Heartbeat Signal Detection From Analysis of Airflow in Rat Airway Under Different Depths of Anaesthesia Conditions

We inserted a tubular flow sensor incorporating micro-electro-mechanical systems technologies directly into the rat airway and analyzed the airflow waveforms obtained under different depths of anaesthesia conditions by using discrete Fourier transformation (DFT) to evaluate the heartbeat frequency. The electrocardiogram (ECG) signal was used as the reference heartbeat frequency. The calibration curve of the flow sensor used to measure the oscillating airflow in the rat airway was determined on the basis of King's law. The airflow waveform at the rat airway caused by only the heartbeat was measured by applying deep anaesthesia; the waveform frequency coincided with the simultaneously measured ECG signal frequency. DFT analysis of the airflow signals measured under deep and shallow anaesthesia conditions verified the fundamental heartbeat frequency values. The airflow components related to heartbeat motion were successfully extracted by using the heartbeat frequency spectrum. The respiration and heartbeat signals were thus successfully detected.