The impact of low frequency (LF), periodic flow motion oscillations that reflect the activity of local vasodilator and constrictor mechanisms on tissue blood perfusion and oxygenation is much debated; and the spatio-temporal relationship between the two unclear. Our aim is to explore the spectral power, synchronicity and complexity of oscillatory rhythms in continuously acquired microvascular blood perfusion and oxygenation signals and to investigate their association with local flow motion and mechanisms of vasomotor control. Microvascular blood flux (BF) and oxygenation (OXY; oxyHb, deoxyHb, total Hb and SO2) signals are recorded simultaneously, at the same site in the skin of healthy individuals, using a combined laser Doppler and white light spectroscopy probe (Moor Instruments Ltd, UK). To investigate system flexibility we have made measurements at a skin temperature of 33oC and during local thermal warming to 43oC (maximal vasodilatation). Power spectral density (PSD) is evaluated within the frequency range (0.0095-1.6Hz) and PSD contribution calculated in the low frequency (LF) intervals corresponding to local endothelial (0.0095- 0.02Hz), sympathetic (0.02-0.06Hz) and myogenic activity 0.06-0.15Hz) and higher frequency (HF) intervals reflecting respiratory (0.15 -0.4Hz) and cardiac (0.4-1.6Hz) activity. A frequency coherence function is used to describe the linear relationship between BF and OXY signals in the frequency domain. The relationship between BF and OXY signals at 33oC was similar to that we have described previously in both the time and frequency domains [1]. During warming microvascular BF increased 15-fold (p <0.001). The increase in BF in the time domain was associated with an increase in total spectral power indicative of an increase in the amplitude of flow motion oscillations in the signal. In contrast, while microvascular oxygenation (OxyHb) increased 5-fold during warming there was little change in total spectral power. In both BF and OXY signals the relative contribution of the LF PSD components fell during warming, in part due to an increase in the contribution from the HF cardiac band. The LF:HF ratios at 33 and 43oC, respectively, were for BF 0.5:0.5 and 0.2:0.8 and for OxyHb 0.9:0.1 and 0.5:0.5 (both p<0.001). Frequency coherence between the LF bands in the BF and OXY signals was high; exceeding 70% in the endothelial band at 33oC. It was unaffected by warming. In order to explore changes in system flexibility the Lempel-Ziv complexity of the spectral properties of the signals was calculated as a measure of randomness of perfusion. There was a significant reduction in the intrinsic variability and complexity of the microvascular signals during thermally-induced vasodilatation, with a fall in mean LZ complexity of BF and OxyHb of 25% and 49%, respectively (p<0.001). Together these approaches demonstrate the relationship between the processes driving microvascular BF and oxygenation and the dissociation that may occur during perturbation of vascular homeostasis. They further show that in healthy individuals there is adaptability of flow motion which becomes less random during a vasodilator challenge. We conclude that simultaneous measurement of skin BF and oxygenation signals in combination with signal processing techniques offers an extended assessment of microvascular function which may eventually inform the clinical evaluation of compromised oxygen transport and tissue status.