Über den Einfluß von Calcium⁺⁺ und Hypothermie auf den mechanischen Systolenbeginn beider Ventrikel des isolierten Katzenherzens

Summary

Experiments in isolated cat hearts showed, that with increased Ca⁺⁺-concentration of the perfusion-medium (0,56 g CaCl₂/1000 ml) the onset of mechanical systole of left ventricle occurred earlier (21,9±3,3 msec after the onset ofQRS-complex in the ECG) than in experiments with a normal Ca⁺⁺-concentration (0,28 g CaCl₂/1000 ml). The onset of mechanical systole of the right ventricle was not effected.

Hypothermie (25–27°C) resulted in an earlier onset of the left chamber's mechanical systole (35,9±5,1 msec after the onset of theQRS-complex in the ECG) than temperature of 35–37°C. This effect was pronounced especially in the right ventricle (88,0±13,5 msec after the beginning of theQRS-complex in the ECG).

The different reactions under these experimental conditions resulted in a tendency of increasing asynchronism in the onset of the mechanical systole of both heart chambers.

In hypothermia the influence of increased aortic or pulmonary resistance on the onset of the mechanical systole of both ventricles was the same (shortening) as in earlier experiments with normal temperature.

In contrast to this, an increased Ca⁺⁺-concentration of perfusion-medium modified this effect on the onset of the left mechanical systole, i. e., under these experimental conditions the shortening of this parameter by increased aortic resistance was much more pronounced.

These results suggest, that the onset of the ventricular systole of both chambers is affected by hemodynamic conditions, which influence the dynamics and the course of the ventricular contraction. Besides, increased Ca⁺⁺-concentration or hypothermia is able to affect the timing of the onset of ventricular systole. It is concluded, that these reactions are the results of altered contractile properties.