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Biomedical subjects

S C Webb

Publications and source records attributed to S C Webb.

25 records · Page 2Linked to original sources
PubMed1986

Potassium exchange in the human heart during atrial pacing and myocardial ischaemia.

Potassium homoeostasis in the heart was studied during atrial pacing in 20 patients undergoing diagnostic coronary angiography. The potassium concentrations in the coronary sinus and a systemic artery were recorded continuously by means of catheter tip potassium electrodes. Ten patients with coronary artery disease and a positive exercise test developed chest pain and ST segment depression on the electrocardiogram during atrial pacing. Potassium concentrations in the coronary sinus rose initially and increased further when myocardial ischaemia developed. Ten patients including five with normal coronary arteries remained symptom free during atrial pacing with no electrocardiographic changes. In these patients coronary sinus potassium concentration increased at the onset of pacing, but returned to near control values despite continued pacing. In both groups arterial potassium concentration remained constant. Immediately after the end of pacing there was an abrupt transient fall in potassium concentrations in the coronary sinus to below control values. These results indicate that in man, as in other species, an increase in heart rate causes the transient movement of potassium out of the cell into the extracellular space. The onset of myocardial ischaemia is associated with a further loss of potassium from the cell. The end of pacing or ischaemia is accompanied by a re-uptake of potassium by heart muscle.

Cardiac Pacing, Artificial↗
PubMed1986

Electrophysiological actions of somatostatin on the atrioventricular junction in sinus rhythm and reentry tachycardia.

Because somatostatin, a neuroregulatory peptide, is found in abundance in the atria and atrioventricular node, its electrophysiological and antiarrhythmic properties were compared with those of verapamil in ten patients with paroxysmal atrioventricular tachycardia. During sinus rhythm, intravenous somatostatin slowed the heart rate whereas verapamil increased it. Though both agents prolonged atrioventricular conduction time and refractoriness, verapamil was more potent. They were equally effective at terminating reentry atrioventricular tachycardia, restoring sinus rhythm in six of seven patients. Whereas verapamil consistently blocked conduction in the atrioventricular node, somatostatin usually induced ventricular extrasystoles at the time of conversion. Somatostatin may have physiological importance in the neurohumoral control of cardiac impulse formation and conduction.

Adult↗
PubMed1985

Absence of a relationship between extracellular potassium accumulation and contractile failure in the ischemic or hypoxic rabbit heart.

Ischemia and hypoxia both cause a rapid loss of potassium from myocardial cells. We have investigated the relationship between the accumulation of potassium in the extracellular fluid and the early loss of contractility. Experiments were performed on the isolated rabbit heart perfused with physiological saline at 36 degrees C, paced at 3 Hz. Tension was recorded from the apex. Extracellular potassium concentration [( K+]o) was recorded with small ion-selective electrodes. After the onset of global ischemia, [K+]o rose within 15 sec and reached 9.5 +/- 1.1 mmoles/liter after 5 min. Developed tension (T) fell to 9 +/- 2% of control over the same period. During substrate-free hypoxia, T declined at a similar rate, and [K+]o rose slowly to 5.5 +/- 0.1 mmoles/liter after 5 min. The relationship between [K]o and T during normal perfusion and oxygenation was investigated by incrementally increasing the perfusate [K+]. T dropped to 78.6 +/- 4.5% of control at a [K+]o of 9 mmoles/liter. Comparison of the relationship between [K+]o and T during high-potassium perfusion, ischemia, and hypoxia shows that extracellular potassium accumulation per se makes almost no contribution to the decline of contractile function in ischemia or hypoxia. (Values are means +/- S.E., N = 5.)

Animals↗
PubMed1983

Coronary sinus potassium concentration recorded during coronary angioplasty.

Coronary sinus potassium concentration was measured continuously in two patients undergoing angioplasty of a significant stenosis of the left anterior descending coronary artery. After each coronary occlusion there was a transient rise in coronary sinus plasma potassium concentration caused by washout of potassium which had accumulated in the extracellular fluid during the short period of ischaemia. There were no significant changes in the surface electrocardiogram and the patients experienced no chest pain. Changes in coronary sinus potassium concentration provide a sensitive and early indication of myocardial ischaemia in man.

Angioplasty, Balloon↗
PubMed1978

Pituitary coma with continuing menstruation.

A case of pituitary coma with continuing menstruation is presented. This association is extremely rare, but a history of recent menstrual periods does not exclude advanced hypopituitarism from the differential diagnosis of severe hyponatraemia.

Coma↗