End-diastolic pressure-volume relationship in sepsis: Relative contributions of compliance and equilibrium chamber volume differ

Background Compliance is a complex parameter to measure both clinically and in the laboratory. Investigations in recent years have interpreted changes in the end-diastolic pressure-volume relationship (EDPVR) as changes in co mpliance. However, without considering the equilibrium chamber volume (LV v olume when transmural pressure = 0), changes in the EDPVR may not reflect c hanges in left ventricular chamber compliance. In the present study, chambe r compliance was differentiated from equilibrium chamber volume to determin e their respective contributions to the EDPVR in a clinically relevant anim al model of chronic sepsis. Materials and methods. Rats were made septic by intraperitoneal injection o f a cecal slurry (200 mg/kg; 5 ml/kg of 5% dextrose in water). At 1, 3, and 7 days post-sepsis induction, hearts were perfused on an isolated heart ap paratus. A latex balloon was placed in the left ventricle to record peak sy stolic and end-diastolic pressures at various volumes, and the starting vol ume in the balloon was recorded. Systolic performance was evaluated by calc ulating the developed pressure (systolic pressure minus end-diastolic press ure) and peak dP/dt at end-diastolic pressures of 5 and 10 mm Hg. Results. Developed pressure and peak dP/dt were impaired 3 days after sepsi s induction and continued to be so through Day 7 of sepsis. The diastolic d ata were fitted to an exponential equation, the results of which indicated a strong leftward shift in the EDPVR through 7 days of sepsis with a concom itant decrease in equilibrium chamber volume. The LV chamber compliance dec reased at 1 day after sepsis induction, as indicated by significant changes in regression coefficients for the curves, transiently returned toward con trol by Day 3, but decreased again by 7 days of sepsis. Conclusions. Our data indicate that early in sepsis, compliance changes con tribute to a left-shifting EDPVR, but at later times in the course of the d isease, unstressed chamber volume becomes an important determinant of the l eft shift. The decrease in compliance (suggesting diastolic dysfunction) oc curred prior to systolic impairment, which may have valuable prognostic imp lications for septic patients.