Unconstrained and noninvasive measurement of heartbeat and respiration using an acoustic sensor enclosed in an air pillow

One of the authors previously developed an unconstrained and noninvasive measurement system of heartbeat and respiration using an acoustic sensor enclosed in an air pillow or air mat. The system measured instantaneous heartbeat and respiration periods by applying Kalman filters and maximum likelihood method to the dynamic models of the heartbeat and respiration signals extracted from the sensor output. To improve the measurement accuracy, this paper proposes a more stable and accurate measurement system of heartbeat and respiration taking into account not only the harmonic component of the heartbeat, but also the sinusoidal component of the frequency of the sum of the fundamental mode frequencies of the heartbeat and respiration signals.