Abstrict An ophthalmic surgical pump system 32 includes a collection reservoir
54 and a venturi pump 56 for creating a vacuum level for aspirating
fluid and tissue from a surgical site to the collection reservoir
54. Aspiration tubing 50 connects to each of a surgical handpiece
46 and the collection reservoir 54. A flow meter 34 is electrically
connected to either the aspiration tube 50 or the collection reservoir
54. Control circuitry 38 is connected to the flow meter 34 and to
the venturi pump 56 for varying a vacuum level of the pump 56 to
maintain a desired flow rate of the fluid and tissue being aspirated
from the surgical site.
Claims We claim:
1. An ophthalmic surgical pump system comprising: a collection
reservoir; a venturi pump for creating a vacuum level for aspirating
fluid and tissue from a surgical site to the collection reservoir;
aspiration tubing for connection to each of a surgical hand piece
and the collection reservoir; a flow meter electrically connected
to one of the aspiration tubing and the collection reservoir; and
control circuitry connected to the flow meter and to the venturi
pump for varying the vacuum level of the pump thereby maintaining
a desired flow rate of the fluid and tissue being aspirated from
the surgical site.
2. The system of claim 1 wherein the collection reservoir is a
rigid-walled cassette.
3. The system of claim 1 wherein the flow meter is a Hall-effect
sensor.
4. A surgical pump system comprising: a pump for aspirating fluid
and tissue from a surgical site to a collection reservoir; aspiration
tubing for connection to each of a surgical handpiece and the collection
reservoir; a flow meter electrically connected to one of the aspiration
tubing and the collection reservoir; and control circuitry connected
to the flow meter and to a console for displaying a flow rate of
the aspirating fluid and tissue from the handpiece to the collection
reservoir.
5. The surgical pump of claim 4 wherein upon the flow meter detecting
a flow rate approaching zero (0), an occlusion warning is issued
to a user.
Description BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention is related to sensing an aspiration
flow rate in a surgical pump system. More particularly, the present
invention is directed towards a flow meter and control system for
use with surgical pump systems.
[0003] 2. Description of Related Art
[0004] The flow and flow rate of tissue and fluids through an aspiration
tube is of interest during operations, including ophthalmic operations.
However, direct measurement of the flow rate is typically impractical.
Flow rates are generally inferred for positive displacement pumps,
e.g., flow-based pumps that are based on pump rotation or other
in-direct periodic measurements, these pumps are also commonly referred
to as peristaltic pumps. Flow rates for venturi-based pumps have
generally not been measured nor has an indirect measurement been
used.
[0005] Measurement of the surgical aspiration flow rate may be
valuable in that it can provide for safe control of the ophthalmic
surgical equipment. In most positive displacement-based systems,
flow has been known to be inferred from the cycle frequency, i.e.,
the rotation rate, of the aspiration pump. However, this inference
may be invalid in situations where there are varying pressure differentials
within the pump system. The pressure variations may occur as a result
of changes in the irrigation-fluid bottle height, changes in the
viscosity of the aspirant, and changing occlusion conditions at
the distal end of the aspiration tube. For known venturi-based aspiration
systems no flow measurement has previously been feasible, nor can
flow be accurately inferred from the vacuum level. This is because
the actual flow rate varies with the viscosity of the aspirant and
the occlusion state of the aspiration tube.
[0006] In the prior art, it is possible to measure the flow rate
in the aspiration tube with a positive displacement or venturi-based
system or any other type of pump system using traditional flow sensors.
These traditional flow sensors include paddle-wheel, hot-wire, or
other devices which are deflected in the presence of fluid flow.
However, these devices become contaminated or closed by the aspirant
and cannot be reused on a different patient, thereby making the
use of such sensors expensive.
[0007] Therefore, it would be desirable to have a low-cost flow
sensor that could be inexpensively incorporated into a disposable
or reusable system to directly measure flow rate. Such a flow measurement
can enable new modes of operation, particularly for vacuum-based
systems. One such application is the emulation of a flow-based pump
by a vacuum-based pump using an additional control loop.
