Influence of positive end-expiratory pressure ventilation (PEEP) on left ventricular pattern of contraction in experimental ARDS.

The aim of the present study was to investigate the pattern of ventricular dynamic contraction and its relation to changes of transseptal pressure gradient during ventilation with positive end-expiratory pressure (PEEP). For that purpose, left (LV) and right ventricular (RV) pressures as well as ventricular shortening in septal-lateral (s.l.) direction were assessed in 8 dogs (RV n = 5) exposed to experimental acute respiratory distress syndrome (eARDS) and PEEP 10 and 20 cmH2O (P10, P20). Despite maintenance of transmural central venous pressure by volume substitution, PEEP resulted in a fall of stroke index (P10 vs. eARDS: -7%, p<0.05; P20 vs. P10: -28%, p<0.05); this was accompanied by a fall of LV end-diastolic diameter (P10 vs. eARDS: -3.1%, p<0.01; P20 vs. P10: -7.4%, p<0.01). Although the transseptal LV to RV end- diastolic pressure gradient changed only minimally, there was a significant increase of paradoxic left ventricular systolic lengthening from 3.1% at eARDS to 4.5% at P10 (p<0.05 vs. eARDS) and 8.4% at P20 (p<0.05 vs. P10). Neither RV end-diastolic diameter nor s.l. shortening were significantly influenced by P10 or P20. It is concluded, that a rearrangement of LV dynamic contraction does occur during ventilation with PEEP, which is compatible with the concept of paradoxic systolic bulging of the interventricular septum towards the lumen of the right ventricle. Since this phenomenon occurred independent from changes of the end-diastolic pressure gradient between both ventricles, we suggest that systolic septal movement to the right is an active contractile process to support the function of a stressed RV.