Systems and methods for determining respiratory effort

• US 8,834,378 B2
• Filed: 07/30/2010
• Issued: 09/16/2014
• Est. Priority Date: 07/30/2010
• Status: Active Grant

• Current Assignee: Nellcor Puritan Bennett Ireland
• Original Assignee: Nellcor Puritan Bennett Ireland
• Inventors: Addison, Paul Stanley, Watson, James N.
• Primary Examiner(s): D'ANGELO, MICHAEL J
• Application Number:
  US12/847,720
• Publication Number:
  US 20120029361A1
• Time in Patent Office: 1,509 Days
• Field of Search: 600/481, 600/483, 600/484, 600/508, 600/509, 600/513, 600/547, 607/17
• US Class Current: 600/483
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• CPC Class Codes: A61B 5/02108 from analysis of pulse wave characteristics
• CPC Class Codes: A61B 5/02125 of pulse wave propagation time
• CPC Class Codes: A61B 5/0816 Measuring devices for examining respiratory frequency measuring frequency of electric signals G01R23/00
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives

Abstract

Systems and methods for calculating a measure of respiratory effort of a subject are provided. The measure of respiratory effort may be calculated based on a differential pulse transit time (DPTT) calculated for received photoplethysmograph signals. The systems and methods may allow for the calculation of respiratory effort in absolute units, and without the need for calibrations from a device that measures blood pressure (e.g., a non-invasive blood pressure cuff).

Claims

1. A method for calculating a measure of respiratory effort of a subject, the method comprising:

receiving two photoplethysmograph (PPG) signals corresponding to two different locations on the subject;

calculating, using electronic processing equipment, differential pulse transit time (DPTT) values for the two PPG signals, wherein the DPTT values represent differences in arrival times between the two locations;

determining, using the electronic processing equipment, a measure of respiratory effort based at least in part on the calculated DPTT values; and

storing, using a storage device, the measure of respiratory effort.

2. The method of claim 1, wherein the determining further comprises:

selecting a plurality of pressure calculation coefficients based on the calculated DPTT values;

selecting a plurality of characteristic DPTT values;

determining, based at least in part on the selected pressure calculation coefficients and selected characteristic DPTT values, a measure of blood pressure; and

calculating, based at least in part on the measure of blood pressure, a measure of respiratory effort.

3. The method of claim 2, wherein the measure of blood pressure is determined solely based on the selected pressure calculation coefficients and selected characteristic DPTT values.

4. The method of claim 2, further comprising:

selecting at least a portion of the calculated DPTT values corresponding to at least one respiratory cycle of the subject; and

selecting a plurality of characteristic DPTT values within the portion of the DPTT values.

5. The method of claim 4, wherein the characteristic DPTT values are selected based on at least a maximum DPTT value and a minimum DPTT value in the portion of the DPTT values.

6. The method of claim 4, further comprising calculating a mean DPTT value corresponding to the at least one respiratory cycle of the subject.

7. The method of claim 2, further comprising:

selecting at least a portion of the calculated DPTT values corresponding to at least two periods of respiratory activity;

calculating a mean DPTT value corresponding to each of the at least two periods of respiratory activity; and

determining, based at least in part on the selected pressure calculation coefficients and calculated mean DPTT values, the measure of blood pressure.

8. The method of claim 7, wherein the at least two periods of respiratory activity correspond to at least one period in which the subject is exercising and at least one period in which the subject is resting.

9. The method of claim 1, wherein the calculation of the measure of respiratory effort is based on a linear relationship between a measure of blood pressure and respiratory effort.

10. A system for calculating a measure of respiratory effort of a subject, comprising:

an input for receiving two photoplethysmograph (PPG) signals corresponding to two different locations on the subject;

a processor configured to use at least portions of the two PPG signals to;

calculate differential pulse transit time (DPTT) values for the two PPG signals, wherein the DPTT values represent differences in arrival times between the two locations; and

determine a measure of respiratory effort based at least in part on the calculated DPTT values; and

a storage device for storing the measure of respiratory effort.

11. The system of claim 10, wherein the processor is configured to use at least a portion of the calculated DPTT values to:

select a plurality of pressure calculation coefficients based on the calculated DPTT values;

select a plurality of characteristic DPTT values;

determine, based at least in part on the selected pressure calculation coefficients and selected characteristic DPTT values, a measure of blood pressure; and

calculate, based at least in part on the measure of blood pressure, a measure of respiratory effort.

12. The system of claim 11, wherein the measure of blood pressure is determined solely based on the selected pressure calculation coefficients and selected characteristic DPTT values.

13. The system of claim 11, wherein the processor is configured to use at least a portion of the calculated DPTT values to:

select at least a portion of the calculated DPTT values corresponding to at least one respiratory cycle of the subject; and

select a plurality of characteristic DPTT values within the portion of the DPTT values.

14. The system of claim 13, wherein the characteristic DPTT values are selected based on at least a maximum DPTT value and a minimum DPTT value in the portion of the DPTT values.

15. The system of claim 13, wherein the processor is further configured to calculate a mean DPTT value corresponding to the at least one respiratory cycle of the subject.

16. The system of claim 11, wherein the processor is configured to use at least a portion of the calculated DPTT values to:

select at least a portion of the calculated DPTT values corresponding to at least two periods of respiratory activity;

calculate a mean DPTT value corresponding to each of the at least two periods of respiratory activity; and

determine, based at least in part on the selected pressure calculation coefficients and calculated mean DPTT values, the measure of blood pressure.

17. The system of claim 16, wherein the at least two periods of respiratory activity correspond to at least one period in which the subject is exercising and at least one period in which the subject is resting.

18. The system of claim 10, wherein the calculation of the measure of respiratory effort is based on a linear relationship between a measure of blood pressure and respiratory effort.

19. Non-Transitory computer readable storage media comprising instructions for:

receiving two photoplethysmograph (PPG) signals corresponding to two different locations on the subject;

calculating differential pulse transit time (DPTT) values for the two PPG signals, wherein the DPTT values represent differences in arrival times between the two locations;

determining a measure of respiratory effort based at least in part on the calculated DPTT values; and

storing the measure of respiratory effort.