Wiktionary
vasomotion
n. A change in the diameter (caliber) of a blood vessel
Wikipedia
Vasomotion
Vasomotion is the spontaneous oscillation in tone of blood vessel walls, independent of heart beat, innervation or respiration. While vasomotion was first observed by Jones in 1852, the complete mechanisms responsible for its generation and its physiological importance remain to be elucidated, however several hypotheses have been put forth.