Thermal method and apparatus for measuring organ blood perfusion
First Claim
1. Apparatus for measuring the true value of local tissue blood flow at a first location in an organ tissue wherein the first location resides outside of the interior of any blood vessels and wherein the organ tissue surrounding and located in close proximity to the first location defines a region of adjacent organ tissue, said apparatus comprising:
- a. heat transfer means positionable at the first location and including means for maintaining said heat transfer means fixed at the first location for converting a flow of electrical current into heat energy and for transferring the heat energy into the adjacent organ tissue;
b. control means electrically coupled to said heat transfer means for operating said heat transfer means in a non-self-heating mode to measure the ambient temperature of the adjacent organ tissue and for operating said heat transfer means in a self-heating mode to establish a temperature gradient between said heat transfer means and the adjacent organ tissue to transfer heat energy into the adjacent organ tissue;
c. means coupled to said control means for measuring the heat energy transferred from said heat transfer means into the adjacent organ tissue, for computing the total conductivity of the adjacent organ tissue, and for generating a total conductivity readout;
d. means for periodically injecting a predetermined volume of a calibration fluid into a blood vessel in fluid communication with but spaced apart from the adjacent organ tissue;
e. calibration means for converting the total conductivity readout into a true local tissue blood flow readout or displacing said heat transfer means from the first location, said calibration means includingi. recording means for recording the changes in the total conductivity readout caused by the passage of said calibration fluid by said heat transfer means;
ii. means for plotting a conductivity washout curve based on the recorded changes in the total conductivity readout to derive a total conductivity to true local blood flow correction factor; and
iii. means for receiving the total conductivity readout and the total conductivity to true local blood flow correction factor and for computing and displaying a true local tissue blood flow readout representative of the true value of the local tissue blood flow at the first location in the organ tissue;
whereby the true local tissue blood flow readout may be displayed on a continuous basis to accurately quantify the local tissue blood flow at the first location on a real time basis.
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Abstract
A ventriculostomy tube having a semi-rigid body and a fluid transmissive passageway extending from a first end to a second end of the tube is inserted through an aperture in a skull. The first end of the tube includes a port for establishing fluid communication between the passageway and a fluid space within the brain tissue surrounding the tube known as the lateral ventricle. By establishing fluid communication between the lateral ventricle of the brain and the second end of the tube, the ventriculostomy tube enables intracranial pressure to be continuously monitored. An electric current is passed through electrical leads extending along the length of the ventriculostomy tube to a thermistor which is secured to the exterior surface of the tube at a first elevation to measure the temperature of the brain tissue at a first elevation. Control means is electrically coupled to the thermistor and provides electrical energy to establish a temperature gradient between the thermistor and the adjacent brain tissue to transfer heat from the thermistor into the brain tissue. Measurement means is coupled to the control means to measure the flow of electrical energy through the thermistor and to compute the thermal conductivity of the brain tissue and blood adjacent to the thermistor to determine local cerebral blood flow (LCBF).
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Citations
17 Claims
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1. Apparatus for measuring the true value of local tissue blood flow at a first location in an organ tissue wherein the first location resides outside of the interior of any blood vessels and wherein the organ tissue surrounding and located in close proximity to the first location defines a region of adjacent organ tissue, said apparatus comprising:
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a. heat transfer means positionable at the first location and including means for maintaining said heat transfer means fixed at the first location for converting a flow of electrical current into heat energy and for transferring the heat energy into the adjacent organ tissue; b. control means electrically coupled to said heat transfer means for operating said heat transfer means in a non-self-heating mode to measure the ambient temperature of the adjacent organ tissue and for operating said heat transfer means in a self-heating mode to establish a temperature gradient between said heat transfer means and the adjacent organ tissue to transfer heat energy into the adjacent organ tissue; c. means coupled to said control means for measuring the heat energy transferred from said heat transfer means into the adjacent organ tissue, for computing the total conductivity of the adjacent organ tissue, and for generating a total conductivity readout; d. means for periodically injecting a predetermined volume of a calibration fluid into a blood vessel in fluid communication with but spaced apart from the adjacent organ tissue; e. calibration means for converting the total conductivity readout into a true local tissue blood flow readout or displacing said heat transfer means from the first location, said calibration means including i. recording means for recording the changes in the total conductivity readout caused by the passage of said calibration fluid by said heat transfer means; ii. means for plotting a conductivity washout curve based on the recorded changes in the total conductivity readout to derive a total conductivity to true local blood flow correction factor; and iii. means for receiving the total conductivity readout and the total conductivity to true local blood flow correction factor and for computing and displaying a true local tissue blood flow readout representative of the true value of the local tissue blood flow at the first location in the organ tissue; whereby the true local tissue blood flow readout may be displayed on a continuous basis to accurately quantify the local tissue blood flow at the first location on a real time basis. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method for measuring the true value of local tissue blood flow at a first location in an organ tissue wherein the first location resides outside of the interior of any blood vessels, said method comprising the steps of:
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a. inserting heat transfer means into the first location and maintaining the position of said heat transfer means fixed at the first location, the organ tissue surrounding and located in close proximity to said heat transfer means at the first location defining a region of adjacent organ tissue having an ambient temperature and a total conductivity; b. operating said heat transfer means in a non-self-heating mode to measure the ambient temperature of the adjacent organ tissue; c. reconfiguring said heat transfer means to operate in a self-heating mode at the first location; d. operating said heat transfer means in the self-heating mode to establish a temperature differential between said heat transfer means and the adjacent organ tissue for transferring heat energy from said heat transfer means to the adjacent organ tissue; e. measuring the quantity of heat energy transferred from said heat transfer means into the adjacent organ tissue; f. computing the total conductivity of the adjacent organ tissue as a function of the ambient temperature of the adjacent organ tissue and the heat energy transferred into the adjacent organ tissue and generating a total conductivity readout; g. calibrating the total conductivity readout to derive a true local tissue blood flow readout i. continuing to operate said heat transfer means in the self-heating mode at that first location and injecting a predetermined volume of a calibration fluid into a blood vessel in fluid communication with but spaced apart from the adjacent organ tissue; ii. recording the changes in the total conductivity readout caused by the passage of said volume of calibration fluid by said heat transfer means without displacing said heat transfer means from the first location; iii. plotting a conductivity washout curve based on the recorded changes in the total conductivity readout to derive a total conductivity to true local blood flow correction factor; iv. applying said correction factor to the total conductivity readout to generate and display a true local tissue blood flow readout representative of the true quantitative value of the local tissue blood flow at the first location in the organ tissue; and h. periodically recalibrating the true local tissue blood flow readout by periodically repeating the calibration step without displacing said heat transfer means from the first location; whereby the true local tissue blood flow readout may be displayed on a continuous basis to accurately quantify the local tissue blood velocity at the first location on a real time basis. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17)
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Specification