Method and device for determining blood volume during an extracorporeal blood treatment
The invention relates to a method for determining blood volume during extracorporeal blood circulation, which is based on measuring the propagation rate or propagation time of the pulse waves propagating in the extracorporeal circulation system. The invention preferably involves the measurement of the propagation rate or propagation time of the pulse waves generated by the blood pump, which is placed in arterial branch of the blood line. The device for determining blood volume can make use of the pressure sensor, which is placed in the venous branch of the blood line and which is already provided in prior art blood treatment devices. As a result, the amount of equipment required is relatively low.
1. A method for the determination of a blood volume during an extracorporeal blood treatment with a blood treatment apparatus in an extracorporeal blood circuit, wherein the extracorporeal blood circuit includes an arterial branch of a blood line leading to the blood treatment apparatus and a venous branch of the blood line leading away from the blood treatment apparatus, the method comprising:
generating pulse waves that originate in the extracorporeal blood circuit, wherein the pulse waves have at least one of a propagation rate and a transit time;
measuring the at least one of the propagation rate and the transit time of the pulse waves; and
determining the blood volume from the at least one of the measured propagation rate and the measured transit time of the pulse waves.
2. The method of claim 1 , wherein the pulse waves are generated by a blood pump arranged in the extracorporeal blood circuit.
3. The method of claim 2 , further comprising:
detecting the pulse waves by a first pressure sensor arranged in the extracorporeal blood circuit.
4. The method of claim 3 , wherein the blood pump is arranged in the arterial branch of the blood line upstream of the blood treatment apparatus, and the first pressure sensor is arranged in the venous branch of the blood line downstream of the blood treatment apparatus.
5. The method of claim 4 , further comprising:
detecting the pulse waves by a second pressure sensor, wherein the second pressure sensor is arranged in the arterial branch of the blood line upstream of the blood treatment apparatus.
6. The method of claim 1 , wherein determining the blood volume comprises determining a relative blood volume RBV(t) from a ratio of the at least one of the measured propagation rates and the measured transit times of the pulse waves at two different times t, t 0 of the extracorporeal blood treatment.
7. The method of claim 5 , wherein determining the blood volume comprises determining a relative blood volume RBV(t) from a ratio of the at least one of the measured propagation rates and the measured transit times of the pulse waves at two different times t, t 0 of the extracorporeal blood treatment.
8. The method of claim 6 , wherein the relative blood volume RBV(t) is calculated from the temporal change in the measured transit times of the pulse waves according to the following equation:
RBV
(
t
)
=
1
-
ρ
w
ρ
(
t
0
)
(
PTT
(
t
)
PTT
(
t
0
)
)
2
-
ρ
w
ρ
(
t
0
)
wherein PTT(t) and PTT(t 0 ) is the measured transit time of the pulse waves over a segment of the extracorporeal blood circuit with a predetermined length L at time t and t 0 , respectively; and wherein r w is the mass density of water and r(t 0 ) is the mass density of the blood at the start of the extracorporeal blood treatment.
9. The method of claim 7 , wherein the relative blood volume RBV(t) is calculated from the temporal change in the measured transit times of the pulse waves according to the following equation:
RBV
(
t
)
=
1
-
ρ
w
ρ
(
t
0
)
(
PTT
(
t
)
PTT
(
t
0
)
)
2
-
ρ
w
ρ
(
t
0
)
wherein PTT(t) and PTT(t 0 ) is the measured transit time of the pulse waves over a segment of the extracorporeal blood circuit with a predetermined length L at time t and t 0 , respectively; and wherein r w is the mass density of water and r(t 0 ) is the mass density of the blood at the start of the extracorporeal blood treatment.
10. A device for the determination of the blood volume during an extracorporeal blood treatment in an extracorporeal blood circuit, wherein the extracorporeal blood circuit includes an arterial branch of a blood line leading to a blood treatment apparatus and a venous branch of the blood line leading away from the blood treatment apparatus, the device comprising:
means for generating pulse waves that originate in the extracorporeal blood circuit, wherein the pulse waves have at least one of a propagation rate and a transit time;
means for measuring the at least one of the propagation rate and the transit time of the pulse waves; and
an analyzing unit configured to determine the blood volume from the at least one of the measured propagation rate and the measured transit time of the pulse waves.
11. The device of claim 10 , wherein the means for generating pulse waves comprises a blood pump arranged in the extracorporeal blood circuit.
12. The device of claim 11 , further comprising:
a first pressure sensor for detecting the pulse waves, wherein the first pressure sensor is arranged in the extracorporeal blood circuit.
13. The device of claim 12 , wherein the blood pump is arranged in the arterial branch of the blood line upstream of the blood treatment apparatus, and the first pressure sensor is arranged in the venous branch of the blood line downstream of the blood treatment apparatus.
14. The device of claim 13 , further comprising:
a second pressure sensor for detecting the pulse waves, wherein the second pressure sensor is arranged in the arterial branch of the blood line upstream of the blood treatment apparatus.
15. The device of claim 10 , wherein the analyzing unit is adapted to determine a relative blood volume RBV(t) from a ratio of the at least one of the measured propagation rates and the measured transit times of the pulse waves at two different times t, t 0 of the extracorporeal blood treatment.
16. The device of claim 14 , wherein the analyzing unit is adapted to determine a relative blood volume RBV(t) from a ratio of the at least one of the measured propagation rates and the measured transit times of the pulse waves at two different times t, t 0 of the extracorporeal blood treatment.
17. The device of claim 15 , wherein the analyzing unit is adapted to calculate the relative blood volume RBV(t) from the temporal change in the measured transit times of the pulse waves according to the following equation:
RBV
(
t
)
=
1
-
ρ
w
ρ
(
t
0
)
(
PTT
(
t
)
PTT
(
t
0
)
)
2
-
ρ
w
ρ
(
t
0
)
wherein PTT(t) and PTT(t 0 ) is the measured transit time of the pulse waves over a segment of the extracorporeal blood circuit with a predetermined length L at time t and t 0 , respectively; and wherein r w is the mass density of water and r(t 0 ) is the mass density of the blood at the start of the extracorporeal blood treatment.
18. The device of claim 16 , wherein the analyzing unit is adapted to calculate the relative blood volume RBV(t) from the temporal change in the measured transit times of the pulse waves according to the following equation:
RBV
(
t
)
=
1
-
ρ
w
ρ
(
t
0
)
(
PTT
(
t
)
PTT
(
t
0
)
)
2
-
ρ
w
ρ
(
t
0
)
wherein PTT(t) and PTT(t 0 ) is the measured transit time of the pulse waves over a segment of the extracorporeal blood circuit with a predetermined length L at time t and t 0 , respectively; and wherein r w is the mass density of water and r(t 0 ) is the mass density of the blood at the start of the extracorporeal blood treatment.