Aortic Pressure and the Diastolic Volume Law of Energy Output in Cardiac Contraction

Conclusions

When very small changes in diastolic ventricular volume are measured one cannot disregard the coronary perfusion pressure as a factor in determining the volume of blood in the coronary vessels. Since the volume of blood in the superficial vessels has no influence upon the fiber length, and the quantity in the deeper vessels has a lesser influence than does the volume within the ventricles, it is obvious that corrections in the measured external diastolic ventricular volume must be made in order to compare energetic conditions at various perfusion pressures. The quantitative results obtained here are of the right order of magnitude to account completely for the small discrepancies found by Kiese and Garan in energy liberation at various aortic pressures. It is believed that the present results invalidate the conclusion that the aortic pressure is a determining factor in the energy liberation by heart muscle. The best evidence therefore indicates that the conditions of loading, other than those determining the initial fiber length, or diastolic ventricular volume, have no influence upon the energy liberated in cardiac contraction. This conclusion is most fully substantiated by the fact that in the tortoise ventricle, where there is no coronary system, the diastolic volume law obtains irrespective of the type of loading.