scholarly journals Introducing BisQ, A Bicoherence-Based Nonlinear Index to Explore the Heart Rhythm

2020 ◽  
Vol 25 (3) ◽  
pp. 45
Author(s):  
José Luis Hernández-Caceres ◽  
René Iván González-Fernández ◽  
Marlis Ontivero-Ortega ◽  
Guido Nolte
Keyword(s):  
Heart Rhythm ◽  
Preterm Neonates ◽  
Nonlinear Frequency ◽  
Bispectral Analysis ◽  
Quantification Analysis ◽  
Nonlinear Index ◽  
Cardiorespiratory Coupling ◽  
Cardiac Regulation ◽  
Frequency Coupling ◽  
Healthy Persons

Nonlinear frequency coupling is assessed with bispectral measures, such as bicoherence. In this study, BisQ, a new bicoherence-derived index, is proposed for assessing nonlinear processes in cardiac regulation. To find BisQ, 110 ten-minute ECG traces obtained from 55 participants were initially studied. Via bispectral analysis, a bicoherence matrix (BC) was obtained from each trace (0.06 to 1.8 Hz with a resolution of 0.01 Hz). Each frequency pair in BC was tested for correlation with the HRV recurrent quantification analysis (RQA) index Lmean, obtained from tachograms from the same ECG trace. BisQ is the result of adding BC values corresponding to the three frequency pairs exhibiting the highest correlation with Lmean. BisQ values were estimated for different groups of subjects: healthy persons, persons with arrhythmia, persons with epilepsy, and preterm neonates. ECG traces from persons with arrhythmia showed no significant differences in BisQ values respect to healthy persons, while persons with epilepsy and neonates showed higher BisQ values (p < 0.05; Mann-Whitney U-test). BisQ reflects nonlinear interactions at the level of sinus-and atrial-ventricular nodes, and most likely cardiorespiratory coupling as well. We expect that BisQ will allow for further exploration of cardiac nonlinear dynamics, complementing available HRV indices.

Some Effects of Piston Friction and Crank or Gudgeon Pin Offset on Crankshaft Torsional Vibration

2010 ◽  
Vol 54 (01) ◽  
pp. 41-52
Author(s):  
A. L. Guzzomi ◽  
D. C. Hesterman ◽  
B. J. Stone
Keyword(s):  
Natural Frequencies ◽  
Nonlinear Frequency ◽  
Significant Finding ◽  
Nonlinear Coupling ◽  
Frequency Content ◽  
Secondary Resonance ◽  
Single Cylinder Engine ◽  
Coupling Behavior ◽  
Frequency Coupling ◽  
Resonance Detection

The varying inertia associated with reciprocating mechanisms leads to nonlinear frequency coupling between rotational speed and an engine system's average torsional natural frequencies. This coupling can cause secondary resonance problems. Recent work by the authors has shown that piston-to-cylinder friction and gudgeon pin or crank offset can modify coupling behavior. These effects can be demonstrated by analysis of an engine's receptance function and through time simulations. This paper presents the derivation of a single-cylinder engine receptance in the presence of piston-to-cylinder friction. Simulations are then used to investigate some of the effects of piston-to-cylinder friction, offset, and excitation phase on the frequency content of the crankshaft velocity. Simulations indicate that nonlinear coupling is affected by these variables, which has implications for secondary resonance detection and prevention. The most significant finding is that stronger coupling behavior can occur when piston-to-cylinder lubrication breaks down.

The S-SH Confusion Test and the Effects of Frequency Lowering

2019 ◽  
Vol 62 (5) ◽  
pp. 1486-1505
Author(s):  
Joshua M. Alexander
Keyword(s):  
Cognitive Processing ◽  
Hearing Aids ◽  
Response Times ◽  
Nonlinear Frequency ◽  
Low Frequencies ◽  
Frequency Compression ◽  
Negative Side ◽  
Minimal Word ◽  
Low Pass ◽  
Negative Side Effects

PurposeFrequency lowering in hearing aids can cause listeners to perceive [s] as [ʃ]. The S-SH Confusion Test, which consists of 66 minimal word pairs spoken by 6 female talkers, was designed to help clinicians and researchers document these negative side effects. This study's purpose was to use this new test to evaluate the hypothesis that these confusions will increase to the extent that low frequencies are altered.MethodTwenty-one listeners with normal hearing were each tested on 7 conditions. Three were control conditions that were low-pass filtered at 3.3, 5.0, and 9.1 kHz. Four conditions were processed with nonlinear frequency compression (NFC): 2 had a 3.3-kHz maximum audible output frequency (MAOF), with a start frequency (SF) of 1.6 or 2.2 kHz; 2 had a 5.0-kHz MAOF, with an SF of 1.6 or 4.0 kHz. Listeners' responses were analyzed using concepts from signal detection theory. Response times were also collected as a measure of cognitive processing.ResultsOverall, [s] for [ʃ] confusions were minimal. As predicted, [ʃ] for [s] confusions increased for NFC conditions with a lower versus higher MAOF and with a lower versus higher SF. Response times for trials with correct [s] responses were shortest for the 9.1-kHz control and increased for the 5.0- and 3.3-kHz controls. NFC response times were also significantly longer as MAOF and SF decreased. The NFC condition with the highest MAOF and SF had statistically shorter response times than its control condition, indicating that, under some circumstances, NFC may ease cognitive processing.ConclusionsLarge differences in the S-SH Confusion Test across frequency-lowering conditions show that it can be used to document a major negative side effect associated with frequency lowering. Smaller but significant differences in response times for correct [s] trials indicate that NFC can help or hinder cognitive processing, depending on its settings.

Sign in / Sign up

Export Citation Format

Share Document