Abstract
Microvascular assessment would benefit from co-registration of blood flow and hemoglobin oxygenation dynamics during stimulus response tests. We used a fiber-optic probe for simultaneous recording of white light diffuse reflectance (DRS; 475-850 nm) and laser Doppler flowmetry (LDF; 780 nm) spectra at two source-detector distances (0.4 and 1.2 mm). An inverse Monte Carlo algorithm, based on a multiparameter three-layer adaptive skin model, was used for analyzing DRS data. LDF spectra were conventionally processed for perfusion. The system was evaluated on volar forearm recordings of 33 healthy subjects during a 5-min systolic occlusion protocol. The calibration scheme and the optimal adaptive skin model fitted DRS spectra at both distances within 10%. During occlusion, perfusion decreased within 5 s while oxygenation decreased slowly (mean time constant 61 s; dissociation of oxygen from hemoglobin). After occlusion release, perfusion and oxygenation increased within 3 s (inflow of oxygenized blood). The increased perfusion was due to increased blood tissue fraction and speed. The supranormal hemoglobin oxygenation indicates a blood flow in excess of metabolic demands. In conclusion, by integrating DRS and LDF in a fiber-optic probe, a powerful tool for assessment of blood flow and oxygenation in the same microvascular bed has been presented.
Highlights
The microcirculatory system is important for delivering oxygen to all cells in the body through the red blood cells (RBC)
An impaired vascular capacity has been found by measuring the laser Doppler flowmetry (LDF) perfusion during local skin heating to 44°C for 25 min.[1,2]
The postocclusive reactive hyperemia after arterial occlusion can be used to differentiate between peripheral arterial occlusive disease and normals by using separately or combinations of LDF, Diffuse reflectance spectroscopy (DRS), tcpO2, or near-infrared (NIR) spectroscopy.[5,6,7,8]
Summary
The microcirculatory system is important for delivering oxygen to all cells in the body through the red blood cells (RBC). By measuring the blood flow and the local tissue oxygenation at rest and during provocations, an assessment of the microcirculation can be obtained. An impaired vascular capacity has been found by measuring the laser Doppler flowmetry (LDF) perfusion during local skin heating to 44°C for 25 min.[1,2] A possible mechanism for the dysfunction in the microcirculation is microangiopathy due to microvascular stenosis.[3] Transcutaneous oxygen measurements (tcpO2) can be used to diagnose peripheral arterial disease, where critical limb ischemia is manifested in a reduced transcutaneous oxygen partial pressure.[4] The postocclusive reactive hyperemia after arterial occlusion can be used to differentiate between peripheral arterial occlusive disease and normals by using separately or combinations of LDF, DRS, tcpO2, or near-infrared (NIR) spectroscopy.[5,6,7,8] Despite assessing various aspects of the microcirculation, these methods do not measure the same vascular bed
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