ABSTRACT
OBJECTIVE: Clinical acceptance of laser-Doppler perfusion monitoring (LDPM) of microcirculation suffers from lack of quantitatively reliable signal data, due to varying tissue constitution, temperature, hydration, etc. In this article, we show that a novel approach using physiological models for response upon provocations provides quantitatively and clinically relevant time constants. METHODS: We investigated this for two provocation protocols: postocclusive reactive hyperemia (PORH) and iontophoresis shots, measured with LDPM on extremities. PORH experiments were performed on patients with peripheral arterial occlusive disease (PAOD) or diabetes mellitus (DM), and on healthy controls. Iontophoresis experiments were performed on pre-eclamptic patients and healthy controls. We developed two dynamical physical models, both based on two characteristic time constants: for PORH, an "arterial" and a "capillary" time constant and, for iontophoresis, a "diffusion" and a "decay" time constant. RESULTS: For the different subject groups, we could extract time constants that could probably be related to physiological differences. For iontophoresis, a shot saturation constant was determined, with very different values for different groups and administered drugs. CONCLUSIONS: With these models, the dynamics of the provocations can be investigated and quantitative comparisons between experiments and subject groups become available. The models offer a quantifiable standard that is independent of the type of LDPM instrumentation.
