Method and apparatus for assessing hemodynamic properties within the circulatory system of a living subject

Abstract

An improved method and apparatus for non-invasively assessing one or more hemodynamic parameters associated with the circulatory system of a living organism. In one aspect, the invention comprises a method of measuring a hemodynamic parameter by measuring a non-calibrated value of the parameter non-invasively, and inducing a stress of the circulatory system while measuring a second parameter. The response of the circulatory system to the stress is determined directly from the subject, and a calibration function is derived from the response and applied to the non-calibrated measured value to produce a calibrated measure of the actual value of the hemodynamic parameter. Methods of generating a tissue transfer function from measurements of the subject, correcting for periodic or aperiodic error components, and providing treatment to the subject based on the measured hemodynamic parameters, are also disclosed.

1 - 63 . (Cancelled)  
     
     
         64 . A method of continuously assessing hemodynamic properties within the circulatory system of a living subject, comprising: 
 measuring a first parameter from a blood vessel of said subject;    variably compressing at least a portion of said blood vessel;    measuring a second parameter from said blood vessel during said act of variably compressing;    deriving a calibration function based at least in part on said second parameter;    calibrating the first parameter using said calibration function;    servoing said compression of said at least portion of said blood vessel based at least in part on the first parameter.    
     
     
         65 . The method of  claim 64 , wherein said act of servoing based at least in part on said first parameter comprises servoing based at least in part on the calibrated value of said first parameter.  
     
     
         66 . The method of  claim 64 , wherein said act of variably compressing comprises applanating said at least portion of said blood vessel according to a predetermined profile.  
     
     
         67 . The method of  claim 64 , wherein said act of measuring a first parameter and variably compressing are performed by at least one pressure transducer.  
     
     
         68 . A method of continuously measuring the pressure within the circulatory system of a living subject, comprising: 
 continuously measuring a non-calibrated pressure from a blood vessel of said subject;    measuring a second parameter from said blood vessel;    creating a stress on said blood vessel during at least a portion of the act of measuring said second parameter, said stress producing a known effect on said second parameter;    identifying at least one marker within said measurement of said second parameter, said at least one marker being related to said known effect;    deriving a calibration function based at least in part on said at least one marker; and    correcting said non-calibrated pressure using the derived calibration function so as to provide a continuous output of corrected blood pressure.    
     
     
         69 . The method of  claim 68 , wherein the act of measuring a second parameter comprises measuring said second parameter using an acoustic wave, and the act of creating a stress comprises variably compressing said blood vessel as a function of time.  
     
     
         70 . The method of  claim 69 , wherein said second parameter comprises the kinetic energy of blood flowing within said blood vessel, and said at least one marker comprises an increase in said kinetic energy.  
     
     
         71 . A method of adaptively measuring the blood pressure of a living subject using at least one blood vessel, comprising: 
 measuring non-calibrated pressure data from said blood vessel;    deriving a calibration function for calibrating said non-calibrated pressure data;    calibrating said pressure data using said derived calibration function at a first interval;    storing said non-calibrated pressure data and said calibration function;    collecting non-calibrated pressure data from said subject during at least one other time;    analyzing the stored pressure data and calibration function, as well as that obtained during said at least one other time, to identify at least one response within said subject; and    adjusting the value of at least said first interval based on said at least one response.    
     
     
         72 . The method of  claim 71 , wherein the act of measuring said non-calibrated pressure data comprises measuring an arterial pressure waveform tonometrically, and the act of deriving comprises: 
 measuring a hemodynamic parameter non-invasively;    applying a stress to said blood vessel while measuring said hemodynamic parameter, said stress inducing a response within second hemodynamic parameter;    identifying at least one marker within said response; and    deriving said calibration function based at least in part on said marker.    
     
     
         73 . An apparatus for measuring hemodynamic properties within the blood vessel of a living subject comprising: 
 a first transducer adapted to measure at least a first hemodynamic parameter associated with said blood vessel;    a second transducer adapted to measure at least a second hemodynamic parameter associated with said blood vessel;    applanation apparatus adapted to controllably apply pressure to said blood vessel; and    a signal processor operatively connected to said first and second transducers and said applanation apparatus, said signal processor being configured to generate a calibration function based at least in part on a signal produced by said second transducer, and apply said calibration function to a signal produced by said first transducer;    wherein said act of generating a calibration function further comprises controlling the level of applanation applied by said applanation apparatus.    
     
     
         74 . The apparatus of  claim 73 , wherein said blood vessel comprises the radial artery of a human being.  
     
     
         75 . The apparatus of  claim 73 , wherein said first transducer comprises a pressure transducer disposed in proximity to said radial artery, and said second transducer comprises an acoustic transducer also disposed in proximity to said radial artery.  
     
