Isochronal behavior in left ventricular systolic pressure-wall thickness relations

Abstract

Regional left ventricular systolic pressure-thickness relations have been used to assess regional load-insensitive contractility with the assumption that they possess linear isochrones that are fundamental to the time-varying elastance model of global pressure-volume relations. We examined the shape and time-varying behavior of pressure-thickness isochrones in six open-chest canine preparations. Transmural wall thickening (sonomicrometry) and ventricular pressure were altered by abrupt preload alterations during control, dobutamine, and propranolol. In all dogs and interventions, linear isochrones (r2 mean +/- SE = 0.91 +/- 0.11) were found at 5-ms intervals. During control, linear isochrone slope rose monotonically from onset to end of systole. Thickness-axis intercepts also varied continuously in time, but peak intercept and maximal slope were asynchronous. Dobutamine caused a steeper earlier maximum slope and increased slope-intercept asynchrony. Propranolol reduced maximum slope and slope-intercept asynchrony. Isochronal data during early systole were better fitted to a parabolic than to the linear model; however, fits to linear and parabolic models were equally good near end of systole. Linear isochronal behavior exists in systolic pressure-thickness relations especially near end systole and is maintained during modest inotropic alterations.

Modeling the Instantaneous Pressure–Volume Relation of the Left Ventricle: A Comparison of Six Models

“…This shape has been reported first by Claessens et al for the mouse, 9 but in general isochrones during isovolumic relaxation have gained little or no attention. Even Funai and Thames 12 who studied isochrones using pressure-wall thickness measurements did not show the isochrones during this phase, while Suga et al 33 in their classical paper reported the largest errors in time-varying elastance during isovolumic relaxation (see Fig. 5 of their article).…”

“…Although the time-varying elastance defines an elastance for each moment in the cardiac cycle, linearity of the isochrones has not been studied very often. Funai and Thames 12 studied the isochronal behavior in left ventricular pressure-wall thickness relations, assuming that the latter relation is closely related to time-varying elastance. In the basal state and during modest inotropic alterations, isochrones were linear near end-systole, but parabolic during early systole.…”

Measuring left ventricular volumes in two-dimensional echocardiography image sequence using level-set method for automatic detection of end-diastole and end-systole frames

“…To typify universal cardiac functions, a significant number of factors have been investigated to measure ES and ED volumes, SV, global EF ratio, CO and wall thickening, all of which are essential parameters to assess heart function ( 10 - 14 ). ED is often used as the landmark by which the timing of other events in the cardiac cycle is referred to ( 15 - 18 ). It is also noteworthy that detecting these frames is basically required for a number of post-processing techniques such as calculating 2D strain rate or color kinesis ( 19 ).…”