Use of a Chebyshev filter as an inverse transfer function for derivation of central from the prepheral pressure

A transfer function based on Chebyshev filter design techniques was used to estimate aortic pressure from the radial pressure waveform. An equation was derived with the filter ripple factor as a function of age, height, weight and heart period. Parameters were estimated from invasive aortic and radial pressure recorded in 51 subjects and the model tested in 21 subjects (age range 38-84 years). The correlation coefficient between measured and estimated aortic pressure was > 0.95 and the maximum average error was 4.4% (for pulse pressure). These findings show that the transfer function can be expressed analytically with filter coefficients and that the ripple factor of the Chebyshev filter can be modified to account for the individual subject parameters to give an accurate estimate of central aortic pressure from the radial pulse.