  The local beat-to-beat local pulse pressure (PP) and blood pressure waveform
of arteries, especially central arteries, are important indicators of the
course of cardiovascular diseases (CVDs). Nevertheless, noninvasive measurement
of them remains a challenge in the clinic. This work presents a three-element
image-free ultrasound system with a low-computational method for real-time
measurement of local pulse wave velocity (PWV) and diameter waveforms, enabling
real-time and noninvasive continuous PP and blood pressure waveforms
measurement without calibration. The developed system has been well-validated
in vitro and in vivo. In in vitro cardiovascular phantom experiments, the
results demonstrated high accuracy in the measurement of PP (error < 3 mmHg)
and blood pressure waveform (root-mean-square-errors (RMSE) < 2 mmHg,
correlation coefficient (r) > textgreater 0.99). In subsequent human carotid
experiments, the system was compared with an arterial tonometer, which showed
excellent PP accuracy (mean absolute error (MAE) = 3.7 +- 3.4 mmHg) and
pressure waveform similarity (RMSE = 3.7 +- 1.6 mmHg, r = 0.98 +- 0.01).
Furthermore, comparative experiments with the volume clamp device demonstrated
the system's ability to accurately trace blood pressure changes (induced by
deep breathing) over a period of one minute, with the MAE of DBP, MAP, and SBP
within 5 +- 8 mmHg. The present results demonstrate the accuracy and
reliability of the developed system for continuous and noninvasive measurement
of arterial PP and blood pressure waveform measurements, with potential
applications in the diagnosis and prevention of CVDs.
