The appearance of the venuloarteriolar reflex during measurements microcirculation of blood by laser Doppler flowmetry caused by a change in the position of the hand

Background and Objectives: The venuloarteriolar reflex is a crucial part of the circulation regulation system, and it's particularly evident in the lower limbs compared to the upper limbs due to the higher transmural pressure in the arteries and veins of the legs. When testing with changes in arm position, vascular responses to increased blood pressure are usually checked by lowering the arm below heart level. The proposed sample examines the vascular response to both a decrease in blood pressure and an increase to its initial level. Materials and Methods: The study was conducted on two groups of volunteers, one of which included 7 healthy young people aged 21–28 years, who did not have a pronounced venuloarteriolar reflex during the exercise test, and the second 7 people aged 45–65 years, in whom the venuloarteriolar reflex was well expressed. Using the method of laser Doppler flowmetry we measured the microcirculation index during the sequence of tests with the change of the hand position according to the set of parameters characterising the dynamics of blood circulation in the microvessels of the finger. Results: When raising the arm, the microcirculation index in the "up" arm position in young volunteers has decreased significantly, while in the age group, the microcirculation index in the "up" arm position has tended to increase after a sharp decrease. We have defined such a significant discrepancy in the blood flow response of young and aged volunteers as an appearance of the venulo-arteriolar reflex. The amplitudes of neurogenic and myogenic fluctuations of microvascular blood flow were mainly multidirectional in different age groups. The experimentally measured increase in blood filling of the arm vessels in age-related volunteers, caused by the appearance of fluctuations in blood flow in the neurogenic range, is explained by the reaction of the sympathetic nervous system, leading to the appearance of the venuloarteriolar reflex, which helps to restore the volume of blood filling. At a young age, the venulo-arteriolar reflex caused by a change in the position of the arm may not appear. Conclusion: The test with the change of limb position can provide valuable information on the preservation of peripheral innervation of microvessels, which justifies the prospect of using this test in the detection of various forms of neuropathies and age-related peculiarities of blood flow regulation.