# US 2020/0390959 A1 · Filtering a pressure signal from a medical apparatus

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- Number: US 2020/0390959 A1
- Document ID: US20200390959A1
- Status: Published application
- Kind: A1
- Application number: 16/969,811
- Filed: 2019-01-31
- Published: 2020-12-17
- Earliest claimed: 2018-02-16
- Assignees: Gambro Lundia AB
- Applicants: Gambro Lundia AB
- Inventors: Bo OLDE; Olof EKDAHL; Christian VARTIA
- Web page: https://patentgrep.com/patent/US20200390959A1

## CPC

- A61M 1/1601: {Control or regulation}
- A61M 1/3639: {Blood pressure control, pressure transducers specially adapted therefor}
- A61M 1/14: Dialysis systems; Artificial kidneys; Blood oxygenators (semi-permeable membranes characterised by the material, manufacturing processes therefor B01D71/00){; Reciprocating systems for treatment of body fluids, e.g. single needle systems for hemofiltration or pheresis}
- A61M 1/36: Other treatment of blood in a by-pass of the natural circulatory system, e.g. temperature adaptation, irradiation {; Extra-corporeal blood circuits}
- A61M 5/14: Infusion devices, e.g. infusing by gravity; Blood infusion; Accessories therefor
- G01B 7/30: for measuring angles or tapers; for testing the alignment of axes
- G01D 5/145: {influenced by the relative movement between the Hall device and magnetic fields (see G01R33/06)}
- G01D 5/244: influencing characteristics of pulses or pulse trains; generating pulses or pulse trains
- A61M 2205/3331: Pressure; Flow
- A61M 2205/52: with memories providing a history of measured variating parameters of apparatus or patient
- A61M: DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY (introducing media into or onto the bodies of animals A61D7/00; means for inserting tampons A61F13/26; devices for administering food or medicines orally A61J; containers for collecting, storing or administering blood or medical fluids A61J1/05); DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY (surgery A61B; chemical aspects of surgical articles A61L); DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR {(Electrotherapy, e.g. producing anaesthesia by the use of alternating or intermittent currents A61N1/36021)}
- G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01D: MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR

## Abstract

A signal filtering device implements a filtering method that involves operating a digital filter (60) on a pressure signal (p), which represents fluid pressure in a medical apparatus, to produce a filtered signal (y). The method further comprises detecting or predicting presence of a disturbance in the pressure signal (p), and selectively modifying a state vector of the digital filter (60) at a selected time point subsequent to the disturbance in the pressure signal (p), so as to suppress influence of the disturbance on the filtered signal (y). The state vector may be modified by replacing the state vector of the digital filter (60) at the selected time point (t2) by a dedicated reconfiguration state vector (Z′).

## Claims

### Claim at position 1

1-27. (canceled)

### Claim 28

A computer-implemented signal filtering method comprising:
receiving, in a processor from a pressure sensor, a pressure signal (p) comprising a time-sequence of data samples representing fluid pressure in a medical apparatus;
operating, using the processor, a digital filter on the pressure signal (p) to produce a filtered pressure signal (y), wherein the digital filter is operated to, at each current time point, compute a current filtered data sample (ym) of the filtered pressure signal (y) as a function of a preceding state vector (Z*) of the digital filter and a current data sample (pm) in the pressure signal (p), and compute a current state vector (Zm) of the digital filter as a function of the preceding state vector (Z*), the current data sample (pm) and, optionally, the current filtered data sample (ym);
detecting or predicting, using the processor, a disturbance in the pressure signal (p); and
selectively modifying, using the processor, the preceding state vector (Z*) of the digital filter at a selected time point (t2) subsequent to the disturbance in the pressure signal (p), so as to suppress influence of the disturbance on the filtered pressure signal (y).

### Claim 29 (depends on 28)

The signal filtering method of claim 28, wherein selectively modifying the preceding state vector (Z*) comprises replacing the preceding state vector (Z*) of the digital filter at the selected time point (t2) by a reconfiguration state vector (Z′).

### Claim 30 (depends on 29)

The signal filtering method of claim 29, further comprising obtaining, using the processor, the reconfiguration state vector (Z′) to match a working point of the medical apparatus at the selected time point (t2).

