Respiratory rate measurement using a combination of respiration signals

• US 9,872,634 B2
• Filed: 02/08/2013
• Issued: 01/23/2018
• Est. Priority Date: 02/08/2013
• Status: Active Grant

• Current Assignee: Vital Connect, Inc.
• Original Assignee: Vital Connect, Inc.
• Inventors: Chan, Alexander, Narasimhan, Ravi
• Primary Examiner(s): Marmor, II, Charles A
• Assistant Examiner(s): COX, THADDEUS B
• Application Number:
  US13/763,391
• Publication Number:
  US 20140228692A1
• Time in Patent Office: 1,810 Days
• CPC Class Codes: A61B 5/002 Monitoring the patient using a local or closed circuit, e.g. in a room or building A61B5/0017 takes precedence
• CPC Class Codes: A61B 5/02405 Determining heart rate variability
• CPC Class Codes: A61B 5/08 Detecting, measuring or recording devices for evaluating the respiratory organs A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/0809 by impedance pneumography
• CPC Class Codes: A61B 5/0816 Measuring devices for examining respiratory frequency measuring frequency of electric signals G01R23/00
• CPC Class Codes: A61B 5/082 Evaluation by breath analysis, e.g. determination of the chemical composition of exhaled breath A61B5/083, A61B5/091 take precedence
• CPC Class Codes: A61B 5/087 Measuring breath flow
• CPC Class Codes: A61B 5/113 occurring during breathing
• CPC Class Codes: A61B 5/1135 by monitoring thoracic expansion
• CPC Class Codes: A61B 5/366 Detecting abnormal QRS complex, e.g. widening
• CPC Class Codes: A61B 5/4818 Sleep apnoea
• CPC Class Codes: A61B 5/6801 specially adapted to be attached to or worn on the body surface
• CPC Class Codes: A61B 5/7221 Determining signal validity, reliability or quality A61B5/7207 and A61B5/7217 take precedence

Abstract

A method and system for measuring respiratory rate are disclosed. In a first aspect, the method comprises measuring at least one respiration signal and filtering the respiration signal using a lowpass filter. The method includes peak-picking the respiration signal to determine the respiratory rate and determining a quality metric of the respiratory rate. In a second aspect, the system comprises a wireless sensor device coupled to a user via at least one electrode, wherein the wireless sensor device includes a processor and a memory device coupled to the processor, wherein the memory device stores an application which, when executed by the processor, causes the processor to carry out the steps of the method.

Claims

1. A system for determining respiratory rates of a user, the system comprising:

at least one electrode adapted to be coupled to the user, wherein the at least one electrode measures at least one respiration signal,

wherein to measure at least one respiration signal is to measure a plurality of respiration signals to determine a plurality of respiration rates (RR_{1 . . . N}), wherein the application further causes the processor to;

determine a quality metric (Q_{1 . . . N}) for each of the plurality of respiration rates; and

combine the plurality of respiration rates by weighting the quality metric for each of the plurality of respiration rates based on a quality process to calculate a weighted respiration rate (RR_weighted);

a processor coupled to the at least one electrode; and

a memory device coupled to the processor, wherein the memory device stores an application which, when executed by the processor, causes the processor to;

filter the at least one respiration signal measured by the at least one electrode using a lowpass filter;

peak-pick the filtered respiration signal to determine a respiratory rate by using a standard deviation of the filtered respiration signal over a changing threshold; and

determine a quality metric of the respiratory rate by using previously learned weights of features of the respiratory rate, wherein the features of the respiratory rate include a coefficient of variation of a difference in minima times (c_t), a coefficient of variation of peak-to-peak values (c_p), a mean peak-to-peak value (m_p), and a ratio of a number of picked extrema to a total number of all local extrema (r_ext).

2. The system of claim 1, wherein the at least one respiration signal is derived using any of a chest-mounted accelerometer, a QRS-area of an EKG signal, a QRS-amplitude of the EKG signal, and a respiratory sinus arrhythmia (RSA).

3. The system of claim 1, wherein the quality metric is weighted using the previously learned weights and transformed using an exponential to get the quality metric to a value between 0 and 1.

4. The system of claim 1, wherein the quality metric is derived within a predetermined time period.

5. The system of claim 4, wherein the predetermined time period is 45 seconds.

6. The system of claim 1, wherein the application further causes the processor to:

perform a smoothing of the respiratory rate to reduce effects of missed and extraneous peaks using a trimmed mean.

7. The system of claim 1, wherein the weighted respiration rate (RR_weighted) comprises:

RR_weighted=RR₁*(Q₁/(Q₁+Q₂+ . . . +Q_N))+RR₂*(Q₂/(Q₁+Q₂+ . . . +Q_N))+RR_N*(Q_N/(Q₁+Q₂+ . . . Q_N)).