Effect of diltiazem on aortic pressure-diameter relationship in dogs

To study the effects of diltiazem (Dz) on aortic (Ao) pressure-diameter (P-D) relationships, the external diameter (D) of the thoracic Ao (sonomicrometry) and Ao pressure (AoP, micromanometer) were simultaneously measured in 10 anesthetized dogs. The P-D relationship from 80 ms after the dicrotic notch of AoP (t80) to 20 ms after the peak of the next R wave on the electrocardiogram (ECG) (t20) was plotted at 30-ms intervals. To depict the P-D relationship in a wide range of AoP, Ao occlusion immediately after the release of inferior vena caval (IVC) occlusion was performed both before and after a Dz (0.03 mg.kg-1.min-1, over 10 min) infusion. The P-D relationship so obtained was a sigmoid curve under both conditions and was reasonably described by a cubic curve (P = aD3 + bD2 + cD + d, where a, b, c, and d are constants and r greater than 0.99). The first derivative of cubic regression equation (dP/dD) value of the cubic curve was used as an index of Ao stiffness. In all dogs, the dP/dD-D relationship, which was parabolic, was similar to the delta P/delta D-D relationship measured from the actual P-D relationship (delta P/delta D is the ratio of the change in AoP to that in AoD), suggesting that it corresponded to a cubic curve.(ABSTRACT TRUNCATED AT 250 WORDS)