Ventricular assist device

1. A ventricular assist device comprising:

an intra-aortic balloon pump sized and shaped to dangle inside a patient's aorta, the pump having a wall made at least in part from a moisture-resistant material;

a skin interface;

an internal drive line connecting the balloon pump to the skin interface;

an external driver comprising a rigid bellows, a prime mover actuating the bellows, and valves arranged to permit multiple pumping modes, the prime mover being operably connected to a power source;

an arterial interface, sized and shaped to pass the internal drive line through an arterial wall;

an external drive line connecting the skin interface to the external driver;

a controller; and

an air pressure sensor configured to detect the pumping air pressure inside the fluid system as a function of time, the air pressure sensor being so connected to the controller as to allow transmission of a signal representative of the pumping air pressure to the controller;

wherein:

the balloon pump, the internal drive line, the skin interface, the external drive line, and the driver form a fluid system for containing pumping air to act as a pumping medium; and

the controller is programmed to:

operate the valves and the prime mover such that the pumping air is not pressurized more than a predetermined amount above a sensed blood pressure, wherein operating the prime mover includes controlling the amount of power provided to the prime mover from the power source;

cause the valves to adopt a closed pumping mode in which no air is added to or vented from the fluid system;

cause the external driver to pump through multiple consecutive inflation-deflation cycles during the closed mode;

cause the valves to adopt an open mode in which contraction of the bellows by the prime mover causes air in the fluid system to be vented from the fluid system and expansion of the bellows by the prime mover causes ambient air to be drawn into the fluid system, thereby charging the fluid system with new pumping air to act as the pumping medium;

detect leaks by:

receiving the signal from the air pressure sensor;

comparing the pressure of the pumping air to a predetermined normal operating range by a predetermined set of operating criteria; and

triggering an error state if the pressure is outside the normal operating range; and

control inflation of the balloon pump by:

based on the signal from the air pressure sensor, determining the time taken to inflate the balloon pump once;

comparing the time required to inflate the balloon pump to a target time stored in the controller;

if the time required to inflate the balloon is not within a predetermined range of the target time, calculating the power input to the external driver necessary to cause the time required to inflate the balloon to match the target time; and

adjusting the amount of power subsequently provided to the driver based on the calculation.

2. The device of claim 1 , wherein the controller is further programmed to detect leaks by:

calculating a rolling mean and a rolling standard deviation of the air pressure of the pumping air at a particular point in the inflation-deflation cycles based on signals from the air pressure sensor at the particular point in multiple consecutive inflation-deflation cycles; and

calculating a difference between (a) an air pressure measured at the particular point in the current inflation-deflation cycle and (b) the rolling mean of the air pressure;

wherein the error state is triggered if the difference is greater than twice the rolling standard deviation of the air pressure.

3. The device of claim 2 , wherein the controller is further programmed to detect leaks by:

incrementing an error counter if the difference between the measured air pressure and the rolling mean is both (a) greater than the rolling standard deviation and (b) less than or equal to twice the rolling standard deviation;

wherein the error state is also triggered if the error counter exceeds a predetermined number of counts.

4. The device of claim 1 , wherein the controller is further programmed to detect leaks by:

calculating a rolling mean and a rolling standard deviation of the air pressure of the pumping air at a particular point in the inflation-deflation cycles based on signals from the air pressure sensor at a particular point in multiple consecutive inflation-deflation cycles;

calculating a difference between (a) an air pressure measured at the particular point in the current inflation-deflation cycle and (b) the rolling mean of the air pressure; and

increment an error counter if the difference between the measured air pressure and the rolling mean is greater than the rolling standard deviation;

wherein the error state is triggered if the error counter exceeds a predetermined number of counts.

5. The device of claim 1 wherein the arterial interface comprises a vascular graft and

a stopper;

wherein:

the vascular graft defines a graft lumen and comprises a distal end so sized and shaped as to be suited for grafting to an artery;

the stopper is secured to and immobilized relative to the graft and fills the graft lumen except for a hole defined through the stopper's length, the hole providing a conduit through the graft lumen;

the internal drive line passes through the conduit;

the graft lumen is wide enough to allow passage of the balloon pump; and

the conduit is too narrow to allow passage of the balloon pump.

6. The device of claim 1 wherein the moisture-resistant material comprises polyurethane modified with hydrophobic end groups.

7. The device of claim 6 wherein the hydrophobic end groups are silicone groups.

8. The device of claim 1 wherein:

the internal drive line has an extravascular region adjacent to the first end, a pump region adjacent to the second end, and an arterial region between the extravascular region and the pump region;

the cross-sectional area of the arterial region is less than 50% of the internal cross-sectional area of the artery in which it is to be deployed;

the cross-sectional areas of the extravascular and pump regions are larger than the cross-sectional area of the arterial region; and

the diameter of the pump region is sized and shaped to connect to the pump.

9. The device of claim 8 wherein:

the extravascular region has an inner diameter of 4 to 8 mm;

the arterial region has an outer diameter of about 5 mm and is adapted to be deployed in the subclavian artery; and

the pump region has an outer diameter of about 6 mm.

10. The device of claim 1 , wherein the predetermined amount is 40 mmHg.

11. The device of claim 1 , further comprising a humidity sensor connected to the controller so as to allow transmission of a signal to the controller, the signal representative of a humidity of the pumping air in the fluid system detected by the sensor; and

wherein the controller is programmed to determine based on the signal from the humidity sensor whether to operate the driver in the closed mode or the open mode.

12. The device of claim 1 , further comprising an electrocardiogram sensor and a pressure sensor;

wherein the electrocardiogram sensor detects an electrocardiogram signal, and is so coupled to the controller as to allow transmission of an electrocardiogram signal to the controller;

wherein the pressure sensor detects or infers a ventricular pressure and is so coupled to the controller as to allow transmission of a pressure signal to the controller; and

wherein the controller is programmed to

detect a QRS complex based on the electrocardiogram signal;

detect a dicrotic notch based on the pressure signal;

trigger the driver to deflate the pump following the QRS complex and inflate the pump following the dicrotic notch.

13. The device of claim 1 , wherein the skin interface comprises:

two portions fixed to one another and rotatable with respect to one another;

receptacles for receiving air and electrical lines on both portions;

an air-tight conduit between the receptacles and running through the interface, for transmitting air through the interface;

a wireless electrical coupling between the receptacles, for transmitting electrical signals and power through the interface;

a memory in which patient-specific parameters are stored; and

a processor configured to receive the electrical signals, digitize them, and produce a digital output indicative of the electrical signals;

wherein the processor and the memory are in communication with the wireless electrical coupling.

14. The device of claim 1 , wherein the controller is configured to receive (a) a blood pressure signal representative of at least a sensed blood pressure, and (b) an electrocardiogram signal, and the controller is programmed to detect a QRS complex based on an electrocardiogram signal received by the controller; detect a dicrotic notch based on a blood pressure signal received by the controller; and trigger the driver to deflate the pump following the QRS complex and inflate the pump following the dicrotic notch.