Spectral analysis of blood velocity fluctuations and characterization of the mechanisms controlling the tone of individual microvessels in frog tongue.

Intravital microscopy and high-frequency ultrasonic system equipped with a microtransducer working at 38.5 MHz were employed to record blood velocity in arterioles and venules in the symmetrical fragments of the microvascular bed in frog tongue. The diameters of the vasculature ranged 75-200 μ. The record length was 2-5 min. The range of blood velocities was wider in the left arterioles than in the right ones, and inversely, it was greater in the right venules than in the left ones. The high-frequency and respiratory harmonics (0.2-1.5 Hz) dominated in the velocity spectrum of microvessels at each side, the greatest values being 64.6 and 72.3% for the left venules and the right arterioles, respectively. The low-frequency harmonics (0.009-0.02 Hz) were rare observed (7.6-15.4% examined vessels). They appeared in vessels with pronounced difference between the maximum and minimum velocities, in the cases with velocity variations looking like batches (bursts), etc. Correlation of velocities in arterioles and venules was positive at the left side (0.451) and negative at the right side (-0.574) of the tongue.