The laser Doppler flowmetry allows the non-invasive assessment of the skin perfusion in real-time, being an attractive
technique to study the human microcirculation in clinical settings. Low-frequency oscillations in the laser Doppler blood
flow signal from the skin have been related to the endothelial, endothelial-metabolic, neurogenic and myogenic
mechanisms of microvascular flow control, in the range 0.005-0.0095 Hz, 0.0095-0.021 Hz, 0.021-0.052 Hz and 0.052-
0.145 Hz respectively. The mean Amplitude (A) of the periodic fluctuations in the laser Doppler blood flow signal, in
each frequency range, derived from the respective wavelet-transformed coefficients, has been used to assess the function
and dysfunctions of each mechanism of flow control. Known sources of flow signal variances include spatial and
temporal variability, diminishing the discriminatory capability of the technique. Here a new time domain method of
analysis is proposed, based on the Time of Correlation (TC) of flow fluctuations between two adjacent sites. Registers of
blood flow from two adjacent regions, for skin temperature at 32 <sup>0</sup>C (basal) and thermally stimulated (42 <sup>0</sup>C) of volar
forearms from 20 healthy volunteers were collected and analyzed. The results obtained revealed high time of correlation
between two adjacent regions when thermally stimulated, for signals in the endothelial, endothelial-metabolic,
neurogenic and myogenic frequency ranges. Experimental data also indicate lower variability for TC when compared to
A, when thermally stimulated, suggesting a new promising parameter for assessment of the microvascular flow control.
Low-frequency fluctuations in the laser Doppler flow signal (LDFS) from the skin are related to microvascular
mechanisms of flow control. Wavelet spectral analysis has been used to correlate fluctuations in the LDFS with the
endothelial, neurogenic and myogenic mechanisms of control in the frequency intervals 0.005-0.02 Hz, 0.02-0.06 Hz and
0.06-0.16 Hz, respectively. Generally the signal power, in each frequency interval, derived from the respective wavelet
coefficients, is used as a measure of the activity of the related mechanism of microvascular control. However, the time-domain
characteristics of the fluctuations in the LDFS in each frequency interval are poorly known. As a consequence,
there is a lack of objective criteria to properly measure, in each frequency interval, the related hemodynamic parameters.
Here a time-domain method is proposed to analyze and quantify fluctuations in the LDFS in each frequency band.
Baseline (32 degrees Celsius) and thermally stimulated (42 degrees Celsius) LDFS of forearms from 15 healthy
volunteers were collected and analyzed. The data obtained indicate that inappropriate time windows, frequently used for
measurements, increase the variability of the measured signal power, diminishing the capability of the method when
assessing microvascular dynamics and dysfunctions. To overcome this limitation, an objective method to measure the
LDFS power in each frequency band is proposed.
The effective irradiance is a useful measure to compare performances of different broadband light sources and to more
precisely predict the outcome of a topical photodynamic therapy. The effective irradiance (or effective fluence rate) and
the exposition time of the optical radiation usually determine the light dose. The effective irradiance (E<sub>eff</sub>) takes into
account the spectral irradiance of the source as well as the action spectrum, where the wavelength dependence of both
optical diffusion through tissue and photosensitizer are considered. In practice there are no standard action spectra for the
currently used photosensitizers. As a consequence, measured values of effective irradiance using different action spectra
can not be compared. In order to solve this problem, the basis of the calibration theory developed for the broadband
ultraviolet radiometry can be applied, where an experimental radiometer is compared with a standard radiometer. Here
is presented a simple set of linear relations in the form E<sub>eff</sub> = k . E, where E is the source irradiance and k a real positive
value, here denoted as a characteristic of the radiometer, as valuable tools for correction of effective irradiances
measured according to different action spectra. As a result, for two effective radiometers with different characteristics k<sub>1</sub>
and k<sub>2</sub>, measured values are Eeff
and Qeff respectively, and it is easily shown that the value E<sub>eff</sub> = Q<sub>eff</sub> • k<sub>1</sub>/k<sub>2</sub> .