Comparison of recurrence plot features of swallowing and breath sounds

Dysphagia Screening: Contributions of Cervical Auscultation Signals and Modern Signal-Processing Techniques

“…Studies that record data from a location inferior to the thyroid cartilage are far more plentiful. Some experiments have placed their transducer at the suprasternal notch [31], [42]–[44], but the majority of researchers record from the skin overlying the cricoid cartilage or immediate area [17], [20], [21], [27], [40], [41], [45]–[52]. The cricoid cartilage is an intuitive and logical recording location given that the anatomical structures present at this level are active during swallowing.…”

“…Unfortunately, these studies have been unable to determine the lower bound on useful frequency components, resulting in much more variability of the placement of the lower notch. While some place it as low as 0.1 Hz in order to maintain a “pure” signal [21], [49], [51], [65], [66], [83], [86], [90], others place it as high as 30 Hz or more in order to eliminate motion artifacts and other low frequency noise [39], [42], [44], [60]–[62], [69]. Since similar bandlimits have yet to be identified for swallowing sounds, studies which use a microphone simply limit the recorded signal to either the human audible range [21], [32], [33], [37], [40], [46], [48], [67], [76]–[78], [86], [89], [95], [97]–[100], [102], [103], [110], [112]–[116] or the range of common stethoscopes used in bedside assessments [13], [22], [28], [39], [56], [69], [73], [88], [91], [92].…”

“…The hermite projection method, which decomposes the signal into hermite polynomials, shares clear similarities to the wavelet transform method, but does not have the same popularity in this field [79]. In addition, swallowing signals have been investigated using a phase space transformation [42], [62], [73], [121]. By applying the method of delays, it is possible to map the time domain swallowing signal onto a multi-dimensional phase portrait and generate a recurrence plot as shown in Figure 6 [42], [62], [73], [121].…”

“…In addition, swallowing signals have been investigated using a phase space transformation [42], [62], [73], [121]. By applying the method of delays, it is possible to map the time domain swallowing signal onto a multi-dimensional phase portrait and generate a recurrence plot as shown in Figure 6 [42], [62], [73], [121]. This plot can be used to analyze the trends and periodic nature of a given signal as it tracks every time the phase portrait overlaps itself.…”

Non-linear recurrent analysis of the behavior of a complex technological object

“…The work [8] is devoted to a fundamental study of the processes, which in nature is characterized by vividly expressed recurrent behavior, such as periodicity or irregular recurrence. Recurrence (repeatability) of states in the sense of following the subsequent trajectory close enough to the previous one is the property of dissipative dynamical systems [9].…”