Noncontact determination of skin blood flow using the laser speckle method: Application to patients with peripheral arterial occlusive disease (PAOD) and to type‐I diabetics

Abstract

The laser speckle method allows the noncontact determination of skin blood flow and its dynamics from a distance of 5 cm. The method is based on the time dependency of the speckle pattern formed by the scattered light of a 5 mW He-Ne laser (632.8 nm). Utilizing the speckle intensity measured through a pinhole, an electronic circuit generates an output signal denoted as blood flow parameter B. All measurements were carried out on the foot dorsum during steady-state, ischemia, and reactive hyperemia induced by a 3-min arterial occlusion. The investigations were carried out in four groups: healthy subjects, asymptomatic smokers, PAOD-patients, and type-I diabetics (D) with severe late complications. As shown by parallel measurements with the tcpO2-method, the initial value Binit of the blood flow parameter B indicates the steady-state blood flow. Binit decreases significantly from 5.95 +/- 2.55 (S.D.) for the control to 4.07 +/- 1.69 (PAOD) and 3.81 +/- 1.51 (D). The half-time BTrh for the increase of B at the beginning of the reactive hyperemia is significantly increased from 4.10 +/- 2.06 s (control) to 14.5 +/- 15.4 s (smokers), 17.6 +/- 32.7 s (PAOD), and 5.31 +/- 3.55 s (D). Other characteristic values such as peak value and time of peak during the reactive hyperemia as well as the final steady-state value and the time of its achievement exhibit similar effects. The correlation coefficients between the different characteristic values obtained from the laser speckle method indicate that the characteristic times of the dynamics and the absolute values of B vary separately and provide supplemental information. A two-dimensional representation of the characteristic values facilitates the differentiation between the four measured groups.