Time-frequency coherence analysis of nonstationary random processes

2002 ◽  
Author(s):  
G. Matz ◽  
F. Hlawatsch
Keyword(s):  
Random Processes ◽  
Coherence Analysis ◽  
Time Frequency ◽  
Frequency Coherence

scholarly journals Cardiopulmonary coupling indices to assess weaning readiness from mechanical ventilation

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Pablo Armañac-Julián ◽  
David Hernando ◽  
Jesús Lázaro ◽  
Candelaria de Haro ◽  
Rudys Magrans ◽  
...  
Keyword(s):  
Heart Rate ◽  
Mechanical Ventilation ◽  
Spontaneous Breathing Trial ◽  
Sinus Arrhythmia ◽  
Time Frequency ◽  
Cardiopulmonary Coupling ◽  
Cardiac Pumping ◽  
Successful Weaning ◽  
Frequency Coherence ◽  
Subspace Projections

AbstractThe ideal moment to withdraw respiratory supply of patients under Mechanical Ventilation at Intensive Care Units (ICU), is not easy to be determined for clinicians. Although the Spontaneous Breathing Trial (SBT) provides a measure of the patients’ readiness, there is still around 15–20% of predictive failure rate. This work is a proof of concept focused on adding new value to the prediction of the weaning outcome. Heart Rate Variability (HRV) and Cardiopulmonary Coupling (CPC) methods are evaluated as new complementary estimates to assess weaning readiness. The CPC is related to how the mechanisms regulating respiration and cardiac pumping are working simultaneously, and it is defined from HRV in combination with respiratory information. Three different techniques are used to estimate the CPC, including Time-Frequency Coherence, Dynamic Mutual Information and Orthogonal Subspace Projections. The cohort study includes 22 patients in pressure support ventilation, ready to undergo the SBT, analysed in the 24 h previous to the SBT. Of these, 13 had a successful weaning and 9 failed the SBT or needed reintubation –being both considered as failed weaning. Results illustrate that traditional variables such as heart rate, respiratory frequency, and the parameters derived from HRV do not differ in patients with successful or failed weaning. Results revealed that HRV parameters can vary considerably depending on the time at which they are measured. This fact could be attributed to circadian rhythms, having a strong influence on HRV values. On the contrary, significant statistical differences are found in the proposed CPC parameters when comparing the values of the two groups, and throughout the whole recordings. In addition, differences are greater at night, probably because patients with failed weaning might be experiencing more respiratory episodes, e.g. apneas during the night, which is directly related to a reduced respiratory sinus arrhythmia. Therefore, results suggest that the traditional measures could be used in combination with the proposed CPC biomarkers to improve weaning readiness.

scholarly journals Quasi-Light-Storage based on time-frequency coherence

2009 ◽  
Vol 17 (18) ◽  
pp. 15790 ◽  
Author(s):  
Stefan Preußler ◽  
Kambiz Jamshidi ◽  
Andrzej Wiatrek ◽  
Ronny Henker ◽  
Christian-Alexander Bunge ◽  
...  
Keyword(s):  
Light Storage ◽  
Time Frequency ◽  
Frequency Coherence

Output Gap, Money Growth and Interest Rate in Japan: Evidence from Wavelet Analysis

2018 ◽  
Vol 18 (2) ◽  
pp. 171-184
Author(s):  
Aviral Kumar Tiwari ◽  
Olaolu Richard Olayeni ◽  
Reza Sherafatian-Jahromi ◽  
Olofin Sodik Adejonwo
Keyword(s):  
Interest Rate ◽  
High Frequency ◽  
Money Growth ◽  
High Frequencies ◽  
Time Frequency ◽  
Long Run ◽  
Direction Of Causation ◽  
Cyclical Relationships ◽  
Frequency Coherence ◽  
The Relationship

This article investigated the relationship between output, money and interest rate, using wavelet tools for the period 1972–2017. Application of such tools is helpful in answering particularly two questions: first, what the strength and direction of the causal relationships between money, output and interest rate is, and second, whether the relationship is cyclical or anti-cyclical in nature. Findings from this article show that output and money are highly coherent in low, middle and high frequencies, and coherence increases while controlling for interest rate, with money growth as the leading variable most of the time across frequencies. Output and interest rate are equally highly coherent, mostly at high frequency and some bits of middle frequency; coherence increases with the control for money, and interest rate often times leads the relationship. Also, money and interest rate are coherent at low, middle and high frequencies with interest rate leading the relationship, and controlling the effect of output increases the coherence at some times and decreases at other times. There are observable evidences of both cyclical and anti-cyclical relationships among the variables. Policy decisions should be cautious of shortrun moves in order not to trigger undesired long-run outcomes since no difference is observed in the direction of causation over time–frequency. JEL: C49, E43, E52

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