Aortic impedance and hydraulic power in the chick embryo from stages 18 to 29.

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Abstract
Little is known about the hemodynamic properties of the rapidly expanding arterial bed during embryonic development. Using a servo-null pressure system and 20-MHz pulsed Doppler velocity meter, we recorded simultaneous dorsal aortic pressure and velocity waveforms. The waveforms were digitized at 3-msec intervals and subjected to Fourier analysis. We calculated hydraulic energy and the impedance spectrum to 10 Hz. From stages 18 to 29, heart rate (148 +/- 3 to 193 +/- 9 beats/min), systolic pressure (1.14 +/- 0.12 to 3.04 +/- 0.10 mm Hg), and mean dorsal aortic blood flow (21 +/- 2 to 214 +/- 19 mm3/min) increased. Peripheral vascular resistance (Z0: 30.4 +/- 4.8 to 6.4 +/- 0.7 dyne x sec/mm5), and the impedance moduli (Z1: 6.5 +/- 1.0 to 1.7 +/- 0.2 dyne x sec/mm5; Z2: 6.1 +/- 1.2 to 1.7 +/- 0.1 dyne x sec/mm5; Z3: 7.3 +/- 1.1 to 1.7 +/- 0.2 dyne x sec/mm5) decreased. Total hydraulic power increased from 48 +/- 7 to 2,606 +/- 96 nW, while the proportion of oscillatory energy increased from 29 +/- 2% to 6...