BRIEF DESCRIPTION OF THE DRAWING
[0008] FIG. 1 is a prior art circuit diagram of a Hall-effect flow
meter;
[0009] FIG. 2 is a partial cut-away view of a pump system in accordance
with the present invention;
[0010] FIG. 3 is a front view of a surgical cassette inserted in
a console in accordance with the present invention;
[0011] FIG. 4. is a surgical cassette in accordance with one aspect
of the present invention;
[0012] FIG. 5 is an illustration of an aspiration tube for connection
to a surgical cassette in accordance with an alternative embodiment
of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0013] Hall-effect flow meters for sensing the flow of conductive
fluids are known. Such a prior art Hall-effect flow meter is shown
in FIG. 1. The flow meter 10 includes a conduit 12 including electrodes
14 that are in communication with the inner diameter of conduit
12 such that the electrodes are in contact with conductive fluids
16 flowing through conduit 12. A magnetic core 18 is placed around
conduit 12 so as to induce an electromagnetic field perpendicular
to a line-drawn through electrodes 14. Transformer 20 is connected
to driver 22 and oscillator 24. Signals from electrodes 14 are amplified
by amplifier 26 and the amplified signals are fed to synchronous
demodulator 28. A signal representative of the flow rate of the
conductive fluid 16 is outputted to node 30.
[0014] Ophthalmic surgical systems can be broadly categorized as
flow-based or vacuum-based. Flow-based pump systems attempt to maintain
a constant or controlled rate of flow within specific vacuum ranges.
A feedback or control loop may be used to ensure the constancy of
the drive system under differing loads conditions. An additional
feedback control loop may exist between a vacuum sensor in the aspiration
line in the motor, to limit the amount of vacuum in the aspiration
tube.
[0015] Vacuum-based systems also have feedback control loops, where
the signal from a vacuum sensor in the aspiration path is compared
to the pre-set desired vacuum level. Error signals are then sent
to a vacuum generator, such as a proportional value and venturi
chamber, to increase or decrease the vacuum level.
[0016] In certain situations, the emulation of a flow-based pump
system by a vacuum-based pump system may be desirable. Such emulation
has not been practical before the present invention, because there
has been no practical means to measure flow rate in the vacuum-based
system.
[0017] The present invention solution for ophthalmic aspiration
flow rate measurement preferably utilizes an isolated Hall-effect
electromagnetic flow meter, such as described above in FIG. 1. The
present invention, shown in FIG. 2 takes advantage of the fact
that the saline solution commonly used in ophthalmic surgery is
electrically conductive. Thus, a Hall-voltage can be induced across
an aspiration tube if a magnetic field is applied. The flow meter
34 (preferably similar to the flow meter 10 of FIG. 1) in the ophthalmic
surgical pump system 32 includes of a magnetic field source or electromagnetic
magnet and meter 34 in use is connected to a disposable electrode
assembly 36 (as shown in FIGS. 3-5). Control electronics assembly
38 (preferably responds to the output of flow meter 34) to control
a proportional value or venturi chamber (not shown) of a venturi
pump 56 to evaluate a peristaltic pump by maintaining a constant
flow rate of fluids and tissues through path or tube 50. The preferred
embodiment shows an aspiration tube 50 but tube 50 could also be
other pathways that allow fluids and tissues to be carried away
from the surgical site.
[0018] FIG. 2. further shows an irrigation-fluid bottle 40 connected
to an irrigation line 42 with arrow 44 showing the direction of
travel of the saline fluid into handpiece 46. Surgical handpiece
46 performs a surgical operation on eye 48. Fluids from bottle 40
and excised surgical tissue are aspirated from eye 48 through aspiration
path 50 (which is preferably standard surgical tubing) in the direction
shown by arrow 52. The aspirated fluid and tissue is received by
collection reservoir 54 which is contained within pump 56 (preferably
a venturi pump though a peristaltic or other pump may be used as
well). The venturi pump is preferably the same pump sold with Bausch
& Lomb's Millennium.RTM. Ophthalmic Surgical System. Venturi
pump 56 creates a vacuum level for aspirating fluid and tissue from
the surgical site at eye 48 to the collection reservoir 54. The
flow meter 34 is electrically connected (connection not shown) to
control circuitry 38 as well as being electrically connected to
one of the aspiration tubing 50 or the collection reservoir 54 as
further described below. Control circuitry 38 is connected to the
flow meter 34 and to venturi pump 56 for varying the vacuum level
of the pump 56 and thereby maintaining a desired flow rate of the
fluid and tissue being aspirated from the surgical site.
[0019] Preferably, collection reservoir 54 is a rigid-walled cassette
so that the cassette will be operable and not collapse during operation
when a vacuum level is applied by the venturi pump 56. Further collection
reservoir 54 is similar to cassettes currently sold by Bausch &
Lomb except as modified and described in this invention. Electrodes
36 are not visible in the view of FIG. 2 though may be seen in alternative
embodiments in FIGS. 3-5.
