Comparison of flow-sound relationship for different features of tracheal sound.

In recent years, respiratory flow estimation using tracheal sounds has received considerable attention. In this paper, four different features of tracheal sound are investigated and their relationships with flow at different target flow rates are examined during inspiration and expiration phases. The features include average power (AvgPwr), logarithm of the variance (LogVar), logarithm of the range (LogRng) and logarithm of the envelop (LogEnv) of tracheal sound. For each feature a linear model is fitted to the flow and the feature. The results show that LogVar is the best feature to describe flow-sound relationship with a linear model, while the slope of the linear model using AvgPwr shows the largest deviation from a line with changes in target flow rates. Also, the distance from origin of the linear model using any feature changes linearly with variations of target flow.