     
         76 . An apparatus for continuously assessing at least one hemodynamic parameter associated with a living subject, comprising: 
 a central processing unit;    a data storage device operatively coupled to said central processing unit, said data storage device being adapted to store and retrieve a computer program;    an input device adapted to receive data inputs from one or more external sources;    tonometric apparatus adapted to compress at least a portion of said living subject; and    a computer program, stored on said data storage device, said program being configured to derive a calibrated value of a first hemodynamic based on first input data and second input data received via said input device, said first input data being substantially continuous in nature and representative of a non-calibrated value of said first hemodynamic parameter, said second input data being representative of a second hemodynamic parameter, said first and second input data being obtained during said compressing, the act of deriving said calibrated value of said first hemodynamic parameter comprising:    analyzing said second input data to identify at least one functional relationship therein;    utilizing said at least one functional relationship to derive a calibration function; and    applying said calibration function to said first input data to determine said calibrated value and provide a substantially continuous output thereof.    
     
     
         77 . The apparatus of  claim 76 , wherein said storage device comprises an embedded memory.  
     
     
         78 . The apparatus of  claim 76 , further comprising a display device for displaying at least said calibrated value to a user.  
     
     
         79 . The apparatus of  claim 76 , further comprising an algorithm adapted to run on said central processing unit, said algorithm being configured to identify error components within said first or second input data.  
     
     
         80 . The apparatus of  claim 76 , wherein said tonometric apparatus is also used to obtain said first input data.  
     
     
         81 . The apparatus of  claim 80 , wherein said tonometric apparatus comprises a pressure transducer at least partly in contact with the tissue of said subject.  
     
     
         82 . A method of assessing blood pressure within the circulatory system of a living subject, comprising: 
 measuring pressure from a blood vessel of said subject;    measuring blood flow velocity or kinetic energy from said blood vessel while inducing a stress thereon;    deriving a calibration function based at least in part on said measured blood flow velocity or kinetic energy; and    calibrating said measured pressure using said calibration function.    
     
     
         83 . The method of  claim 82 , wherein said act of inducing a stress comprises inducing a stenosis in said blood vessel.  
     
     
         84 . The method of  claim 83 , wherein said act of inducing a stenosis comprises variably compressing said blood vessel as a function of time in order to induce a range of different blood flow velocities and/or kinetic energies.  
     
     
         85 . The method of  claim 82 , wherein said act of deriving a calibration function comprises: 
 (i) identifying at least one artifact within said measured blood flow velocity or kinetic energy; and    (ii) establishing a relationship between the actual intra-vascular blood pressure and said measured pressure based at least in part on said act of identifying.    
     
     
         86 . The method of  claim 85 , wherein said act of identifying at least one artifact comprises identifying at least one inflection point in said measured blood flow velocity or kinetic energy.  
     
     
         87 . The method of  claim 82 , further comprising selectively controlling the subsequent application of said stress so as to maintain a desired condition.  
     
     
         88 . The method of  claim 87 , wherein said act of selectively controlling comprises servoing to a stress level which approximately maintains a zero transmural pressure condition in said blood vessel.  
     
     
         89 . A method of continuously measuring the blood pressure of a living subject, comprising: 
 measuring pressure from a blood vessel of said subject using at least one pressure transducer;    inducing a stress on at least a portion of said blood vessel using said at least one transducer, said stress producing at least one artifact in a hemodynamic parameter;    determining a calibration function based at least in part on said at least one artifact; and    calibrating said measured pressure using said calibration function.    
     
     
         90 . A method of continuously measuring the blood pressure of a living subject, comprising: 
 tonometrically measuring the pressure from a blood vessel of said subject;    applying a stress to at least a portion of said blood vessel, said stress producing at least one artifact in a hemodynamic parameter;    determining a calibration function based at least in part on said at least one artifact;    calibrating said tonometrically measured pressure using said calibration function at a first time; and    continuously measuring blood pressure from said blood vessel subsequent to said first time at least in part by servoing said applied stress to a desired level determined by said at least one artifact.    
     
     
         91 . The method of  claim 90 , wherein said acts of tonometrically measuring pressure and applying a stress are both performed using at least one pressure transducer.  
     
     
         92 . The method of  claim 91 , wherein said act of applying a stress comprises performing an applanation sweep of said blood vessel using said at least one pressure transducer.  
     
     
         93 . The method of  claim 92 , wherein said act of servoing to a desired level comprises servoing to a condition of approximately zero transmural pressure.  
     
     
         94 . The method of  claim 90 , wherein said method further comprises calibrating said tonometrically measured pressure based at least in part on transfer loss associated with tissue proximate to said blood vessel.