Detection of pulse and respiratory signals from the wrist using dry electrodes

A dry, tetrapolar electrode array was used to detect the differential impedance signal at the wrists of 11 adult human subjects. Experiments were conducted to determine the importance of potential-sensing electrode spacing to detect each wearer's pulse rate and respiratory rate. The current-injecting electrodes were at the sides of the wrist; the potential-sensing electrodes were on the volar wrist surface. The bandwidth-filtered root-mean-square amplitudes of the pulse and respiratory components were computed and found to increase with increasing electrode spacing. Optimum spacings were slightly different for the pulse and respiration and were slightly different in the male and female subjects. A spacing for the potential electrodes of about 60% of the wrist hemicircumference is a good compromise for detecting respiration and pulse.