PLEURAL AND PERICARDIAL PRESSURES LIMIT FETAL RIGHT-VENTRICULAR OUTPUT

Background The chest wall, lungs, and pericardium limit diastolic fill ing of the left ventricle in the fetus, neonate, and adult. To determi ne the effect that these tissues have on the fetal right ventricle (RV ), we studied six fetal lambs (142 days of gestation). Methods and Res ults Pregnant ewes were anesthetized (ketamine and alpha-chloralose), and the fetuses were partially delivered by cesarean section. Fetuses were instrumented to record RV stroke volume, RV end-diastolic pressur e (Prved), intrapericardial pressure (Pip), and pleural pressure. Prve d was varied between 2 and 20 mm Hg under three conditions: initially with a dosed chest and a closed pericardium (CCCP); subsequently with an open chest (chest wall and lungs retracted) and a closed pericardiu m (OCCP); and finally after the chest wall, lungs, and pericardium wer e retracted (OCOP). At equal Prved, stroke volume increased substantia lly when the chest wall and lungs were retracted from the heart and in creased further on subsequent retraction of the pericardium (eg, at Pr ved of 9 mm Hg, stroke volume increased from 1.2+/-0.2 mt [mean+/-SEM] in the CCCP condition to 2.9+/-0.4 and 4.2+/-0.3 mi, in the OCCP and OCOP conditions, respectively, P less than or equal to.05). The limita tion of stroke volume in the CCCP and OCCP conditions occurred because Pip increased in an almost one-to-one fashion as Prved increased; as a consequence. RV preload (RV end-diastolic transmural pressure, Prved minus Pip) was relatively unchanged. Conclusions The chest wall-lung combination and the pericardium each significantly constrain the fetal RV and together limit RV stroke volume.