Device for monitoring blood flow to brain

Abstract

A method of estimating blood flow in the brain, comprising: a) causing currents to flow inside the head by producing electric fields inside the head; b) measuring at least changes in the electric fields and the currents; and c) estimating changes in the blood volume of the head, using the measurements of the electric fields and the currents.

1 . A method of estimating perfusion in the brain comprising:
 a) causing currents to flow inside the head by producing an electric field inside the head, using two current-carrying electrodes each attached to the head close to a temporal artery, and applying two different electric potentials to the current-carrying electrodes, keeping the current constant;   b) measuring relative changes in the electric field at the constant current;   c) estimating relative changes in the blood volume of the head, using the measurements of the relative changes in the electric field at the constant current; and   d) estimating perfusion in the brain, from the relative changes in blood volume of the head.   
     
     
         2 . An apparatus for estimating blood flow to the brain, comprising:
 a) a power supply;   b) an electric field source, comprising at least two current-carrying electrodes, adapted for forming a good electrical connection to the head, and connected to the power supply, which uses the power supply to produce an electric field in the head, at a safe amplitude and frequency, thereby producing a current in the head;   c) an electrical element which determines at least changes in the electric field in the head, using two voltage measuring electrodes adapted for forming a good electrical connection to the head, and at least changes in the current in the head, having sufficient precision to at least estimate changes in the impedance of the head; and   d) a monitor which displays at least information telling a user when changes in the impedance of the head show a significant change in blood flow rate;   
       wherein at least one of the electrodes is adapted by its size and shape to be placed on a surface of the head near an opening of the skull, in such a manner that it conforms to the curvature of the head. 
     
     
         3 . An apparatus according to  claim 2 , wherein the electrical element comprises:
 a) a controller in the power supply which controls one of the output voltage and the output current of the power supply, or a combination of the output voltage and output current; and   b) a meter which measures one of voltage across the head, current through the head, or a combination of voltage across the head and current through the head which is not controlled by the controller.   
     
     
         4 . An apparatus according to  claim 3 , wherein the controller in the power supply controls the output current, and the meter is a voltmeter, connected to the voltage-measuring electrodes. 
     
     
         5 . An apparatus according to  claim 4 , wherein the current-carrying electrodes comprise at least three current-carrying electrodes, and at least two of the current-carrying electrodes are connected in parallel to the same voltage. 
     
     
         6 . An apparatus according to  claim 2 , and including at least one electrode structure to which at least one current-carrying electrode and at least one voltage-measuring electrode are mechanically connected. 
     
     
         7 . An apparatus according to  claim 2 , wherein the voltage-measuring electrodes are adapted to be placed inside an opening in the head. 
     
     
         8 . An apparatus according to  claim 7 , wherein the voltage-measuring electrodes are adapted to be placed inside the ears. 
     
     
         9 . An apparatus according to  claim 8 , wherein the voltage-measuring electrodes are conical and padded, thereby allowing them to be pressed firmly enough into the ears to make good electrical contact, without damaging the ear drums. 
     
     
         10 . An apparatus according to  claim 8 , and including a probe adapted for measuring blood flow photoplethysmographically in the ears, which probe is combined with the voltage-measuring electrodes. 
     
     
         11 . An apparatus according to  claim 2 , wherein the opening is an eye socket, and the electrode is shaped to fit over a closed eyelid. 
     
     
         12 . An apparatus according to  claim 2 , wherein the opening is the foramen magnum, and the electrode is shaped to fit near the base of the skull. 
     
     
         13 . An apparatus according to  claim 2 , wherein the opening is an ear, and the electrode is sized and shaped to be placed in the ear canal. 
     
     
         14 . An apparatus according to  claim 2 , wherein the opening is an ear, and the electrode is sized and shaped to be placed behind the ear. 
     
     
         15 . An apparatus according to  claim 2 , wherein the at least two current-carrying electrodes comprise at least three current-carrying electrodes, and the power supply is capable of simultaneously applying at least three different voltages to the current-carrying electrodes, whereby a desired current distribution is produced inside the head. 
     
     
         16 . An apparatus according to  claim 15 , wherein the current-carrying electrodes are adapted to be placed in locations on the head such that the desired current distribution is concentrated in a desired region of the brain. 
     
     
         17 . An apparatus according to  claim 2 , and including a photoplethysmographic blood-flow measuring probe, sized and shaped to be placed in the ears. 
     
     
         18 . An apparatus according to  claim 17 , where the probe is sufficiently wide at its base that it cannot damage the eardrum when inserted into the ears. 
     
     
         19 . An apparatus according to  claim 17 , wherein the probe is surrounded by a holding element which, when inserted into the ear, holds the probe in a position and orientation to allow repeated optical measurements of the same location. 
     
     
         20 . An apparatus according to  claim 2 , which is portable enough for use in the field by emergency medical technicians. 
     
     
         21 . An apparatus according to  claim 2 , and including:
 a) a head motion sensor; and   b) a controller which uses data from the head motion sensor to reduce motion artifacts in estimating the blood flow.   
     
     
         22 . An apparatus for estimating blood flow to the brain, comprising:
 a) a power supply;   b) an electric field source, comprising at least two current-carrying electrodes, adapted for forming a good electrical connection to the head, and connected to the power supply, which uses the power supply to produce an electric field in the head, at a safe amplitude and frequency, thereby producing a current in the head;   c) an electrical element which determines at least changes in the electric field in the head, using two voltage measuring electrodes adapted for forming a good electrical connection to the head, and at least changes in the current in the head, having sufficient precision to at least estimate changes in the impedance of the head; and   d) a monitor which displays at least information telling a user when changes in the impedance of the head show a significant change in blood flow rate;   
       wherein at least a portion of one current-carrying electrode is adjacent on two opposite sides to two portions of a same voltage-measuring electrode, or at least a portion of one voltage-measuring electrode is adjacent on two opposite sides to two portions of a same current-carrying electrode, or both. 
     
     
         23 . An apparatus according to  claim 22 , wherein at least one of said electrodes comprises an annular-shaped electrode that surrounds the electrode or the portion of the electrode that said annular-shaped electrode is adjacent to. 
     
     
         24 . An apparatus according to  claim 22 , wherein at least portions of the voltage-measuring electrode and the current-carrying electrode form intertwined spirals. 
     
     
         25 . A method of estimating changes in blood volume of the head, comprising:
 a) causing currents to flow inside the head by producing electric fields inside the head, by placing at least two current-carrying electrodes on the head, and applying at least two different electric potentials to the current-carrying electrodes;   b) measuring at least changes in the electric fields using at least two voltage-measuring electrodes placed on the head, and at least changes in the currents; and   c) estimating changes in the blood volume of the head, using the measurements of the electric fields and the currents;   
       wherein at least one of the electrodes is placed on or near an opening in the skull, when causing the currents to flow and when measuring at least the changes in electric fields and currents. 
     
     
         26 . A method according to  claim 25 , wherein at least one electrode placed on or near an opening of the skull is placed in an ear canal, or behind an ear. 
     
     
         27 . A method according to  claim 25 , wherein at least one electrode placed on or near an opening of the skull is placed on a closed eyelid. 
     
     
         28 . A method according to  claim 25 , wherein at least one electrode placed on or near an opening of the skull is placed near a foramen magnum.