Oxygen saturation, red blood cell tissue fraction and speed resolved perfusion — A new optical method for microcirculatory assessment

Abstract

We have developed a new fiber-optic system that combines diffuse reflectance spectroscopy (DRS) and laser Doppler Flowmetry (LDF) for a multi-modal assessment of the microcirculation. Quantitative data is achieved with an inverse Monte Carlo algorithm based on an individually adaptive skin model. The output parameters are calculated from the model and given in absolute units: hemoglobin oxygen saturation (%), red blood cell (RBC) tissue fraction (%), and the speed resolved RBC perfusion separated into three speed regions; 0-1 mm/s, 1-10 mm/s and above 10 mm/s (% mm/s). The aim was to explore microcirculatory parameters using the new optical method, integrating DRS and LDF in a joint skin model, during local heating of the dorsal foot and venous and arterial occlusion of the forearm in 23 healthy subjects (age 20-28 years). There were differences in the three speed regions in regard to blood flow changes due to local heating, where perfusion for high speeds increased the most. There was also a high correlation between changes in oxygenation and changes in perfusion for higher speeds. Oxygen saturation at baseline was 44% on foot, increasing to 83% at plateau after heating. The larger increase in perfusion for higher speeds than for lower speeds together with the oxygenation increase during thermal provocation, shows a local thermoregulatory blood flow in presumably arteriolar dermal vessels. In conclusion, there are improved possibilities to assess microcirculation using integrated DRS and LDF in a joint skin model by enabling both oxygenation and speed resolved blood flow assessment simultaneously and in the same skin site. Output parameters in absolute units may also yield new insights about the microcirculatory system.

The relationship between forearm skin speed‐resolved perfusion and oxygen saturation, and finger arterial pulsation amplitudes, as indirect measures of endothelial function

“…The microcirculation was measured using a PeriFlux 6000 EPOS system, integrating DRS and LDF in a fiber optic probe. The system has been described in detail elsewhere . During the measurements, the probe was fixated to the skin using rings of double‐sided adhesive tape, not covering the fiber ends.…”

“…The following parameters were calculated from the EPOS system; tissue C RBC (g RBC/100 g tissue = %), (%), Perf conv (AU), and Perf SR,tot (%RBC × mm/s), as well as perfusion divided into three speed regions (0‐1 mm/s: Perf SR,<1 [%RBC × mm/s]; 1‐10 mm/s: Perf SR,1‐10 [%RBC × mm/s]; above 10 mm/s: Perf SR,>10 [%RBC × mm/s]). The preprocessing of data obtained from the EPOS system and calculation of the microcirculatory parameters are detailed elsewhere …”

“…The possibility to separate the effect in capillaries from those in larger microvascular vessels using the speed‐resolved perfusion measure has been useful in measuring shunt flow for the first time in type 2 diabetes . Previous studies have also shown that oxygen saturation, RBC tissue fraction, and speed‐resolved perfusion in absolute units had different responses and time to response using standard reactivity tests . The underlying microcirculatory control mechanism that causes these response differences is however unclear.…”

A dataset of speed-resolved blood perfusion and oxygen saturation in human skin response to thermal stimulation

“…Recently, a multiparameter model based on the Monte Carlo algorithm has provided the possibility of further distinguishing the different velocity components in microcirculation perfusion [5][6][7]. This new method may provide further insight into evaluating vascular dysfunction at the systemic level [8,9]. According to previous studies, blood perfusion signals recorded by LDF can be separated into different frequency bands in the frequency domain [10][11][12][13]; these frequency bands might reflect different physiological rhythms [14].…”

A multipixel diffuse correlation spectroscopy system based on a single photon avalanche diode array

“…A recent development in LDF is to include optical parameters from diffuse reflectance spectroscopy in the perfusion modeling. Another is to differentiate the perfusion estimate into different speed components by the use of inverse Monte Carlo light transport modeling .…”