PULMONARY BLOOD FLOW (Qp) AND BREATHING MOVEMENTS IN FETAL SHEEP

Abstract

Post-natally, Qp is influenced by respiratory movements, but little is known of the relationship between Qp and fetal breathing movements (FBM). To define this relationship, we studied 6 chronically instrumented fetal sheep (gest. 125-143 d) for a total of 2602 min. Each fetus had an electromagnetic flow probe on the left pulmonary artery (LPA), electrocortical (ECoG) electrodes, and catheters in the trachea (to evaluate FBM), main pulmonary artery, carotid artery and amniotic cavity. Mean Qp to LPA showed a wide range and was similar during high and low voltage ECoC and in the presence or absence of FBM (Table). Fluctuations in mean Qp did not relate to arterial pH, PCO2 or PO2, or to changes in ECoG activity, or onset or cessation of FBM. In contrast, phasic Qp consistently changed with FBM. During the inspiratory phase, Qp increased while pulmonary and carotid arterial blood pressures decreased; during the expiratory phase, Qp decreased while blood pressures increased. We conclude that in fetal sheep: (a) mean Qp shows wide fluctuations not related to FBM, ECoG activity, arterial pH, PCO2 or PO2; (b) during FBM phasic Qp increases during inspiration and decreases during expiration.