Pulsatility detection

Abstract

Apparatus and methods are described including a ventricular assist device that includes a blood pump configured to be placed inside a left ventricle of a subject and to pump blood from the subject's left ventricle to an aorta of the subject. A blood pressure sensor measures aortic pressure of the subject. A computer processor varies a flow rate that is that is generated by the blood pump, and determines a relationship between arterial pulsatility of the subject and the flow rate that is generated by the blood pump, based upon aortic pressure that is measured by the blood pressure sensor as the flow rate that is generated by the blood pump is varied. The computer processor estimates native cardiac output of the subject at least partially based upon the relationship. Other applications are also described.

1 . An apparatus, comprising:
 a ventricular assist device comprising a blood pump configured to be placed inside a left ventricle of a subject and to pump blood from the subject's left ventricle to an aorta of the subject;   a blood pressure sensor configured to measure aortic pressure of the subject;   a computer processor configured to:
 vary a flow rate that is that is generated by the blood pump; 
 determine a relationship between arterial pulsatility of the subject and the flow rate that is generated by the blood pump, based upon aortic pressure that is measured by the blood pressure sensor as the flow rate that is generated by the blood pump is varied; and 
 estimate native cardiac output of the subject at least partially based upon the relationship. 
   
     
     
         2 . The apparatus according to  claim 1 , wherein the blood pump comprises an impeller, wherein the computer processor is configured to vary the flow rate that is generated by the blood pump by changing a rotation rate of the impeller. 
     
     
         3 . The apparatus according to  claim 1 , wherein the blood pump comprises a continuous flow blood pump, which is configured to generate continuous flow when the blood pump is operating at its maximum pumping rate. 
     
     
         4 . The apparatus according to  claim 1 , wherein the computer processor is configured to extrapolate the relationship between the subject's arterial pulsatility and the flow rate that is generated by the blood pump to derive what the pump flow rate would be when the subject's arterial pulsatility reaches zero, and wherein the computer processor is configured to determine the subject's native cardiac output based on what the pump flow rate would be when the subject's arterial pulsatility reaches zero. 
     
     
         5 . The apparatus according to  claim 4 , wherein the computer processor is configured to determine that the derived flow rate when the subject's arterial pulsatility reaches zero provides an approximation of the subject's native cardiac output. 
     
     
         6 . A method, comprising:
 pumping blood from a left ventricle of a subject to an aorta of the subject using a ventricular assist device;   measuring aortic pressure of the subject by operating a blood pressure sensor;   operating a computer processor to:
 vary a flow rate that is that is generated by the blood pump; 
 determine a relationship between arterial pulsatility of the subject and the flow rate that is generated by the blood pump, based upon aortic pressure that is measured by the blood pressure sensor as the flow rate that is generated by the blood pump is varied; and 
 estimate native cardiac output of the subject at least partially based upon the relationship. 
   
     
     
         7 . The method according to  claim 6 , wherein pumping blood from the subject's left ventricle to the subject's aorta of the subject comprises pumping blood from the subject's left ventricle to the subject's aorta using an impeller and operating the computer processor to vary the flow rate that is that is generated by the blood pump comprises operating the computer processor to vary a rotation rate of the impeller. 
     
     
         8 . The method according to  claim 6 , wherein pumping blood from the subject's left ventricle to the subject's aorta of the subject comprises pumping blood from the subject's left ventricle to the subject's aorta using a continuous flow blood pump, which is configured to generate continuous flow when the blood pump is operating at its maximum pumping rate. 
     
     
         9 . The method according to  claim 6 , wherein operating the computer processor to estimate native cardiac output of the subject at least partially based upon the relationship comprises operating the computer processor:
 to extrapolate the relationship between the subject's arterial pulsatility and the flow rate that is generated by the blood pump to derive what the pump flow rate would be when the subject's arterial pulsatility reaches zero, and   to determine the subject's native cardiac output based on what the pump flow rate would be when the subject's arterial pulsatility reaches zero.   
     
     
         10 . The method according to  claim 9 , wherein operating the computer processor to estimate native cardiac output of the subject at least partially based upon the relationship comprises operating the computer processor to determine that the derived flow rate when the subject's arterial pulsatility reaches zero provides an approximation of the subject's native cardiac output.