MEASUREMENT OF OXYGEN CONSUMPTION OF THE PELVIC LIMB IN FETAL SHEEP

Abstract

Accurate measurement of substrate uptake by fetal hindlimb tissues has been limited due to difficulties with simultaneous substrate sampling and blood flow measurement. We describe continuous ultrasonic blood flow measurement in 5 fetal sheep (8-14 days post-op) catheterized for sampling unobstructed blood flow to and from a pelvic limb. Each flow transducer (Transonics Systems, Inc) was calibrated in vitro, in vivo (zero flow) and compared with microsphere measurement. Six sample sets for O2 content were drawn from the external iliac artery ([O2]a, mM) and vein ([O2”v, mM) while blood flow through the external iliac artery (F, ml/min) was measured continuously under control conditions and after pancuronium. O2 uptake (VO2, μm/min) was calculated; results are expressed as mean ± sem for the five fetuses and mean coefficient of variation within sample sets: The study limb blood flow ratio (ultrasonic/microsphere) = 1.033. The microsphere blood flow ratio (study limb/non-study limb) = 1.028. We conclude that 1) the described method for continuous blood flow measurement is accurate, and 2) the spontaneous variability of [O2], F, and VO2 can be decreased by neuromuscular blockade. Tissues with spontaneous changes in metabolic activity, such as the pelvic limb, require Doth continuous blood flow recording and multiple determinations of substrate arteriovenous differences to best describe their metabolism.