Evaluation of the non-invasive determination of arterial compliance with the Goldwyn-Watt model by a transmission line model study

The Goldwyn-Watt model is a 4-element lumped parameter model for the vascular system used in order to estimate total arterial compliance non-invasively from a peripherally measured arterial pressure wave. We aim to evaluate the method's stability by making use of a distributed transmission line model, simulating different haemodynamic conditions. A mathematical transmission line model is used to compute the arterial pressure wave 44 cm downstream from the heart (brachial artery) at 55, 65 and 75 beats/minute, and at four levels of arterial compliance (0.86 to 3.45 ml/mm Hg), covering the physiological and pathological range. The Goldwyn-Watt model was used to derive the model parameters (compliance C₁ and C₂ and inertance L) from the computed pressure waves. We found the model parameters C₁, C₂ and L to vary with both heart rate and compliance level. The estimated total compliance differed more from the exactly known value with increasing heart rate and compliance level. We showed that C₂ cannot be interpreted as the compliance of some distal part of the circulation. We conclude that the application of the Goldwyn-Watt model for the estimation of cardiovascular parameters from peripheral wave contour analysis is sensitive to the heart rate and the actual compliance of the arteries. The physical interpretation of C₂ and L especially is not straightforward, and consequently neither is its diagnostic value.