Radar-based detection of thoracoabdominal asynchrony during breathing using autocorrelation function analysis

During periodic breathing motion, chest and abdomen do not necessarily move in a synchronous way. A large degree of asynchrony, which can be characterized by the value of the phase lag angle between the chest and the abdominal motion, indicates the presence of certain breathing disorders, such as bronchopulmonary dysplasia, certain neuromuscular diseases or an airway obstruction. In order to detect these abnormalities and decide on the course of treatment, it is necessary to determine the value of the phase lag. We propose to use a frequency shift keying radar-based sensor, which records the superposition of the reflected electromagnetic waves originating from the chest and the abdominal regions. Using an analytical model for the chest-abdomen motion, we have shown that the degree of thoracoabdominal asynchrony can be extracted by analyzing the changes in the features of the Fourier transform of the signal autocorrelation function, as the carrier frequency is varied. Our findings are corroborated by Matlab simulations.