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Cerebral spinal fluid shunt evaluation system Number:7,520,862 from the United States Patent and Trademark Office (PTO) owispatent

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Title: Cerebral spinal fluid shunt evaluation system

Abstract: A method for evaluating cerebrospinal fluid (CSF) flow rate in a CSF shunt applied to a patient for transmitting the CSF between first and second locations of the patient includes applying temperature sensors to the CSF shunt for determining a flow rate of the CSF through the shunt to provide a determined CSF flow rate and applying an error correction sensor to the patient for providing an error correction signal. The determined CSF flow rate is adjusted in accordance with the error correction signal to provide a corrected CSF flow rate. The sensor can be a temperature sensor such as a thermistor. The CSF is cooled and a temperature value of the CSF is measured in accordance with the cooling. A time value is determined in accordance with the temperature value and the CSF flow rate is determined in accordance with the time value.

Patent Number: 7,520,862 Issued on 04/21/2009 to Neff

Inventors: Neff; Samuel (Haddon Heights, NJ)
Assignee: Neuro Diagnostic Devices, Inc. (Philadelphia, PA)
Appl. No.: 10/770,754
Filed: February 3, 2004

Current U.S. Class: 600/549 ; 604/290; 604/6.13
Current International Class: A61B 5/00 (20060101); A61M 3/00 (20060101); A61M 37/00 (20060101)
Field of Search: 600/549 604/6.13,290

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Other References

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Primary Examiner: Hindenburg; Max
Assistant Examiner: Hoekstra; Jeffrey G
Attorney, Agent or Firm: Caesar, Rivise, Bernstein, Cohen & Pokotilow, Ltd
Claims


What is claimed is:

1. A method for evaluating an internal cerebrospinal fluid (CSF) flow rate using external measurements, said CSF flow rate occurring in a CSF shunt within a body of a patient, and said CSF shunt transmitting said CSF between differing locations of said body, the method comprising: (a) applying a plurality of temperature sensors to said body over said CSF shunt at exterior locations on said body to determine an externally determined CSF flow rate signal representative of said CSF flow rate to provide an externally determined CSF flow rate; (b) applying a background temperature sensor to said body at an exterior location on said body to determine an externally measured background induced error correction signal representative of a temperature of said exterior of said body simultaneously with said evaluating of said CSF flow rate for correcting a measurement error induced in said externally determined CSF flow rate signal by a background condition; (c) adjusting said CSF flow rate determination in accordance with said externally measured background induced error correction signal to provide a more accurate representation of said externally determined CSF flow rate, whereby said more accurate representation of said CSF flow rate determination is determined independently of any internally determined temperature signals provided in accordance with any temperature sensors located in the interior of said body, and whereby said CSF flow rate determination is (i) provided only according to external measurement and (ii) corrected only according to external measurement performed simultaneously with said evaluating of said externally determined CSF flow rate; and (d) whereby said CSF flow rate determination is provided according to a comparison of temperature values that are measured simultaneously with said evaluating of said externally determined CSF flow rate only and independently of any comparison with a predetermined control value of temperature for controlling a temperature of a fluid to make said temperature of a fluid equal to said predetermined control value of temperature.

2. A method for evaluating internal CSF flow rate in a CSF shunt applied to the body of a patient of claim 1, further comprising determining a zero CSF flow rate.

3. A method for evaluating internal CSF flow rate in a CSF shunt applied to the body of a patient of claim 1, further comprising determining a non-zero CSF flow rate.

4. A method for evaluating internal CSF flow rate in a CSF shunt applied to the body of a patient of claim 1, further comprising determining that said CSF flow rate exceeds a predetermined threshold.

5. A method for evaluating internal CSF flow rate in a CSF shunt applied to the body of a patient of claim 1, wherein said at least one temperature sensor of said plurality of temperature sensors comprises a thermistor.

6. A method for evaluating internal CSF flow rate in a CSF shunt applied to the body of a patient of claim 1, further comprising cooling said CSF.

7. A method for evaluating internal CSF flow rate in a CSF shunt applied to the body of a patient of claim 6, further comprising measuring a temperature value of said CSF in accordance with said cooling.

8. A method for evaluating internal CSF flow rate in a CSF shunt applied to the body of a patient of claim 7, further comprising determining a time value in accordance with said temperature value.

9. A method for evaluating internal CSF flow rate in a CSF shunt applied to the body of a patient of claim 8, further comprising determining said externally determined CSF flow rate in accordance with said time value.

10. A method for evaluating internal CSF flow rate in a CSF shunt applied to the body of a patient of claim 9, further comprising determining said externally determined CSF flow rate in accordance with a plurality of temperature values.

11. A method for evaluating internal CSF flow rate in a CSF shunt applied to the body of a patient of claim 7, further comprising providing a frequency signal in accordance with said measured temperature value.

