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

• US 20050038346A1
• Filed: 01/17/2003
• Published: 02/17/2005
• Est. Priority Date: 03/23/2000
• Status: Abandoned Application

• Current Assignee: Frank R. Miele
• Original Assignee: Frank R. Miele
• Inventors: Miele, Frank R.
• Application Number:
  US10/346,939
• Publication Number:
  US 20050038346A1
• Time in Patent Office: Days
• US Class Current: 600/485
• CPC Class Codes: A61B 2562/0247 Pressure sensors
• CPC Class Codes: A61B 5/0053 by applying pressure, e.g. compression, indentation, palpation, grasping, gauging
• CPC Class Codes: A61B 5/02028 Determining haemodynamic parameters not otherwise provided for, e.g. cardiac contractility or left ventricular ejection fraction
• CPC Class Codes: A61B 5/021 Measuring pressure in heart or blood vessels A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/02116 of pulse wave amplitude A61B5/02225 takes precedence
• CPC Class Codes: A61B 8/06 Measuring blood flow measuring volume flow in general G01F, e.g. G01F1/66, G01F1/72; measuring speed of fluids in general G01P5/00
• CPC Class Codes: A61B 8/0858 involving measuring tissue layers, e.g. skin, interfaces

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.

Claims

1-63. -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.