Fast response intra-aortic balloon pump

Details Fast response intra-aortic balloon pump Fast response intra-aortic balloon pump

1999-07-16

2001-06-05

Mendez, Manuel (Department: 3763)

Surgery

Means for introducing or removing material from body for...

Treating material introduced into or removed from body...

C600S018000

Reexamination Certificate

active

06241706

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to intraortic balloon pumps, and more particularly, to systems for inflating and deflating intra-aortic balloons. Still more particularly, the present invention relates to such a system incorporating one or more strategically placed valves enabling more rapid inflation and deflation of the intra-aortic balloon.
BACKGROUND OF THE INVENTION
Intra-aortic balloon pump therapy is frequently prescribed for patients who have suffered a heart attack or some other form of heart failure. In such therapy, a thin balloon is inserted through an artery into the patient's aorta. The balloon is connected through a series of tubes to a complex drive apparatus which causes the balloon to inflate and deflate repeatedly in time with the patient's heartbeat, thereby removing some of the load from the heart and increasing blood supply to the heart muscle during the therapy period.
The inflation/deflation apparatus supplies positive pressure for expanding the balloon during an inflation cycle and negative pressure for contracting the balloon during a deflation cycle. In a conventional prior art apparatus shown schematically in
FIG. 1
, an intra-aortic balloon
10
is surgically inserted into a patient's aorta and is connected through a catheter
12
having a small diameter lumen and an extender
14
having a relatively large diameter lumen to an isolator
18
divided by a pliant membrane
20
into a primary side
22
and a secondary side
24
. The entire volume between membrane
20
and balloon
10
is completely filled with a gas, such as helium, supplied by a gas source
26
. A positive pressure source
28
is connected through a solenoid valve
30
to the input or primary side
22
of isolator
18
. Similarly, a negative pressure source
32
is connected through a solenoid valve
34
to the input or primary side
22
of isolator
18
. The primary side
22
of isolator
18
is also connected through a solenoid valve
36
to a vent or exhaust port
38
. Typically in such systems, the isolator, gas source, negative and positive pressure sources, vent port and their associated valves together comprise a reusable drive unit, and the extender, catheter and balloon are disposable so as to accommodate sterility concerns.
During an inflation cycle, solenoid valve
30
is opened to permit positive pressure from positive pressure source
28
to enter primary side
22
of isolator
18
. This positive pressure causes membrane
20
to move toward secondary side
24
, thereby forcing the helium in the secondary side to travel toward and inflate balloon
10
. For deflation, solenoid valve
30
is closed and solenoid valve
36
is opened briefly to vent the gas from primary side
22
, after which valve
36
is closed. Solenoid valve
34
is then opened, whereupon negative pressure source
32
creates a negative pressure on the primary side
22
of isolator
18
. This negative pressure pulls membrane
20
toward primary side
22
, whereby the helium is drawn out from the balloon.
It is desirable in intra-aortic balloon pump therapy to inflate and deflate the balloon as rapidly as possible. Rapid cycling would permit the therapy to be performed more effectively, and would enable smaller diameter catheters to be used, thereby reducing the possibility of limb ischemia. Although the prior art system described above permits rapid inflation and deflation cycles, the configuration of this system creates inherent limitations in the cycle speed which can be achieved.
Thus, in a typical inflation cycle, pressurized gas from positive pressure source
28
, at an initial pressure of about 8 psi, is used to inflate balloon
10
to an end inflation pressure of about 2 psi, which is about the blood pressure of a normal patient. (In the present specification, all references to psi, unless otherwise noted, are to gauge pressures, not absolute pressures.) In the initial portion of the inflation cycle, the 8 psi gas pressure on the primary side
22
of isolator
18
drives membrane
20
toward the secondary side
24
, forcing the gas in secondary side
24
into extender
14
. Because of its small diameter, however, catheter
12
acts as a constriction to the rapid flow of gas to balloon
10
. Hence, when membrane
20
has moved fully forward (i.e., it hits the wall on secondary side
24
), there is a relatively large pressure differential across catheter
12
, and balloon
10
is only partially inflated. The process of balloon inflation continues as the gas in extender
14
flows through catheter
12
to the balloon until a state of equilibrium is reached in the closed portion of the system. It is therefore apparent that the pressure differential across catheter
12
is highest at the beginning of the inflation cycle and drops to zero at the end of the inflation cycle. Since the rate at which gas flows from extender
14
to balloon
10
is dependent upon the pressure differential across catheter
12
, this gradual decay in the pressure differential results in a steadily decreasing flow rate and, therefore, a longer overall time until equilibrium is reached and the balloon is fully inflated.
A similar situation occurs during the deflation portion of the cycle. Thus, as the deflation cycle begins, a large negative pressure is created on primary side
22
of isolator
18
by negative pressure source
32
. This negative pressure pulls membrane
20
toward primary side
22
, whereupon the gas in extender
14
is drawn into the secondary side
24
of the isolator. Again, the small diameter of catheter
12
constricts the flow of gas out from balloon
10
such that, with membrane
20
moved to its fully retracted position (i.e., against the wall on primary side
22
), a relatively large pressure differential exists across catheter
12
, and balloon
10
is only partially deflated. As helium flows slowly from balloon
10
through catheter
12
, the balloon continues to deflate until equilibrium is reached. Here again, the pressure differential across catheter
12
which drives balloon deflation is at its highest at the beginning of the deflation cycle and drops to zero at the end of the cycle. The gradual decrease in the pressure differential results in a steadily decreasing flow rate across catheter
12
, lengthening the overall time until the balloon is fully deflated.
At first blush, it would appear that more rapid inflation/deflation cycles can be achieved simply by using a higher positive pressure during inflation and a lower negative pressure during deflation. The use of a higher positive pressure, however, creates the risk of over inflating and stressing the balloon, with the attendant risk of a neurization or rupturing of the balloon. Alternatively, simply increasing the volume of the isolator so that the maximum pressure differential across catheter
12
would be maintained for a longer period of time before membrane
20
has bottomed out would, without other modification to the system, create problems. Not only would there be a risk of damaging the balloon through over inflation, there would also be a need to remove a larger amount of gas from the balloon during deflation, which requirement would increase the deflation time.
There are generally three aspects of the operation of intra-aortic balloon pumps which contribute to inflation/deflation cycle times—the time required to deliver electrical signals from the controller to the various valves; the time required to effect the mechanical operations, i.e., movement of the isolator membrane and actuation of the valves between open and closed positions; and the time required to move the gas, either between the positive and negative pressure sources and the isolator on the primary side, or between the balloon and the isolator on the secondary side. By reducing the time needed to perform any one of these operations, more rapid inflation/deflation cycles may be achieved.
One approach for increasing inflation and deflation speeds by reducing gas movement time is shown schematically in FIG.
2
and described in

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