DETERMINATIONS OF REFRACTORY PERIODS IN THE TURTLE HEART

Publisher Website
Google Scholar
Abstract
Double condenser stimuli were used for detn. of the refractory period curves of the turtle ventricle and atrium. Although the time to max. of the stimuli used was in most exps. 0.018 sec., this time may be varied over a considerable range without changing the form of the excitability curves plotted. Absolute values may be changed by such change of shock form. For either ventricle or atrium of the normally beating heart, excitability as detd. by such stimuli begins to rise at the end of the period of absolute refractoriness, continues to rise without intermission, and is still rising at the beginning of the next normal beat. Under vagus inhibition there is a shortening of the absolutely refractory phase of the atrium. However, the relatively refractory period is prolonged and recovery to normal threshold level may be delayed indefinitely. Vagus stimulation was not in any exp. observed to produce any direct effect upon the excitability of the ventricle. Attention is called to the importance of considering the relative as well as the absolute refractory phase in studies of functional cardiac changes.

This publication has 2 references indexed in Scilit: