A Novel Noninvasive Measurement Technique for Analyzing the Pressure Pulse Waveform of the Radial Artery

Previous noninvasive measurements of the pulse waveform of the radial artery have not employed standard positioning procedures. Here, we propose a new noninvasive measuring apparatus that has a two-axis mechanism and employs a standard positioning procedure for detecting the optimal site for accurately measuring the pressure pulse waveform (PPW). A modified sensor was designed to simultaneously measure the arterial diameter changed waveform (ADCW) and PPW. Considering the artery as a cylinder, the measured waveform would be distorted if the sensor were not at the middle of arterial width. Moreover, a blood vessel is elastic, and its compliance changes with the transmural pressure, being maximal when the transmural pressure is equal to zero. The sensor should detect the PPW with the lowest possible distortion and, hence, an analysis of the vascular geometry and an arterial model were used to design a standard positioning procedure based on the ADCW for the $X$ and $Z$ axes. In order to verify the resolution of the $X$ axis scanning procedure, the echo method was used to measure the radial artery outer diameter in ten healthy subjects. The difference between the scanning width and the actual arterial diameter was 0.36 $\pm$ 0.23 mm $({\rm mean}\pm{\rm SD})$. Finally, the PPW as measured at the optimal position was used to diagnose myocardial ischemia symptoms in 60 elderly subjects whose chief complaint was chest pain, with the exercise electrocardiogram being used as a reference to compare between individuals with and without myocardial ischemia. The PPW analysis used the harmonic components in the frequency domain. We found that the fourth harmonic of the Fourier series differed significantly between the groups $(p=0.0039)$, which is consistent with previous studies. The results indicate that our noninvasive measurement apparatus is very suitable for analyzing the PPW of the radial artery.