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

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Abstract
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 4 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 the mVcf (mean velocity circumferential fiber shortening) and LVSP before and during pressure loading, .DELTA.mVcf/.DELTA.LVSP, respectively. The average of E(D)max at each stage of HR was 9.45, 12.63, 12.59, 11.22 mm Hg/mm and .DELTA.mVcf/.DELTA.LVSP was -0.009, -0.006, -0.007, -0.009 circ [circulation]/s mm Hg, respectivley. E(D)max increased more at S-II and S-III than at S-I, and reversely, E(D)max decreased more at S-IV than at S-II. Similarly, .DELTA.mVcf/DLVSP increased more at S-II than at S-I and decreased more at S-IV than at S-II, while .DELTA.LVSP and .DELTA.EDD (end-diastolic diameter) were not different betwene stages. These changes in E(D)max and .DELTA.mVcf/.DELTA.LVSP presented the mountainous pattern effected by alterations in HR, whose changes were almost similar to that of LV peak positive dp/dt [change in pressure with time] 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 is dependent on HR and is a sensitive indicator of LV contractility.