Jari Miettinen

Use of EMFi as a blood pressure pulse transducer

This paper describes and tests two prototype series of pressure transducer arrays based on electromechanical film (EMFi). By offering high (/spl sim/T/spl Omega/) resistance, EMFi is an excellent material for low-current long-term measurement applications. About 50 transducer arrays were designed and tested using different configurations and electrode materials to sense low-frequency pressure pulsations on the radial artery in the wrist. Essential requirements included an adequate linear response in the desired temperature range and uniform quality. Transducer sensitivity was tested as a function of temperature in the range of 25/spl deg/C-45/spl deg/C at varying dc and ac pressures. The average sensitivity of the EMFi used in the transducers proved adequate (/spl sim/2.2mV/mmHg and /spl sim/7 mV/mmHg for normal and high-sensitive films) for the intended purpose. Moreover, EMFis spectral response covered the required range for biomedical applications, but it was unable to measure static pressure (f/sub 3 dB//spl ap/38 /spl mu/Hz). The sensitivity of the EMFi material was sufficiently constant for measuring blood pressure pulses in the desired range (0-300 mmHg), and the best achieved deviation in sensitivity was /spl plusmn/5.1%. It was also established that in addition to sensitivity and its standard deviation, crosstalk between electrode elements also depends strongly on electrode thickness.

Arterial pulse shape measurement using self-mixing inteferometry

This paper investigates the correlation between the shape of the first derivative of a blood pressure pulse and the corresponding Doppler spectrogram, reconstructed from a Doppler signal produced by the movement of the skin above the radial artery in the human wrist. The aim is to study to what extent the arterial pulse shape can be measured using self-mixing interferometry. To obtain a point of reference, a commercial non-invasive blood pressure monitor was first used to measure both blood pressure and pulse shape. Then, a self-mixing interferometer was applied to measure the arterial pulse above the radial artery. Measurements on 10 volunteers yielded a total of 738 pulses for analysis. A cross correlation of 0.84 ± 0.05 was established between the shape of the first derivative of the pressure pulse and the Doppler spectrogram. Using an empirical constant of 0.7 as a limit for successfully detected pulses produced a detection accuracy of 95.7%. The results show that self-mixing interferometry lends itself to the measurement of the arterial pulse shape, and that the thus obtained shape is in good agreement with that produced by a commercial blood pressure monitor.