Detection of the third heart sound using a tailored wavelet approach: method verification.

Heart sounds can be considered as mechanical fingerprints of myocardial function. The third heart sound normally occurs in children but disappears with maturation. The sound can also appear in patients with heart failure. The sound is characterised by its low-amplitude and low-frequency content, which makes it difficult to identify by the traditional use of the stethoscope. A wavelet-based method has recently been developed for detection of the third heart sound. This study investigated if the third heart sound could be identified in patients with heart failure using this detection method. The method was also compared with auscultation using conventional phonocardiography and with characterisation of the patients with echocardiography. In the first study, 87% of the third heart sounds were detected using the wavelet method, 12% were missed, and 6% were false positive. In study 2, the wavelet-detection method identified 87% of the patients using the third heart sound, and regular phonocardiography identified two (25%) of the subjects.

An improved bioacoustic method for monitoring of respiration.

Reliable monitoring of respiration plays an important role in a broad spectrum of applications. Today, there are several methods for monitoring respiration, but none of them has proved to be satisfactory in all respects. We have recently developed a bioacoustic method that can accurately time respiration from tracheal sounds. The aim of this study is to tailor this bioacoustic method for monitoring purposes by introducing dedicated signal processing. The method was developed on a material of ten patients and then tested in another ten patients treated in an intensive care unit. By studying the differences in the variation of the spectral content between the different phases of respiration, the described method can distinguish between inspiration and expiration and can extract respiration frequency, and respiration pause periods. The system detected 98% of the inspirations and 99% of the expirations. This method for respiration monitoring has the advantage of being simple, robust and the sensor does not need to be placed closed to the face. A commercial heart microphone was used and we anticipate that further improvement in performance can be achieved trough optimization of sensor design.

Detection of the third heart sound using a tailored wavelet approach.

The third heart sound is normally heard during auscultation of younger individuals but disappears with increasing age. However, this sound can appear in patients with heart failure and is thus of potential diagnostic use in these patients. Auscultation of the heart involves a high degree of subjectivity. Furthermore, the third heart sound has low amplitude and a low-frequency content compared with the first and second heart sounds, which makes it difficult for the human ear to detect this sound. It is our belief that it would be of great help to the physician to receive computer-based support through an intelligent stethoscope, to determine whether a third heart sound is present or not. A precise, accurate and low-cost instrument of this kind would potentially provide objective means for the detection of early heart failure, and could even be used in primary health care. In the first step, phonocardiograms from ten children, all known to have a third heart sound, were analysed, to provide knowledge about the sound features without interference from pathological sounds. Using this knowledge, a tailored wavelet analysis procedure was developed to identify the third heart sound automatically, a technique that was shown to be superior to Fourier transform techniques. In the second step, the method was applied to phonocardiograms from heart patients known to have heart failure. The features of the third heart sound in children and of that in patients were shown to be similar. This resulted in a method for the automatic detection of third heart sounds. The method was able to detect third heart sounds effectively (90%), with a low false detection rate (3.7%), which supports its clinical use. The detection rate was almost equal in both the children and patient groups. The method is therefore capable of detecting, not only distinct and clearly visible/audible third heart sounds found in children, but also third heart sounds in phonocardiograms from patients suffering from heart failure.

Some related aspects of platypus electroreception: temporal integration behaviour, electroreceptive thresholds and directionality of the bill acting as an antenna.

This paper focuses on how the electric field from the prey of the platypus is detected with respect to the questions of threshold determination and how the platypus might localize its prey. A new behaviour in response to electrical stimuli below the thresholds previously reported is presented. The platypus shows a voluntary exploratory behaviour that results from a temporal integration of a number of consecutive stimulus pulses. A theoretical analysis is given, which includes the threshold dependence on the number of receptors and temporal integration of consecutive stimuli pulses, the close relationships between electrical field decay across the bill, electroreceptive thresholds and directionality of the platypus bill acting as an antenna. It is shown that a lobe shape, similar to that which has been measured, can be obtained by combining responses in a specific way from receptors sensing the electric field decay across the bill. Two possible methods for such combinations are discussed and analysed with respect to measurements and observed behaviour of the platypus. A number of factors are described which need to be considered when electroreceptive thresholds are to be determined. It is shown that some information about the distance to the source is theoretically available from the pattern of field decay across the platypus's bill. The paper includes a comparative analysis of radar target tracking and platypus prey localization.