Apparatus and method for estimating respiration rate
Inventors
MCCANN, Christopher Thomas • Whiting, Stewart William
Assignees
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Publication Number
US-11759121-B2
Publication Date
2023-09-19
Expiration Date
Abstract
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 subjects 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.
Core Innovation
The invention provides a method of measuring the respiratory rate of a subject using an upper arm unit attached to the subject’s upper arm. The upper arm unit includes at least one movement sensor and a photoplethysmograph (PPG) configured to monitor blood volume within the subject’s upper arm while the upper arm unit is worn. The method processes both the output of the at least one movement sensor and the output of the photoplethysmograph to calculate an estimate of the rate of respiration, and then outputs the calculated estimate of the rate of respiration.
The invention specifically includes detecting respiratory movement of the thorax using the at least one movement sensor within the upper arm unit as part of processing the movement-sensor output. Respiratory-cycle induced variations are extracted from the PPG and from the movement signals, and the extracted variations are analyzed to determine respiratory rate-related information. In the described approach, the determination is grounded in frequency analysis of respiratory-cycle induced variations.
The invention further describes determining a first estimate of the rate of respiration by determining the frequency of a respiratory cycle induced variation in the output of the photoplethysmograph, and/or determining a second estimate by determining the frequency of a respiratory cycle induced variation in the output of the at least one movement sensor. The second estimate is an estimated respiratory rate induced variation in the output of the at least one movement sensor within the upper arm unit, thereby enabling respiratory-rate estimation based on movement-sensor respiratory-cycle induced variations in addition to PPG-based estimation.
Claims Coverage
The provided independent claims cover upper-arm respiratory-rate estimation with four main inventive feature areas: combining upper-arm PPG and movement sensing, detecting respiratory movement of the thorax via the movement sensor, frequency-based estimation from respiratory-cycle induced variations, and confidence/output logic based on processed outputs.
Upper-arm combined PPG and movement sensing
An upper arm unit attached to a subject’s upper arm includes at least one movement sensor and a photoplethysmograph (PPG) configured to monitor blood volume within the subject’s upper arm while worn, where processing combines outputs to calculate and output an estimate of the rate of respiration.
Thorax respiratory movement detection using upper-arm movement sensor
Processing the output of the at least one movement sensor comprises detecting respiratory movement of the thorax using the at least one movement sensor within the upper arm unit.
First respiration-rate estimate from PPG respiratory-cycle induced variation frequency
A first estimate of the rate of respiration is calculated by determining the frequency of a respiratory cycle induced variation in the output of the photoplethysmograph.
Second respiration-rate estimate from movement-sensor respiratory-cycle induced variation frequency
A second estimate of the rate of respiration is calculated by determining the frequency of a respiratory cycle induced variation in the output of the at least one movement sensor, where the second estimate is the estimated respiratory rate induced variation in the output of the at least one movement sensor within the upper arm unit.
Confidence status and selectable output behavior
A processor calculates a confidence status based on processed outputs from the output of the at least one movement sensor and the output of the photoplethysmograph, and a display shows a selectable confidence-status value such that at least one confidence status results in no displayed respiration-rate estimate while at least two other confidence statuses correspond to different levels of confidence and trigger both a displayed respiration-rate estimate and confidence-status representative data.
Movement-sensor placement not configured on the thorax
The monitoring apparatus is configured so that none of the at least one movement sensors are placed on the thorax.
Overall, the independent-claim coverage centers on upper-arm respiration-rate estimation by processing both upper-arm PPG and movement-sensor outputs, with respiration-rate determination based on the frequency of respiratory-cycle induced variations, and optional confidence-status output behavior.
Stated Advantages
Enables respiratory rate estimation by processing both PPG blood-volume information and movement-sensor output associated with respiratory-cycle induced variations.
Supports output behavior that with low-confidence conditions results in no displayed respiration-rate estimate while other confidence levels provide displayed estimates with confidence-status representative data.
Documented Applications
Monitoring respiratory rate of a subject using a wearable upper arm unit that estimates respiration rate from upper-arm PPG and movement sensor outputs while attached to the subject’s upper arm.
Providing a monitoring apparatus with a display that outputs an estimated respiratory rate and a selectable confidence-status value based on processed movement-sensor and PPG outputs.
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