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Physiol Meas. 2019 Jun 3. doi: 10.1088/1361-6579/ab2651. [Epub ahead of print]

On the suitability of laser-Doppler flowmetry for capturing microvascular blood flow dynamics from darkly pigmented skin.

Author information

1
Department of Physics, Lancaster University, Lancaster, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND.
2
Department of Physics, Lancaster University, Lancaster, LA1 4YB, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND.
3
Department of Physics, Lancaster University, Lancaster, Lancashire, LA1 4YB, Lancaster, LA1 4YB, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND.

Abstract

Laser Doppler flowmetry (LDF) provides for the noninvasive monitoring of microvascular blood flow dynamics. It has been used extensively on light-skinned subjects, i.e.\ on skin with low melanin concentration, in both the healthy and pathological states. Because the optical properties of human skin could well affect the reliability of optically-based diagnostic equipment, the effectiveness of LDF needs to be checked and evaluated on dark skin, too, if this method is to be useful in global health care. Here we assess the performance of LDF in measuring blood perfusion from darkly-pigmented skin, i.e.\ skin with high melanin concentration. Thirteen dark-skinned subjects and ten light-skinned subjects were included in the study. Microvascular blood flow dynamics was measured on both the right and left ankles using LDF with a laser diode of wavelength 780~nm. The characteristics of time-varying blood flow oscillations were investigated by wavelet analysis, nonlinear mode decomposition and wavelet phase coherence. No significant differences were observed between the groups in the mean blood perfusion ($p>0.1$), or wavelet power ($p>0.6$). The instantaneous heart rate (IHR), extracted from the LDF at each of the recording sites, and from the electrocardiogram (ECG), did not differ significantly between the groups ($p>0.8$). Nor did the wavelet power of the IHR differ ($p>0.2$) between the groups. The only significant difference found between the groups lay in left/right ankle blood flow coherence near the cardiac frequency, attributable to known ethnic physiological differences. These results indicate that high melanin concentrations in skin exert no significant influence on the ability of LDF to monitor microvascular blood flow dynamics when using a laser diode of wavelength 780~nm. Hence LDF can help in the diagnosis and exploration of the pathogenesis of diseases such as diabetes, hypertension, or malaria in darkly pigmented patients across sub-Saharan Africa.

KEYWORDS:

biological oscillations; ethnic disparity; melanin; microvascular flow; skin optics; time-varying dynamics; wavelet based phase coherence and decomposition

PMID:
31158825
DOI:
10.1088/1361-6579/ab2651

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