INPUT IMPEDANCE OF THE CANINE VERTEBRAL ARTERY

¹ Department of Applied Physiology and Surgical Sciences, Royal College of Surgeons of England, Lincoln's Inn Fields, London WC2

In experiments on six anaesthetized dogs it was found that the vertebral artery contributed 69·2 ± 1·7% of cerebral and 41·5 ± 2·5% of cephalic flow. The input characteristics were that the vertebral artery had a flow of 0·71 ± 0·05 ml.s^-1 into an input impedance of 23·7 ± 1·9 GN.m^-5.s. This compared to external and internal carotid flows of 0·69 ± 0·05 and 0·31 ± 0·02 ml.s^-1 into input impedances of 23·9 ± 2·1 and 52·1 ± 2·7 GN.m^-5.s respectively. Standardized per 100 g of tissue the impedances of the vertebral and internal carotid arteries were similar at 18·6 ± 2·0 and 19·1 ± 1·5 GN.m^-5.s.100 g^-1 respectively, while that for the external carotid was higher at 129·9 ± 10·2 GN.m^-5.s.100 g^-1. The impedance spectrum for the vertebral artery was of low impedance type, settling about a characteristic impedance of 2·01 ± 0·28 GN.m^-5.s without significant oscillation, associated with the phase only becoming slightly positive above 10 Hz and reflexion coefficients of less than 0·25 by a frequency of 6 Hz. This was similar to the spectrum for the internal carotid artery and contrasted with the high impedance spectrum with major reflexion found for the external carotid artery.