Surgery – Means for introducing or removing material from body for... – With means for cutting – scarifying – or vibrating tissue
Reexamination Certificate
2001-01-16
2003-10-07
Hayes, Michael J. (Department: 3763)
Surgery
Means for introducing or removing material from body for...
With means for cutting, scarifying, or vibrating tissue
C604S118000, C607S107000, C607S140000
Reexamination Certificate
active
06629948
ABSTRACT:
The present invention is generally directed to a method and apparatus for controlling the flow of fluid from a source to a patient and removal of fluids from the patient through a phacoemulsification handpiece as well as controlling power provided to the phacoemulsification handpiece.
The flow of fluid to and from a patient through a fluid infusion or extraction system and power control to a phacoemulsification handpiece is critical to the procedure being performed.
A number of medically recognized techniques has been utilized for lens removal and among these, a popular technique is phacoemulsification, irrigation and aspiration. This method includes the making of a corneal incision, and the insertion of a handheld surgical implement which includes a needle which is ultrasonically driven in order to emulsify the eye lens. Simultaneously with this emulsification, a fluid is inserted for irrigation of the emulsified lens and a vacuum provided for aspiration of the emulsified lens and inserted fluids.
Currently available phacoemulsification systems include a variable speed peristaltic pump, a vacuum sensor, an adjustable source of ultrasonic power and a programmable microprocessor with operator-selected presets for controlling aspiration rate, vacuum and ultrasonic power levels.
Many surgical instruments and controls in use today linearly control the vacuum or linearly control the flow of aspiration fluid. This feature allows the surgeon to precisely “dispense” or control the “speed” at which he/she employs, either the vacuum or the flow, but not both. However, there often are times during surgery when the precise control when one of the variables (vacuum, aspiration rate, or ultrasonic power) is desired over the other. The experienced user, understanding the relationship between the vacuum and the flow, may manually adjust the preset variable appropriately at the console in order to obtain an acceptable performance. However, if this adjustment is overlooked, then the combination of both high vacuum and high flow can cause undesirable fluidic surges at the surgical site with possible damage inflicted on the patient.
It should be apparent that the control of handheld surgical instruments for use in phaco surgery is complex. Phacoemulsifier apparatus typically comprises a cabinet, including a power supply, peristaltic pump, electronic and associated hardware, and a connected, multi-function and handheld surgical implement, or handpiece, including a hollow slender-like needle tube as hereinabove described, in order to perform the phacoemulsification of the cataractous lens.
It should be appreciated that a surgeon utilizing the handheld implement to perform the functions hereinabove described requires easy and accessible control of these functions, as well as the ability to selectively shift or switch between at least some of the functions (for example, irrigation and irrigation plus aspiration) as may arise during phacoemulsification surgery.
In view of the difficulty with adjusting cabinet-mounted controls, while operating an associated handheld medical implement, control systems have been developed such as described in U.S. Pat. No. 4,983,901. This patent is to be incorporated entirely into the present application, including all specification and drawings for the purpose of providing a background to the complex controls required in phacoemulsification surgery and for describing apparatus which may be utilized or modified for use with the method of the present invention.
To further illustrate the complexity of the control system, reference is also made to U.S. Pat. No. 5,268,624. This patent application is to be incorporated in the present application by this specific reference thereto, including all specifications and drawings for the purpose of further describing the state-of-the-art in the field of this invention.
It should thus be apparent, in view of the complex nature of the control system of fluids and ultrasonic power in the case of phacoemulsification procedures, that it is desirable for a surgeon to have a system which is programmable to serve both the needs of the surgical procedure and particular techniques of the surgeon, which may differ depending on the experience and ability of the surgeon.
The present invention more specifically relates to power control to a phacoemulsification handpiece based on the determination of the phase angle between voltage applied to a handpiece piezoelectric transducer and the current drawn by the piezoelectric transducer and/or the amplitude of power pulses provided to the handpiece.
Phacoemulsification systems typically include a handpiece having an ultrasonically vibrated hollow needle and an electronic control therefor.
As is well known in the art, the phacoemulsification handpiece is interconnected with a control console by an electric cable for powering and controlling the piezoelectric transducer and tubing for providing irrigation fluid to the eye and withdrawing aspiration fluid from an eye through the handpiece.
The hollow needle of the handpiece is typically driven or excited along its longitudinal axis by the piezoelectric effect in crystals created by an AC voltage applied thereto. The motion of the driven crystal is amplified by a mechanically resonant system within the handpiece, such that the motion of the needle connected thereto is directly dependent upon the frequency at which the crystal is driven, with a maximum motion occurring at a resonant frequency.
The resonant frequency is dependent, in part upon the mass of the needle interconnected therewith, which is vibrated by the crystal.
For pure capacitive circuits, there is a 90 degree phase angle between a sine wave representing the voltage applied to the handpiece and the resultant current into the handpiece. This is expressed by the angle {grave over (ø)} equaling −90 degrees. For a purely inductive circuit, the phase angle {grave over (ø)} equals +90 degrees and, of course, for purely resistive circuits {grave over (ø)}=0.
A typical range of frequency used for phacoemulsification handpiece is between about 30 kHz to about 50 kHz. A frequency window exists for each phacoemulsification handpiece that can be characterized by the handpiece impedance and phase.
This frequency window is bounded by an upper frequency and a lower cutoff frequency. The center of this window is typically defined as the point where the handpiece electrical phase reaches a maximum value.
At frequencies outside of this window, the electrical phase of the handpiece is equal to −90 degrees.
Handpiece power transfer efficiency is given by the formula (V*I) (COS {grave over (ø)}). This means that the most efficient handpiece operating point occurs when the phase is closest to 0 degrees.
In order to maintain optimum handpiece power transfer efficiency, it is important to control the frequency to achieve a phase value as close to zero degrees as possible.
This goal is complicated by the fact that the phase angle of the ultrasonic handpiece is also dependent on the loading of the transducer which occurs through the mechanically resonant system which includes the needle.
That is, contact with the needle with tissue and fluids within the eye create a load on the piezoelectric crystals with concomitant change in the operating phase angle.
Consequently, it is important to determine and measure the phase angles at all times during operation of the handpiece in order to adjust the driving circuitry to achieve an optimum phase angle in order to effect constant energy transfer into the tissue by the phaco handpiece, regardless of loading effects.
Thus, it is important to provide automatic tuning of the handpiece during its use in phacoemulsification tissue and withdrawing same from an eye. This auto tuning is accomplished by monitoring the handpiece electrical signals and adjusting the frequency to maintain consistency with selected parameters.
In any event, control circuitry for phacoemulsification handpiece can include circuitry for measuring the phase between the voltage and the cur
Kadziauskas Kenneth E.
Rockley Paul W.
Staggs James W.
Advanced Medical Optics
Gluck Peter Jon
Hackler Walter A.
Hayes Michael J.
Kontos Lina R
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