SOME ASPECTS OF CARDIAC DYNAMICS IN OCTOPUS-VULGARIS (LAM)

Some dynamic characteristics of the systemic heart of O. vulgaris, det ermined with in vitro and in situ techniques, are reported. The simult aneous recording in the in situ perfused heart of the electrical ventr icular cardiogram, of ventricular, atrial and aortic pressures, and of aortic flow, allows identification of four phases in the cardiac cycl e: isovolumetric contraction (stage I), ejection (stage II), isovolume tric relaxation (stage III) and diastolic filling (stage IV). About 70 % of the total volume flowing through the coronary system occurs durin g systole, although the coronary flow is delayed with respect to aorti c flow, because there is a peak in the coronary resistance at the end of stage I. The pressure-volume loops determined by applying a plethys mographic technique to the isolated perfused heart have two main chara cteristics: (a) the peak pressure during systole is reached with minim al volume changes and mosi of the volume changes are accompanied by a reduction of pressure, and (b) stage III is not really isovolumic, bec ause there is residual coronary flow occuring during this stage. An in vitro preparation of the Octopus systemic heart is also described; in this the aorta is clamped, so that the coronary output is the only ou tput from the heart. The direct dependence of coronary flow on intrave ntricular pressure was demonstrated. By determining the volume changes in this preparation it was possible to quantify the effect of contrac tion on the coronary flow in terms of opening pressure (3.2 kPa, again st 1.4 kPa during relaxation) and the slope of the linearized relation ship between resistance and intraventricular pressure.