A noninvasive telemetric heart rate monitoring system based on phonocardiography

A reliable, noninvasive, biotelemetric heart rate monitoring system, causing minimal constraints to patients, for studies of heart rate variability, is described. Heart sounds arise from the activity of muscles, valves or blood flux in the heart. Piezoelectric transducers allow the detection on the human chest surface of the acoustic vibration produced by the mechanical action of the heart. As such, it is feasible to develop a small-size intelligent probe, with sensor, signal processing and telemetric capabilities, which is glued to the chest surface for heart rate monitoring. The concept of telemetric phonocardiography has some advantages over electrocardiography in heart rate monitoring, since it only requires a single probe, there are no wire connections and the patient does not need to carry an Holter. This new heart rate monitoring system relies on the identification of heart sound S1, the most prominent natural sound signal occurring during each cardiac cycle. The S1 detection is complicated by two factors: (i) wide variation in heart sounds' morphologies and rhythms, and (ii) noise from various sources may corrupt the phonocardiogram recording. These conditions imply the use of a heart sound probe self-adjustable to sound signal levels and selecting only heart sounds.