[Response of skin blood flow to several respiratory maneuvers in healthy subjects]

In the diagnosis of autonomic disturbances, the variability of skin blood flow (SBF) and the sympathetic skin response (SSR) in response to several respiratory maneuvers are not routinely studied.

We sought to standardize the method of SBF variability and SSR in healthy subjects during four respiratory maneuvers: 1) spontaneous breathing (SB); 2) rhythmic breathing at a rate of 6 per minute (RB); 3) sudden deep inspiration (SDI); 4) Valsalva maneuver (VM). SUBJECTS, MATERIAL AND METHOD: We studied 30 healthy subjects with a mean age of 32 years, 60% were men and 40% women. We used a photopletysmograph in the finger pad to measure SBF and surface electrodes on the palms of the hand to register the SSR. We also recorded the ECG and the respiratory movements. The variables were: 1) amplitude of SBF; 2) latency and duration of SSR; 3) percentage of decrease of the SBF during the maneuvers compared with the basal flow.

During spontaneous breathing there was no respiratory modulation of the SBF and during RB the SBF was modulated with respiration. With SDI there was a 60% decrease of the SBF. VM induced a larger SBF decrease of 72 per cent. A significant statistical difference was revealed when we compared the decrease of SBF basal breathing with SDI and VM (P < 0.001). The difference was also significant between the SDI and VM (P < 0.001). The SBF decrease recovered more slowly after the SDI (beat 7) than after the VM (veat 6). The SBF decrease was more pronounced in magnitude during the VM. The latency of the SSR appears spontaneously and at random in 57% of subjects during normal breathing but it appeared consistently during RB, SDI, and VM. The latency of SSR was longer during SB (1.7 +/- 0.7 s), RB (1.6 +/- 0.7 s) than SDI (0.7 +/- 0.5 s) and VM (0.8 +/- 0.9 s) (P > 0.050). Duration of the SSR was significantly longer in the SDI (around 7.8 +/- 2.4 s) and during the VM (8 +/- 2.5 s) as compared to normal breathing (6.3 +/- 1.0 s) and RB (6.4 +/- 1.5 s) (P < 0.009).

SB and RB induce periodic modulation of sympathetic activity to skin blood vessels and sweat glands. SDI and VM produced a much greater activation of sympathetic skin activity than SB and RB. The increased SSR duration and the profound SBF decrease with SDI and VM as compared to SB or RB are consistent with this hypothesis. The latency of the SSR is much shorter with SDI and VM than with SB or RB. The most likely explanation is that the SSR, under these circumstances, results from a central command. The recovery to normal SBF is faster after the VM as compared to SDI. This suggests that the withdrawal of sympathetic responses is faster after the VM. The explanation for this is unknown but suggests that it might be baroreceptor mediated.