Tissue motion--a disturbance in the laser-Doppler blood flow signal?

The tissue matrix in the human body is continuously in motion driven by forces generated by the circulatory and respiratory systems. The linear velocities recorded can be as high as 300 microm/s. The question raised: is the motion of tissue matrix generating an error signal in laser-Doppler (LD) recordings that is misinterpreted as solely a blood flow signal. The problem is studied by using a physical model demonstrating the contribution from a flow channel and, in addition, from a linear motion of the flow tube. Measurements of skin motion in the forearm have been performed. The corresponding spectra have been compared with blood flow spectra recorded with the LD method at the same sites. The two types of spectra overlap each other indicating that motion induced signals can be interpreted as a flow signal. The "blood flow" contribution from tissue motion varies strongly with the site studied.