Changes of left ventricular pressure-diameter-velocity relations by alterations of heart rate in conscious dogs.

Changes of left ventricular (LV) pressure-diameter-velocity relations by alterations in heart rate (HR) were investigated in 6 conscious dogs, instrumented with a pair of ultrasonic crystal probe, a micromanometer in LV and pacing electrodes on the left atrium. By atrial pacing the following four stages of HR were produced: stage (s)-I 112, S-II 134, S-III 158 and S-IV 179 bpm (mean HR). these alterations in HR were repeated before and during acute pressure loadings by methoxamine infusion. LV pressure-diameter and pressure-velocity relations were evaluated by the slope value of LV peak systolic pressure (LVSP)-end-systolic diameter, E(D) max, and by the ratio of changes in mVcf (mean velocity circumferential fiber shortening) and LVSP before and during pressure loading, ΔmVcf/ΔLVSP, respectively. The average of E(D() max at each stage of HR was 9.45, 12.63, 12.59, 11.22 mmHg/mm, and ΔmVcf/ΔLVSP was -0.009, -0.006, -0.007, -0.009 circ./sec.mmHg, respectively. E(D) max increased more at S-II and S-III than at S-I, and reversely, E(D) max increased more at S-IV than at S-II. Similarly, ΔmVcf/ΔLVSP increased more at S-II than at S-I and decreased more at S-IV than at S-II, while ΔLVSP and ΔEDD (end-diastolic diameter) were not different between stages. These changes in E(D) max and ΔmVcf/ΔLVSP presented the mountainous pattern effected by alterations in HR, whose changes were almost similar to that of LV peak positive dp/dt and mVcf before pressure loading. Thus, E(D) max is augmented by an increase in HR, which suggests the Bowditch-effect. Reversely, a decrease in E(D) max at a higher rate indicates a depressed inotropic state. E(D) max id dependent on HR and is a sensitive indicator of the contractility of LV.