormone binding by the GnRH receptor. The additional observation that pimozide inhibits Ca2+ ionophore (A23187 and ionomycin)-stimulated LH release suggests that the locus of pimozide action is after Ca2+ mobilization. Pimozide is known to bind and inactivate the Ca2+-calmodulin complex, and as Ca2+ is a second messenger for GnRH, it is possible that calmodulin is the target of pimozide in this system.

Animals↗
PubMed1981

Preservation of the myocardium during coronary artery bypass grafting.

The influence of three methods of myocardial preservation used during coronary artery bypass grafting on operative mortality and perioperative myocardial infarction was evaluated in seven institutions participating in the Coronary Artery Surgery Study (CASS). Both operative mortality and perioperative infarctions were comparable with either normothermic and topical hypothermic myocardial preservation. The addition of potassium cardioplegia to hypothermia lowered both operative mortality and perioperative myocardial infarction (p less than 0.01 and p less than 0.001, respectively). Stepwise multivariate discriminant analysis revealed that the high-risk clinical and angiographic variables were the most important determinants of operative mortality, followed by surgical priority and the use of potassium cardioplegia. However, none of the clinical, angiographic and surgical variables other than the use of potassium cardioplegia influenced the incidence of perioperative myocardial infarction.

Adult↗
PubMedDate not supplied

Data compression for storage of resting ECGs digitized at 500 samples/second.

Data compression of resting electrocardiograms (ECGs) digitized at 500 samples per second (sps) is presented. Tradeoffs between the fidelity of reconstructed data and the overall compression are examined. Data of the median (average) complexes are retained at 500 sps and full resolution and encoded only to reduce redundancy. The raw data for rhythm analysis are evaluated for lowpass filtering and down-sampling (decimation) and requantization. After subtracting the medians from the raw data, the resulting residue signal is examined in detail for data reduction and encoding. Various options for compression of the residue signal are presented. Specific issues examined are the acceptable decimation and requantization of the residue signal. Another important aspect evaluated is the bimodal decimation of the QRS and the rest of the cardiac complex. Here, the QRS complexes are kept at 500 sps and the rest of the data decimated to lower sampling rates. This novel approach reduces data distortion while achieving significant compression. Details of the compression scheme and its evaluation on uncompressed 500-sps ECGs from the European Common Standards for Electrocardiography (CSE) database (128 ECGs with normal sinus rhythm, atrioventricular blocks, atrial fibrillation and flutter, ventricular arrhythmias, and excessive noise) are elucidated. Performance indexes [root mean square (RMS) error, percent RMS difference, normalized RMS difference, maximum peak error, and compression ratio] are computed. To validate the compression method, qualitative evaluation was performed by two physicians overreading the ECGs by comparing the reconstructed waveforms with the original uncompressed data. The median data are retained at 500 sps and full precision. For rhythm data, the bimodal decimation of the residue signal to 125 sps at 10 microvolts resolution preserved the fidelity of the ECG signals well, while giving good data compression. Abnormal atrial activity was well preserved and the QRS was retained without distortion. The average size of a 10-sec compressed ECG with the medians is around 4.5 kilobytes.

Diagnosis, Computer-Assisted↗