[0020] FIG. 3 shows a partial front view of a venturi pump 56 including
a collection reservoir 54 for use in surgical pump system 32. Collection
reservoir 54 is preferably a rigid-walled cassette adapted for connection
to the aspiration tubing 50 and receives fluid and tissue aspirated
from a surgical site. Collection reservoir 54 also includes a pair
of electrodes 36 positioned so that the electrodes are electrically
connectable to flow meter 34. During operation, the electrodes 36
are exposed to the fluid and tissue such that the flow meter 34
shall indicate a flow rate of the fluid and tissue from the surgical
site. Preferably, electrodes 36 are positioned so that, in operation,
electrodes 36 align perpendicular to an electromagnet 60 thereby
forming a Hall-effect flow meter. FIG. 4 shows a side elevation
view of a collection reservoir 54 as described above. Electrodes
36 may be molded into the reservoir 54 or inserted by any other
known method, but in any case, the electrodes should form a sufficient
seal with reservoir 54 to prevent fluids from leaking.
[0021] FIG. 5 is an alternate embodiment of the present invention,
wherein surgical tubing 62 is essentially the same as tube 50 except
that tube 62 includes a pair of electrodes 64 for cooperation with
electromagnet 60 and flow meter circuitry 34 and is shown to be
connectable with a collection reservoir 66. Surgical tubing 62 carries
fluid to or from a surgical site and includes a pair of electrodes
positioned within the tubing such that the electrodes, in operation,
are exposed to the fluids and wherein the electrodes are electrically
connectable to a flow meter for indicating a flow rate of the fluids
through the tubing. Preferably, the electrodes 64 are positioned
so that, in operation the electrodes are perpendicular to an electromagnet,
such as that shown in FIG. 3 to form a Hall-effect flow meter.
Electrodes 64 may be molded into tubing 62 or may be press fit and
should form a liquid tight seal with tubing 62.
[0022] The flow meter 34 provides a magnetic field required to
produce the Hall-effect voltage. The magnetic driver can be constructed
of a permanent or preferably an electromagnet. An electromagnet
is preferred so that the magnetic field may be oscillated. Alternatively,
the field may be oscillated by rotation of a fixed cylindrical magnet
(not shown). In either configuration, an air gap is required so
that the aspiration tube may be inserted within the magnetic field.
The disposable electrodes 64 or 36 must be in contact with the aspirant.
These electrodes may be molded into an aspiration tube 60 as shown
in FIG. 5 into a cassette 54 as shown in 3 and 4 or into a reflux
bulb 68 at low cost. It is also noted that a Hall-effect flow meter
as described, can be connected to irrigation tubing 42 to provide
an accurate flow rate of the saline solution into the eye.
[0023] The metal electrodes 36 or 60 are in contact with the aspirated
saline solution resulting in an electrochemical reaction, such as
corrosion, which, in turn, produces electrical signals. The use
of an alternating magnetic field from the Hall-effect flow meter
induces alternating voltages. The amplitude of this alternating
field is then correlated to a flow rate. Electrochemical voltages
not associated with the flow rate are filtered and eliminated easily
because they are steady currents.
[0024] Thus, there has been shown an inventive flow meter for an
ophthalmic surgical pump system. This flow meter could be used with
flow-based pumps or vacuum-based pumps as described above.
[0025] Important application using the flow meter 34 in connection
with the venturi-based pump system is the emulation of a positive
displacement pump. The flow rate output of meter 34 can be used
in a feedback control loop to adjust the vacuum level. This feedback
control loop is preferably part of control circuitry 38. This control
loop consists of measuring the flow rate with meter 34 and comparing
that rate to the commanded flow rate. If the sense flow rate is
lower than commanded, a vacuum generator level is increased to generate
additional vacuum. This in turn increases the flow rate. Conversely,
if the flow rate is too high, the vacuum generator level is decreased
resulting in a decreased flow rate. In this way, using control system
design the characteristics of a flow-based pump may be emulated
using venturi pump 56. With or without a feedback control loop,
it is preferred that the flow rate detected by flow meter 34 be
displayed (not shown) by pump system 32.
[0026] An additional application of flow sensor 34 is occlusion
detection. Essentially, occlusion detection is simply another flow
rate detection scheme where the flow rate detected approaches zero
(0) when tissue blocks the tip of a surgical device or the aspiration
tube. When the flow rate approaches zero (0) dangerous conditions
result such as overheating of the surgical device or occlusion of
the aspiration pathway and quick detection of such a condition is
highly desirable. Therefore, detection of a flow rate approaching
zero (0) could be used to warn the user (audibly or visually) that
the system has an occlusion or upon detection the aspiration could
be slowed or stopped. As those skilled in the art will appreciate,
the detection and warning of flow rate need not be at zero (0),
but could occur at some flow rate above zero (0), but where overheating
may still be of concern.
[0027] Thus, there has been shown an inventive ophthalmic surgical
pump system providing a low-cost aspirant flow meter. In addition,
such a system may be used in other surgical pump systems, such as
endoscopic pumps. |