METHOD AND DEVICE FOR THE DETERMINATION OF BREATH FREQUENCY

• US 20100004552A1
• Filed: 11/28/2007
• Published: 01/07/2010
• Est. Priority Date: 12/21/2006
• Status: Abandoned Application

• Current Assignee: Fresenius Medical Care Deutschland GmbH (Fresenius Medical Care AG)
• Original Assignee: Fresenius Medical Care Deutschland GmbH (Fresenius Medical Care AG)
• Inventors: Zhang, Wei, Mueller, Carsten
• Application Number:
  US12/448,312
• Publication Number:
  US 20100004552A1
• Time in Patent Office: Days
• US Class Current: 600/529
• CPC Class Codes: A61B 5/0816 Measuring devices for examining respiratory frequency measuring frequency of electric signals G01R23/00
• CPC Class Codes: A61B 5/7257 using Fourier transforms

Abstract

The present invention provides a method for determining the respiratory rate of a patient comprising the steps of determining at least two time dependent respiratory signals by at least two different methods as well as a determining of a respiratory rate on the basis of the at least two time dependent respiratory signals. In this connection, the resulting respective instantaneous respiratory rates f_i(n) (i=1, 2, . . . ) are determined from the at least two time dependent respiratory signals s_i(t) (i=1, 2, . . . ) and an average respiratory rate f(n) determined by a weighted averaging of the respiratory rates f_i(n) (i=1, 2, . . . ) is produced. In this averaging, the weightings k_i(n) (i=1, 2, . . . ) of the individual respiratory rates f_i(n) (i=1, 2, . . . ) depend on a difference between the respective respiratory rates f_i(n) (i=1, 2, . . . ) and an estimate f_i(n) which is determined on the basis of at least two respiratory signals s_i(t) (i=1, 2, . . . ). An apparatus for carrying out the method is likewise provided.

Claims

1. A method of determining the respiratory rate of a patient comprising the steps:

determining at least two time dependent respiratory signals s_i(t) (i=1,2, . . . ) by at least two different methods;

determining the resulting respective instantaneous respiratory rates f_i(n) (i=1,2, . . . ) from the at least two time dependent respiratory signals s_i(t) (i=1, 2, . . . )

determining an average respiratory rate f(n) by a weighted averaging of the respiratory rates f_i(n) (i=1,2, . . . ), characterized in that

the weightings k_i(n) (i=1,2, . . . ) of the individual respiratory rates f_i(n) (i=1,2, . . . ) depend on a difference between the respective respiratory rates f_i(n) (i=1,2, . . . ) and an estimate f_s(n) determined on the basis of at least two respiratory signals s_i(t) (i=1,2, . . . ).

2. A method in accordance with claim 1, wherein the estimate f_s(n) is determined on the basis of a preceding, already determined average respiratory rate f(n−

1).

3. A method in accordance with claim 1, wherein the estimate f_s(n) is determined, in particular for initialization by a combination of rate information from at least two time dependent respiratory signals s_i(t) (i=1,2, . . . ) or by forming an average of the current respiratory rates f_i(n) (i=1, 2, . . . ).

4. A method in accordance with claim 1, wherein the at least two time dependent respiratory signals s_i(t) (i=1,2, . . . ) are determined from measured physiological signals.

5. A method in accordance with claim 4, wherein the measured physiological signals form a selection from the following signals:

bioimpedance signal;

heart rate variability signal;

photoplethysmographic signal (PPG signal);

statistical source signal of the ECG;

pulse wave transit time signal (PTT signal).

6. A method in accordance with claim 4, wherein the determination of the at least two time dependent respiratory signals s_i(t) (i=1,2, . . . ) takes place from the measured physiological signals by a band pass filter.

7. A method in accordance with claim 6, wherein the band pass filter allows frequencies in a range from approx. 0.12 Hz to 0.42 Hz to pass.

