Complex Admittance Apnea Detection

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Solution Overview

Problem

Existing systems for distinguishing between open and closed apneas during sleep are less accurate, especially when there is moderate leak and resistance in the airpath, as they fail to account for capacitive and inductive components of airway impedance, leading to inappropriate adjustments in CPAP treatment pressure.

Innovation Solution

The method involves applying an oscillatory pressure waveform to the airway, measuring flow and pressure, and calculating the complex admittance, including its phase angle, to differentiate between open and closed apneas by comparing the admittance values to threshold regions, thereby improving the accuracy of airway patency determination.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If traditional pressure measurement methods are used to distinguish open and closed apneas, then the system is simple to operate, but the measurement precision is insufficient especially when there is moderate leak and resistance in the airpath

Engineering Contradiction:

Improveairway patency determination accuracyVSAvoidmeasurement system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent transforms the measurement from simple pressure values to complex admittance values by incorporating phase angle information. The oscillatory pressure waveform approach changes the parameter being measured from static pressure to dynamic pressure-flow relationship, enabling differentiation between open and closed apneas even in the presence of moderate leak and resistance.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces traditional mechanical pressure measurement with an oscillatory excitation approach that measures the respiratory system's impedance characteristics. By applying forced oscillations and measuring the resulting flow and pressure, the system substitutes direct mechanical interpretation with impedance-based inference, improving accuracy in distinguishing airway states.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If CPAP pressure is increased to treat all apneas, then treatment coverage is maximized, but central apneas with open airway are inappropriately treated causing reflex inhibition of breathing

Engineering Contradiction:

Improvetreatment appropriatenessVSAvoidreflex breathing inhibition

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

Instead of treating all apneas with increased CPAP pressure, the patent inverts the approach by first characterizing the type of apnea through admittance measurement. Closed apneas (obstructive) receive increased pressure treatment, while open apneas (central) are identified and excluded from pressure increase, thereby preventing the harmful reflex inhibition effect.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent implements feedback by continuously monitoring complex admittance values during sleep and using this information to guide CPAP pressure adjustments. The system measures admittance, determines airway patency status, and accordingly modifies treatment pressure, creating a closed-loop control system that prevents inappropriate treatment of central apneas.

Inventive Principle:

Principle #23Feedback

3Measurement precision

If complex admittance measurement with phase angle is implemented, then the separation of open and closed apnea data is significantly enhanced, but the calculation complexity increases

Engineering Contradiction:

Improveapnea type discrimination accuracyVSAvoidcalculation system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent employs periodic oscillatory pressure waveforms to excite the respiratory system during measurement. This periodic excitation allows the system to measure frequency-dependent impedance characteristics, and by analyzing the phase angle of the response at the oscillation frequency, the system can distinguish between open and closed apneas with high accuracy despite the increased computational requirements.

Inventive Principle:

Principle #19Periodic action

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

This approach significantly enhances the separation of open and closed apnea data, allowing for more precise control of CPAP treatment pressure, reducing the risk of exacerbating breathing disorders and improving sleep quality.

Implementation Method 1

applying an oscillatory pressure waveform to the airway, measuring flow and pressure, and calculating the complex admittance

Methodology Applied

Scientific EffectForced oscillation technique: Driven Harmonic Oscillation

Data Source

PatentUS10918329B2Distinguishing closed and open respiratory airway apneas by complex admittance values

Publication Date: 2021.02.16 RESMED PTY LTD

AI summary

Methods and apparatus are disclosed for determining the occurrence of a closed or open apnea. Respiratory air flow from a patient is measured to give an air flow signal. The determination of an apnea is performed by applying an oscillatory pressure waveform of known frequency to a patient's airway, calculating a complex quantity representing a patient admittance (12) and comparing its value with ranges (14, 16) indicative of open or closed apneas. The method distinguishes open from closed apneas even when the model used to calculate admittance is not based on details of the respiratory apparatus. In addition the patient admittance may be compared with admittance during normal breathing to avoid having to characterize the airway.