Extraction of heartbeat signal from airflow at mouth by flow sensor

We previously proposed detecting both heartbeat and respiration signals from the airflow at the mouth by using a single catheter flow sensor [1]. This time, a rat under heavy anesthesia was used to evaluate the detection performance when extracting heartbeat signals from the airflow. A catheter flow sensor with an outer diameter of 1.8 mm was fabricated by micro-electro-mechanical systems technology, and it was directly inserted to the rat´s airway. The airflow signal caused by the heartbeat was clearly observed in the time interval between the signals caused by breathings with the lungs. The frequency components of the obtained airflow signal were analyzed by discrete Fourier transform, and a heartbeat spectrum of 3.56 Hz was identified. This value was coincident with that of the electrocardiogram graph. Finally, we successfully extracted the heartbeat signal from the airflow waveform measured in the rat´s airway by using the frequency spectrum.