Individualizing the aorto-radial pressure transfer function: feasibility of a model-based approach

We fitted a three-segment transmission line model for the radial-carotid/ao rta pressure transfer function (TFF) in 31 controls and 30 patients with co ronary artery disease using noninvasively measured (tonometry) radial and c arotid artery pressures (P-car). Except for the distal reflection coefficie nt (0.85 +/- 0.21 in patients vs. 0.71 +/- 0.25 in controls; P < 0.05), mod el parameters were not different between patients or controls. Parameters w ere not related to blood pressure, age, or heart rate. We further assessed a point-to-point averaged TFF (TFFavg) as well as upper (TFFmax) and lower (TFFmin) enveloping TFF. Pulse pressure (PP) and augmentation index (AIx) w ere derived on original and reconstructed P-car (P-car,P-r). TFFavg yielded closest morphological agreement between P-car and P-car,P-r (root mean squ are = 4.3 +/- 2.3 mmHg), and TTFavg best predicted PP (41.5 +/- 11.8 vs. 41 .1 +/- 10.0 mmHg measured) and AIx (20.02 +/- 0.19 vs. 0.01 +/- 0.19). PP a nd AIx, calculated from P-car or P-car,P-r, were higher in patients than in controls, irrespectively of the TFF used. We conclude that 1) averaged TFF yield significant discrepancies between reconstructed and measured pressur e waveforms and subsequent derived AIx; and 2) different TFFs seem to prese rve the information in the pressure wave that discriminates between control s and patients.