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Biomedical subjects

C W White

Publications and source records attributed to C W White.

At least 163 records · Page 9Linked to original sources
PubMed1976

Effects of angiographic contrast media on sino-atrial nodal function.

Injection of meglumine diatrizoate (Renografin-76) into the selectively perfused sinus node artery of the dog produces bradycardia which is unaltered by autonomic blockade or by changes in sinus node artery pressure. Contrast agents and other hyperosmolar substances prolong the R-R interval in proportion to their osmolarity. Selective injection of contrast media into other cannulated segments of the coronary tree produces no change in heart rate. Transfemoral arteriography, however, produces bradycardia with both right and left coronary injections. Both direct and reflex sinus node depression occur with coronary arteriography in the dog. Direct effects are mediated by hyperosmolarity.

Adrenergic beta-Antagonists↗
PubMed1976

Reduced cholinergic sinus node restraint in hyperthyroidism.

The role of the cholinergic nervous system in the tachycardia of hyperthyroidism was investigated in this study of dogs made severely thyrotoxic by the administration of Na-L-thyroxine over a six to nine month period. Differences in heart rate between control and thyrotoxic unanesthetized dogs could be abolished by cumulative doses of intravenous atropine both before and after beta-adrenergic blockade with propranolol, and at submaximal as well as maximal heart rates. There were no differences in the heart rate response of control and thyrotoxic anesthetized dogs to vagal stimulation or to the selective injection of hypertonic saline or acetylcholine into the perfused sinus node artery. The results indicate that in addition to the direct effects of thyroid hormone on sinus node automaticity there is an abnormality in parasympathetic control of heart rate in hyperthyroidism. The data suggest that this abnormality is not due to a decreased responsiveness of the sinus node or an impaired release of the cholinergic neurotransmitter, but may reflect a reduction in cholinergic efferent activity in the thyrotoxic state.

Acetylcholine↗
PubMed1975

Prolonged left ventricular ejection time in the post-premature beat. A sensitive sign of idiopathic hypertrophic subaortic stenosis.

Failure of the pulse pressure to increase in the post-premature beat is considered characteristic of idiopathic hypertrophic subaortic stenosis (IHSS). The sensitivity and specificity of this response were compared to the change in left ventricular ejection time (LVET) in 12 patients with IHSS, in ten control patients with valvular aortic stenosis (AS) and in five normal subjects. The post-PVC pulse pressure increased in all normals and in nine of the ten patients with AS. In IHSS this response was inconsistent. A positive Brockenbrough sign was seen in only 33%. On the other hand, LVET increased greater than 20 msec in eleven of twelve patients with IHSS, whereas all normal subjects and all patients with AS showed either decreases in LVET or increases smaller than 20 msec. Prolongation of the LVET during the post-PVC beat greater than 20 msec appears, therefore, to be a more sensitive sign of IHSS than the corresponding change in pulse pressure.

Adult↗
PubMed1975

Idiopathic hypertrophic subaortic stenosis presenting as cough syncope.

In a patient with idiopathic hypertrophic subaortic stenosis, syncope developed as a result of a sustained decrease in aortic pressure induced by severe cough paroxysms. Treatment with propranolol was effective in abolishing the syncopal episodes, by reducing the post-tussive gradient and facilitating a more rapid return to normal of aortic pressure. Post-tussive syncope in IHSS may result from both an unusually strong cough paroxysm and augmented left ventricular outflow obstruction consequent to reflex sympathetic stimulation.

Cardiomyopathy, Hypertrophic↗
PubMed1974

Mechanisms mediating bradycardia during coronary arteriography.

Cardiac slowing occurring during diagnostic coronary arteriography was studied in 78 patients. Comparable degrees of slowing occurred with injections into the right and into the left coronary arteries into the contralateral artery, and with injections into the coronary artery giving rise to the sinus node artery and into the contralateral artery. Rapid intracoronary injections of isosmotic dextrose solution produced significantly less slowing than comparable injections of contrast medium. Slow injections of contrast medium produced cardiac slowing comparable to that caused by rapid injections of contrast medium. However, the cardiac slowing was significantly greater than that produced by rapid injections of dextrose solution. Inhalation of 100% oxygen did not alter the heart rate response to injections of contrast medium. Atropine produced dose-related attenuation of cardiac slowing. Bradycardia persisting after cholinergic blockade was significantly greater after injections into the coronary artery supplying the sinus node than it was after injections into the contralateral artery. Coronary arteriography produced transient, occasionally profound, arterial hypotension in 38 of 41 patients in whom arterial pressures were recorded. Arterial pressure did not change in three patients. This study suggests that the cardiac slowing which occurs during coronary arteriography in man is due primarily to a cholinergic reflex which may be a human counterpart of the Bezold-Jarisch reflex, observed heretofore only in experimental animals. This slowing appears to be mediated primarily by receptors sensitive to contrast medium, rather than by changes of coronary artery pressure, and secondarily, by direct depression of sinus node function by contrast medium.

Adult↗
PubMed1971

Effect of iododeoxyuridine upon conjugation and the fate of transferred deoxyribonucleic acid in Escherichia coli K-12.

The incorporation of 5-iododeoxyuridine (IUdR) into Escherichia coli K-12 deoxyribonucleic acid (DNA) has been found to decrease significantly the viability of female strains A288 and JC411(r) but to have only minor effect upon their ability to act as conjugational recipients and to perform recombination after conjugation. In contrast, IUdR incorporation into male strain HfrC appears to interfere with both chromosome transfer and genetic recombination. By using IUdR to densitylabel female DNA, and carrying out large-scale matings with (3)H-thymidine-labeled male cells, we examined the fate of transferred DNA. After a 30-min mating, the T6-sensitive male cells were lysed, and the DNA of the merozygotes and remaining female cells was isolated. Initial centrifugation of this DNA in a CsCl gradient showed that the male and female DNA species were associated. The nature of this association of the parental DNA species was determined by formaldehyde denaturation followed by CsCl centrifugation. Denaturation of DNA isolated immediately after T6 lysis gave a peak of radioactivity banding at the density of light single-stranded DNA. However, denaturation of DNA isolated after T6 lysis and dilution of the cells into fresh medium, exhibited peaks of radioactivity banding at positions corresponding to single-stranded, density-labeled DNA. The results indicate that recombination after conjugation in E. coli takes place by a breakage-and-reunion mechanism. The process of recombination can be separated into two stages. In the first stage, the donor and recipient DNA molecules become associated. The second stage consists of the formation of phosphodiester bonds between the donor and recipient segments comprising the recombinant molecule.

Bacteriological Techniques↗