Time-dependent behavior of microvascular blood flow and oxygenation: a predictor of functional outcomes

This study investigates the timedependent behaviour and algorithmic complexity of low frequency, periodic oscillations in blood flux and oxygenation signals from the microvasculature. Methods: Microvascular blood flux (BF) and oxygenation (OXY: oxyHb, deoxyHb, totalHb and SO2%) was recorded from 15 healthy young adult males using combined laser Doppler fluximetry and white light spectroscopy with local skin temperature clamped to 33°C and during local thermal hyperaemia (LTH) at 43°C. Power spectral density (PSD) of the BF and OXY signals was evaluated within the frequency range (0.0095-1.6Hz). Signal complexity was determined using the Lempel-Ziv (LZ) algorithm. Results: Foldincrease in BF during LTH was 15.6 (10.3,22.8) and in OxyHb 4.8 (3.5,5.9) (median, range). All BF and OXY signals exhibited multiple oscillatory components with clear differences in signal power distribution across frequency bands at 33°C and 43°C. Significant reduction in the intrinsic variability and complexity of the microvascular signals during LTH was found, with mean LZ complexity of BF and OxyHb falling by 25% and 49%, respectively (p<0.001). Conclusion: These results provide corroboration that in human skin microvascular blood flow and oxygenation are influenced by multiple, time-varying oscillators that adapt to local influences and become more predictable during increased haemodynamic flow. Significance: Recent evidence strongly suggests that the inability of microvascular networks to adapt to an imposed stressor is symptomatic of disease risk which might be assessed via BF and OXY via the combination signal analysis techniques des