Brachial pressure waveforms: measuring and modelling

Abstract

Hypertension is a major risk factor of stroke, myocardial infarction, heart failure and organ damage. Although hypertension is currently defined based on the pressure measured in the brachial artery, a number of studies have shown that central aortic blood pressure is a better predictor of cardiovascular events. Central aortic pressure can only be measured invasively, which is undesirable for a patient. It is preferable to measure central blood pressure non-invasively with the same diagnostic efficacy since it is much simpler method that does not require as much expertise. Aortic pressure waveform, measured invasively in patients, is used as an input into nu- merical one-dimensional model of the arterial network to generate brachial pressure wave- forms. Modelled brachial pressure waveforms are compared with those measured invasively (with a pressure wire) and non-invasively (with a cuff-based device). An unpredicted os- cillatory behaviour of the pressure waveform in the brachial artery due to the occlusion of the artery during the cuff inflation is observed. Disagreement in systolic and diastolic pressures between invasive and non-invasive mea- surements led to a study of the propagation of the pressure waveform from the brachial artery through the soft tissue to the surface of the skin, where it is commonly measured. A simplified upper arm model (consisting of one artery and a bone surrounded by soft tissue) of the pressure propagation from the artery to the skin is built in the Comsol Multiphysics software using poroelastic theory to describe the material properties. The brachial pres- sure is approximated with a sinusoidal wave of varying frequency and used as an input in the upper arm model. The results of this model show small uctuations in the cuff pressure. Since our hypothesis that the pressure waveform is being damped when propagating through the soft tissue has not been confirmed, some ideas for model improvement are also presented.