![]() For the smaller bandwidths, it is possible that only one of the observers would consistently underestimate this value. ![]() 6 would consistently result in an underestimation of DBP for both observers. The largest bandwidth of 100 Hz represented in Fig. We can see that it is likely that each observer would measure different DBP. However, by using these results as reference, we can notice the effect that different observers have on the interpretations of auscultation measurements. II B, our experimental conditions are different from this type of test. Their results were obtained from a discrimination test in which the intensity of a narrowband test noise was adjusted to be barely discernible in the presence of a masking noise of the same narrowband and fixed intensity. The DL from Bos and de Boer were included in Figs. This allowed for better consistency in the results as the effect was similar to having the observer listen to each for the first time. ![]() These occasions were spaced by several days and up to a few weeks while the computational algorithm was developed and improved, and the recordings were listened to in a different order than was used during the previous occasion. A single observer was responsible for this classification, and this decision to use a single observer is backed for the following reasons: the observer was trained by medical experts in the practice of BP measurement and KS identification and had two years of experience in identifying KSs with acoustic and electronic stethoscopes at the time that the measurements were collected, which is deemed sufficient in a clinical aspect in terms of KS classification, the conditions of the experiment and materials used greatly facilitate this procedure, given that the measurements are free of external sound artifact and use of an electronic stethoscope allows the user to adjust filters and volume levels to better perform this task and, finally, the KS identification procedure was repeated on three separate occasions for each measurement. It was set under the same principles as the volume used during data collection where most of the fainter sounds at the diastolic end were perceptible, yet, the louder sounds were not uncomfortable to hear. It is anticipated that this approach could have profound effects on future development of automated auscultation BP measurements.Īll of the files were listened to with the same set of headphones, and the playback volume was the same for all of the measurements. Comparing these ratios to difference limen in the psychoacoustic masking literature, an approximate threshold for sound audibility is obtained. By time-segmenting the recorded sound around Korotkoff peaks into a test segment and a masking segment, performing Fourier transforms on the segments, and comparing frequency-band sound energy levels, signal-to-noise ratios of a sound to its masking counterpart can be defined. KSs are collected during auscultation with an electronic stethoscope, which allows simultaneously observing sound audibility and recording the sound electronically. Here, during manual auscultation of BP, a direct comparison is made between what an observer perceives as audible and the electronic analysis of audibility level determined from masking of sound signal levels. ![]() While absolute sound level audibility is well researched, the problem has not been approached from the point of view of psychoacoustic masking of the sounds. Critical to determining BP levels via auscultation is the determination of KS audibility. Measurement of blood pressure (BP) through manual auscultation and the observation of Korotkoff sounds (KSs) remains the gold standard in BP methodology.
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