Tissue Oxygen Saturation

The local average oxygen saturation of the hemoglobin in all red blood cells (RBC) is referred to as the tissue oxygen saturation or RBC oxygen saturation. This is an important parameter to measure in order to assess both oxygen delivery and uptake in tissue. It differs from the commonly known pulse oximetry as it reveals the oxygen saturation of all blood, including the microcirculation and both arterial and venous. In pulse oximetry, the output is isolated to the oxygen saturation in the pulsatile arteries.

By combining measurements of tissue oxygen saturation and speed resolved perfusion, a comprehensive view of the microcirculation and the tissue metabolism can be achieved. We offer the PeriFlux 6000 EPOS instrument to measure these microvascular parameters in the same sampling volume using an integrated fiber-optic probe and advanced model-based signal analysis. The parameters from the EPOS are:

• RBC oxygen saturation (%)
• RBC tissue fraction: gram RBC / 100 gram tissue (%)
• Oxygenized and reduced hemoglobin tissue concentration (µM)
• Speed-resolved perfusion: gram RBC / 100 gram tissue × mm/seconds (% RBC × mm/second). Three different speed regions: < 1 mm/second, 1 to 10 mm/second, and > 10 mm/second
• Measurement depth (mm)

Various provocations protocols, such as local heating or brachial occlusion, are preferably used in combination with these microcircular measurements, in order to reveal more information about the microvascular function. There is built-in automatic support for those provocations in the EPOS instrument.

Figure caption: Post occlusive reactive hyperemia measurement on forearm, five-minute brachial occlusion between 2 and 7 minutes.

References:

1. Inverse Monte Carlo in a multilayered tissue model: merging diffuse reflectance spectroscopy and laser Doppler flowmetry. Fredriksson I, Burdakov O, Larsson M, Strömberg T. Journal ofBiomedical Optics. 18(12), 2013.
2. Oxygen saturation, red blood cell tissue fraction and speed resolved perfusion – A new optical method for microcirculatory assessment. Jonasson H, Fredriksson I, Pettersson A, Larsson M, Strömberg T. Microvascular Research. 102, 2015.
3. Skin microvascular endothelial dysfunction is associated with type 2 diabetes independently of microalbuminuria and arterial stiffness. Jonasson H, Bergstrand S, et al. Diabetes and Vascular Disease Research. 14(4), 2017.
4. The relationship between forearm skin speed-resolved perfusion and oxygen saturation, and finger arterial pulsation amplitudes, as indirect measures of endothelial function. Bergstrand S, Morales M-A, Coppini G, Larsson M, Strömberg T.Microcirculation. 25(2), 2018.
5. Validation of speed-resolved laser Doppler perfusion in a multimodal optical system using a blood-flow phantom. JonassonH, Fredriksson I, Larsson M, Strömberg T, Journal of Biomedical Optics 24(9), 2019.
6. Normative data and the influence of age and sex on microcirculatory function in a middle-aged cohort: results from the SCAPIS study. Jonasson H, Bergstrand S, et al. American Journal of Physiology-Heart and Circulatory Physiology 318(4),2020.