12. A method for evaluating internal CSF flow rate in a CSF shunt applied to the body of a patient of claim 11, further comprising providing said frequency signal in accordance with a temperature sensor resistance.

13. A method for evaluating internal CSF flow rate in a CSF shunt applied to the body of a patient of claim 12, further comprising providing said frequency signal using an oscillator having an oscillation frequency dependent upon said temperature sensor resistance.

14. A method for evaluating internal CSF flow rate in a CSF shunt applied to the body of a patient of claim 13, wherein said oscillator comprises a relaxation oscillator.

15. A method for evaluating internal CSF flow rate in a CSF shunt applied to the body of a patient of claim 11, further comprising determining a frequency oscillation value in accordance with a measured frequency of said frequency signal.

16. A method for evaluating internal CSF flow rate in a CSF shunt applied to the body of a patient of claim 15, further comprising providing said corrected CSF flow rate in accordance with said frequency oscillation value.

17. A method for evaluating internal CSF flow rate in a CSF shunt applied to the body of a patient of claim 1, further comprising: applying a further background temperature sensor at an exterior location on said body for providing a further externally determined background temperature correction signal; and providing said corrected CSF flow rate in accordance with said further externally determined background temperature correction signal.
Description


BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to cerebrospinal fluid shunts and, more particularly, to apparatus and methods for quantitatively detecting the flow of cerebrospinal fluid in such shunts noninvasively.

2. Description of Related Art

A cerebrospinal fluid (CSF)shunt includes a system of tubing that allows CSF to flow from a patient's brain to another part of the body (e.g., abdomen to relieve pressure in the spinal column). As a result, it is desirable to know, periodically, that the pathway of the CSF shunt remains unobstructed to permit CSF flow and what the flow rate is. It is also desirable to make these determinations non-invasively when quantifying the CSF flow.

The following describe different apparatus and methodologies that have been used to monitor, determine or treat body fluid flow, including CSF flow through a shunt.

"A Thermosensitive Device for the Evaluation of the Patency of Ventriculo-atrial Shunts in Hydrocephalus", by Go et al. (Acta Neurochirurgica, Vol. 19, pages 209-216, Fasc. 4) discloses the detection of the existence of flow in a shunt by placement of a thermistor and detecting means proximate the location of the shunt and the placement of cooling means downstream of the thermistor. The downstream thermistor detects the cooled portion of the CSF fluid as it passes from the region of the cooling means to the vicinity of the thermistor, thereby verifying CSF flow. However, among other things, the apparatus and method disclosed therein fails to teach or suggest an apparatus/method for quantifying the flow of the fluid through the shunt.

In "A Noninvasive Approach to Quantitative Measurement of Flow through CSF Shunts" by Stein et al., Journal of Neurosurgery, 1981, April; 54(4):556-558, a method for quantifying the CSF flow rate is disclosed. In particular, a pair of series-arranged thermistors is positioned on the skin over the CSF shunt, whereby the thermistors independently detect the passage of a cooled portion of the CSF fluid. The time required for this cooled portion to travel between the thermistors is used, along with the shunt diameter, to calculate the CSF flow rate. See also "Noninvasive Test of Cerebrospinal Shunt Function," by Stein et al., Surgical Forum 30:442-442, 1979; and "Testing Cerebropspinal Fluid Shunt Function: A Noninvasive Technique," by S. Stein, Neurosurgery, 1980 Jun. 6(6): 649-651. However, the apparatus/method disclosed therein suffers from, among other things, variations in thermistor signal due to environmental changes.

U.S. Pat. No. 4,548,516 (Helenowski) discloses an apparatus for indicating fluid flow through implanted shunts by means of temperature sensing. In particular, the apparatus taught by Helenowski comprises a plurality of thermistors mounted on a flexible substrate coupled to a rigid base. The assembly is placed on the skin over the implanted shunt and a portion of the fluid in the shunt is cooled upstream of the assembly. The thermistors detect the cooled portion of the fluid as it passes the thermistor assembly and the output of the thermistor is applied to an analog-to-digital converter for processing by a computer to determine the flow rate of the shunt fluid.

U.S. Pat. No. 6,413,233 (Sites et al.) discloses several embodiments that utilize a plurality of temperature sensors on a patient wherein a body fluid (blood, saline, etc.) flow is removed from the patient and treated, e.g., heated or cooled, and then returned to the patient. See also U.S. Pat. No. 5,494,822 (Sadri). U.S. Pat. No. 6,527,798 (Ginsburg et al.) discloses an apparatus/method for controlling body fluid temperature and utilizing temperature sensors located inside the patient's body.

U.S. Pat. No. 5,692,514 (Bowman) discloses a method and apparatus for measuring continuous blood flow by inserting a catheter into the heart carrying a pair of temperature sensors and a thermal energy source. See also U.S. Pat. No. 4,576,182 (Normann).

