Measuring and testing – Fluid pressure gauge – Diaphragm
Reexamination Certificate
1998-11-09
2001-08-14
Oen, William (Department: 2855)
Measuring and testing
Fluid pressure gauge
Diaphragm
Reexamination Certificate
active
06272930
ABSTRACT:
The present invention relates to a device for measuring the pressure of a liquid flowing in a tube and extracted from the human body.
More precisely, the invention relates to a device that makes it possible continuously to measure the pressure of a liquid flowing in a tube connected to a portion of the human body, said tube serving to extract the liquid from the human body, the pressure then naturally being negative relative to atmospheric pressure, suction also being provided by means of a pump.
Such a problem arises particularly, but naturally not exclusively, when implementing the so-called “phaco-emulsification” technique. That technique relates to surgery of the eye and consists in removing the lens by breaking it up by means of an ultrasound emitter. The lens fragments obtained in this way are extracted from the eye via a cannula, and more precisely they are extracted from the capsular bag which contains the lens. This extraction is performed by means of a tube connected to an extractor pump, thus making it possible to extract the lens fragments that are immersed in a liquid which is of the physiological serum type. Simultaneously, another cannula is naturally used to inject synthetic physiological liquid into the eye and more precisely into the capsular bag, in order to replace at least temporarily the lens material that has been extracted, said injection generally being performed merely under the effect of gravity.
In that type of operation, it is extremely important for the lens region to contain at all times a volume of liquid and solid material that is substantially constant so as to keep the shape of the anterior chamber substantially constant. Otherwise, in particular in the event of a large and sudden decrease in volume, there could be major and irreversible damage to the eye and in particular to the retina by the retina becoming detached, due to a sudden drop in the pressure to which it is subjected by the vitreous humor.
Unfortunately, in the phaco-emulsification operation, and more precisely while sucking out the lens fragments, such sudden pressure variations can indeed occur, for example when a lens fragment temporarily blocks the extractor cannula. Under such circumstances, when the lens fragment ceases to block the cannula, because of the suction that is established in the tube, liquid is sucked out at a very high rate that is not compensated by the inflow of the replacement liquid.
It should also be recalled that because of the extraction that is taking place, the “normal” pressure of the liquid is lower than atmospheric pressure. Under normal operating conditions, the pressure drop relative to atmospheric pressure is of the order of 50 mm to 500 mm of mercury, and more usually lies in the range 150 mm to 350 mm of mercury.
Under such circumstances, as in other applications, it is important to be able to monitor the pressure that actually obtains in the tube, whether the tube is a suction tube or an injection tube, and to do so continuously, accurately, reliably, and with a time constant that is very short.
Unfortunately, in particular in phaco-emulsification techniques, pressure in the tube is monitored via a duct element branching off from the main tube and connected to a pressure sensor. This branch tube is filled with air in order to protect the sensitive membrane of the sensor from the damage it might suffer from coming into contact with the liquid flowing in the tube. If there is a sudden change of pressure, the air held captive in the branch tube is naturally far more compressible than the liquid flowing in the main tube, and this can give rise firstly to significant error in the pressure value as measured, and above all it can give rise to a significant delay between pressure varying in the tube and that variation being detected by the pressure sensor. As explained above, such measurement errors can lead to very damaging consequences during an operation, in particular when performing phaco-emulsification.
An object of the present invention is to remedy that drawback by providing a pressure measuring device which can be fitted to a tube that is being used to suck a liquid from the human body, the device making it possible at all times to measure the actual pressure of the liquid flowing in the tube with great accuracy and with a very short time constant.
According to the invention, this object is achieved by a device for measuring the pressure of liquid flowing in a tube for causing a liquid to flow out from the human body, which device is characterized in that it comprises:
duct means having an axial bore whose wall has an inside face that is substantially flush with the tube, said means including an orifice passing through the wall and opening out in the inside face, a first end connected to a first portion of said tube and a second end connected to a second portion of the tube; and
a pressure sensor for measuring the pressure of said liquid in the tube, said sensor having a surface which is subjected to the pressure of said liquid, at least a portion of said sensor being mounted in sealed manner in said orifice, in such a manner that said sensitive surface is substantially flush with the inside face of the wall of the duct means.
In a preferred embodiment of the invention, the device comprises:
an elongate body having first and second ends and with an axial bore formed therein, the bore opening out into said first and second ends and being defined by an inside wall, each end having means for connection to said tube, said body also having a recess that opens out into said axial bore between its first and second ends; and
a pressure sensor mounted in said recess, said sensor having a surface which is subjected to said pressure and whose shape is substantially flush with the inside wall of the bore at said recess.
It will be understood that because of this integrated disposition of the pressure sensor, the face of the sensor which is subjected to said pressure is substantially flush with the tube element defined by the body of the pressure measuring device. This avoids any accidental accumulation of air or any other gas which could cause disturbances in the speed and the magnitude of the measurement of the pressure that actually obtains in the tube.
In the present text, the term “substantially flush” means that the pressure sensitive surface of the sensor is not strictly speaking a portion of the corresponding surface of the inside wall of the duct means, but that relative to the corresponding surface of the inside wall said pressure sensitive surface leaves an empty volume that is very small. This volume is preferably less than 10 mm
3
, and more preferably less than 5 mm
3
.
Other characteristics and advantages of the invention appear better on reading the following description of an embodiment of the invention given by way of non-limiting example.
REFERENCES:
patent: 3863504 (1975-02-01), Borsanyi
patent: 5581038 (1996-12-01), Lampropoulos et al.
patent: 5605360 (1997-02-01), Kurisaki et al.
patent: 0 092 827 (1984-05-01), None
patent: 59-012254 (1984-01-01), None
patent: 7-155857 (1995-06-01), None
patent: 7-198521 (1995-08-01), None
Bos Gilles
Crozafon Philippe
Ortuno Angel
Corneal Industrie
Oen William
Wolf Greenfield & Sacks P.C.
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