Increasing the diagnostic signifcance of the laser Doppler flowmetry in assessing skin microcirculation in hypertension

Background. Hypertension (HTN) is associated with impaired skin microcirculation. Laser Doppler flowmetry is an objective, quantitative, instrumental method that allows evaluating skin microcirculation. However, the method was not widely used clinically due to high variability of perfusion and small difference between healthy people and HTN patients and, as a consequence, low diagnostic signifcance.

Objective. To provide the grounds for the approaches increasing the informative value of skin microcirculation measurement by laser Doppler flowmetry in HTN patients.

Design and methods. The study involved HTN patients (n = 13, the median age was 60 (49; 63) years) and young otherwise healthy volunteers without HTN (n = 12, the median age 26 (25; 27) years). Microcirculation measurement was performed by laser Doppler flowmetry using LAKK-02 device. Registration of microcirculation on the forearm skin was carried out during the occlusionheating test. The Mann-Whitney test was used to compare the parameters in two groups. The diagnostic accuracy of the method for the inverse classifcation of the subjects was evaluated using ROC analysis.

Results. In HTN patients, the median baseline perfusion was 3,1 (1,84; 4,31) perfusion units (PU), in healthy volunteers — 4,29 (3,66; 8,14) PU (p = 0,04). The median area under the microcirculation curve for the frst 2 minutes of heating in HTN patients was 1206,7 (813; 1449) PU × s, in healthy volunteers — 1552,3 (1310; 1624) PU × s (p = 0,035). In healthy volunteers, the heating increased the perfusion by 596 % (386%; 878%), and in HTN patients perfusion increased only by 265% (180 %; 318%) (p = 0,01). The relative increase in perfusion during postocclusion hyperemia with continued heating compared with the baseline in healthy volunteers was 651% (493 %; 999%), and in HTN patients — 302 % (182 %; 436%) (p = 0,005). Thus, when comparing the average parameters for each period in the occlusion-heating test, only basic perfusion showed signifcant differences. However, when changed from absolute to relative parameters (the increase in microcirculation in relation to the vasodilating effects), the difference was signifcant. Moreover, sensitivity achieved was 75 % and specifcity — 84,6% (the inverse classifcation of groups).

Conclusions. The physiological (the local heating of the forearm skin at a rate of 2 degrees Celsius per second, a combination of vasodilating effects) and mathematical (the transition from absolute to relative values) approaches provided an increase of the informative value of the laser Doppler flowmetry, as well as its sensitivity and specifcity.

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