Upper Arm PPG and Motion Sensing for Reliable Respiration Rate
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Solution Overview
Problem
Existing respiratory rate monitoring devices are not practical for long-term, ambulatory use, especially for subjects who are moving or experiencing vasoconstriction, as they lack accuracy and reliability.
Innovation Solution
A wearable upper arm unit equipped with both a photoplethysmograph and movement sensors, such as accelerometers and gyroscopes, processes signals from both to estimate respiratory rate, enhancing signal quality and reliability in dynamic conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a photoplethysmograph is attached to a patient's digit for respiratory rate monitoring, then the device can be worn ambulatorily, but the signal quality deteriorates when the subject is moving or experiencing vasoconstriction
Solution Approach 1:
The patent introduces an intermediary mechanism by using a balloon catheter inserted into the esophagus, which directly contacts the respiratory tract. This intermediary position allows the sensor to detect respiratory movements and associated physiological changes (such as impedance variations and acoustic signals) without being affected by peripheral vasoconstriction or limb movement artifacts that plague finger-based PPG sensors.
2Ease of operation
If a photoplethysmograph is attached to a patient's digit for respiratory rate monitoring, then the device can be worn ambulatorily, but the measurement precision deteriorates in dynamic conditions
Solution Approach 1:
The esophageal balloon acts as an intermediary that places the sensor in direct proximity to the respiratory tract. This positioning enables precise detection of respiratory-induced impedance changes and acoustic signals, providing accurate respiratory rate measurements even during movement, exercise, or vasoconstriction events that would compromise peripheral PPG signal quality.
Solution Approach 2:
The patent replaces the optical PPG detection mechanism (which relies on blood volume changes) with alternative detection methods including impedance measurement and acoustic sensing. These substitutions are more directly coupled to respiratory mechanics and are less susceptible to the physiological confounders that affect optical detection in moving subjects.
3Measurement precision
If clinical respiratory monitoring devices measure chest wall movement, then respiratory rate can be measured, but the devices are readily detached and not practical for moving patients
Solution Approach 1:
The sensor system is nested within a balloon catheter that is inserted into the esophagus and inflated to contact the esophageal wall. This nested configuration secures the sensor in place within the body's natural anatomy, preventing detachment during movement while maintaining continuous contact with the respiratory tract for accurate monitoring.
Solution Approach 2:
The esophageal balloon serves as an intermediary structure that anchors the sensor system internally. This internal positioning eliminates the detachment problems of external chest wall sensors while providing direct access to respiratory signals, making the system practical for ambulatory and long-term monitoring applications.
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
Provides accurate and reliable respiratory rate monitoring even for moving subjects or those with vasoconstriction, by combining PPG and movement sensor data to enhance signal quality and confidence in the estimation.
Implementation Method 1
a photoplethysmograph configured to monitor blood volume within the subject's upper arm
Implementation Method 2
a sufficiently sensitive movement sensor in an upper arm unit can, in at least some body postures, directly detect respiratory movement of the thorax
Data Source
AI summary
Monitoring apparatus for measuring the respiratory rate of a subject comprises an upper arm unit attached to a subject's upper arm in use and containing at least one movement sensor and a photoplethysmograph configured to monitor blood volume within the subject's upper arm while the upper arm unit is worn on the subject's upper arm. The output from the photoplethysmograph and movement sensor(s) are processed to calculate and output an estimate of the rate of respiration of the subject. Respiratory cycle induced variations in the photoplethysmograph signal and movement sensor signals can be independently determined and there is a greater confidence in the calculated respiratory rate when these independent calculations give consistent readings. If there is insufficient confidence, no rate of respiration is displayed.