U.S. patent application number 10/341983 was filed with the patent office on 2003-06-05 for balloon catheter leak detection method and apparatus.
Invention is credited to Williams, Jonathan.
Application Number | 20030101800 10/341983 |
Document ID | / |
Family ID | 26991654 |
Filed Date | 2003-06-05 |
United States Patent
Application |
20030101800 |
Kind Code |
A1 |
Williams, Jonathan |
June 5, 2003 |
Balloon catheter leak detection method and apparatus
Abstract
An intra-aortic balloon pump system having a leak detector
comprising a processor, a pressure sensor, and optionally a
temperature sensor. Gas leaks from the intra-aortic balloon pump
system are detected by comparing shuttle gas pressure readings,
taken just prior to IAB inflation, with similar thermodynamic
histories, i.e. similar equilibrium times.
Inventors: |
Williams, Jonathan;
(Montville, NJ) |
Correspondence
Address: |
Datascope Corp.
14 Philips Parkway
Montvale
NJ
07645
US
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Family ID: |
26991654 |
Appl. No.: |
10/341983 |
Filed: |
January 14, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10341983 |
Jan 14, 2003 |
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09903447 |
Jul 11, 2001 |
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6536260 |
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09903447 |
Jul 11, 2001 |
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09339492 |
Jun 24, 1999 |
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Current U.S.
Class: |
73/40 ;
340/605 |
Current CPC
Class: |
A61M 2205/15 20130101;
A61M 2205/3303 20130101; A61M 60/50 20210101; A61M 60/135 20210101;
A61M 2205/33 20130101; G01M 3/3218 20130101; A61M 60/40 20210101;
A61M 2230/04 20130101; A61M 2230/04 20130101; A61M 2230/005
20130101 |
Class at
Publication: |
73/40 ;
340/605 |
International
Class: |
G01M 003/04 |
Claims
What is claimed is:
1. A leak detector device for a pressurized cardiac assist device
for use on a patient comprising a processor and a pressure sensor
communicating with said processor for sensing the pressure of a gas
in said pressurized cardiac assist device, said pressurized cardiac
assist device comprising one or more chambers, said one or more
chambers being filled and evacuated of the gas by a pump, during
therapy said one or more chambers being maintained in an evacuated
state during at least a portion of the patient's heartbeat and
being maintained in a filled state during at least a portion of a
patient's heartbeat, the processor comparing pressure measurements
taken by the pressure sensor from different fill/evacuation cycles
having similar evacuation interval durations and indicating a
pressure loss or gain if the pressure measurements vary beyond a
predetermined level.
2. The device as claimed in claim 2 wherein the processor compares
pressure measurements taken by the pressure sensor from
fill/evacuation cycles of the one or more chambers having similar
fill and evacuation interval durations.
3. A leak detector device for a pressurized cardiac assist device
for use on a patient comprising a processor and a pressure sensor
communicating with said processor for sensing the pressure of a gas
in said pressurized cardiac assist device, said pressurized cardiac
assist device comprising one or more chambers, said one or more
chambers being filled and evacuated of the gas by a pump, during
therapy said one or more chambers being maintained in an evacuated
state during at least a portion of the patient's heartbeat and
being maintained in a filled state during at least a portion of a
patient's heartbeat, the processor comparing pressure measurements
taken by the pressure sensor from different fill/evacuation cycles
having similar fill interval durations and indicating a pressure
loss or gain if the pressure measurements vary beyond a
predetermined level.
4. The leak detector device as claimed in claim 1 wherein the
cardiac assist device comprises a balloon catheter, said balloon
catheter comprising a tube connected on one end to a balloon
membrane, and wherein the chamber comprises a volume defined by the
balloon membrane and the pump being connected to the tube.
5. The leak detector device as claimed in claim 3 wherein the
cardiac assist device comprises a balloon catheter, said balloon
catheter comprising a tube connected on one end to a balloon
membrane, and wherein the chamber comprises a volume defined by the
balloon membrane and the pump being connected to the tube.
