Respiratory Impedance Estimation via Time-Frequency Transform
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Solution Overview
Problem
Current methods for estimating respiratory impedance from forced pressure oscillations lack reliability in short time intervals, essential for accurately diagnosing respiratory diseases like COPD and asthma, due to limitations in time-frequency resolution and increased dependence on chance events.
Innovation Solution
A method and apparatus that generate pressure waves in a patient interface device, transform flow and pressure time series into the time-frequency domain, estimate power and cross spectra, and calculate respiratory impedance, utilizing a processor to achieve optimal time-frequency resolution and confidence limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If prior art methods are used to estimate respiratory impedance, then the measurement process is simple, but the reliability in short time intervals is poor
Solution Approach 1:
The patent transforms the time series data into the time-frequency domain using spectral analysis, adding a frequency dimension to the analysis. This allows simultaneous assessment of impedance characteristics across multiple frequencies within short time intervals, resolving the contradiction between reliability and time loss by operating in an expanded dimensional space rather than simple temporal averaging
Solution Approach 2:
The patent replaces traditional mechanical signal processing methods with spectral analysis and cross-spectrum estimation techniques. By using frequency-domain analysis instead of time-domain filtering and averaging, the system achieves reliable impedance estimates in short intervals without being constrained by the time constants of mechanical filtering systems
2Measurement precision
If traditional filtering methods are used, then the implementation is straightforward, but the time-frequency resolution is insufficient
Solution Approach 1:
The patent employs spectral analysis to transform signals from the time domain to the time-frequency domain, enabling precise measurement of impedance characteristics at specific frequencies and time points. This dimensional transformation provides high time-frequency resolution while managing complexity through established spectral estimation techniques
Solution Approach 2:
The patent changes the analysis parameters from simple time-domain averages to frequency-specific spectral components. By estimating cross-spectra and impedance at discrete frequency points rather than continuous time averaging, the system achieves high measurement precision with computationally manageable complexity
3Productivity
If short time intervals are used for estimation, then the diagnostic capability for dynamic conditions is improved, but the dependence on chance events increases
Solution Approach 1:
The patent uses frequency-domain analysis to extract multiple impedance parameters simultaneously from short time intervals. By analyzing the spectral content across different frequencies rather than relying on single-time-point measurements, the system reduces dependence on chance events while maintaining high diagnostic speed
Solution Approach 2:
The patent employs cross-spectrum estimation which inherently uses feedback from the relationship between pressure and flow signals. This statistical approach averages out random fluctuations and chance events by exploiting the consistent phase and amplitude relationships between related physiological signals, even in short time intervals
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables reliable estimation of respiratory impedance in short time intervals, providing accurate diagnostic tools for assessing airway obstruction and disease severity, as well as optimizing treatment settings for respiratory conditions.
Implementation Method 1
an excitation source for generating oscillating pressure, flow, or volume of gas in such an airway of such a subject
Data Source
Figure 1~2
Figure 3A~4B
Figure 5~6B
AI summary
The acoustic impedance of the respiratory system can be inferred from oscillations that are generated in an airway of a subject. The impedance describes the frequency-dependent relation between the resulting oscillations in flow and pressure. When the impedance varies from inspiration to expiration, it has to be estimated with a high time resolution. A method is provided that reliably estimates the impedance in time intervals that are short enough for physiological purposes. A simple version of the uncertainty principle has been derived for discrete time and frequency. A discrete time- frequency transform has been developed that gives an optimal time-frequency resolution according to this principle. The transform is orthonormal, which permits an analysis of variance in the discrete time- frequency domain. The impedance follows from bivariate least-squares analysis in the time- frequency domain, under the assumption that noise is present in both flow and pressure.