Methods: Anesthetized dogs (n=26) were instrumented with a LV micromanometer. In 8 dogs chronic myocardial edema (2 month) was produced by pulmonary artery banding. Polyethylene capsules for interstitial pressure (Pint) measurement were implanted in each left ventricular myocardium. End diastolic pressure (EDP), end diastolic volume (EDV) and Pint, was measured. After baseline (BL) measurements, extravascular fluid (EVF) was increased by ligating the coronary sinus and hemodilution. After 1-6 h measurements were repeated, left ventricular compliance was calculated and the EVF was obtained from the unitless blood-free (wet weight-dry weight)/dry weight ratio. Data were analyzed with ANOVA and t-test.

Results: Acute increase in EVF (from 2.9±0.07 to 3.9±0.06) results in a linear increase in left ventricular interstitial pressure (from 14.9±1.1 to 45.5±2.5 mmHg). Chronic EVF elevation results in significant lower interstitial pressure at baseline (22.2±1.4 mmHg) compared to acute edematous dogs at same EVF values (37.5±1.8). A small increase in EVF (from 3.5±0.03 to 3.6±0.04), however, leads to a dramatic increase in interstitial pressure (from 22.2±1.4 to 45±2.4 mmHg). Further elevation of EVF in chronic edematous hearts results in small interstitial pressure increase. With increase in EVF the left ventricle is less compliant in both groups but is higher in the chronic animals.