Patent Publication Number: US-2021187274-A1

Title: Catheter pump system and method of controlling a catheter pump drive

Description:
FIELD AND BACKGROUND OF THE INVENTION 
     The invention relates to a catheter pump system and to a method of controlling a pump chive of a catheter system. 
     In various clinical situations, such as when weaning from cardiopulmonary bypass, in the event of cardiogenic shock, insufficiently powerful heart function or acute heart attack, as well as for support during for instance high-risk percutaneous transluminal coronary (balloon) angioplasty, rotoblator procedures, and coronary stent placement, mechanical circulatory support is used to improve the condition of the patient and to increase the likelihood of recovery. 
     For this purpose, a catheter pump may be used, which pumps blood away from the heart or from closely downstream of the heart. The pump function can be controlled to be pulsatile in synchronization with the beating heart, so that the flow rate at which blood is pumped is increased at the start of systole to support outflow away from the left ventricle and decreased at the start of diastole, so that the outflow of blood during systole is supported and counter pressure encountered by outflowing blood during systole is reduced and contraction of the left ventricle is facilitated. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a catheter pump for providing pulsatile cardiac support, which is particularly simple and reliable. 
     According to the invention, this object is achieved by providing a catheter pump system according to claim  1 . The invention can also be embodied in a catheter pump system according to claim  8 , a method according to claim  10  and in a method according to claim  11 . 
     For providing circulatory support, an intra-aortic balloon pump (IABP), is standard inventory available in virtually every hospital. An IABP is a balloon mounted on a catheter, which is generally inserted into the aorta through the femoral artery in the leg. The balloon is usually guided into the descending aorta to a position at approximately 2 cm from the left subclavian artery. At the start of diastole (when the aortic valve is closed), the balloon is inflated, augmenting coronary perfusion and at the beginning of systole (when the heart ejects blood from the left ventricle through the aortic valve), the balloon is deflated so that the heart can discharge blood more easily. Thereby, overall cardiac output is increased and the left ventricular stroke work and myocardial oxygen requirements are decreased. 
     Connecting the pressure sensing port of the motor controller to the output port of an IABP driver provides a simple and reliable solution for controlling pulsatile operation of the motor and the pump in sync with pulsations of the heart, such that blood flow out of the heart is supported primarily during systole. 
     Control of motor speed can also be achieved in a particularly simple, reliable and smooth manner, regardless whether timing signals for the pulsatile operation of the motor and the pump are obtained from an IABP driver output port, if the motor is a pneumatic motor and motor control is achieved in response to control signals by a variable restriction valve reducing flow through the supply channel and allowing an increase of flow through the supply channel in response to control signals received via the input interface. 
     Particular elaborations and embodiments of the invention are set forth in the dependent claims. 
     Further features, effects and details of the invention appear from the detailed description and the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of a first example of a catheter pump system according to the invention in operation; 
         FIG. 2  is a schematic functional representation of the pump system according to  FIG. 1 ; 
         FIG. 3  is a schematic functional representation of a second example of a pump system according to the invention; 
         FIG. 4  is a schematic functional representation of a third example of a pump system according to the invention; and 
         FIG. 5  is a graph showing the relationship between IABP driving pressure and pump flow rate of an example of pump system according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The invention is first described with reference to the example shown in  FIGS. 1 and 2 . A catheter pump system  1  according to this example has catheter  2  for insertion into a patient  3 . As shown in  FIG. 1 , the catheter  2  can be brought into a position extending through an opening  4  made in the patient body, an external iliac artery  5  and an Aorta  6  of the patient  3 . For bringing the catheter  2  into such a position, it preferably has an insertable length of at least 40 cm (more preferably at least 50 cm) and at most-90 cm (more preferably at most 75 cm). The catheter may for instance be of a 7 to 9 Fr. thickness. Insertion into the aorta via a subclavian artery  20  is also possible. The insertable length can then be shorter e.g. by 10-20 cm. A distal end portion of the catheter  2  is located in a position extending through an aortic valve  7  of the patient  3 . In some cases a position of the distal end  8  of the catheter  2  near the aortic valve  7  of the patient  3  can be sufficient. The catheter  2  has an inlet port  9  near the distal end  8  and an outlet port  10  proximally of the inlet port  9 . The inlet port may also be located at the distal end of the catheter, but if, as in the present example, the catheter  2  has an end portion  11  that is more flexible than a proximally adjacent section of the catheter  2  and curved for facilitating navigating the catheter tip into position, a position of the inlet port  9  at 1-3 cm from the catheter tip  8  is particularly practical. The outlet port  10  communicates with the inlet port  9  via a blood flow channel  12 . 
