Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
2000-01-14
2001-07-24
Lacyk, John P. (Department: 3736)
Surgery
Diagnostic testing
Cardiovascular
C600S485000, C600S488000, C600S561000
Reexamination Certificate
active
06264612
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to catheters. More specifically, this invention relates to catheters for sensing vertebrate conditions.
BACKGROUND OF THE INVENTION
Catheters known in the prior art have been used in humans and animals for diagnostic, monitoring and treatment purposes. Such catheters must be small and flexible in order to function without irritating a body part into which they are inserted. Catheters have been used to infuse medications or remove samples of tissue and fluid for analysis. Multi-lumen catheters have been used to infuse medication and remove samples at the same time.
If a sample must be removed for purposes of analysis, and taken to a laboratory for subsequent analysis, the delay in performing analysis and transmitting the data back to a doctor sometimes can be fatal to a patient. Catheters have also been used to form hydraulic columns for transmitting pressure readings to an external sensor. In pressure sensing catheters, the hydraulic column may have problems with air bubbles, kinks in the tubing, and blood clots affecting the reliability and accuracy of critical readings.
Catheters used for monitoring variations in blood pressure within a blood vessel include those using catheter tip transducers insertable into a blood vessel with the transducer providing direct pressure monitoring by transducing blood pressure at the region of interest. Such catheters have used a semiconductor material constructed and arranged with strain sensing beams for creating a proportionate electrical signal representative of the monitored pressure and transmitting the signal by electrical conductors through the length of the catheter to meters or the like located externally of the monitored body.
An example of such a catheter is seen in U.S. Pat. No. 4,274,423. This catheter includes a pressure sensor disposed within the end portion of a catheter. The pressure sensor uses a pressure sensitive diaphragm constructed from block of semiconductor material. The diaphragm is located adjacent a side port in the catheter housing connected to the end of the catheter with the port providing access to the pressure environment. The diaphragm is directly deflected relative to the pressure exerted thereon and the deflection is sensed by one or more strain gauges located within the diaphragm itself. The strain gauges are connected by conductors to a processor circuit located external of the catheter.
A concern with such catheters is to provide a transducer which is small, while also being sufficiently responsive to pressure variations to provide meaningful electrical output signals. The semiconductor block with the diaphragm or membrane of the type employed in U.S. Pat. No. 4,274,423, may well have a width on the order of 1.2 mm, which limits the size of the catheter and, hence, its application for use in measuring blood pressure and other conditions within a blood vessel.
U.S. Pat. No. 4,722,348, shows a pressure sensing catheter of small size, however, since the catheter body shown has side port pressure inlet apertures which are depressed into the catheter body, this catheter is susceptible to air bubbles being trapped within the pressure apertures, resulting in inaccurate sensor measurements. This catheter is also connected to a detector circuit located outside of the catheter.
SUMMARY OF THE INVENTION
This invention is directed to a catheter having a piezoresistive pressure sensor directly electrically coupled to an integrated circuit for measuring physiological conditions of a vertebrate. The physiological condition is measured by a pressure change which is directly related to the condition and that pressure is detected by the piezoresistive sensor which transmits an electrical impulse directly to the circuit.
In one form of the invention, a catheter with an elongated axis carries a conductive member coupled to plural piezoresistive sensors for measuring physiological conditions of a vertebrate. Each sensor is directly electrically coupled with a bonding pad to a discrete integrated circuit carried internally of the catheter.
In another form of the invention, the catheter has a mechano-responsive element in functional relationship with the piezoresistive sensor. The mechano-responsive element acts as a transfer medium between a vertebrate condition and the piezoresistive sensor which is directly electrically coupled to integrated circuit.
Various physiological vertebrate conditions, e.g., pressure, pH, glucose, water, and temperature, may be detected by the pressure responsive sensors of the catheter. These conditions are transmitted to a computer based data acquisition system. In a preferred embodiment, a stranded copper wire is connected to an application specific integrated circuit and a piezoresistive sensor coupled therewith internally of the catheter. The piezoresistive sensor is directly electrically coupled to the integrated circuit with a solder bonding pad by low temperature thermal compression bonding. In this preferred embodiment, the sensor has a trough in its top surface that receives therein a mechano-responsive element. The mechano-responsive element comprises a fluid or a gel that is sealed from coming into direct contact with the body by a permeable film which acts as a sheath over the piezoresistive sensor. The mechano-responsive element enables conditions such as pH, glucose, water, and temperature to be detected and the detecting signal to be converted into pressure which is sensed by the piezoresistive sensor and then thereby converted to an electrical impulse which is transmitted to the circuit for ultimate processing by a computer. Each sensing site is connected to other sensing sites with the stranded copper wire. Data received at a sensing site from a condition measured from a vertebrate body is transmitted to the data acquisition system via monolithic circuitry. That is, each circuit amplifies and multiplexes signals from plural sensors using a simple count and select scheme.
Other advantages of the invention will become more apparent to those of ordinary skill upon review of the following detailed description of the preferred embodiment taken in conjunction with the accompanying detailed drawings.
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McConnell Keith B.
Rudolph Colin D.
Children's Hospital Medical Center
Lacyk John P.
Natnithithadha Navin
Wood Herron & Evans L.L.P.
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