Two-frequency coherence function for the field of a wave reflected from a randomly inhomogeneous ionospheric layer

2019 ◽  
Author(s):  
Mikhail Tinin ◽  
Sergey Knizhin
Keyword(s):  
Coherence Function ◽  
Ionospheric Layer ◽  
Frequency Coherence

Propagation of the two-frequency coherence function in an inhomogeneous background random medium

2004 ◽  
Vol 14 (3) ◽  
pp. 389-409 ◽  
Author(s):  
Alexander Kalugin ◽  
Alexander Bronshtein ◽  
Reuven Mazar
Keyword(s):  
Random Medium ◽  
Coherence Function ◽  
Frequency Coherence

The two-frequency coherence function for the fluctuating ionosphere: narrowband pulse propagation

1997 ◽  
Vol 59 (14) ◽  
pp. 1831-1841 ◽  
Author(s):  
Vadim E. Gherm ◽  
Nikolay N. Zernov ◽  
Bengt Lundborg ◽  
Anders Västberg
Keyword(s):  
Pulse Propagation ◽  
Coherence Function ◽  
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.

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