The reversible displacement of the passive diastolic p-V curve in the isolated guinea pig left ventricle.

Abstract

We studied viscoelastic behaviour of the isolated diastolic guinea pig left ventricle (LV), manifested in changes of the hysteresis loop of the pressure-volume (p-V) diagram, produced by acute volume loading. Specifically, we investigated how the width of the hysteresis depends on the way LV volume loading, and whether changes in the hysteresis width are reversible. Each of 11 LV was instrumented with a catheter for injection and withdrawal of saline, and a micromanometer (Millar, 2F) to measure LV pressure. LV were loaded by the computer controlled injection of saline in 6-8 sequential injection steps of 100 μl each with a pause of 5 s, followed by a similar withdrawal pattern. In protocol A (N=5), a 100 μl higher maximal LV volume (LVVmax) was reached during injection than in the control run, and in protocol B (N=6), the time spent at LVVmax was longer (20 vs. 5 s pause). In both protocols a reproducible displacement of the passive p-V curve during volume unloading was observed, reflected in the increase of the hysteresis width by 23±8 % in protocol A, and 12±3 % in protocol B. Reversible displacement of the passive diastolic p-V curve after large aperiodic volume change suggests participation of reversible phenomena, like extracellular fluid filtration, and may in part provide an answer to the phenomenon of preconditioning.