Effect of altering filling pattern on diastolic pressure-volume curve

The early-to-late ventricular filling ratio (E:A) is widely used to index diastolic function. While filling patterns reflect diastolic properties, they can also modulate chamber pressures due to myocardial viscoelasticity. We hypothesized that such feedback can potentially temper effects of delayed relaxation and/or volume loading on diastolic pressures.

Six isolated blood-perfused canine left ventricles were studied with ejection and filling controlled by an intracavitary volume servo-pump. Diastolic filling was determined by a simulated atrial pressure source that was either constant or varied to yield dual-phase filling at a specified E:A ratio. E:A ratio was randomly set to 3:1, 1:3, or 1:1, and data were recorded at each ratio at three different preloads. With principally early filling (E:A=3:1), diastolic pressure rise from viscosity increased in proportion with the relaxation time constant (r=.91, P<.0001). However, this dependence was lost as E:A ratio declined (eg, P=.63 for E:A 1:3). Furthermore, E:A=3:1 yielded 37% to 50% lower end-diastolic pressures at similar volumes (versus E:A=1:3) as initial viscous forces decayed. Offsetting early and late filling effects led to little net change in mean diastolic pressure independent of E:A ratio or preload.

Diastolic filling pattern itself influences chamber pressures early and late in diastole due to viscoelasticity, with larger net effects on end-diastolic pressure. Since E:A ratio normally falls with delayed relaxation but rises with higher preload or reduced compliance, the present results suggest that changes in filling pattern may modulate direct effects of such factors on elevating diastolic pressure.