The Muscular Reactions of the Mammalian Ven- Tricles to Artificial Surface Stimuli

The muscular reactions of the mammalian ventricles to localized artificial stimuli have not been studied with the degree of precision that the subject merits. This is due partly to the fact that, until recently, we have possessed no graphic appliances capable of recording the ventricular contractions in an accurate manner. The details of the premature contraction curve, the latent period, the extent of the refractory phase, the physiological conditions affecting it, the factors determining effectiveness or ineffectiveness of premature beats, etc., can be accurately analyzed only when a contraction curve is recorded on which the beginning and end of systole are clearly indicated and on which the separate phases of systole and diastole are clearly demarcated as well. Such a record is supplied by the optically recorded intraventricular pressure curve supplemented for special purposes by similar pressure curves from the auricle and aorta (Wiggers, 1921). Experimental procedures. The heart was exposed in dogs under morphine and chloretone anesthesia and after the institution of art.ificial respiration. Whenever possible, the pericardium was left intact and small slits were made for the insertion of the optical manometer and the application of electrodes. One optical manometer was inserted into the left ventricle and another was introduced into the aorta so that the cannula was placed just outside of the semilunar valves. For special purposes, the experiments were varied by recording the second pressure curve from the other ventricle or from the left auricle. The theory, construction and application of these instruments as well as the nature of the optical curves recorded and the criteria that they contain for determining the consecutive phases of the heart cycle have been previously described (Wiggers, 1914, 1921 a, b, 1924). A reasonable familiarity with these communications is essential in order to follow the data and conclusions presented in this paper. Induction shocks were applied to the left ventricle by means of two small hook-electrodes, well insulated except for their ends. These were