Detection of inspiratory efforts by complex demodulation of pulse transit time in children

It has been recently demonstrated that the pulse transit time (PTT) variation between inspiration and expiration is a sensitive descriptor of inspiratory effort in healthy awake children and in standardize condition. Aim of this study was to automatically extract the amplitude variations of PTT at the respiration frequency by implementing a complex demodulation algorithm. Inspiratory effort was simulated by a custom designed nasal and mouth two-way non rebreathing face mask (Series 7910-Hans Rudolph Inc, Kansas City, Missouri-USA), with reduced inhalation valve port diameter (3, 5 and 8 mm). After the calculus of PTT, a complex demodulation algorithm has been used to extract its amplitude fluctuations. Results obtained from 5 children, who attended the pediatric service for routine assessment and without active nocturnal and diurnal respiratory symptoms and chronic cardiorespiratory diseases, show that the higher the inhalation valve port diameter, the smaller the PTT amplitude fluctuations.