Continuous monitoring of arterial blood pressure (ABP) can provide vital information on the cardiovascular system in clinical practice and research. To achieve this, methods have been developed to determine ABP continuously and noninvasively, including the wrist volume clamp method, which uses reflection-mode photoplethysmography (PPG) to indicate the volume change of the radial artery. However, this kind of indication is reportedly not accurate enough, and an in-vivo test for its accuracy is still lacking. Our aim was to fix this gap.
As ultrasound can detect the arterial diameter accurately; we have developed a sensor comprised a PPG sensor and an ultrasound transducer, which can collect reflection-mode PPG and A-mode ultrasound signals, simultaneously. Tests on 15 volunteers were conducted under the similar conditions of using wrist volume clamp method for a comparison between the PPG signal and the radial arterial diameter.
It was observed that there were obvious differences between the shapes of these two signals, mainly between their drifting trend parts, with the pulsatile components of the signals matching very well. The mean root mean square value of the differences of the trend parts (0.287±0.072) was found to be much larger than that of the pulsatile parts (0.107±0.028).
The results indicated that using PPG signal as a reference for ABP measurement at the wrist region might not be accurate enough, and ultrasound has the potential for replacing it in the wrist volume clamp method for more accurate ABP determination.