Apparatus and method of controlling an extracorporeal blood treatment

Patent metadata

Field	Value
Publication number	US-9770546-B2
Application number	US-201314428276-A
Country	US
Kind code	B2
Filing date	Aug 8, 2013
Priority date	Sep 28, 2012
Publication date	Sep 26, 2017
Grant date	Sep 26, 2017

Abstract

An apparatus is described for extracorporeal blood treatment ( 1 ), comprising a treatment unit ( 2 ), an extracorporeal blood circuit ( 8 ) and a fluid evacuation line ( 10 ). The apparatus comprises a control unit ( 21 ) connected with a pressure sensor ( 13, 14 ) and with a blood pump ( 9 ) and configured to move the blood pump ( 9 ), generating a variable flow (Q(t)) with a constant component (Q b ) and a variable component (Qvar(t)) having a nil average value; the variable flow generates, in the expansion chamber ( 11, 12 ), a progression of the pressure that is variable over time (P(t)) with a pressure component (Pvar(t)) oscillating about an average value (P av g). The control unit receives, from the sensor, a plurality of values (P j ) and calculates the average value of the pressure (P av g), acquires an estimated value of volume variation (AP) in the expansion chamber ( 11, 12 ) connected to the variable flow component (Qvar(t)), calculates, as a function of the pressure values (P j ), an estimated value of pressure variation (AP) in the expansion chamber ( 11; 12 ) that is representative of the oscillating pressure component (Pvar(t)) and determines a representative magnitude of a blood level (L) in the expansion chamber ( 11, 12 ) as a function of the average value (P av g) of the pressure (P(t)), of the estimated value of volume variation (AV) and of the estimated pressure variation (AP) in the expansion chamber.

First claim

The invention claimed is:

1. An apparatus for extracorporeal blood treatment comprising:
at least a treatment unit having at least a first chamber and at least a second chamber separated from one another by a semipermeable membrane;
at least a blood removal line connected to an inlet port of the first chamber and predisposed to remove blood from a patient;
at least a blood return line connected to an outlet port from the first chamber and predisposed to return treated blood to the patient;
at least an expansion chamber placed at least in one of the blood removal line and the blood return line, the expansion chamber being arranged in use to contain a predetermined quantity of gas in an upper portion and a predetermined quantity of blood at a predetermined level in a lower portion thereof, the blood removal line, the blood return line, the first chamber and the at least an expansion chamber being part of an extracorporeal blood circuit;
at least a blood pump operating at the extracorporeal blood circuit such as to move the blood in the circuit;
at least a pressure sensor associated to the expansion chamber and configured to enable determining pressure values internally of the expansion chamber;
at least a fluid evacuation line connected to an outlet port of the second chamber; and
a control unit connected to the at least a pressure sensor, with the pump, and configured to:
move the blood pump to generate a variable blood flow comprising a constant flow component equal to a desired value of blood flow and a variable flow component oscillating about the constant component and having a substantially nil average value, the variable blood flow component generating, at least in the expansion chamber, a pressure progression that is variable over time comprising a pressure component oscillating about an average value;
receive from the at least a pressure sensor a plurality of measured pressure values for a time period comprising a plurality of oscillations of the pressure about the average value, the pressure values being measured in successive time instants;
calculate, as a function of the pressure values, an average value of the pressure;
acquire an estimated volume variation value in the expansion chamber linked to the variable flow component;
calculate, as a function of the pressure values, an estimated pressure variation in the expansion chamber representing the oscillating pressure component; and
determine a representative magnitude of a blood level in the expansion chamber as a function of the average value of the pressure, the estimated volume variation value and the value of the estimated pressure variation in the expansion chamber.

2. The apparatus of claim 1 , wherein the control unit is programmed to determine the representative magnitude of the blood level in the expansion chamber by exploiting the ideal gas law, the ideal gas law being applied to a modelled representation of the apparatus substantially constituted by a superposing of:
an open system in which the expansion chamber is considered to be in a stationary state and interested only by the constant flow component and the internal pressure in the expansion chamber is correspondingly a constant pressure equal to the mean value; and
a partially closed system in which only an access to the expansion chamber, selected from between an inlet for the blood and an outlet for the blood, is open and subject to a volume variation representative of the variable flow component oscillating about the constant component and a pressure value representing the oscillating pressure component.

3. The apparatus of claim 1 , wherein the control unit is programmed to determine the magnitude representing the blood level in the expansion chamber using the following mathematical relation:

Vair
=

Δ
⁢

⁢

V
·

(

Pavg
+

Δ
⁢

⁢
P

)

(

Δ
⁢

⁢
P

)

in which:
‘V air ’ is the volume of air inside the expansion chamber;
‘ΔV’ is the volume variation linked to the variable flow component;
‘P avg ’ is the average pressure value; and
‘ΔP’ is the pressure variation in the expansion chamber representing the oscillating pressure component.

4. The apparatus of claim 1 , wherein the average pressure value is calculated as a function of a plurality of measured pressure values relating to a time period comprising a plurality of blood flow oscillations about the constant component and consequently a plurality of oscillations of the pressure about the average value.

5. The apparatus of claim 4 , wherein the time period comprises at least three oscillations.

6. The apparatus of claim 1 , wherein the step of acquiring an estimated value of volume variation in the expansion chamber comprises a sub-step of reading from a memory of an estimated pre-set value of volume variation, the selection being operated according to at least one of parameters included in the group consisting of:
a type of extracorporeal circuit installed on the apparatus;
a type of extracorporeal blood treatment;
a type of blood pump;
the desired blood flow value;
a pressure upstream or downstream of the blood pump;
a type of pump tract;
the average pressure in the expansion chamber;
an index of ageing of the pump tract; and
the number of revolutions accumulated by the blood pump.

7. The apparatus of claim 1 , wherein the step of acquiring an estimated value of volume variation in the expansion chamber comprises a sub-step of calculating the estimated value as a function of at least a parameter selected in the group consisting of: the pressure values measured, the constant blood flow component, an indicator of an ageing of a blood tract and a preceding estimated air volume in the expansion chamber.

8. The apparatus of claim 1 , wherein the step of acquiring an estimated value of volume variation in the expansion chamber comprises a sub-step of calculating the estimated value using the following mathematical relation:
Δ V n =k 0 +k 1 · P n + k 2 ·n imp n +k 3 · Q b n + k 4 ·V n-1

in which:
n is the generic index indicating the n-th measurement output of the air volume;
ΔV n is the estimated variation of volume ΔV at the nth step of measurement of the air volume;
k 0 , k 1 , k 2 , k 3 , k 4 are experimentally-determined constants;
P n is the average of the pressure values measured at the end of the n-th measuring step of the air volume;

n_imp n is the accumulated number—or a value proportional to the accumulated number—of revolutions of the blood pump;
Q bn is the average value of the blood flow at the end of the n-th measuring step of the air

Assignees

• Gambro Lundia Ab

Inventors

• Vasta Alessandro

Classifications

• A61M2205/3306

  Optical measuring means · CPC title

• A61M2205/3379

  Masses, volumes, levels of fluids in reservoirs, flow rates · CPC title

• A61M2205/3365

  Rotational speed · CPC title

• A61M2205/3389

  Continuous level detection (A61M2205/3393 takes precedence) · CPC title

• A61M2205/3375

  Acoustical, e.g. ultrasonic, measuring means · CPC title