Fetal Lamb Ventricles Respond Differently to Filling and Arterial Pressures and to in Utero Ventilation

Abstract

ABSTRACT. Right and left ventricular function were in-function curve. but differs in that it is positioned "above" the vestigated in 12 fetal lambs (127-140 days gestation) left ventricular curve. Although these experiments support the instrumented with electromagnetic flow sensors on the concept of right ventricular dominance, statistical significance ascending aorta and the main pulmonary artery, and with between the positions of the function curves was not achieved vascular catheters. Nine fetuses were equipped with a possibly because of biologic variability between animals. postductal aortic occluder and the trachea was cannulated When assessing the response to changes in arterial pressure, in eight. Control arterial blood values were pH 7.36 + 0.02 the two ventricles have been found to differ significantly (4. 5).(SD), PC02 49.3 + 2.3 torr, PO2 18.4 + 1.7 torr, and In the arterial pressure range from 20-90 tom, right ventricular hematocrit 37.3 2 4.4%. Biventricular function curves stroke volume was very negatively influenced by arterial pressure. relating stroke volume to mean right and left atrial pressure while left ventricular stroke volume was minimally affected. were generated by rapid withdrawal and reinfusion of fetal These preliminary findings indicate that the two fetal ventricles blood. Both function curves were composed of steep as-distinctly differ in their response to changes in arterial pressure. cending and plateau limbs that intersected a t a breakpoint. Animuls.Ewes of mixed breeds were bred at our institutional From early investigations on acutely instrumented, anesthe-farm to provide dated pregnancy and were brought to the labotized animals, it was concluded that the fetal ventricles have ratory Pens Several days before surgery to become accustomed similar outputs (I). Subsequent studies in chronically instru-to the surroundings. Fetuses of known gestation (123-133 days) mented, unanesthetized fetal lambs have shown a consistent were selected for right ventricular dominance under control with the Surgicul procedtrres. Ewes and fetuses underwent sterile surright ventricular output comprising 55-67% of the combined geV using protocols ~reviously described (4. 5, 7). ~n e s t h e s i a fetal cardiac output (2, 3). ~~~~l right and left ventricular stroke was induced with intravenous methohexitol and maintained with volumes have been measured separately during changes in filling 1 % halothane in nitrous oxide and oxygen. h he fetus was delivpressure produced by hemorrhage and crystalloid infusion. and ered through a midline laparotomy and hysterotomy. ~o l~v i n~l during changes in arterial pressure (4, 5). These studies have catheters (V-5, 1.3 mm O D or V-8 1.7 m m OD, Bolab Inc., ~a k e shown that the right ventricular function curve relating stroke Havasu City. AZ) were placed in the right carotid artery and volume to atrial pressure has a shape similar to the left ventricular advanced to the brachiocepha1ic artery and in the right Jugular vein and advanced to the right atrium. The trach...

Atrial Myocardial Blood Flow during Acute Right Ventricular Pressure Load and Adenosine Infusion in Late Gestation Fetal Sheep

“…4 0 kPa(48.9 + 3.0 mm Hg), P0~2.61 + 0.25 kPa (19.6 f 1.9 mm Hg), Ca02 8.3 h 1.4 mL/dL, and hematocrit 37.5 + 6.2%. Hemodynamic parameters including heart rate, carotid artery pressure, pulmonary artery pressure, and right atrial pressure (Table I) were comparable to previously published data for chronically instrumented fetal lambs (12). Right ventricular stroke volume was defined as 100% at baseline and decreased to 52% of baseline with the maximal applied pulmonary artery pressure load.…”

Determinants of Increased Left Ventricular Output during In Utero Ventilation in Fetal Sheep

“…Previous studies showed that in utero oxygen ventilation creates a central circulatory pattern identical with that in the immediate postnatal period (18,19,32,33). The arterial blood gases obtained at a time when the umbilical cord was occluded support the notion that the lungs became the sole site for gas exchange.…”

Dynamic characterization and hemodynamic effects of pulmonary waves in fetal lambs using cardiac extrasystoles and beat-by-beat wave intensity analysis

“…It is likely that these functions play a role in a range of fetal hemodynamic phenomena, including the recognized lability of the fetal pulmonary circulation (38), the observation of a 5-8 mmHg higher systolic blood pressure in the pulmonary trunk compared with the ascending aorta (36), and the propensity of an increase in afterload to reduce fetal RV output (35,37).…”