The effects of hemorrhagic shock on the diastolic properties of the left ventricle in the conscious dog

Although the depressed left ventricular (LV) performance and elevated filling pressure frequently observed following resuscitation from hemorrhagic shock (HS) usually have been attributed to impaired contractile function, the same findings could be explained by a loss of ventricular compliance. To determine the effects of HS on diastolic mechanics, the normalized LV diastolic pressure-dimension (P-D) relationship was studied in 10 chronically instrumented conscious dogs. Minor axis circumference (C) was obtained from ultrasonic dimension measurements of the external minor axis diameter (D). Circumferential strain (ε(c)) was calculated from C, normalized to the unstressed circumference (C(o)) obtained at zero transmural pressure (P(TM)) during a transient vena caval occlusion. To minimize viscous effects, the static diastolic P-D relationship was determined by fitting only diastatic points (Dε(c)/DT=0±0.03 sec^-1) to the equation P(TM)=α (e(βε)c-1) where α and β are calculated elastic constants. After study in the control state, each dog was subjected to 2 hours of HS (mean arterial pressure = 40 mm Hg), followed by reinfusion of all shed blood. In all 10 dogs the P-D curve immediately after reinfusion demonstrated a shift to the left, indicating a loss of ventricular compliance. C(o) remained unchanged (15.4±0.9 cm control vs. 16.5±0.9 cm immediately after HS), indicating that the shift did not represent a change in the unstressed circumference. Five survivors each displayed a progressive return of compliance to control during the 4 day study period. However, five nonsurvivors all demonstrated a progressive loss of compliance prior to death. These results indicate that HS results in a progressive potentially reversible loss of ventricular compliance. This may explain the observation of depressed ventricular performance with normal or increased contractile function in HS.