Feasibility of Accelerometer-Based Arterial Pulse Measurement: Part II—Experimental Investigation

This study, the second of two parts, experimentally investigates accelerometer (ACC)-based arterial pulse measurement in comparison with tactile-based measurement. Two ACCs, one digital and one analog, were used to measure radial, lateral, and axial arterial wall motions at the carotid artery (CA) in a total of ten subjects. Subsequently, both the analog ACC and a tactile sensor were used to conduct measurements sequentially at the CA of another three subjects. A single-degree-of-freedom time-frequency (SDOF-TF) method was applied to the measured acceleration signals to remove motion artifacts (MA) and sensor noise; reconstruct the pulse waveform in the acceleration domain, APWa, and displacement domain, as well as APW; and extract arterial indices. The same method was applied to the displacement signals measured by the tactile sensor. The results reveal that the analog ACC acquires higher-quality pulse signals than the digital ACC. Radial wall motion measured by the ACC corresponds well with the pulse signal measured by the tactile sensor, whereas axial wall motion presents substantial practical challenges for reliable measurement for cardiovascular (CV) assessment. Compared with tactile-based measurements, ACC-based measurements present two practical challenges: (1) achieving firm sensor fixation and (2) the acceleration-sensing nature of the ACC, which permits extraction of only APWa and its associated arterial indices, rather than APW. They also exhibit two fundamental differences: (1) as theoretically identified in Part I, acceleration sensing introduces an additional term into the instantaneous frequency (IF) of individual arterial pulse harmonics, thereby affecting both the IF-based arterial indices and the frequency spectrum of the IF; and (2) variations in the tissue-contact sensor (TCS) stacks contribute to substantial differences in the normalized harmonic amplitude distributions between ACC-based and tactile-based measurements. Overall, ACC-based measurement provides a simple approach for CV assessment; however, tactile-based measurement remains necessary for reliable acquisition of arterial pulse signals and accurate CV indices.