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Hindlimb blood flow and oxygen consumption in the late gestation fetal lamb

University of British Columbia

The purpose of this research was to examine hindlimb blood flow and oxygen supply in the late-gestation fetal lamb under normal and pathophysiological conditions. Although the carcass, or non-visceral tissue, accounts for a large proportion of fetal weight and oxygen demand, it has received little research attention. Because the hindlimb is composed of skin, bone, and skeletal muscle, it is representative of the carcass. We implanted vascular catheters in fetal lambs to permit sampling of blood entering and leaving the hindlimb, and a transit-time flow transducer on the external iliac artery to measure hindlimb blood flow. In late-gestation, there are specific patterns of electrocortical (ECoG) and electroocular activity (EoG), which are associated with episodic fetal breathing and body movements. Hindlimb blood flow tends to be higher and more variable during high voltage ECoG activity. To determine whether this is due to the increased body movements during this state, the neuromuscular blocking agents gallamine and pancuronium were administered. Mean hindlimb blood flow fell 8.3 ± 3.5% following blockade, but flow still tended to be higher during quiet sleep. As neuromuscular blockade did not appear to effect the behavioural state modulation of hindlimb blood flow, this relationship may be directly mediated by the central nervous system. The effects of hypoxemia and ischemia on hindlimb metabolism were compared. No difference was seen in the relationship between oxygen delivery and consumption or in the overall magnitude of hindlimb lactate release for the two perturbations. Thus, for similar reductions in oxygen deliver, we found no difference in hindlimb oxygen consumption or lactate production between hypoxemia and ischemia. Therefore, there is no evidence that hypoxemia is less well tolerated than hindlimb ischemia. As arginine vasopressin (AVP) has vasoconstrictor action's in the fetus and adult, the effect of exogenous AVP was examined in fetal and non-pregnant adult sheep. Both groups exhibited similar degrees of hypertension, reduced hindlimb blood flow, and increased hindlimb vascular resistance. However, heart rate declined significantly more in the adults. Therefore, there is no evidence for a greater sensitivity of fetal vascular smooth muscle to vasopressin, but the fetus does appear to be less sensitive to the negative chronotropic effects of AVP. In conclusion, our studies indicate that the hindlimb, and thus the carcass, plays a major role in the dynamic nature of the fetus under normal conditions as well as in its ability to adapt to pathophysiological situations.

Thesis/Dissertation

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2009-06-30

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http://hdl.handle.net/2429/9896

Reproductive and Developmental Sciences

University of British Columbia

UBCV

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