Apparatus and method for determining a physiologic parameter of a patient applying fourier transformation

• US 20080033306A1
• Filed: 07/23/2007
• Published: 02/07/2008
• Est. Priority Date: 08/03/2006
• Status: Active Grant

• Current Assignee: PULSION Medical Systems SE (Getinge AB)
• Original Assignee: Pulsion Medical Systems AG
• Inventors: Joeken, Stephan
• Granted Patent: US 8,556,818 B2
• Time in Patent Office: Days
• US Class Current: 600/485
• CPC Class Codes: A61B 5/029 Measuring or recording blood output from the heart, e.g. minute volume A61B8/065 takes precedence
• CPC Class Codes: A61B 5/7257 using Fourier transforms

Abstract

The apparatus comprises a pressure sensor providing readings of a blood pressure of the patient and storage means for storing the readings as a pressure curve over time. Blood pressure is measured. The frequency difference between heart rate and breathing rate is used to separate the respiratory effect from the heart activity. In particular, the Fourier transform of the blood pressure and the spectral density are used to determine the contribution of each frequency. The respiratory and cardiac power spectra are determined. The ratio between both powers is calculated as the quotient of the integrals over the cardiac power spectrum and the respiratory power spectrum. A parameter usable to characterize volume responsiveness is determined using above ratio and a correction factor.

Claims

1. Apparatus for determining at least one physiologic parameter of a patient, said apparatus comprising

(a) at least one pressure sensor device adapted to provide readings of a blood pressure of said patient, and

(b) storage means for storing said readings as at least one pressure curve over time,

(c) fourier transformation means for subjecting said at least one pressure curve to a fourier transformation, and

(d) evaluation means adapted to retrieve at least one of

a cardiac power value representing cardiac power and

a respiratory power value representing respiratory power

from at least one fourier transform received from said fourier transformation and to determine said physiologic parameter from at least one of said cardiac power value and respiratory power value.

2. Apparatus according to claim 1, wherein said evaluation means are adapted to separate harmonics using at least one of a heart rate and a breathing rate as a basic frequency.

3. Apparatus according to claim 1, wherein said evaluation means are adapted to extract at least one of a cardiac power-spectrum and a respiratory power spectrum from at least one fourier transform received from said fourier transformation and to determine at least one of

said cardiac power value using summation over at least part of said cardiac power-spectrum

said cardiac power value using integration over at least part of said cardiac power-spectrum

said respiratory power value using summation over at least part of said cardiac power-spectrum

said respiratory power value using integration over at least part of said respiratory power-spectrum.

4. Apparatus according to claim 3, wherein said evaluation means are adapted to determine a width at a predetermined fraction of the maximum of a peak of at least one of said cardiac power-spectrum and said respiratory power-spectrum and to use said width to separate harmonics.

5. Apparatus according to claim 4, wherein said evaluation means are adapted to use said width to determine the amount of said harmonics from at least one of said cardiac power-spectrum and said respiratory power-spectrum.

6. Apparatus according to claim 1, wherein said at least one physiologic parameter of a patient includes a parameter for volume-responsiveness.

7. Apparatus according to claim 6, wherein said evaluation means are adapted to determine said parameter for volume-responsiveness from the quotient of said cardiac power-value and said respiratory power-value.

8. Apparatus according to claim 6, wherein said evaluation means are adapted to determine said parameter for volume-responsiveness using a correction factor.

9. Apparatus according to claim 8, wherein said evaluation means are adapted to determine said parameter for volume-responsiveness to be a product of said correction factor and the quotient of said cardiac power-value and said respiratory power-value.

10. Apparatus according to claim 8, wherein said evaluation means are adapted to determine a cardiac power-spectrum and a respiratory power spectrum from at least one fourier transform received from said fourier transformation, to determine said cardiac power value using summation or integration over at least part of said cardiac power-spectrum and said respiratory power value using summation or integration over at least part of said respiratory power-spectrum, and to determine at least one of the following characteristic parameters

a width (WC, WR) at a predetermined fraction of the maximum of a peak of said cardiac power-spectrum,

a slope of logarithmic spectral density of said cardiac power-spectrum over logarithmic frequency for frequency tending towards infinity,

a slope of logarithmic spectral density of said respiratory power-spectrum over logarithmic frequency for frequency tending towards infinity,

a limit of the spectral density of said cardiac power-spectrum tending towards zero,

a limit of the spectral density of said respiratory power-spectrum tending towards zero,

a limit of the spectral density of the superposition of said cardiac power-spectrum and said respiratory power-spectrum tending towards zero,

and wherein said correction factor is a function of at least one of said characteristic parameters.

11. Apparatus according to claim 1, wherein said evaluation means are adapted to determine both said cardiac power-value and said respiratory power-value from a fourier transform received from said fourier transformation based on the same pressure curve.

12. Apparatus according to claim 1 comprising at least two pressure sensor devices adapted to provide readings of a blood pressure of said patient,

wherein the apparatus is adapted to store readings of a first one of said pressure sensor devices as a first pressure curve over time and readings of a second one of said pressure sensor devices as a second pressure curve over time,

and wherein said evaluation means are adapted to determine said cardiac power-value from a fourier transform received from said fourier transformation based on said first pressure curve and said respiratory power-value from a fourier transform received from said fourier transformation based on said second pressure curve.

13. Apparatus according to claim 12, wherein said first pressure sensor device is an arterial pressure sensor device and said second pressure device is one of a central venous pressure device and a pulmonary artery pressure device.

