Identification of the dynamic component of the finger arterial pressure-volume relationship

Abstract

Similar to most biological tissues, the arterial wall has both elastic and viscous properties. This is the reason why recordings of the pressure-volume (P-P) characteristics show a shape of hysteresis loops and are different for static and dynamic measurements. The exact model of the viscoelastic P-V relationship would be complicated, containing several sections with potentially nonlinear properties. The volume changes, in the simplest arrangement, can be viewed as a sum of fast and slower components. We propose a method to identify the fast (dynamic) component of the nonlinear P-V relationship. Continuous finger blood pressure is measured by applying the Finapres monitor, while volume pulses at a controlled cuff pressure are recorded by the transmittance mode photoplethysmograph. The nonlinear relationship is modelled by five parameters. The identification is based on the fitting of parameters of the P-V relationship to obtain maximum similarity between the filtered waveforms of the modelled and measured volume signals. The method was tested on 9 normal subjects. The results show that the applied algorithm can be used even in case of remarkable viscous creep effects.