Microvascular vasomotion: origin of laser Doppler flux motion

Intravital microscopy and laser Doppler fluxmetry (LDF) were used to assess vasomotion and flux motion in skeletal muscle microcirculation. To clarify the relation between vessel type and LDF signals, arterioles, capillaries, and venules were sequentially studied. We used as an experimental model the hamster skin fold window preparation to record vasomotion and flux motion under control conditions and after injection of an alpha 2-adrenoceptor antagonist, yohimbine, since terminal arterioles appear to be subserved primarily by alpha 2-adrenoceptors. LDF signals were characterized by using an autoregressive modeling power spectrum technique. This analysis indicated that the flux motion fundamental frequency of terminal arterioles coincided with order 2 arteriole vasomotion fundamental frequency. The LDF fundamental frequency of order 3 arterioles was synchronous with the vasomotion frequency in the same-order vessels. The LDF fundamental frequency of order 3 venules corresponded to the frequency component coincident with the respiratory rate. The pattern of LDF oscillations was peculiar for each type of vessels, and the total power was greater in larger arterioles than in venules. Yohimbine reduced frequency and amplitude of vasomotion and flux motion in terminal arterioles, but it was possible to detect LDF oscillatory patterns due to the activity of parent vessels with a low frequency. In conclusion, the flux motion is fundamentally dependent on the type of vessel from which it originates and is directly related to the vasomotion of the arterioles.