Some aspects of cardiac dynamics in Octopus vulgaris (LAM)

Some dynamic characteristics of the systemic heart of O. vulgaris, determined with in vitro and in situ techniques, are reported. The simultaneous recording in the in situ perfused heart of the electrical ventricular cardiogram, of ventricular, atrial and aortic pressures, and of aortic flow, allows identification of four phases in the cardiac cycle: isovolumetric contraction (stage I), ejection (stage II), isovolumetric relaxation (stage III) and diastolic filling (stage IV). About 70% of the total volume flowing through the coronary system occurs during systole, although the coronary flow is delayed with respect to aortic flow, because there is a peak in the coronary resistance at the end of stage I. The pressure-volume loops determined by applying a plethysmographic technique to the isolated perfused heart have two main characteristics: (a) the peak pressure during systole is reached with minimal volume changes and mosi of the volume changes are accompanied by a reduction of pressure, and (b) stage III is not really isovolumic, because 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 output from the heart. The direct dependence of coronary flow on intraventricular pressure was demonstrated. By determining the volume changes in this preparation it was possible to quantify the effect of contraction on the coronary flow in terms of opening pressure (3.2 kPa, against 1.4 kPa during relaxation) and the slope of the linearized relationship between resistance and intraventricular pressure.