Instantaneous pressure-volume relation of the ejecting canine left atrium.

Abstract

To characterize the pump function of the left atrium, we determined the instantaneous pressure-volume relation of the isolated supported left atrium. A physiologic after-loading system for the low-pressure atrium was created by coupling it to a real-time computer-simulated ventricle and a simulated venous impedance network via a volume servo-pump. In 10 atria loaded with such systems, multiple isochronal sets of pressure-volume data were collected from many ejecting or isovolumic contractions obtained under a constant inotropic state, and the time-varying elastance, E(t), as well as the volume-axis intercepts, VO(t), were calculated. E(t) is the ensemble of slopes, and VO(t), the volume-axis intercepts resulting from the linear regression of instantaneous pressure on instantaneous volume at multiple instants throughout the cardiac cycle. The systolic portion of the left atrial E(t) was insensitive to loading conditions, as was VO(t), which, in addition, proved to be similar to the right atrial and right v...