According to the technique find more (single-point or integrating LDF, LDI, or LSCI) and the test, the reproducibility of the measurements is drastically influenced by the way of expressing

data, as detailed above and summarized in Table 1. Recent work has shown that normalizing data to maximum flux provides similar responses to thermal stimuli (skin-surface cooling and whole body heat stress) whether assessed with single-point LDF, integrating LDF, or LDI [13]. Scaling data to maximal vasodilation after local heating to 42–44°C is acceptable in mechanistically driven, carefully controlled studies, when skin blood flux is assessed with LDF or LSCI [100,117]. However, such data expression may not be appropriate when studying reactivity in patients, in whom maximal vasodilation may be altered [100]. Full-field techniques such as LDI or LSCI may be of particular interest in such situations. Selleck C646 For laser Doppler measurements, skin blood flux does not reach the value of zero when perfusion is absent due to Brownian motion of macromolecules (reached after 3–5 minutes of cuff occlusion) [77]. Part of this

signal may also be attributed to remaining red blood cells in venules. Whether data analysis should take into account this residual flux (referred to as “biological zero”, BZ) remains controversial. Indeed, BZ (recorded with LDF) has been shown to be additive to the flow signal [77]. The authors therefore suggested measuring BZ under every experimental condition and subtracting it from the flux Methocarbamol signal [77]. This is technically a wise precaution, but in practice, it is only possible when considering PORH (during which BZ is obtained de facto). In other conditions, occluding large vessels for 3–5 minutes would induce tremendous changes in microvascular reactivity, and bias the response.

A solution would be to occlude arterial flow after other challenges, but this is not advisable as temperature or drugs (i.e., conditions of high blood flux) increase BZ recorded with LDF [77] and LDI [93]. In such circumstances, as the absolute difference is small, BZ subtraction has little influence when quantifying absolute hyperemic perfusion. Subtracting the biological zero did not improve one-week PORH reproducibility [114]. Furthermore, it may introduce bias when data are expressed as a percentage increase from baseline flux [93]. To our knowledge, little data are available concerning BZ assessed with LSCI. A recent study has shown higher BZ with LSCI than with LDI, thus again raising the issue of its influence on data analysis [98]. Subtracting BZ did not alter its correlation with LDI, but shifted the regression line toward the origin. However, BZ subtraction introduced some variability in baseline, thus worsening the correlation when data were expressed as a percentage increase from baseline.