### Claim 31 (depends on 30)

The signal filtering method of claim 30, further comprising:
acquiring, using the processor, from a digital storage memory, at least one state vector ([Z]) for the working point of the medical apparatus at the selected time point (t2); and
obtaining, using the processor, the reconfiguration state vector (Z′) as a function of the at least one state vector ([Z]).

### Claim 32 (depends on 31)

The signal filtering method of claim 31, wherein the digital storage memory stores a database that comprises state vectors for a plurality of different working points of the medical apparatus, and wherein said at least one state vector ([Z]) is selected among the state vectors stored in the database based on the working point of the medical apparatus at the selected time point (t2).

### Claim 33 (depends on 32)

The signal filtering method of claim 32, further comprising populating, using the processor, at least part of the database during operation of the digital filter prior to the disturbance, by storing one or more of the preceding state vectors (Z*) in association with a respective current working point of the medical apparatus.

### Claim 34 (depends on 31)

The signal filtering method of claim 31, further comprising selectively storing, using the processor, when detecting or predicting the presence of the disturbance in the pressure signal (p), a preceding state vector (Z*) at a first time point (t1), wherein the at least one state vector ([Z]) is acquired to comprise the preceding state vector (Z*) at the first time point (t1).

### Claim 35 (depends on 34)

The signal filtering method of claim 34, wherein the selected time point (t2) is selected based on the first time point (t1).

### Claim 36 (depends on 34)

The signal filtering method of claim 34, wherein the selected time point (t2) is selected such that the working point of the medical apparatus at the selected time point (t2) corresponds to the working point of the medical apparatus at the first time point (t1).

### Claim 37 (depends on 30)

The signal filtering method of claim 30, wherein the pressure signal (p) comprises pulsations originating from a repetitive pulse generator in the medical apparatus, and wherein the working point is at least partly given by a phase of the repetitive pulse generator.

### Claim 38 (depends on 37)

The signal filtering method of claim 37, wherein the repetitive pulse generator operates in a sequence of pulse cycles (R), each pulse cycle (R) resulting in at least one pulsation in the pressure signal (p), and wherein the phase corresponds to a location within the pulse cycle (R).

### Claim 39 (depends on 38)

The signal filtering method of claim 38, further comprising:
obtaining, using the processor, the reconfiguration state vector (Z′) associated with a selected location within the pulse cycle (R); determining the selected time point (t2), based on a phase signal (θ) indicative of the phase of the repetitive pulse generator, to correspond to the selected location; and
setting, using the processor, the preceding state vector (Z*) at the selected time point (t2) to the reconfiguration state vector (Z′).

### Claim 40

The signal filtering method of 37, wherein the working point is further given by at least one of a current operating frequency (ω) of the repetitive pulse generator, an average fluid pressure (P) in the medical apparatus, and an amplitude of pressure variations in the pressure signal (p).

### Claim 41 (depends on 37)

The signal filtering method of claim 37, wherein the repetitive pulse generator comprises a pump for pumping a fluid in the medical apparatus.

### Claim 42 (depends on 41)

The signal filtering method of claim 41, wherein the phase corresponds to a stroke position of the pump.

### Claim 43 (depends on 41)

The signal filtering method of claim 41, wherein the pump is a peristaltic pump comprising a rotation element for engaging a tube segment, and wherein the phase corresponds to an angular position of the rotation element.

### Claim 44 (depends on 28)

The signal filtering method of claim 28, further comprising:
determining, using the processor, based on a phase signal (θ) indicative of a phase of a repetitive pulse generator in the medical apparatus, a first phase value at a first time point (t1) preceding the disturbance;
storing, in the digital storage memory, the current state vector (Zm) computed at the first time point (t1);
obtaining, using the processor, a selected phase value as a function of the first phase value;
determining, using the processor, the selected time point (t2), based on the phase signal (θ), to correspond to the selected phase value;
acquiring, using the processor, from the digital storage memory, a reconfiguration state vector (Z′) as a function of the current state vector (Zm) computed at the first time point (t1); and
setting, using the processor, the preceding state vector (Z*) at the selected time point (t2) to the reconfiguration state vector (Z′).

### Claim 45 (depends on 28)

The signal filtering method of claim 28, wherein the digital filter, when computing the current state vector (Zm), is operated to modify the current data sample (pm) by a first set of filter coefficients (b2, . . . bn) and, optionally, to modify the current filtered data sample (ym) by a second set of filter coefficients (a2, . . . an).