     The pump system  1  further includes a pump  13  having a fluid displacement member  14  in the blood flow channel  12  and a motor  15  coupled to the pump  13  for driving the pump  13 . 
     A motor controller  16  is provided for controlling motor speed. The motor controller  16  has a pressure sensing port  18  for connection to a control pressure source  17  which generates a pressure that varies in sync with pulsations of the heart  19 . The motor controller  16  is arranged for causing motor speed to be increased in response to a reduction of pressure applied to the pressure sensing port  18  and for causing motor speed to be reduced in response to an increase of pressure applied to the pressure sensing port  18 . 
     In operation, the inlet port  9  is in a left ventricle  35  of the patient  2  or, alternatively, closely downstream of the aortic valve  7  of the patient  2  and the outlet port  10  is downstream of the inlet port  9  and of the aortic valve  7  and communicates with the inlet port  9  via the blood flow channel  12 . The motor  16  drives the pump  13  which is coupled to the motor  16 . The motor controller  16  controls the speed of the motor  15 . 
     For providing signals to the motor controller  16  on the basis of which timing of speeding up and slowing down of the motor  15  is determined, the source of variable pressure is provided in the form of an IABP driver  17 . Such IABP drivers  17  are commonly available in hospital departments involved in the treatment of cardiac dysfunction and have a detector  21  detecting diastole and systole of the patient&#39;s heart from for instance an electrocardiogram, blood pressure or a pacemaker signal. The IABP driver  17  further has a pressure controller  22 , a pressure source  23 , a balloon port  26  in fluid communication with the pressure source  23  and for connection to an intra aortic balloon. In this example, the pressure source  23  includes a linear actuator  24  and a bellows  25  coupled to the actuator  24 , so that the bellows  25  is expanded and compressed when the actuator  24  retracts and, respectively, expands. The interior of the bellows  25  communicates with balloon port  26  so that pressure applied to the balloon port  26  varies cyclically if the bellows  25  is reciprocally expanded and compressed. Other mechanisms for applying a variable pressure to the balloon port are also conceivable, but not described since IABP drivers are standard hospital equipment. The pressure controller  22  and the pressure source  23  of the IABP driver  17  according to this example are arranged for generating a balloon inflation pressure at the start of diastole and removing or at least reducing balloon inflation pressure at the start of systole as is illustrated by the IABP pressure curve in  FIG. 5 . 
     The motor controller  16  has a pressure sensing port  18  in fluid communication with the balloon port  26 , so that the pressure applied to the pressure sensing port  18  varies in unison with the pressure applied to the balloon port  26 . The motor controller  16  is arranged for causing the speed of the motor  15  to be increased in response to a reduction of pressure applied to the pressure sensing port  18  and for causing the speed of the motor  15  to be increased in response to a reduction of the pressure applied to the pressure sensing port  18 . Thus, as is illustrated by the ‘Pump Flow Rate’ curve in  FIG. 5 , the pump flow rate increases if IABP pressure decreases and vice versa. 
     In this embodiment and other embodiments, a certain shift (towards in advance or as a delay) in the response of the pump flow rate variation to the IABP pressure variation may occur. The shift is preferably less than a quarter and more preferably less than an eighth of a full cycle. 
     In the present example, the motor  15  is a pneumatic motor and the motor controller  16  has a supply channel  27  extending through the motor controller  16  between an inlet  28  for connection to a pressure source  29  and an outlet  30  in fluid communication with the motor  15 . A variable restriction valve  31  is arranged for reducing flow through the supply channel  27  in response to an increase of pressure applied to the pressure sensing port  18  and for allowing an increase of flow through the supply channel  27  in response to a reduction of pressure applied to the pressure sensing port  18 . This allows control of motor speed to be achieved in a particularly simple, reliable and smooth manner. 
     The motor  15  and the pump  13  are arranged for operation at a pressure difference between an inlet  32  and an outlet  33  of the motor  15  of at least 2 bars at a flow rate of at least 30 l/min (more preferably at least 2.5 bar at a flow rate of at least 40 l/min). Because an IABP driver is typically not capable of supplying such a pneumatic power, the pneumatic pressure is supplied to the motor controller  16  from a pressure source  29  that has been provided in addition to the IABP driver  17 . 