6. The leak detector device as claimed in claim 1 wherein the
cardiac assist device comprises a balloon catheter, said balloon
catheter comprising a tube connected on one end to a balloon
membrane, and wherein the chamber comprises a volume defined by the
balloon membrane and the pump being connected to the tube, the
processor measures the gas pressure in the balloon catheter at the
same point in a plurality of fill/evacuation cycles of the
balloon.
7. The leak detector device as claimed in claim 3 wherein the
cardiac assist device comprises a balloon catheter, said balloon
catheter comprising a tube connected on one end to a balloon
membrane, and wherein the chamber comprises a volume defined by the
balloon membrane and the pump being connected to the tube, the
processor measures the gas pressure in the balloon catheter at the
same point in a plurality of fill/evacuation cycles of the
balloon.
8. The leak detector device as claimed in claim 1 wherein the
cardiac assist device comprises a balloon catheter, said balloon
catheter comprising a tube connected on one end to a balloon
membrane, and wherein the chamber comprises a volume defined by the
balloon membrane and the pump being connected to the tube, the
processor compares pressure measurements taken just prior to the
fill of the balloon.
9. The leak detector device as claimed in claim 3 wherein the
cardiac assist device comprises a balloon catheter, said balloon
catheter comprising a tube connected on one end to a balloon
membrane, and wherein the chamber comprises a volume defined by the
balloon membrane and the pump being connected to the tube, the
processor compares pressure measurements taken just prior to the
fill of the balloon.
10. The leak detector device as claimed in claim 1 wherein the
cardiac assist device comprises a balloon catheter and a memory
unit connected to the processor for storing pressure measurements,
said balloon catheter comprising a tube connected on one end to a
balloon membrane, and wherein the chamber comprises a volume
defined by the balloon membrane and the pump being connected to the
tube.
11. The leak detector device as claimed in claim 3 wherein the
cardiac assist device comprises a balloon catheter and a memory
unit connected to the processor for storing pressure measurements,
said balloon catheter comprising a tube connected on one end to a
balloon membrane, and wherein the chamber comprises a volume
defined by the balloon membrane and the pump being connected to the
tube.
Description
RELATED APPLICATIONS
[0001] This application is a divisional application of application
Ser. No. 09/903,447, filed on Jul. 11, 2001, which is a
continuation-in-part application of application Ser. No.
09/339,492, filed on Jun. 24, 1999, all herein incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a leak detector for a pressurized
device. More particularly, the invention relates to a detector for
detecting a gas leak from an intra-aortic balloon ("IAB") catheter
system.
[0004] 2. Description of the Prior Art
[0005] In counterpulsation therapy, a long cylindrical intra-aortic
balloon is inserted percutaneously into a patient's femoral artery.
The balloon is then advanced until it is located in the descending
aorta. Once in place, the balloon is inflated and deflated
anti-phase to the pumping action of the patient's left ventricle,
i.e. the balloon is held inflated during at least a portion of
diastole and is held deflated during at least a portion of systole.
The IAB catheter is connected to a pump (IABP) for inflation and
deflation of the balloon membrane on the distal end of the
catheter.
[0006] IAB therapy is most effective when the transitions between
the inflated and deflated states of the balloon membrane are rapid,
typically, less than 0.1 second. When inflated and deflated in this
manner, coronary blood flow is increased and cardiac work is
decreased. This lifesaving therapy supports the heart during
ischemic events or cardiogenic shock.
[0007] When sized for adult patients, the IAB balloon typically has
a volume of 40 cubic centimeters. A small diameter catheter having
an outside diameter of less than 0.1 inches (2.5 mm) is integral to
the IAB. The catheter provides pneumatic access to the IAB. By
design, the catheter's diameter is small to reduce its impact upon
blood flow in the patient's femoral artery. As a result, the
catheter's small internal diameter impedes the flow of shuttle gas
to and from the IAB balloon. Also, the catheter's pressure drop at
the catheter and balloon junction is large because the gas velocity
in the catheter is high, approximately 500 ft/sec.
