Robust respiratory flow estimation using statistical properties of tracheal sounds

For any respiratory sound analysis or assessment, respiratory flow must also be measured simultaneously with the sounds. However, due to difficulties and/or inaccuracy of the most flow measurement techniques, several researchers have attempted to estimate flow from respiratory sounds. However, all of the proposed methods heavily depend on the availability of different rates of flow for calibration of the model, which makes their use limited by a large degree. In this paper, a robust and novel method for estimating flow using entropy of the band pass filtered tracheal sounds is proposed. The proposed method is independent of the flow rate chosen for calibration; it requires only one breath for calibration and can estimate any flow rate even out of the range of calibration flow. The method was tested on data of 10 healthy subjects at three different flow rates above 15 ml/s/kg. The estimation error was found to be 7.3 +/- 2.0% and 7.4 +/- 3.2% for inspiration and expiration phases, respectively.