8. A method in accordance with claim 1, wherein the determination of the respective instantaneous respiratory rates f_i(k_i), in particular of f_hr(m), f_amp(n) and f_pt(k), from the time dependent respiratory signals s_i(t) (i=1,2, . . . ) takes place by determining the time indices t_max(k_i), in particular t_max(m), t_max(n) and t_max(k), of the maxima of the time dependent respiratory signals s_i(t) (i=1,2, . . . ).

9. A method in accordance with claim 8, wherein a consistency check takes place for the time indices k_i (i=1, 2, . . . ), in particular m, n and k, of the instantaneous respiratory rates.

10. A method in particular in accordance with claim 1, wherein a consistency check of the respiratory rates f_i(n) (i=1,2, . . . ) is carried out.

11. A method in accordance with claim 10, wherein the consistency check takes place by a comparison of the respiratory rates f_i(n) (i=1,2, . . . ) among one another.

12. A method in accordance with claim 11, wherein the differences between the respective respiratory rates f_i(n) (i=1,2, . . . ) is determined and is compared with a permitted tolerance A.

13. A method in accordance with claim 10, wherein only those respiratory rates are used for the weighted averaging of the respiratory rates f_i(n) (i=1,2, . . . ) which pass the consistency check.

14. A method in accordance with claim 1, wherein the signal quality is in particular determined via a consistency check and is optionally displayed.

15. A method, in particular in accordance with claim 1, comprising

the generation of at least two frequency signals FT_i(f) (i=1,2, . . . ) by transformation of at least two time dependent respiratory signals s_i(t) (i=1, 2, . . . ) into the frequency space

determination of a frequency signal FT(f) by a combination of the frequency signals FT_i(f) (i=1,2, . . . ),

wherein a respiratory rate f is determined on the basis of the frequency signal FT(f).

16. A method in accordance with claim 15, wherein the frequency signal FT(f) is determined by an averaging of the frequency signals FT_i(f) (i=1,2, . . . ).

17. A method in accordance with claim 15, wherein the respiratory rate f is determined by peak detection of the frequency signal FT(f).

18. A method in accordance with claim 15, wherein the respiratory rate f is determined by back transformation of the frequency signal FT(f)and an evaluation of the resulting signal s(t).

19. A method in accordance with claim 1, wherein the respiratory rate f is used for the initialization of the weighted averaging.

20. A method in accordance with claim 1, wherein the at least two time dependent respiratory signals s_i(t) (i=1,2, . . . ) are acquired from a PPG signal and an ECG signal.

21. A method in accordance with claim 1, wherein the at least two time dependent respiratory signals s_i(t) (i=1, 2, . . . ) form a selection from the following signals:

a respiratory signal determined from the heart rate s_HR(t),

a respiratory signal determined from the PPG signal s_PPG(t),

a respiratory signal determined from the PTT signal s_PTT(t),

a respiratory signal determined from the kurtosis of the ECG signal s_kurt(t).

22. A method in accordance with claim 21, wherein at least three respiratory signals are used.

23. An apparatus for determining the respiratory rate of a patient by means of a method in accordance with claim 1.

24. An apparatus, in particular in accordance with claim 23, comprising a separate sensor unit for measuring the physiological signals from which the at least two time dependent respiratory signals can be determined and a processing unit for the evaluation of the data transmitted by the sensor unit.

25. An apparatus in accordance with claim 24, wherein the data generated by the sensor unit are transmitted to the processing unit in a wireless manner.

26. An apparatus in accordance with claim 24, wherein the sensor unit is fastened to the patient'"'"'s wrist.

27. An apparatus in accordance with claim 24, wherein the at least two time dependent respiratory signals are determined from the physiological signals in the sensor units and are thereupon transmitted to the processing unit.

28. An apparatus in accordance with claim 23, comprising sensors for the measurement of the ECG signal and the PPG signal.

29. An apparatus in accordance with claim 28, wherein the heart rate, the pulse amplitude and the pulse wave transit time are determined from the ECG signal and the PPG signal.

30. An apparatus in accordance with claim 24, wherein the processing unit is part of a medical device, in particular of a medical device for extracorporeal blood treatment.

31. An apparatus in accordance with claim 24, wherein the processing unit is part of a computer network.