[0008] To reduce the impact of these effects: (1) helium gas is
used as the working (shuttle) gas to inflate and deflate the IAB;
and (2) a larger diameter "extension" catheter is used to
interconnect the IAB's catheter to the intra-aortic balloon pump's
pneumatic port. The extension catheter's diameter is larger, and
thus, it's pressure drop is lower.
[0009] During the pumping process, the shuttle gas is pressurized
and de-pressurized each heartbeat by the IAB pump. The sources of
the pressure changes are the pump and the restriction of the IAB's
catheter. As a thermodynamic consequence, on each inflation of the
IAB, heat energy is stored in the shuttle gas, and on each
deflation, heat is released.
[0010] Consequently, after each inflation or deflation event, the
shuttle gas pressure changes as it attempts to thermally
equilibrate with its environment. Typically, the pressure decays
toward the appropriate average shuttle pressure in an exponential
manner with a time constant on the order of approximately 1
second.
[0011] During IAB therapy, thermal equilibrium is not achieved
because the durations of IAB inflation and deflation are too brief,
i.e. the shuttle gas is re-compressed before it "recovers" from
deflation and vice versa. The durations of the deflate and inflate
intervals, are approximately 0.375 seconds at a typical patient
heart rate of 80 beats per minute. The duration of the deflate
interval is defined as the duration the balloon remains in the
deflated state during systole plus the amount of time it takes for
the balloon to deflate. The duration of the inflate interval is
defined as the duration the balloon remains in the inflated state
during diastole plus the amount of time it takes for the balloon to
inflate.
[0012] If the shuttle gas leaks out of the IABP system, the IAB
will not fully inflate. This diminishes therapy and can be harmful
if gas is lost to the patient's blood stream. Accordingly, there is
a need for detection of gas leaks from the IAB system's shuttle gas
system. Detection systems have been incorporated into most existing
IABP systems.
[0013] In principle, detection of gas loss appears straightforward.
In accordance to the Ideal Gas Law, the quantity (mass) of a gas in
a known volume can be determined by measurement of its static
pressure, and temperature.
[0014] Accordingly, for leak detection using the Ideal Gas Law,
IABP systems have a shuttle gas pressure sensor. To meet the Law's
"known volume" requirement, the shuttle gas pressure is measured
when the IAB is in its deflated state. This assures that the gas
resides in the more stable and predicable geometries of the
catheter(s) and intra-aortic balloon pump's drive.
[0015] To meet the Law's static pressure criteria, the shuttle gas
pressure is measured as "late" as possible after IAB deflation.
This maximizes the time interval available for IAB deflation. When
the IAB is fully deflated, the shuttle gas is no longer moving and
the "static" criteria is met. This corresponds to measuring the
pressure just prior to IAB inflation.
[0016] The Law's final criteria, measurement of shuttle gas
temperature, is more difficult to adequately satisfy. This is
because the shuttle gas temperature is the sum of two components, a
local ambient temperature component and a thermal transient
component, due to gas compression and decompression. Temperature
sensors with the necessary speed of response to measure the thermal
transients are fragile and expensive. For this reason, shuttle
temperature is not measured by most IAB systems.
[0017] When the Ideal Gas Law is used for leak detection, and the
effect of temperature is ignored, it is mathematically equivalent
to assuming that the gas temperature is constant. In the case of
local ambient temperature (average shuttle gas temperature), this
is likely to be true if leak detection comparisons are limited to
readings which were taken close in time. This is true if one
presumes that the ambient's effect upon the average temperature of
the shuttle gas is slow, i.e. on the order of minutes.
[0018] However, in the case of the thermal transient component, it
is not sufficient to compare heartbeats taken at similar times. An
additional criteria must be added to avoid false alarms. This is a
consequence of the thermal transient's effect upon shuttle gas
pressure. Specifically, after the gas is decompressed, its pressure
exponentially decays toward the average shuttle gas pressure level.
