Key result
Velocity pulse precedes pressure pulse by ~44° in rat pial arterioles.
Effect estimate: Phase difference 43.6±6.9°
In rat pial arterioles, upstream changes in blood flow are transmitted by the velocity pulse faster than by the pressure pulse, with a phase difference of approximately 45°.
Supports velocity precedence in cerebral arteriolar flow; hypothesis-generating for human cerebrovascular dynamics.
In order to clarify the phase relationship between velocity pulse and pressure pulse propagating along microvessels, the red cell velocity and intravascular pressure were simultaneously measured in the rat pial arterioles of 41–53 μm in diameter with a high temporal resolution by a laser‐Doppler anemometer and a servo‐null micropressure system. It was found that the velocity pulse preceded the pressure pulse in all the measured arterioles by 18.7–35.6 ms. The corresponding phase difference was 43.6±6.9° (mean ± SD), which is not statistically different from 45°. The value is consistent with the phase difference predicted for the blood flow in microvessels with a small reflection coefficient at frequencies as low as the heart rate of the rats. The present results suggest that the upstream changes in blood flow are transmitted by the velocity pulse faster than by the pressure pulse in the microvasculature.
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Seki et al. (2004) studied this question. Simultaneous measurement of red cell velocity and intravascular pressure was evaluated on Phase relationship between velocity pulse and pressure pulse (Phase difference 43.6±6.9°). In rat pial arterioles, the velocity pulse preceded the pressure pulse by 18.7–35.6 ms, corresponding to a phase difference of 43.6±6.9°.
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