Figure 3 shows the mean values of baseline, early peak, nadir, and plateau SkBF. The visual impression conveyed by Figure 2, was confirmed by the statistical analysis of these parameters. From T0 to T2, the mean decrease in the plateau SkBF and increase in early peak were, respectively, −9% to −16% and +10% to +18% of the value at T0 (p values below 0.05 for all conditions). As occurred with the plateau, the nadir tended to be lower at T2 than at T0 in the
four conditions Selleck Hydroxychloroquine tested, but the difference reached statistical significance only in the case of the custom-made chamber probed with LDI. Finally (and not obvious in Figure 2), the baseline SkBF, in all conditions, was slightly and significantly lower at T2, in comparison
with T0. At T2, the higher peak response was associated with a higher mean BP and therefore could reflect a change in perfusion pressure rather than in vascular tone. Against this interpretation, cutaneous vascular conductance (i.e., SkBF divided by mean BP) consistently increased from T0 to T2 (LDI NVP-BKM120 in vitro custom-made chamber: from 4.7 ± 1.5 to 5.8 ± 1.9 PU/mmHg, p < 0.001; LDI commercial chamber: from 4.0 ± 2.0 to 5.3 ± 2.6 PU/mmHg, p < 0.001; LDF custom-made chamber: from 6.8 ± 4.0 to 8.3 ± 4.7 mV/mmHg, p = 0.001; LDF commercial chamber: from 6.2 ± 2.7 to 7.7 ± 3.4 mV/mmHg, p = 0.001). Finally, the plateau response was somewhat lower with the custom commercial, when compared with the custom-made chamber. Although statistically significant, this effect was minor and could have been related to small differences in heating rate and temperature reached. The present study confirms our previous observation that the repeated application of a local thermal stimulus on the same skin patch,
at least when carried out within two hours, leads to a reduction in the elicited vasodilatory response. However, two studies [4,20] have not noticed this phenomenon. Therefore, the questions that must be asked are the reasons for this apparent discrepancy and whether differences in methods could be involved. The major difference relates to the equipment, both for measuring SkBF (LDF vs LDI) and for local heating (commercially available vs MTMR9 custom-made chambers, which may not have the same surface area and heating rate). Any of these factors could have contributed to the discrepancy between our previous observations [3] and those made by these other groups [4,20]. However, in the present study, desensitization clearly occurred in all tested conditions, supporting its independency from the measuring equipment and heating system used in the experiment. In the work by Shastry et al., 10 subjects participated, five men and five women. The laser-Doppler flowmeter (PF 5010; Perimed) was single point at 780 nm, based on exactly the same technology as the less recent Perimed 4001 used in the present study.