Combining laser-Doppler flowmetry measurements with spectral analysis to study different microcirculatory effects in human prediabetic and diabetic subjects

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.