Relationship between phasic changes in human skin blood flow and autonomic tone.

Heart rate beat-to-beat oscillations synchronous with respiration and blood pressure waves, have been found to be a marker of sympathovagal interaction in man and animals. Oscillations of heart rate, respiration, and cutaneous blood flow were simultaneously recorded to assess the relationship between autonomic nervous control and cutaneous circulation in a group of 21 healthy subjects and in a group of 6 healthy patients after brachial plexus anesthesia and consequent sympathetic blockade. In the first group, changes in posture were employed to modify autonomic tone. Relative changes in cutaneous blood flow were recorded by laser-Doppler flowmetry. Spectral analysis techniques (cross-correlation) were used to quantify the relationship between oscillations common to the recorded signals. A standing maneuver induced a significant decrease of the cross-correlation between respiratory and heart rate fluctuations (from 4.93 +/- 0.16 to 4.44 +/- 0.16 a.u.; P less than 0.001), and a significant increase of the cross-correlation between heart rate and skin blood flow fluctuations (from 0.64 +/- 0.31 to 1.33 +/- 0.21 a.u.; P less than 0.001), but did not modify the cross-correlation between respiratory and skin blood flow fluctuations (from 2.87 +/- 0.15 to 3.04 +/- 0.14 a.u.; NS). After the standing maneuver the maximum correlation between heart rate and skin blood flow was always due to oscillations in the range of 0.1 Hz (or 10-sec period), similar to the oscillations described in large arteries. Sympathetic blockade reduced significantly the cross-correlation between heart rate and skin blood flow (P less than 0.001). These results suggest that the cross-correlation between skin blood flow and heart rate at 10-sec period fluctuations can be used as an index of the influence of the autonomic tone on skin blood circulation.