Article

A robust method for estimating respiratory flow using tracheal sounds entropy

Dept. of Electr. Eng., Sharif Univ. of Technol., Tehran, Iran
IEEE Transactions on Biomedical Engineering (Impact Factor: 2.23). 05/2006; 53(4):662 - 668. DOI: 10.1109/TBME.2006.870231
Source: IEEE Xplore

ABSTRACT The relationship between respiratory sounds and flow is of great interest for researchers and physicians due to its diagnostic potentials. Due to difficulties and inaccuracy of most of the 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 calibrating 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 novel in terms of being 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. After removing the effects of heart sounds (which distort the low-frequency components of tracheal sounds) on the calculated entropy of the tracheal sounds, the performance of the method at different frequency ranges were investigated. Also, the performance of the proposed method was tested using 6 different segment sizes for entropy calculation and the best segment sizes during inspiration and expiration were found. The method was tested on data of 10 healthy subjects at five different flow rates. The overall estimation error was found to be 8.3 ± 2.8% and 9.6 ± 2.8% for inspiration and expiration phases, respectively.

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Available from: Azadeh Yadollahi, May 12, 2014
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    • "When calculating entropy of tracheal sound, the pdf of the signal in each segment is estimated using a kernel estimator, which is the most time consuming part of the flow-estimation process [8]. Although it was shown that the method proposed for estimating flow from tracheal sound entropy can be performed in real time, its computational cost was more than that of other methods based on the average power of tracheal sound [8]. "
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    ABSTRACT: Flow estimation from respiratory sounds, in particular tracheal sounds, has drawn much attention in recent years. This article briefly discusses previous studies that have been proposed for flow estimation. Recently, a method based on entropy was shown to have a superior performance compared to the other methods. The robustness of this entropy-based model in terms of its sensitivity to the changes of the tracheal sound signal's amplitude is presented here. Furthermore, with the aid of a new and simple technique to cancel the effect of heart sounds on the tracheal sound, the method was also able to estimate flow at very shallow breathing, which had not been done in previous studies. Flow variation effects the amplitude of tracheal sound. Therefore, the robustness of any flow estimation method to amplitude and the entropy method in particular is of interest
    IEEE Engineering in Medicine and Biology Magazine 02/2007; 26(1-26):56 - 61. DOI:10.1109/MEMB.2007.289122 · 26.30 Impact Factor
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    • "Then, using the method described in [9] [10] Shannon entropy was calculated in each window that represents the changes in the signal's pdf. The effect of heart sounds which is most evident in the frequency range below 200 Hz was removed by the method introduced in [9] [10]. Fig. 1 shows the calculated entropy and its corresponding flow signal for a typical subject. "
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    ABSTRACT: In this paper a new non-invasive method for apnea detection is proposed. Eight healthy subjects participated in this study. They were instructed to breathe very shallow with different periods of breath hold to simulate sleep apnea. Following our previous study in successful use of entropy for flow estimation, in this study the Otsu threshold was used to classify the calculated entropy into two classes of breathing and apnea. The results show that the method is capable of detecting the apnea periods even when the subjects breathe at very shallow flow rates. The overall lag and duration errors between the estimated and actual apnea periods were found to be 0.207+/-0.062 and 0.289+/-0.258 s, respectively. The results are encouraging for the use of the proposed method as a fast, easy and promising tool for apnea detection.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2006; 1:4623-6. DOI:10.1109/IEMBS.2006.260391
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    • "Airflow has been estimated using respiratory sounds by applying different models with training dataset required [6][7]. A relatively high estimation accuracy has been achieved in [7] but the predefined linear model applied does not support flow estimation for different types of TS other than normal TS. "
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    ABSTRACT: This paper addresses the problem of non-invasive respiratory rate (RR) monitoring using single channel tracheal sound (TS) recordings. We have recently developed a robust res-piratory phase segmentation method based on genetic algo-rithm (GA) which works well only for preprocessed clean TS. Therefore, an enhanced respiratory phase monitoring method is proposed in this paper by exploiting the signal re-dundancy to our existing method. In this context, appropriate overlapping windows have been applied to ensure sufficient redundancy of TS signals. The performance of the enhanced method is analyzed for different types of real TS and stan-dard preprocessed TS. The average accuracy of respiratory phase segmentation found for real TS is comparable to that of the standard preprocessed data by our proposed method.
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