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Biomedical subjects

K Landmark

Publications and source records attributed to K Landmark.

At least 91 records · Page 5Linked to original sources
PubMed1977

Plasma levels and electrophysiological effects of acebutolol (M & B 17.803) in the dog heart in situ.

The effect of acebutolol a beta-adrenergic receptor blocking agent was tested on the dog heart in situ. The drug decreased heart rate, and caused a reduction in the conduction velocity and a significant increase in the functional refractory period of the atrioventricular node. The functional and the effective refractory period of the right atrium was increased by acebutolol. During sinus rhythm, the drug did not affect conduction velocity in the rest of the conduction pathway. During atrial pacing, however, the intra-atrial and His-Purkinje conduction times were slightly increased. The plasma concentrations of acebutolol were in the range between 0.09 and 0.5 mug/ml, which is far below those values expected to cause a membrane-stabilizing or quinidine-like effect. The clinical applications of the results are discussed.

Acebutolol↗
PubMed1977

The effect of calcium and beat interval on the contractile force and refractoriness of the isolated rat atrium in the absence and presence of nifedipine: a possible mechanism for the negative staircase phenomenon.

An increase in the calcium concentration of the Ringer solution increased the contractile force and reduced the effective refractory period of the isolated rat left atrium paced at a frequency of 60 per min. An increase in the frequency of stimulation decreased the contractile force (negative staircase) and reduced the effective refractory period; these effects being most pronounced at the highest calcium levels. A calcium-antagonistic drug, nifedipine, decreased the contractile force and the effective refractory period. The effect of an increased frequency of stimulation on the contractile force at different calcium levels in the absence and presence of nifedipine paralleled its effect on the effective refractory period. This observation suggests that both these phenomena are caused by a decreased quantity of inflowing calcium ions during the period of exciation, and thus might explain the absence of positive staircase in the rat myocardium.

Action Potentials↗
PubMed1976

Determination of pressure gradient in mitral stenosis with a non-invasive ultrasound Doppler technique.

A 2 MHz continuous waveform non-invasive ultrasound doppler system has been used in the present investigation. With the aid of the audio signals of the frequency shifts, the ultrasound probe was positioned on the external chest so that the axis of the incident ultrasonic beam coincided with the direction of the maximum velocity vectors of the mitral jet. The frequency shifts due to the mitral jet were frequency analyzed and the time course of the maximum frequency shift was determined. The time course of the maximum mitral jet velocity was then determined from the doppler equation and the time course of the mitral pressure gradient from an orifice equation. The usefulness of the technique was evaluated by studying 25 patients with mitral stenosis and 10 without heart disease. The patients with mitral stenosis were studied during cardiac catheterization and the ultrasound data, the pulmonary artery wedge pressure, and the left ventricular pressure were recorded simultaneously. A table is presented where the gradient determined with the ultrasound technique, deltaPU, is compared with the gradient determined from the pressure tracing, deltaPM. Averaged over the 25 patients studied, deltaPU was 1.7 mmHg smaller than deltaPM at 0.08 sec diastolic time and 1.8 mmHg smaller at 0.25 sec diastolic time. The findings in the patients without heart disease differed distinctly from those in the patients with mitral stenosis. The investigation demonstrated that the non-invasive ultrasound technique can be used with confidence to gain an impression of the magnitude of the mitral pressure gradient. The findings also suggest that deltaPU represents the actual pressure gradient more accurately than deltaPM. Another investigation is proposed to assess the accuracy of the technique more completely.

Adult↗
PubMed1976

A study of the verapamil-induced changes in conductivity and refractoriness and monophasic action potentials of the dog heart in situ.

In the dog heart in situ, verapamil 0.30 mg/kg injected intravenously did not impair intraatrial, His--Purkinje and intraventricular conduction. The monophasic action potential (MAP) derived from the right atrium and ventricle was not altered by the drug. The functional refractory period (FRP) and the effective refractory period (ERP) of the atrium was not changed by verapamil. However, the drug caused a small but statistically significant decrease in the ratio between 50 and 90% repolarization, respectively, and the ERP of the right atrium, i.e. the ERP of the atrium increased in relation to the MAP duration. Verapamil used a marked reduction of the conduction velocity within and a pronounced increase of the AV nodal FRP and ERP. These changes were reversed by a rapid injection of calcium gluconate 40 mg/kg. The sinus node automaticity was not influenced by verapamil.

Action Potentials↗