Arterial pulse wave velocity measurement: different techniques, similar results--implications for medical devices

Different characteristic points used for the evaluation of pulse wave velocity (PWV) give significantly different results. Hence, the accuracy of using these points is questionable. There is need for quantitative comparison of different techniques to determine PWV. Previous studies aimed at comparing different PWV measurement techniques have been noted, however, on a limited number of smaller animals (mice, dogs, etc.). This simulation-based study aims to compare different techniques for PWV measurement in a large representative human population. A computer model is developed for simulating the pressure wave propagation between the carotid and femoral arteries. Using relationships observed in clinical trials, the model input parameters for a statistically representative population are expressed in terms of a person's age, gender and height. The model is used to calculate the carotid-femoral pressure ratio for different individuals, which is then parameterised into a number of features, and the equivalent propagation time is calculated using the phase-slope method. Using this time, the apparent phase velocity is determined and compared with PWV determined by the foot-to-foot technique. The two velocities compare well with a difference of 0.0059±0.0904 m/s. An averaging criterion for the calculation of apparent phase velocity has been tested and shown to give good estimates compared to the foot-to-foot technique. As it does not involve the identification of characteristic points on the measured pressure waves, the phase-slope method is more suitable for implementation in PWV monitors.

Non-invasive model-based estimation of aortic pulse pressure using suprasystolic brachial pressure waveforms

Elevated central arterial (aortic) blood pressure is related to increased risk of cardiovascular disease. Methods of non-invasively estimating this pressure would therefore be helpful in clinical practice. To achieve this goal, a physics-based model is derived to correlate the arterial pressure under a suprasystolic upper-arm cuff to the aortic pressure. The model assumptions are particularly applicable to the measurement method and result in a time-domain relation with two parameters, namely, the wave propagation transit time and the reflection coefficient at the cuff. Central pressures estimated by the model were derived from completely automatic, non-invasive measurement of brachial blood pressure and suprasystolic waveform and were compared to simultaneous invasive catheter measurements in 16 subjects. Systolic blood pressure agreement, mean (standard deviation) of difference was -1 (7)mmHg. Diastolic blood pressure agreement was 4 (4)mmHg. Correlation between estimated and actual central waveforms was greater than 90%. Individualization of model parameters did not significantly improve systolic and diastolic pressure agreement, but increased waveform correlation. Further research is necessary to confirm that more accurate brachial pressure measurement improves central pressure estimation.