Combining laser-Doppler flowmetry measurements with spectral analysis to study different microcirculatory effects in...

We aimed to identify the microcirculatory regulatory mechanisms in diabetic and prediabetic humans using a noninvasive method combining spectral analysis with laser-Doppler flowmetry (LDF) measurements on the skin surface. LDF signals were measured by a moorVMS-LDF device to measure the microcirculatory blood flow flux with a time constant of 0.001 s, a cutoff frequency of 14.9 kHz, and a sampling frequency of 40 Hz. The laser operating wavelength and output power were 400-700 nm and 6 mW, respectively. LDF signals were obtained noninvasively in 115 subjects, who were assigned to three groups (diabetic, prediabetic, and normal) according to the results of the oral glucose tolerance tests. A Morlet mother wavelet transform was applied to the measured 20-min LDF signals, and periodic oscillations with five characteristic frequency peaks were obtained within the following frequency bands: 0.0095-0.02, 0.02-0.06, 0.06-0.15, 0.15-0.4, and 0.4-1.6 Hz (defined as FR1-FR5), respectively. The relative energy contribution (REC) of FR1 was significantly smaller (by using the Kruskal-Wallis test followed by Dunn's multiple-comparison tests) in diabetic subjects than in normal subjects. The REC of FR2-FR3 was significantly smaller in diabetic and prediabetic subjects than in normal subjects. The REC of FR1-FR3 from normal to prediabetic and diabetic subjects showed a progressive decrease. The present findings may aid in the development of a noninvasive method for the early detection of prediabetes and the monitoring of disease progression. This may be useful in preventing disease progression and reducing the risk of concomitant end-organ damage.