Wavelet phase coherence analysis: Application to skin temperature and blood flow

The technique of wavelet phase coherence analysis is introduced and used to explore relationships between oscillations on blood flow and temperature in the skin of 10 healthy subjects. Their skin temperature and blood flow were continuously recorded: under basal conditions for 30 minutes; during local cooling of the skin with an ice-pack for 20 minutes: and 30 minutes thereafter. The group mean basal skin temperature of 33.4C was decreased to 29.2C during the cooling period, and had recovered to 32.1C by the end of the recording. The wavelet transform was used to obtain the time-frequency content of the two signals, and their coherence. It is shown that cooling increases coherence to a statistically significant extent in two frequency intervals, around 0.007 and 0.1 Hz, suggesting that these oscillatory components are involved in the regulation of skin temperature when cold is applied as a stress.