     The motor  15  is coupled to the pump  13  via a flexible drive shaft  34  extending through a lumen of the catheter  2  so that the motor  15  can drive the pump  13  via the flexible drive shaft  34 . This allows the motor  15  to be located outside of the body  3  of the patient, i.e. proximally of an opening  4  made in the body  3  of the patient. Locating the motor  15  outside the body  3  of the patient is advantageous for safety reasons, because in the event of a leak in a portion of the catheter inside the patient&#39;s body  3 , pressurized air would be injected into the blood of the patient. Such dangers can be reduced by using helium as a driving gas, but that would increase operating costs and complexity and still a larger leak would constitute a substantial hazard. 
     To ensure effective discharging of blood out of the left ventricle, the inlet port  9  and the outlet port  10  are at a mutual distance of at least 5 cm and more preferably at least 6 cm. This distance is preferably less than 10 cm. 
     To avoid disturbing expansion of the left ventricle during diastole, the motor controller  16 , the motor  15  and the pump  13  are arranged for varying flow rate generated by the pump  13  from a lowest flow rate of less than 3 l/min at a difference between pressure at the outlet port  10  and pressure at the inlet port  9 , as a result pumping action of the heart and the pump  13 , of 80-120 mmHg. 
     For effectively supporting the discharging of blood out of the left ventricle during systole, the motor controller  16 , the motor  15  and the pump  13  are arranged for causing the flow rate generated by the pump  13  to reach a highest flow rate of at least 4 l/min (and more preferably at least 5 l/min) at a difference between pressure at the outlet port and pressure at the inlet port  9 , as a result pumping action of the heart and the pump  13 , of 15-90 mmHg. 
     In another embodiment, shown in  FIG. 3 , a catheter pump system includes a catheter  102  for insertion into a patient  3  into a position extending through the aorta  6  of the patient&#39;s body  3 . As in the embodiment described above, a pneumatic motor  115  is provided for driving the pump  113  and a flexible drive shaft  134  extends through a lumen of the catheter  102 . The drive shaft  134  couples the pump  113  to the motor  115  so that the pump  113  can be driven by the motor  115 . The motor controller  116  for controlling motor speed has a supply channel  127  extending through the motor controller  116  between an inlet  128  for connection to a pressure source  129  and an outlet  130  in fluid communication with the motor  115 . A variable restriction valve  131  is arranged for controlling flow through the supply channel  127  and an input interface  118  is provided for inputting control signals. The variable restriction valve  131  is arranged for reducing flow through the supply channel  127  and allowing an increase of flow through the supply channel  127  in response to control signals received via the input interface  118 . The input interface  118  can for instance be connected to an apparatus  117  for sensing cardiac signals, such as an ECG (electrocardiogram) device, to a blood pressure transducer at or near the distal tip of the catheter or to a pacemaker. 
     In operation, the motor controller  116  receives control signals via the input interface  118  and the variable restriction valve  131  is operated for reducing flow through the supply channel  127  and allowing an increase of flow through the supply channel  127  in response to the control signals received via the input interface  118 . 
     In  FIG. 4 , a further example of a catheter pump system according to the invention is shown. In this system, a motor controller control  216  is coupled to the balloon port  226  of an IABP driver  217  and to an electric power source  229 . The motor  215  is a variable speed electric motor  215  and is coupled to a power output  230  of the motor controller  216  so that electric power can be supplied to the motor  215  under control of the motor controller  216 . The motor controller  216  further has a pressure sensing port  218  coupled to a balloon port  226  of the IABP driver  217 , so as to receive pressure outputted by the IABP driver  217 . The motor  215  is coupled to the pump  213  for driving the pump. In this example, the motor  215  is arranged close to the pump  213  in a distal end portion of the catheter, i.e. inside the patient when in operation. 
     In operation, the motor controller  216  controls power supply to the motor  215  so that, in response to pressure variations applied to the pressure sensing port  218  by the IABP driver  217 , the motor speed increases in response to a reduction of pressure applied to the pressure sensing port  218  and the motor speed reduces in response to an increase of pressure applied to the pressure sensing port  218 , in a manner as is illustrated by  FIG. 5 . Also in this embodiment, a certain time shift (advance or delay) between maximum IABP pressure and minimal flow rate generated by the pump  213  as well as between minimal IABP pressure and maximal flow rate generated by the pump  213  may occur. Such a time shift may be constant or vary over the cycle of pressure increase and reduction. 
     Several features have been described as part of the same or separate embodiments. However, it will be appreciated that the scope of the invention also includes embodiments having combinations of all or some of these features other than the specific combinations of features embodied in the examples.