Contribution of internal and external carotid beds to common carotid artery input impedance in the dog.

The input impedance of the canine common carotid artery has been obtained using high fidelity pressure and flow recordings at the level of the superior thyroid artery. From the impedance spectra initially, and following internal and external carotid artery occlusion, separate estimations of internal carotid, external carotid and external/internal collateral bed impedances were derived by the use of network theory. Studies were carried out on six dogs. The common carotid input resistance was 10.98 +/- 1.42 (S.E.M.) X 10(6) kN.m-5.s, while those for the internal, external and collateral beds were 48.80 +/- 7.12, 14.94 +/- 2.37 and 171.42 +/- 46.83 X 10(6) kN.m-5.s respectively. The impedance spectrum of the common carotid, external carotid and collateral beds were of a high impedance type with major reflexions, while that for the internal carotid bed was of low impedance type with much less reflexion. On standardization of impedance for tissue mass the resistance levels became 17.44 +/- 2.91 X 10(6) kN.m-5.s. 100 g-1 for internal and 85.41 +/- 4.75 X 10(6) kN.m-5.s. 100 g-1 for external carotid beds. Thus, common carotid input impedance differences between dog and man are due to differences in relative mass of tissue perfused by internal and external carotid arteries, rather than to different peripheral-bed characteristics in the two species.