Personalization of the Oscillometric Blood-Pressure Measurement

Oscillometric blood-pressure (BP) measurement can result in substantial error depending on the physiological parameters of the tested person. Especially the rigidity of the arteries can influence the oscillometric amplitudes. Personalization can greatly improve the accuracy and reproducibility of the measurement. The personalization process requires several measurements taken from a person applying special cuff pressure (CP)-time functions. A BP measuring device was developed to generate different CP-time functions. It is able to sustain the CP at a constant value during both inflation and deflation. The device also measures ECG in Einthoven I lead and photoplethysmographic (PPG) signal at the fingertip. This makes possible to calculate the pulse wave transit time (PWTT). The sampling frequency is 1 ksample/s thus PWTT values are calculated with 1 ms resolution. Recordings were taken from ten healthy subjects, both senior and young ones. The deflation was stopped and the CP was held constant at 90 mmHg and then at 60 mmHg for 60 s each. The subjects were at rest. Pulse wave transit times were determined from the heart to the cuff (PWTTHC) and to the fingertip (PWTTHF). Mean value as well as the trend of change of PWTTHC and PWTTHF over the 60 s intervals with constant CP are person specific, not age-group specific. The change in PPG signal amplitude resulting from cuff occlusion was found to be substantially smaller for senior than for young persons. As a result of the personalization it is possible to define a specific CP-time function providing information not only on actual BP but also on the rigidity of the brachial artery. The recordings taken with constant CP parts help also compensate the effect of breathing.