INTERRELATION BETWEEN VENTRICULAR-FUNCTION, MYOCARDIAL BLOOD-FLOW, AND O-2 CONSUMPTION CHANGES AT BIRTH IN LAMBS

We studied the interrelation of changes in ventricular external work, myocardial blood flow, and O-2 consumption at birth. Eleven fetal shee p were instrumented under general anesthesia at 133-134 days gestation with arterial, peripheral venous, and left atrial catheters, and in f ive fetuses, a catheter was also inserted into the coronary sinus. Fet al left ventricular (LV) and right ventricular (RV) outputs and myocar dial blood flows (radioactive microspheres), hemodynamics, and LV O-2 consumption were measured 1 wk later. Fetuses were delivered by cesare an section, and measurements were repeated 1 and 4 h after birth. RV m inute work (mmHg . l . kg(-1)) was greater in fetuses (10.8 +/- 0.5 vs . 15.6 +/- 1.0, P < 0.001), but because of increased LV minute work (t o 20.9 +/- 1.4, P < 0.005) and unchanged RV minute work, this pattern was reversed by 1 h after birth. RV myocardial blood flow (ml . min(-1 ). 100 g(-1)) was predominant in fetuses (234 +/- 25 vs. 306 +/- 27, P < 0.001), but this also reversed in lambs; this reversal was related to unchanged l-h (248 +/- 16) and lower 4-h LV myocardial blood flow ( 199 +/- 9, P < 0.05) and a progressive fall in RV myocardial blood flo w (1 h: 245 +/- 20, P < 0.05; 4 h: 174 +/- 12, P < 0.005). LV O-2 cons umption (ml . min(-1). 100 g(-1)) increased between fetal (8.1 +/- 0.6 ) and 1-h lambs (18.9 +/- 1.3, P < 0.005) because of a rise in the LV arteriovenous O-2 content difference (3.6 +/- 0.4 vs. 7.5 +/- 0.6 ml/d l, P < 0.005). External work performed per unit myocardial blood flow (mmHg . l . ml(-1)) in the LV increased between fetal and 1-h lambs (1 .92 +/- 0.14 to 3.33 +/- 0.15, P < 0.001) and, in the RV, between feta l and 4-h lambs (2.09 +/- 0.18 to 2.92 +/- 0.24, P < 0.01). The propor tion of consumed O-2 converted to external work was, however, similar in fetal (34.6 +/- 3.1%) and 1-h (31.3 +/- 2.9%) and 4-h lambs (34.5 /- 3.6%). These findings indicate that 1) a switch from a fetal RV to a newborn LV dominance is due to increased LV pumping performance, 2) an associated switch in LV and RV myocardial blood flow patterns is ma inly related to a fall in RV myocardial blood flow 3) a postnatal rise in LV O-2 consumption results from enhanced LV arteriovenous O-2 extr action, not increased LV myocardial blood flow, 4) ventricular externa l work per unit myocardial blood flow increases postnatally, particula rly in the LV, and 5) LV mechanical efficiency is not altered after bi rth.