Respiration signal extraction from photoplethysmogram using pulse wave amplitude variation

Respiratory information is usually measured directly with chest and abdominal belt or from the nasal airflow. There are several methods to extract respiration also from the electrocardiogram (ECG) and photoplethysmogram (PPG). In this paper we propose a methodology that detects the amplitude changes in the PPG signal to estimate the respiration rate. During exhalation, our parasympathetic nervous system makes the blood vessels more flexible than during inhalation. Blood vessels flexibility affects the propagation velocity of the pulse wave. In that way respiration also modulates the amplitude of the pulse wave signal. Comparing with other respiration signal extraction techniques our method has excellent results with limited processing power. The long-term objective of this work is to use the respiration signal together with heart rate and blood oxygen saturation level (SpO2), that are extracted from the pulse wave, for sleep apnea detection and screening purposes.