Principal Investigator Hae-Seung (Harry) Lee
Co-investigator Charles Sodini
An arterial blood pressure (ABP) waveform provides valuable information for understanding cardiovascular diseases. The ABP waveform is usually obtained through an arterial line in an intensive care unit (ICU). Although considered the gold standard, this method brings the disadvantage of its invasive nature. Noninvasive methods based on vascular unloading, such as Finapres, are not suitable for prolonged monitoring due to their obstructive nature. Therefore, reliable non-invasive ABP waveform estimation has long been desired by medical communities. Medical ultrasound is an attractive imaging modality because it is inexpen- sive, free of ionizing radiation, and suitable for portable system implementation.
The proposed ultrasonic ABP waveform monitoring is achieved by observing the pulsatile changes of the cross-sectional area and identifying the elastic property of the arterial vessel, represented by the pulse wave velocity (PWV; the propagation speed of a pressure wave along an arterial tree) with a diastolic blood pressure measurement as a baseline. The PWV can be estimated by obtaining a flow-area plot and then measuring the slope of an initial linear region in the flow-area plot during a reflection-free period (e.g. the early systolic stage).
A prototype ultrasound device was designed to conduct application-specific ultrasonography in a portable form factor. The first human subject validation shows the agreement between this method on the common carotid artery and the ABP waveform obtained at a middle finger using the vascular unloading method. Motion-tolerant ultrasonography is explored to improve the measurement stability from the first design for long term monitoring. The second human subject study in a transient stress situation demonstrates the proof-of-concept of this method for the stress testing. Currently, the human subject study to compare the A-line with this method in collaboration with Boston Medical Center is in progress.