Effects of Aortic Distensibility on the Cardiac Force in Man

The left ventricular myocardial function in the ejection phase of auxotonic contraction was investigated in direct relation to aortic distensibility in twenty-five patients with varying heart lesions. Analysis of the aortic pressure curve and the ascending aorta volume obtained by routine left heart catheterization and biplane angiocardiography provided an approach to compute aortic distensibility. The mean value of the aortic distensibility in all patients was 0.847 ± 0.430 S.D. percent per mmHg pulse pressure. In patients with normal left ventricular (LV) function, the aortic distensibility demonstrated a significant inverse relationship to the duration of the LV wall stress at top 20 percentile of its peak (r=-0.71), and also a positive one to the contractile element velocity at the peak stress (r=0.70). Patients with LV dysfunction defined by ejection fraction of below 50% showed an increase in duration of higher stress with relatively low aortic distensibility. This characteristic feature of the aortic property and stress-time relation in the ejection phase observed in LV dysfunction were not always found to concur with low maximal contractile element velocity (Vmax) which was computed in the isovolumic phase. These results suggest that the aortic distensibility is one of the major determinants on LV myocardial force and velocity development, and that evaluation of myocardial functions in the ejection phase should be made as well as in the isovolumic phase.