The measurement of blood pressure without contact: An LDV-based technique

This work is aiming to demonstrate the possibility to assess arterial blood pressure without the need to put any element in physical contact with the subject (except for the signal calibration). The authors have developed a measurement technique for the non contact measurement of blood pressure (BP) as manifest in the carotid artery, based on the use of a laser Doppler vibrometer (LDV). The LDV produces a signal that can be related to the continuous pressure pulse waveform. As such, the signal supports the calculation of some physiologically important time intervals. In this paper, we provide a comparison with the pressure waveform recorded using conventional applanation tonometry: the waveform has an analogous shape and, overall, provides the same characteristics in the time axis. More in details, results show that the systolic blood pressure have a mean deviation of 8% with respect to the reference value (obtained from tonometric data). Fundamental aspects to be considered are the precise laser pointing perpendicularly to the measurement site (to optimize the signal-to-noise ratio), the measurement conditions (e.g. the subject has to remain as still as possible) and also the reflective properties of the subject's skin, which can be improved by applying a proper reflective lotion or tape. The major factors contributing to uncertainty of the LDV measures have been evaluated, in order to identify ways to enhance performance. The current uncertainty value of 15% is not negligible, but does not greatly exceed that of the standard BP measuring devices.