Dorsal aortic impedance in the stage 24 chick embryo following acute changes in circulating blood volume. Yoshigi, Masaaki, Norman Hu, Bradley B. Keller. NIH SCOR in Pediatric Cardiovascular Diseases, Strong Children's Research Center, Department of Pediatrics, University of Rochester School of Medicine and Dentistry, 601 Elmwood Avenue, Box 631, Rochester, NY 14642
APStracts 2:0459H, 1995.
The effects of acute changes in circulating blood volume on embryonic vascular hemodynamics were evaluated using input impedance. We simultaneously measured dorsal aortic pressure with a servonull system and flow velocity with a 20-MHz pulsed Doppler system in n=90 stage 24 chick embryos. We withdrew or infused 1, 3, or 5 l of blood via a second order vitelline vein (n=10 per group). In addition, we withdrew then infused or infused then withdrew 3 l (n=5 per group). Characteristic impedance, peripheral resistance, arterial compliance and elastance, and hydraulic power as well as basic hemodynamic parameters were evaluated on the basis of the three-element Windkessel model. In response to withdrawal, mean and pulse pressure, mean flow, arterial compliance, and hydraulic power decreased whereas peripheral resistance and arterial elastance increased in a dose dependent manner. Results in response to infusion were converse in effect. Characteristic impedance was unchanged by volume alterations. Oscillatory fraction of hydraulic power was higher than mature circulation and maintained relatively constant during interventions, which indicates well-regulated energy efficiency for vascular growth in the embryonic circulation. A hysteresis relevant to altered peripheral resistance was present following multiple interventions. Embryonic vasculature is sensitive to circulating blood volume and preserve blood pressure at the expense of blood flow. In the absence of autonomic innervation, embryonic vascular tone may be regulated by mechanical properties of the vessel (the law of Laplace) and/or vasoactive substances. 

Received 28 July 1995; accepted in final form 28 September 1995.
APS Manuscript Number H714-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95