U.S. Pat. No. 4,684,367 (Schaffer et al.) discloses an ambulatory intravenous delivery system that includes a control portion of an intravenous fluid that detects a heat pulse using a thermistor to determine flow rate.

U.S. Pat. No. 4,255,968 (Harpster) discloses a fluid flow indicator which includes a plurality of sensors placed directly upon a thermally-conductive tube through which the flow passes. In Harpster a heater is located adjacent to a first temperature sensor so that the sensor is directly within the sphere of thermal influence of the heater.

U.S. Pat. No. 3,933,045 (Fox et al.) discloses an apparatus for detecting body core temperature utilizing a pair of temperature sensors, one located at the skin surface and another located above the first sensor wherein the output of the two temperature sensors are applied to a differential amplifier heater control circuit. The control circuit activates a heat source in order to drive the temperature gradient between these two sensors to zero and thereby detect the body core temperature.

U.S. Pat. No. 3,623,473 (Andersen) discloses a method for determining the adequacy of blood circulation by measuring the difference in temperature between at least two distinct points and comparing the sum of the detected temperatures to a reference value.

U.S. Pat. No. 3,762,221 (Coulthard) discloses an apparatus and method for measuring the flow rate of a fluid utilizing ultrasonic transmitters and receivers.

U.S. Pat. No. 4,354,504 (Bro) discloses a blood-flow probe that utilizes a pair of thermocouples that respectively detect the temperature of a hot plate and a cold plate (whose temperatures are controlled by a heat pump. The temperature readings are applied to a differential amplifier. Energization of the heat pump is controlled by a comparator that compares a references signal to the differential amplifier output that ensures that the hot plate does not exceed a safety level during use.

All references cited herein are incorporated herein by reference in their entireties.

BRIEF SUMMARY OF THE INVENTION

A method for evaluating cerebrospinal fluid (CSF) flow rate in a CSF shunt applied to the body of a patient for transmitting the CSF between first and second locations of the body includes the steps of applying a plurality of temperature sensors to the CSF shunt for determining a flow rate of the CSF through the shunt to provide a determined CSF flow rate and applying an error correction sensor to the body of the patient for providing an error correction signal. The CSF flow rate determination is adjusted in accordance with the error correction signal to provide a corrected CSF flow rate. The sensor can be a temperature sensor such as a thermistor. The CSF is cooled and a temperature value of the CSF is measured in accordance with the cooling. A time value is determined in accordance with the temperature value and the CSF flow rate is determined in accordance with the time value. The CSF flow rate can be determined in accordance with a plurality of temperature values. A temperature correction value can be determined using the error correction sensor. The temperature correction value can be a background temperature value and the corrected CSF flow rate can be provided in accordance with the temperature correction value.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

The invention will be described in conjunction with the following drawings in which like reference numerals designate like elements and wherein:

FIG. 1 shows a schematic representation of a prior art cerebral spinal fluid shunt evaluation system for monitoring the fluid flow through the shunt.

FIG. 2 shows a schematic representation of a prior cerebral spinal fluid shunt evaluation system for monitoring the fluid flow through the shunt.

FIG. 3 shows a schematic representation of the cerebral spinal fluid shunt evaluation system of the present invention for monitoring the fluid flow through the shunt.

FIG. 4 shows a schematic representation of a circuit suitable for use in the cerebral spinal fluid shunt evaluation system of FIG. 3.

FIG. 5 shows a cerebral spinal fluid flow rate calculation system including the circuit of FIG. 4.

FIG. 6 shows a graphical representation of the response time of two sensors within the cerebral spinal fluid shunt evaluation system of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, there is shown a prior art cerebral spinal fluid (CSF) shunt evaluation system 10. The CSF shunt evaluation system 10 includes a shunt tubing 18 that allows CSF to flow from the brain of a patient to another part of the body of the patient such as the abdomen, e.g., for treatment of a patient with hydroencephalus. The CSF shunt evaluation system 10 monitors the flow of the CSF through the shunt tubing 18 by means of upstream cooling of the CSF and a downstream sensor 14. The sensor 14 can be a temperature sensor, such as a thermistor, a thermocouple or a semiconductor sensor. The downstream sensor 14 is disposed over the shunt tubing 18 in the vicinity where the shunt tubing 18 empties into the abdominal cavity in order to detect changes in temperature as the cooled CSF is transported from the cooled region to the abdominal cavity.

The sensor 14 could be conventional temperature sensitive device wherein the internal resistance of the sensor 14 varies, either directly or inversely, according to the temperature of the sensor 14. Thus, changes in the temperature of the sensor 14 were detected by merely making a determination of its resistance or, equivalently, a measurement of the changes in the amount of current through the sensor 18.

In operation, a user of the shunt evaluation system 10 could place an ice cube on the scalp of the patient over the shunt tubing 18 for about one minute using, for example, forceps. While the safety of using ice m


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