Typically, a leak detection pressure measurement is taken before
this decay process is complete. As a result, the pressure reading
has a transient component whose value depends upon the time when
the reading was taken, relative the decompression event.
Comparisons of pressure readings with different decay times result
in false leak detection alarms, unless the alarm's limits are made
larger, and thus less sensitive, to exclude these errors.
[0019] Gas loss alarms can be absolute or relative. An absolute
alarm compares the current gas pressure against a fixed pressure
limit. To avoid false alarms due to the variability of temperature
and volume, the absolute alarm limits must be large, on the order
of three to five cubic centimeters per hour.
[0020] U.S. Pat. No. 3,698,381, issued to Federico et al., is an
example of an absolute alarm system. Frederico et al. disclose an
absolute leak detection method for an intra-aortic balloon catheter
which involves monitoring the pressure of the shuttle gas just
prior to inflation of the balloon. Leaks are detected on a
beat-to-beat basis by comparing the measured pressure to fixed
alarm limits. If the pressure of any single heartbeat is outside
the fixed alarm or prescribed limits an alarm is declared. As
discussed, the leak detection disclosed by Federico et al. is
likely to cause false alarms because the effect of temperature is
completely ignored.
[0021] A "relative" or differential gas alarm checks for gas loss
from a known datum. The datum is an initial shuttle gas pressure
measurement taken when the system is deemed leak free. After this
initial datum is taken it is compared to subsequent pressure
readings to determine if gas loss has occurred. An alarm is issued
if the difference between the datum and a new reading exceeds a
predefined limit.
[0022] The sensitivity of a relative gas alarm can be much higher
than the absolute alarm because the initial datum implicitly
includes the effects of current ambient temperature. This initial
datum also implicitly captures the effect of tolerance of volumes.
However, unless proper steps are taken, it does not include the
effect of the thermodynamic temperature transient component induced
by pumping.
[0023] The present invention comprises a differential leak
detection method for an IAB catheter for detecting the loss of
shuttle gas due to an IAB perforation. Perforations are typically
due to abrasion of the IAB membrane by aortic plaque, and occur
after an initial, leak free interval of pumping. The detection
method accounts for the effects of the thermodynamic temperature
transient induced by pumping by comparing shuttle gas pressure
readings, taken just prior to IAB inflation, with similar
thermodynamic histories, i.e. similar equilibrium times.
SUMMARY OF THE INVENTION
[0024] Accordingly, it is an object of the invention to produce a
leak detector for an IAB system capable of making an accurate leak
detection, by measuring changes in the gas pressure, despite
thermodynamic variations in the shuttle gas temperature and the
mechanical tolerances on pump volumes.
[0025] The invention is a leak detector for an intra-aortic balloon
pump system comprising a processor, a pressure sensor, and
optionally a temperature sensor. Gas leaks from the intra-aortic
balloon pump system are detected by comparing shuttle gas pressure
readings, taken just prior to IAB inflation, with similar
thermodynamic histories, i.e. similar equilibrium times.
[0026] To the accomplishment of the above and related objects the
invention may be embodied in the form illustrated in the
accompanying drawings. Attention is called to the fact, however,
that the drawings are illustrative only. Variations are
contemplated as being part of the invention, limited only by the
scope of the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] In the drawings, like elements are depicted by like
reference numerals. The drawings are briefly described as
follows.
