Respiratory Rate And Rhythm Extraction From PPG Signal

Respiratory rate and respiratory rhythm(inspiratory phase and expiratory phase) are important rehabilitation clinical data. Respiratory rate and respiratory rhythm feedback timely can monitor respiratory status and guide in the respiratory rehabilitation training. Now, the common respiratory monitor technologies are based on respiratory airflow and impedance. However, the disadvantages of both feedback technologies are the high cost, monitoring discomfort patient and wearing inconveniently. Photoplethysmography(PPG) is a widely clinical used non-invasive monitoring technology, using the convenient and comfortable way feed signal back. PPG probe emits light through human tissue, the signal changes not only contains heart rate and blood oxygen information, further comprising blood volume change with respiration control, therefore respiratory information can be extracted from the PPG signal.In this paper, the acquisition circuit meets the needs of respiratory information extraction for respiratory rehabilitation training, in a manner that contains respiratory frequency and stably to do the PPG signal acquisition. To save PPG data and respiratory extraction, design software for PPG signal acquisition and respiration feedback was designed and implemented. The functions of software are respiratory waveform extraction, respiratory rhythm extraction, information saving and waveform display.In this paper, respiratory rate and respiratory rhythm extraction has been processed. When being respiratory rate extraction, using mother wavelet selection with similarity comparing original signal to improve the accuracy of the respiration rate estimates from PPG signal. When being respiratory rhythm extraction, using respiratory effect in PPG signal including respiratory-induced frequency variation(RIFV), respiratory-induced intensity variation(RIIV) and respiratory-induced amplitude variation(RIAV) to extract respiratory rhythm. This paper proposed an evaluation method of ratio between the same rhythm distribution and the reference time breathing rhythm distribution; this method was used for evaluation of respiratory rhythm.Error analysis results describe that the method of using the similarity comparing raw signal to mixed mother wavelet selection for respiratory rate estimation achieved the lowest error. This paper proposed an evaluation method to estimate the respiratory rhythm error analysis, the evaluation results described that direct average method and respiratory rhythm-based RIIV obtain the lowest error value. Innovations in this paper is using the similarity comparing raw signal to mixed mother wavelet selection for respiratory rate estimation, respiratory waveform extraction from PPG signal with mixing mother wavelet selection method closed to gold standard waveform, this method improved respiratory rate accuracy; this paper also proposed a new evaluation method of respiratory rhythm, proposed an evaluation method of ratio between the same rhythm distribution and the reference time breathing rhythm distribution. This method evaluated the accuracy of respiratory rhythm(expiratory and inspiratory phase) in an acceptable manner.