Cardiac and respiratory oscillations of the blood flow in microvessels of the human skin

Abstract  Laser Doppler flowmetry with wavelet analysis, spectrophotometry, computer-aided capillaroscopy, and thermometry were used to study cardiac and respiratory oscillations of the blood flow in the skin microvessels of 30 subjects. The amplitudes of the cardiac and respiratory rhythms (Ac and Ar, respectively) were found to be determined predominantly by the distribution of perfusion and pressure in larger vessels (arterioles and venules). The cardiorespiratory coupling is a regulatory factor in the microcirculatory system; at rest, the value of Ac/Ar reflects the capillary arteriovenous ratio. In the structure of the microcirculation index (MI) and Ac, the velocity-to-volume ratio depends on the perfusion of the corresponding skin region: at rest, the volume-related component is expressed only in the skin with arteriolovenular anastomoses, whereas, in the skin without these anastomoses, MI and Ac are predominantly correlated with the dynamic velocity-related component. Ac is inversely dependent on both stationary and oscillatory components of the microvascular tone. The nature of the respiratory wave depends not only on the respiratory modulation of the venous outflow, but also on the perfusion pressure in the microvessels and venular hematocrit. The correlation of Ar with the total blood flow in the skin microvessels and the individual contributions of velocity-and volume-related components to Ar were significant only in situations where the blood flow was above a certain threshold, below which the respiratory waves can penetrate into the microvessels but their correlation with the total perfusion is nonsignificant.