Method for determining a flow rate of a fluid flowing through an implanted vascular support system, and implantable vascular support system
The invention relates to a method for determining a flow rate of a fluid flowing through an implanted vascular assist system ( 1 ), said method comprising the following steps: a) carrying out a first pulsed Doppler measurement at a first pulse repetition rate by means of an ultrasonic sensor ( 2 ) of the assist system ( 1 ); b) carrying out a second pulsed Doppler measurement at a second pulse repetition rate by means of the ultrasonic sensor ( 2 ) of the assist system ( 1 ), wherein the second pulse repetition rate differs from the first pulse repetition rate; c) determining the flow rate using measurement results of the first pulsed Doppler measurement and the second pulsed Doppler measurement.
1. A method for determining a flow rate v of blood flowing through a cardiac assist system, comprising:
performing a first pulsed Doppler measurement at a first pulse repetition rate PRF 1 using an ultrasonic sensor of the cardiac assist system;
performing a second pulsed Doppler measurement at a second pulse repetition rate PRF 2 using the ultrasonic sensor of the assist system, wherein the second pulse repetition rate PRF 2 is greater than the first pulse repetition rate PRF 1 ; and
determining the flow rate using measurement results of the first pulsed Doppler measurement and the second pulsed Doppler measurement by solving for an integer n 1 , an integer n 2 , and a main component f 1 of the first pulsed Doppler measurement and a main component f 2 of the second pulsed Doppler measurement using a linear Diophantine equation, wherein the linear Diophantine equation comprises:
n 1 ·PRF 1 −n 2 ·PRF 2 =f 2 −f 1
for a boundary condition of:
v
<
a
·
PRF
1
·
c
0
2
f
0
assuming
−| a|≤n 1 ≤|a | and −| b|≤n 2 ≤|b|,
wherein
a
:
=
P
R
F
2
2
·
ggT
(
PRF
1
,
PR
F
2
)
and
b
:=
P
R
F
1
2
·
ggT
(
PRF
1
,
PR
F
2
)
,
wherein ggT (PRF 1 , PRF 2 ) comprises the largest common divisor of PRF 1 and PRF 2 ,
and wherein f 0 comprises the ultrasonic transmission frequency of the ultrasonic sensor and c 0 comprises a speed of sound in the blood.
2. The method of claim 1 , wherein at least one of performing a first pulsed doppler measurement and performing a second pulsed doppler measurement comprises emitting a new ultrasonic pulse using an ultrasonic element only after an echo of an immediately previously emitted ultrasonic pulse has been received by the ultrasonic sensor.
3. The method of claim 1 , wherein PRF 1 or PRF 2 is smaller than twice a maximum occurring Doppler shift.
4. The method of claim 1 , wherein determining the flow rate comprises using a correlation between a detected main frequency component of the Doppler frequency spectrum of the first pulsed Doppler measurement and the first pulse repetition rate PRF 1 or the second pulsed Doppler measurement and the second pulse repetition rate PRF 2 .
5. The method of claim 1 , wherein determining the flow rate comprises solving the linear Diophantine equation using Bezout coefficients or an exhaustion method.
6. The method of claim 1 , wherein an observation window of the ultrasonic sensor is in a range of 25 mm to 55 mm from an ultrasonic element of the ultrasonic sensor.
7. A cardiac assist system comprising:
an ultrasonic sensor configured to perform a first pulsed Doppler measurement at a first pulse repetition rate PRF 1 and a second pulsed Doppler measurement at a second pulse repetition rate PRF 2 , wherein PRF 2 is greater than PRF 1 ; and
a processing unit configured to:
determine a flow rate of a fluid flowing through the cardiac assist system using measurement results of the first pulsed Doppler measurement and the second pulsed Doppler measurement,
wherein determining the flow rate using the measurement results of the first pulsed Doppler measurement and the second pulsed Doppler measurement comprises solving for an integer n 1 , an integer n 2 and a main component f 1 of the first pulsed Doppler measurement and a main component f 2 of the second pulsed Doppler measurement using a linear Diophantine equation comprising:
n 1 ·PRF 1 −n 2 ·PRF 2 =f 2 −f 1
for the boundary condition:
v
<
a
·
PRF
1
·
c
0
2
f
0
assuming:
−| a|≤n 1 ≤|a | and −| b|≤n 2 ≤|b|,
wherein
a
:=
P
R
F
2
2
·
ggT
(
PRF
1
,
PR
F
2
)
and
b
:=
P
R
F
1
2
·
ggT
(
PRF
1
,
PR
F
2
)
,
wherein ggT (PRF 1 , PRF 2 ) comprises the largest common divisor of PRF 1 and PRF 2 ,
and wherein f 0 is the ultrasonic transmission frequency of the ultrasonic sensor and c 0 is a speed of sound in the fluid.
8. The cardiac assist system of claim 7 , wherein the processing unit is configured to solve the linear Diophantine equation using Bezout coefficients or an exhaustion method to determine the flow rate.
9. The cardiac assist system of claim 7 , wherein the processing unit is configured to calculate a fluid flow based on the flow rate.
10. The system of claim 7 , wherein the ultrasonic sensor comprises an observation window in a range of 25 mm to 55 mm from an ultrasonic element of the ultrasonic sensor.
11. The system of claim 7 , further comprising a cannula, wherein the ultrasonic sensor is configured to perform the first pulsed Doppler measurement and the second pulsed Doppler measurement within the cannula.
12. The system of claim 11 , wherein the ultrasonic sensor is integrated into the tip of the cannula.
13. A method for determining a fluid flow through a cardiac assist system comprising:
determining a flow rate v of blood flowing through the cardiac assist system, wherein determining the flow rate v comprises:
performing a first pulsed Doppler measurement at a first pulse repetition rate PRF 1 using an ultrasonic sensor of the cardiac assist system;
performing a second pulsed Doppler measurement at a second pulse repetition rate PRF 2 using the ultrasonic sensor of the assist system, wherein the second pulse repetition rate PRF 2 is greater than the first pulse repetition rate PRF 1 ; and
determining the flow rate using measurement results of the first pulsed Doppler measurement and the second pulsed Doppler measurement by solving for an integer n 1 , an integer n 2 , and a main component f 1 of the first pulsed Doppler measurement and a main component f 2 of the second pulsed Doppler measurement using a linear Diophantine equation, wherein the linear Diophantine equation comprises:
n 1 ·PRF 1 −n 2 ·PRF 2 =f 2 −f 1
for a boundary condition of:
v
<
a
·
PRF
1
·
c
0
2
f
0
assuming
−| a|≤n 1 ≤|a | and −| b|≤n 2 ≤|b|,
wherein
a
:=
P
R
F
2
2
·
ggT
(
PRF
1
,
PR
F
2
)
and
b
:=
P
R
F
1
2
·
ggT
(
PRF
1
,
PR
F
2
)
,
wherein ggT (PRF 1 , PRF 2 ) comprises the largest common divisor of PRF 1 and PRF 2 ,
and wherein f 0 comprises the ultrasonic transmission frequency of the ultrasonic sensor and c 0 comprises a speed of sound in the blood; and
determining the fluid flow in the cardiac assist system based on the flow rate v.