1. Conclusion(2)  Different data were involved in each study, as present in table 1.  Hard to determining the most successful technique.  PSD were used to compared filtered data with original lung sound within and outside heart sound region is most useful [14], [21], [25], [29], [32], [35].  Strict qualitative was achieved in only one study[25] by a panel unbiased researchers listen before and after reduction, and fill out a questionnaires.

2. Conclusion(3)  Indeed, all studies were based on data that had been in acquired under ideal conditions, such as a quiet environment, and also in know cardiac and respiratory state, with most subjects being healthy.  In addition, heart sound cancellation studies did not account for heart sounds other than first and second sounds.

3. Conclusion(4)  The potential useful of any method for filtering heart sound from lung sound rests on its ability to perform clinical setting.  Future study need to focus on challenging the performance of techniques in data recording that are appropriate to clinical application in terms of environment and respiratory cardiac illness.

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