[0028] FIG. 1 is block and partly schematic diagram of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] FIG. 1 illustrates a block diagram of the present invention,
generally designated 10, comprising an intra-aortic balloon 12, an
intra-aortic balloon pump 14, an intra-aortic balloon catheter 16
connecting said intra-aortic balloon pump 14 and said intra-aortic
balloon 12, a processor 18 connected to said intra-aortic balloon
pump 14, a memory unit 20 and a sensor 22 both connected to the
processor 18. Processor 18 can take the form of a computer, a more
simplified circuit or control device, or can be part of the control
device built into the intra-aortic balloon pump 14. The
intra-aortic balloon pump 14 shuttles a gas, generally helium, back
and forth into the intra-aortic balloon 12. For each heartbeat of a
patient, a pressure reading is taken by sensor 22 preferably just
prior to the inflation of intra-aortic balloon 12. This timing of
the reading allows for the longest amount of time for the shuttle
gas pressure to stabilize, i.e. achieve static conditions and
thermal equilibrium. This timing also assures that the volume of
shuttle gas is known because at this time the shuttle gas resides
in mechanical elements of known geometry, i.e. intra-aortic balloon
pump 14 and intra-aortic balloon catheter 16. Pressure measurements
can be taken at other points in time but it is preferred that they
are taken at the same point in each inflate/deflate cycle of
intra-aortic balloon 12.
[0030] The pressure readings are stored in memory unit 20.
Affiliated data may also stored in memory unit 20, including but
not limited to the inflate and deflate durations of intra-aortic
balloon 12 and the time of occurrence of the heartbeat. The
duration of the deflate interval is defined as the duration the
balloon remains in the deflated state during systole plus the
amount of time it takes for the balloon to deflate. The duration of
the inflate interval is defined as the duration the balloon remains
in the inflated state during diastole plus the amount of time it
takes for the balloon to inflate. Processor 18 sorts all of the
pressure measurements by the duration of the inflate/deflate
intervals from which the pressure measurements were taken.
Periodically, processor 18 subtracts "similar" pressure readings,
i.e. pressure readings taken from intra-aortic balloon 12 cycles
having similar inflate/deflate durations. Processor 18 preferably
uses the pressure readings having the most similar inflate/deflate
durations. An alarm condition is declared if any of the differences
exceed a fixed limit. Also periodically, the processor may
eliminate from the memory unit 20 data read from heartbeats that
are too old, i.e heartbeats for which the assumption of constant
ambient temperature is invalid.
[0031] The determination as to whether pressure readings are
"similar" may be made by comparing intra-aortic balloon 12 deflate
interval durations or preferably both inflate and deflate interval
durations.
[0032] Inflate/deflate intervals of similar duration have thermal
transients of similar amplitude and character. Consequently, when
pressure readings from similar interval durations are subtracted,
the component of the pressure reading due to transient thermal
energy subtracts out. Accordingly, any residual pressure difference
is due to a loss of gas. If the pressure difference is found to be
excessive, then an alarm is issued.
[0033] The more similar the interval durations for the pressure
measurements chosen are the more accurate the gas loss
determination will be. Accordingly, it is preferred to compare
pressure measurements from the most similar interval durations.
However, the term "similar" with respect to inflate/deflate
interval durations can mean any interval chosen specifically so as
to reduce the transient thermal energy component to the pressure
measurement. Note that it is preferable to select the longest
deflate durations for use in alarm detection because (i) the decay
of the thermal transient is more complete and (ii) the gas is more
likely to have reached a static state, i.e. the time available for
IAB deflation is maximized. Consequently, when pressure readings
from long duration heartbeats are compared (subtracted), the
residual errors due to these effects are minimized. Similarly, in
the event that there is a residual component in the measured
pressure due to shuttle gas flow, an additional benefit of this
approach is that it also tends to subtract out, provided that
identical deflation intervals are subtracted.
[0034] The present invention comprises at least two types of gas
alarms, namely, a slow gas alarm and a rapid gas alarm. To test for
the rapid loss of gas, processor 18 compares "similar" pressure
readings that meet two criteria. First, the pressure readings must
taken from inflate/deflate intervals of similar duration. Second,
the readings are preferably from heartbeats which were captured
close in time, e.g. heartbeat data captured within a one to five
minute interval or preferably within a one to three minute
interval. If the pressure drop between these beats exceed a
predetermined alarm limit, then a rapid gas loss event is
declared.
[0035] The sensitivity of the rapid gas loss alarm is highest for a
number of reasons. First, comparing heartbeats of similar duration
eliminates the effect of the thermal transient pressure component.
