Method and system for controlling blood pump flow
A heart assist device, for example a left ventricular assist device (LVAD) including a blood pump, is controlled on the basis of a ratio of the pump's speed and the patient's heart rate. The patient's activity and a required cardiac assist level can be defined via the heart beat rate of the patient and a rotational speed of the LVAD pump. Controlling the pump of the heart assist device based on the pump speed and the patient's heart rate enables the heart assist device to respond to changes in the patient's activity level.
1. A method for controlling a blood pump connected to a patient, comprising the following steps:
determining a value for the heart rate of the patient;
determining a value for the speed of the pump;
calculating the ratio of said heart rate value and said speed value; and
regulating the speed of the pump in accordance with said ratio.
2. The method of claim 1 , wherein the speed of the pump is regulated to achieve a target flow rate that is a monotonic function of said ratio within a defined range of flow rates.
3. The method of claim 2 , wherein said monotonic function is linear, and
said target flow rate Qtarget=K 1 *M+K 2
where M=HR/f(N), HR is the patient's heart rate, N is the speed of the pump, and K 1 , K 2 are constants.
4. The method of claim 3 wherein f(N)=N n , where n is related to at least one of a type and size of the pump.
5. The method of claim 3 , wherein:
K 1 =(Qmax−Qmin)/(Mmax−Mmin); and
K 2 =Qmin−(Qmax−Qmin)*Mmin/(Mmax−Mmin);
where Qmax is a maximum allowable flow rate of the pump, Qmin is a minimum allowable flow rate of the pump, Mmax is a maximum threshold value of the ratio M, and Mmin is a minimum threshold value of the ratio M.
6. The method of claim 5 , wherein:
Mmax=HRmax/(Nmin) n ; and
Mmin=HRmin/(Nmax) n.
7. The method of claim 1 , further comprising the step of:
changing the pump speed when flow pulsatility falls below a defined threshold.
8. The method of claim 7 , wherein said threshold is a predefined monotonic function based on hydraulic performance of the pump.
9. The method of claim 7 , wherein the step of changing the pump speed is carried out prior to the step of regulating the speed of the pump in accordance with said ratio.
10. A blood pump system for assisting a patient's heart, the system comprising:
a blood pump adapted to be connected to the patient; and
a controller that receives input signals, determines a pump speed value and a patient heart rate value from said input signals, determines a ratio of the patient's heart rate value and the pump speed value, and regulates the pump speed based upon said determined ratio.
11. The system of claim 10 , wherein the controller regulates the speed of the pump to achieve a target flow rate that is a monotonic function of said ratio within a defined range of flow rates.
12. The system of claim 11 , wherein said monotonic function is linear, and
said target flow rate Qtarget=K 1 *M+K 2
where M=HR/f(N), HR is the patient's heart rate, N is the speed of the pump, and K 1 , K 2 are constants.
13. The system of claim 12 , wherein f(N)=N n , where n is related to at least one of a type and size of the pump.
14. The system of claim 12 , wherein:
K 1 =(Qmax−Qmin)/(Mmax−Mmin); and
K 2 =Qmin−(Qmax−Qmin)*Mmin/(Mmax−Mmin);
where Qmax is a maximum allowable flow rate of the pump, Qmin is a minimum allowable flow rate of the pump, Mmax is a maximum threshold value of the ratio M, and Mmin is a minimum threshold value of the ratio M.
15. The system of claim 14 , wherein:
Mmax=HRmax/(Nmin) n ; and
Mmin=HRmin/(Nmax) n .
16. The system of claim 10 , wherein the controller changes the pump speed when flow pulsatility falls below a first threshold.
17. The system of claim 16 , wherein said threshold is a predefined monotonic function based on hydraulic performance of the pump.
18. The system of claim 16 , wherein the controller performs said changing of pump speed prior to regulating the speed of the pump based on said ratio.
19. A machine readable medium comprising a computer program that receives input signals, determines a value of the speed of a blood pump connected to a patient and a value of the patient's heart rate from said input signals, determines a ratio of the patient's heart rate to the speed of the pump, and regulates the pump speed based upon said ratio.
20. The machine-readable medium of claim 19 , wherein the speed of the pump is regulated to achieve a target flow rate that is a monotonic function of said ratio within a defined range of flow rates.
21. The medium of claim 19 , wherein:
said target flow rate Qtarget=K 1 *M+K 2 ,
where M=HR/N n , HR is the patient's heart rate, N is the speed of the pump, n is related to at least one of a type and size of the pump, and K 1 , K 2 are constants.
22. The medium of claim 21 , wherein:
K 1 =(Qmax−Qmin)/(Mmax−Mmin); and
K 2 =Qmin−(Qmax−Qmin)*Mmin/(Mmax−Mmin);
where Qmax is a maximum allowable flow rate of the pump, Qmin is a minimum allowable flow rate of the pump, Mmax is a maximum threshold value of the ratio M, and Mmin is a minimum threshold value of the ratio M.
23. The medium of claim 22 , wherein:
Mmax=HRmax/(Nmin) n ; and
Mmin=HRmin/(Nmax).