### Claim 46 (depends on 28)

The signal filtering method of claim 28, wherein the current state vector (Zm) comprises a predefined number of state values (z1, . . . zn−1) associated with the current time point, wherein the digital filter is operated to compute the state values as:
z
1
=
b
2
·
p
m
+
z
2
*
-
a
2
·
y
m

⋮
z
n
-
2
=
b
n
-
1
·
p
m
+
z
n
-
1
*
-
a
n
-
1
·
y
m
z
n
-
1
=
b
n
·
p
m
-
a
n
·
y
m
wherein z2*, . . . zn−1* are state values of the preceding state vector (Z*), pm is the current data sample, ym is the current filtered data sample, and a2, . . . an and b2, . . . bn, are filter coefficients, and wherein a2, . . . an may be set to zero.

### Claim 47 (depends on 28)

The signal filtering method of claim 28, wherein the digital filter is operated to compute the current filtered data sample (ym) as a function of a state value (z1*) of the preceding state vector (Z*), and the current data sample (pm) modified by a filter coefficient (b1).

### Claim 48 (depends on 47)

The signal filtering method of claim 47, wherein the digital filter is operated to compute the filtered data sample as: ym=b1·pm+z1*, wherein b1 is said filter coefficient, pm is the current data sample, and z1* is said state value of the preceding state vector (Z*).

### Claim 49 (depends on 28)

The signal filtering method of claim 28, wherein the digital filter is operated to compute the current state vector (Zm) for each current data sample (pm) in the pressure signal (p).

### Claim 50 (depends on 28)

The signal filtering method of claim 28, further comprising stopping, using the processor, the operation of the digital filter during at least part of the predicted or detected disturbance in the pressure signal (p).

### Claim 51 (depends on 28)

The signal filtering method of claim 28, wherein the medical apparatus is one of an extracorporeal blood processing apparatus and an infusion apparatus.

### Claim 52 (depends on 28)

The signal filtering method of claim 28, further comprising detecting, using the processor, a fluid pressure in a fluid line based on the filtered pressure signal (y).

### Claim 53 (depends on 28)

A non-transitory, computer-readable medium storing instructions, which when executed by the processor, cause the processor to perform the method of claim 28.

### Claim 54

A signal filtering device comprising:
a memory; and
a processor in communication with the memory, the processor configured to:
obtain a pressure signal (p) comprising a time-sequence of data samples representing fluid pressure in a medical apparatus;
operate a digital filter on the pressure signal (p) to produce a filtered pressure signal (y), wherein the digital filter is configured to, at each current time point, compute a current filtered data sample (ym) of the filtered pressure signal (y) as a function of a preceding state vector (Z*) of the digital filter and a current data sample (pm) in the pressure signal (p), and compute a current state vector (Zm) of the digital filter as a function of the preceding state vector (Z*), the current data sample (pm) and, optionally, the current filtered data sample (ym);
detect or predict a disturbance in the pressure signal (p); and
selectively modify the preceding state vector (Z*) of the digital filter at a selected time point (t2) subsequent to the disturbance in the pressure signal (p), so as to suppress influence of the disturbance on the filtered pressure signal (y).

### Claim 55

A medical system comprising:
a medical apparatus;
a pressure sensor arranged to be responsive to fluid pressure in the medical apparatus; and
a signal filtering device including a processor in communication with a memory, the processor configured to:
obtain a pressure signal (p) comprising a time-sequence of data samples representing fluid pressure in a medical apparatus;
operate a digital filter on the pressure signal (p) to produce a filtered pressure signal (y), wherein the digital filter is configured to, at each current time point, compute a current filtered data sample (ym) of the filtered pressure signal (y) as a function of a preceding state vector (Z*) of the digital filter and a current data sample (pm) in the pressure signal (p), and compute a current state vector (Zm) of the digital filter as a function of the preceding state vector (Z*), the current data sample (pm) and, optionally, the current filtered data sample (ym);
detect or predict a disturbance in the pressure signal (p); and
selectively modify the preceding state vector (Z*) of the digital filter at a selected time point (t2) subsequent to the disturbance in the pressure signal (p), so as to suppress influence of the disturbance on the filtered pressure signal (y),
wherein the signal filtering device is connected to the pressure sensor and is configured to obtain the pressure signal (p) from the pressure sensor.