14. Apparatus according to claim 1, wherein at least one pressure sensor device is adapted for non-invasively measuring an arterial pressure of said patient.

15. Apparatus according to claim 1, wherein said at least one physiologic parameter of said patient includes cardiac output, and wherein said evaluation means are adapted to determine cardiac output using said cardiac power-value.

16. Apparatus according to claim 12, wherein said evaluation means are adapted to determine cardiac output from the quotient of said cardiac power-value and an averaged pressure calculated from said readings of a blood pressure of said patient.

17. Apparatus according to claim 1, wherein said at least one physiologic parameter of said patient includes tidal volume, and wherein said evaluation means are adapted to determine tidal volume using said respiratory power-value.

18. Apparatus according to claim 1, wherein said evaluation means are adapted to determine at least one further hemodynamic parameter from said at least one pressure curve over time.

19. Method for determining at least one physiologic parameter of a patient, said method including

(a) providing readings of a blood pressure of said patient,

(b) storing said readings as at least one pressure curve over time,

(c) subjecting said at least one pressure curve to a fourier transformation

(d) retrieving at least one of

a cardiac power value representing cardiac power and

a respiratory power value representing respiratory power

from at least one fourier transform received from said fourier transformation and

(e) determining said physiologic parameter from at least one of said cardiac power value and respiratory power value.

20. Method according to claim 19, wherein harmonics are separated using at least one of a heart rate and a breathing rate as a basic frequency.

21. Method according to claim 19, wherein at least one of a cardiac power-spectrum and a respiratory power spectrum is extracted from at least one fourier transform received from said fourier transformation and

said cardiac power value is determined using one of

summation over at least part of said cardiac power-spectrum and

integration over at least part of said cardiac power-spectrum.

22. Method according to claim 19, wherein at least one of a cardiac power-spectrum and a respiratory power spectrum is extracted from at least one fourier transform received from said fourier transformation and

said cardiac power value is determined using one of

summation over at least part of said respiratory power-spectrum and

integration over at least part of said respiratory power-spectrum.

23. Method according to claim 19, wherein a width at a predetermined fraction of the maximum of a peak of at least one of said cardiac power-spectrum and said respiratory power-spectrum is determined, and said width is used to separate harmonics.

24. Method according to claim 23 wherein said width is used to determine the amount of said harmonics from at least one of said cardiac power-spectrum and said respiratory power-spectrum.

25. Method according to claim 19, wherein said at least one physiologic parameter of said patient includes a parameter for volume-responsiveness.

26. Method according to claim 25, wherein said parameter for volume-responsiveness is determined from the quotient of said cardiac power-value and said respiratory power-value.

27. Method according to claim 25, wherein said parameter for volume-responsiveness is determined using a correction factor.

28. Method according to claim 27, wherein said parameter for volume-responsiveness is determined to be a product of said correction factor and the quotient of said cardiac power-value and said respiratory power-value.

29. Method according to claim 27, wherein a cardiac power-spectrum and a respiratory power spectrum are determined from at least one fourier transform received from said fourier transformation,

said cardiac power value is determined using summation or integration over at least part of said cardiac power-spectrum and said respiratory power value is determined using summation or integration over at least part of said respiratory power-spectrum, and

at least one of the following characteristic parameters is determined:

a width at a predetermined fraction of the maximum of a peak of said cardiac power-spectrum,

a slope of logarithmic spectral density of said cardiac power-spectrum over logarithmic frequency for frequency tending towards infinity,

a slope of logarithmic spectral density of said respiratory power-spectrum over logarithmic frequency for frequency tending towards infinity,

a limit of the spectral density of said cardiac power-spectrum tending towards zero,

a limit of the spectral density of said respiratory power-spectrum tending towards zero,

a limit of the spectral density of the superposition of said cardiac power-spectrum and said respiratory power-spectrum tending towards zero,

and wherein said correction factor is a function of at least one of said characteristic parameters.

30. Method according to claim 19, wherein both said cardiac power-value and said respiratory power-value are determined from a fourier transform received from said fourier transformation based on the same pressure curve.

31. Method according to claim 19, wherein readings of a blood pressure of said patient at a first location and of a blood pressure of said patient at a second location are provided, the readings of the blood pressure at said first location are stored as a first pressure curve over time and the readings of the blood pressure at said second location are stored as a second pressure curve over time,

and wherein said cardiac power-value is determined from a fourier transform received from said fourier transformation based on said first pressure curve and said respiratory power-value is received from a fourier transform received from said fourier transformation based on said second pressure curve.

32. Method according to claim 31, wherein said first location is an arteria of the systemic circulation of said patient and said second location is a central vein or the pulmonary artery of said patient.

33. Method according to claim 19, wherein an arterial pressure of said patient is measured non-invasively.

34. Method according to claim 19, wherein said at least one physiologic parameter of said patient includes cardiac output, and wherein cardiac output is determined using said cardiac power-value.

35. Method according to claim 34, wherein cardiac output is determined from the quotient of said cardiac power-value and an averaged pressure calculated from said readings of a blood pressure of said patient.

36. Method according to claim 19, wherein said at least one physiologic parameter of said patient includes tidal volume, and wherein tidal volume is determined using said respiratory power-value.

37. Method according to claim 19, wherein at least one further hemodynamic parameter is determined from said at least one pressure curve over time.