Separation of interference pulses from physiological pulses in a pressure signal

Patent metadata

Field	Value
Publication number	US-10314965-B2
Application number	US-201414917099-A
Country	US
Kind code	B2
Filing date	Sep 8, 2014
Priority date	Sep 9, 2013
Publication date	Jun 11, 2019
Grant date	Jun 11, 2019

Abstract

A filtering device receives a signal from a pressure sensor in an extracorporeal fluid circuit connected to a subject and processes the signal to separate physiological pulses, e.g. from the subject's heart, from interference pulses, e.g. from a pump in the fluid circuit. The device repeatedly (iteratively) processes a signal segment by alternately subtracting (S3) a template signal from the signal segment, and applying a refinement processing (S6) to the resulting difference signal to generate a new template signal. By proper selection (S2) of the initial template signal, consecutive difference signals will alternately approximate the sequence of interference pulses in the signal segment and the sequence of physiological pulses in the signal segment. The refinement processing (S6) aims at alternately cleaning up unwanted residuals from interference pulses and physiological pulses, respectively, in the respective difference signal, so as to improve the accuracy of the template signal between the subtractions.

First claim

The invention claimed is:

1. A device for processing a pressure signal obtained from a pressure sensor in an extracorporeal fluid circuit, said device comprising:
an input for receiving the pressure signal from the pressure sensor; and
a signal processor connected to the input and being configured to:
extract, from the pressure signal, a signal segment that comprises a sequence of interference pulses originating from an interference generator associated with the extracorporeal fluid circuit, and a sequence of physiological pulses originating from a physiological pulse generator in a subject which is connected to the extracorporeal fluid circuit;
process the signal segment for separation of the interference pulses from the physiological pulses by:
a) subtracting at least one initial template signal from the signal segment to generate a first difference signal that represents the sequence of physiological pulses and residuals of the interference pulses;
b) processing the first difference signal to generate a first template signal in which the residuals of the interference pulses are suppressed in relation to the sequence of physiological pulses;
c) subtracting at least the first template signal from the signal segment to generate a second difference signal that represents the sequence of interference pulses and residuals of the physiological pulses; and
d) processing the second difference signal to generate a second template signal in which the residuals of the physiological pulses are suppressed in relation to the sequence of interference pulses; and

evaluating a property of the extracorporeal fluid circuit using the second template signal.

2. The device of claim 1 , wherein the signal processor is configured to, subsequent to the steps a)-d), process the signal segment for separation of the interference pulses from the physiological pulses by:
e) subtracting at least the second template signal from the signal segment to generate the first difference signal; and
repeating the steps b)-e) in at least one iteration.

3. The device of claim 2 , wherein the signal processor is configured to repeatedly execute steps b)-e) until a predefined convergence criterion is fulfilled or until a predefined time limit is exceeded.

4. The device of claim 3 , wherein the predefined convergence criterion is defined to detect a predefined suppression of the residuals of the physiological pulses in the second difference signal or the second template signal, or to detect a predefined suppression of the residuals of the interference pulses in the first difference signal or the first template signal.

5. The device of claim 1 , wherein the signal processor is further configured, in step b), to: identify a set of predefined first cycles of the physiological pulses in the first difference signal, determine a first signal profile for each of the predefined first cycles, and generate the first template signal by tiling the first signal profiles such that the timing of the first signal profiles in the first template signal matches the timing of the set of predefined first cycles in the first difference signal.

6. The device of claim 5 , wherein the signal processor is further configured, in step b), to: identify a respective reference time point for each of the predefined first cycles in the first difference signal, and generate the first template signal by tiling and time-scaling the first signal profiles with respect the reference time points.

7. The device of claim 5 , wherein the signal processor is further configured, in step b), to: determine a length of the respective predefined first cycle in the first difference signal; and select the first signal profile among at least two candidate profiles based on the length of the respective predefined first cycle.

8. The device of claim 5 , wherein the signal processor is further configured, in step b), to determine the first signal profile by at least one of:
retrieving the first signal profile from an electronic memory associated with the device, wherein the first signal profile is fixed and pre-defined, or generated and stored in the electronic memory by the signal processor during processing of a preceding signal segment in the pressure signal;
generating the first signal profile as a function of the predefined first cycles in the first difference signal;
generating the first signal profile by processing the pressure signal while the interference generator is intermittently disabled; and
generating the first signal profile by processing a further pressure signal acquired from a further pressure sensor in the extracorporeal fluid circuit.

9. The device of claim 1 , wherein the signal processor is further configured, in step d), to: identify a set of predefined second cycles in the second difference signal; determine a second signal profile for each of the predefined second cycles; and generate the second template signal by tiling the second signal profiles such that the timing of the second signal profiles in the second template signal matches the timing of the set of predefined second cycles in the second difference signal.

10. The device of claim 9 , wherein the signal processor is further configured, in step d), to: identify a respective reference time point for each of the predefined second cycles in the second difference signal, and generate the second template signal by tiling and time-scaling the second signal profiles with respect to the reference time points.

11. The device of claim 9 , wherein the signal processor is further configured, in step d), to determine the second signal profile by one of:
retrieving the second signal profile from an electronic memory associated with the device, wherein the second signal profile is fixed and pre-defined, or generated and stored in the electronic memory by the signal processor during processing of a preceding signal segment in the pressure signal;
retrieving the second signal profile from the electronic memory based on an operating condition of the extracorporeal fluid circuit, wherein a plurality of second signal profiles are stored in the electronic memory in association with different operating conditions;
generating the second signal profile as a function of the predefined second cycles in the second difference signal;
mapping the predefined second cycles in the second difference signal to corresponding subsets of the signal segment, and generating the second signal profile as a function of the corresponding subsets; and
generating the second signal profile by processing a further pressure signal acquired from a further pressure sensor in the extracorporeal fluid circuit.

12. The device of claim 1 , wherein the signal processor is further configured, in step d), to: determine a current operating condition of the interference generator; and generate the second template signal as a combination of sinusoids at a plurality of harmonic frequencies associated with the current operating condition.

13. The device of claim 1 , wherein the signal processor is further configured, in step a), to: acquire said at least one initial template signal as an initial estimate of the shape, the magnitude and the timing of the interference pulses in the signal segment.

14. The device of claim 1 , wherein the signal processor is further configured, in step a), to acquire said at least one initial template signal by one of:
determining a current operating condition of the interference generator, determining an initial signal profile for predefined second cycles in the signal segment, and generating said at least one initial template signal by tiling the initial signal pr

Assignees

• Gambro Lundia Ab

Inventors

• Holmer Mattias
• Olde Bo
• Solem Kristian
• Sornmo Leif

Classifications

• A61B5/7235

  Details of waveform analysis (detecting specific parameters of the electrocardiograph cycle A61B5/349) · CPC title

• A61M1/3656 Primary

  Monitoring patency or flow at connection sites; Detecting disconnections · CPC title

• A61B5/02108

  from analysis of pulse wave characteristics · CPC title

• A61M2205/3331

  Pressure; Flow · CPC title

• A61M2230/30

  Blood pressure (A61M2230/04 takes precedence) · CPC title