On the cause of the increase in light transparency of erythrocyte suspension in flow

Opacity pulse propagation in internal and external carotid vascular beds of experimental animals

Opacity pulses and opacity pulse propagation times were recorded from the external carotid arterial bed (ear) and from the ipsilateral internal carotid arterial bed of the pial-cortical surface within the closed skull of conscious monkeys and anesthetized cats during the resting state and during carotid compression. Propagation of opacity pulses to the ear precedes those to the ipsilateral brain by 10 to 100 msec. Mean values of all pulse propagation time measurements to both brain and ear during successive cardiac cycles are stable from one minute to the next in the resting state. With compression of the common carotid artery, pulse propagation time to both beds is prolonged for the duration of compression, returning promptly to precompression levels with release of the artery, but the degree of prolongation is more marked in the external carotid bed. It is suggested that the consistent differences observed in both species between opacity pulses and pulse propagation times in the two beds, as well as the difference in responses to carotid compression, may result from inherent differences in properties of the vascular wall in the beds concerned, and/or from differences in collateral circulatory pathways subserving these beds during carotid artery obstruction.