Second, comparing heartbeats taken close together in time
eliminates the effect of local ambient temperature. When heartbeats
taken close together in time are subtracted, the effect of local
ambient temperature is eliminated, i.e. it subtracts out. Since the
effects of ambient temperature and thermal transients are
eliminated, the sensitivity of this alarm exceeds that of a fixed
alarm system.
[0036] As discussed above, Federico et al. compare pressure
readings to a fixed alarm limit, irrespective of their duration or
proximity in time. Consequently, to avoid false alarms due ambient
temperature and thermal transients, the alarm limit is necessarily
larger and thus, less sensitive.
[0037] To test for the slow loss of gas, the pressure measurements
must be compared over a longer period of time. The pressure
measurements, taken from heartbeats of similar duration, are stored
and periodically plotted against time by processor 18. The slope of
the plot is used as an indicator of the rate of gas loss.
Typically, IAB membranes and pump materials are permeable to
diffusion of helium. Consequently, there is an expected slow loss
of shuttle gas to the diffusion process. A slow gas alarm is issued
when either the rate or total amount of shuttle gas loss exceeds
the expected limits.
[0038] It may also be useful to maintain multiple plots, each plot
being computed from data relating to a specific heart rate or
narrow range of heart rates. In this case, each plot would provide
its own estimate of current slow gas rate.
[0039] In current intra-aortic balloon pump systems, the pressure
readings are not adjusted for the effects of temperature and also
are taken at random points in the inflate/deflate cycle of the
intra-aortic balloon 12. The underlying basis of the present device
and method disclosed is that when "similar" pressure readings are
used, i.e. pressure readings measured at the same point in
inflate/deflate intervals of similar durations, the transient
temperature effect, due the lack of thermal equilibration, will
subtract out.
[0040] Given the elimination of the transient thermal pressure
component, if the subtraction of pressure readings yields a
significant difference it must be due to a gas loss or gain. In the
case of the slow gas alarm, pressure readings from heart beats
which are not in close proximity in time are compared.
Consequently, the alarm is vulnerable to changes in local ambient
temperature. For this reason, the slow gas alarm is less sensitive
than the rapid gas alarm. Often, the pump's local ambient
temperature is relatively constant. In this case, the effects of
ambient temperature subtract out.
[0041] The sensitivity of the slow gas alarm can be improved by
using a temperature sensor (not shown in FIG. 1) to measure local
ambient temperature or preferably average shuttle gas pressure. The
sensor's reading is then used, in conjunction with the Ideal Gas
Law, to compute an adjusted pressure reading for each heart beat.
As in the above, the adjusted readings are then stored along with
their associated durations and periodically plotted against time by
the processor 18. The slope of the plot is used as an indicator of
the rate of gas loss. Note that in this case, a fast responding
temperature sensor is not required since we are using the
temperature readings to correct only for the slow effect of ambient
temperature. The effect of thermal transients is excluded by
limiting computations and comparisons to measurements of like
durations.
[0042] Note that it is anticipated to use the present invention for
the detection of gas gains, i.e. a leak of gas into the shuttle gas
system. This can occur if there is a leak to atmospheric pressure
or if there is a leakage into the system due to the failure of one
or more IABP 14 helium fill valves (not shown). Note also that the
term shuttle gas may also include a fluid or any other medium known
in the art useful for inflating and deflating an expandable
chamber. In reference to an IAB catheter, Helium is the preferred
shuttle gas.
[0043] Note also that the present invention is not limited to use
with intra-aortic balloon catheters. Any pressurized cardiac assist
device having one or more chambers being filled and evacuated of a
working fluid, such as gas, may benefit from the enhanced pressure
loss or gain sensitivity realized through use of the present
invention.
[0044] As many apparently widely different embodiments of the
present invention can be made without departing from the spirit and
scope thereof, it is to be understood that the invention is not
limited to the specific embodiments thereof except as defined in
the appended claims.
* * * * *