In vitro evaluation of a laser Doppler flowmetry implantable fibre system: the effect of flow velocity and concentration on perfusion assessment.

The utility of laser Doppler flowmetry (LDF) is limited by the requirement for placement of the LDF probe directly on the bone surface. A system of implantable and detachable fibres was developed so that repeated non-anaesthetized measurements could be made. Using a specially designed flow chamber and a flow medium of latex particles, we compared the in vitro properties of the implantable fibre and the standard probe, by determining the effect of flow velocity and concentration on perfusion assessment. For both probes, the LDF output increased in response to increasing flow velocities and concentrations of the flow medium. With increasing velocities of the flow medium, both probes responded similarly when assessing perfusion through cortical bone, but differed when measuring flow through cancellous bone. A difference between the probes also existed when determining the effect of concentration on perfusion assessment. With increasing concentrations of the latex particles, the rate of LDF output increased more rapidly when perfusion was measured end on to the direction of flow by the standard probe, compared to the implantable fibre. This situation was reversed when assessing perfusion tangential to the direction of flow. The differences in the properties of the two probe systems are related to the direction of flow assessment and the type of bone through which flow was measured. These factors should be considered when measuring blood flow with either the LDF implantable fibre system or the standard LDF probe.