Non-invasive blood pressure sensor with motion artifact reduction and constant gain adjustment during pressure pulses

• US 6,245,022 B1
• Filed: 06/30/1999
• Issued: 06/12/2001
• Est. Priority Date: 10/16/1998
• Status: Expired due to Fees

• Current Assignee: Medwave, Inc.
• Original Assignee: Medwave, Inc.
• Inventors: Thede, Roger C., Curran, Timothy G., Poliac, Marius O., Archibald, G. Kent, Danielson, Orland H.
• Primary Examiner(s): Nasser, Robert L.
• Application Number:
  US09/343,903
• Time in Patent Office: 713 Days
• Field of Search: 600/485, 600/490, 600/493-496, 600/500, 600/503
• US Class Current: 600/485
• CPC Class Codes: A61B 2562/0247 Pressure sensors
• CPC Class Codes: A61B 5/022 by applying pressure to close blood vessels, e.g. against the skin; Ophthalmodynamometers
• CPC Class Codes: A61B 5/02225 using the oscillometric method
• CPC Class Codes: A61B 5/6843 Monitoring or controlling sensor contact pressure

Abstract

A non-invasive blood pressure sensor includes a first fluid filled sensing chamber having a diaphragm. A first transducer is fluidly coupled to the first sensing chamber to sense fluid pressure within the first chamber. A flexible body conformable wall surrounds the sensing chamber. The wall applies force to the artery while preventing pressure in a direction generally parallel to the artery from being applied to the sensing chamber. The flexible body conformable wall includes a second fluid filled chamber. A second transducer fluidly coupled to the second chamber senses fluid pressure within the second chamber. As varying pressure is applied to the artery pressure waveforms are sensed by the first transducer. Using output signals of the first and second transducers, the sensed pressure waveform data is analyzed to derive waveform parameters from which blood pressure values are derived. The effects of motion artifacts are reduced by the use of signals from both the first and second transducers. Part of the analysis of the waveform data includes the use of an adjusted gain that is substantially constant during pressure pulses, but that may vary from pulse to pulse. Signal values obtained from the second transducer are multiplied by the adjusted gain.

Claims

1. A method for determining blood pressure of an artery having a pulse, the method comprising:

applying pressure to the artery;

sensing pressure data produced by the artery, the pressure data including data for a plurality of beats;

sensing noise data;

adjusting the noise data with a gain having a substantially fixed value during each beat, the gain being variable from beat to beat;

correcting the pressure data based upon thc noise data to produce corrected pressure data;

deriving a plurality of parameters from the corrected pressure data; and

determining a blood pressure value based upon the parameters.

2. The method of claim 1 wherein sensing noise data comprises sensing pressure applied to the artery.

3. A method for determining blood pressure of an artery, the method comprising:

applying pressure to the artery so that the artery exhibits a plurality of pressure waveforms;

producing sensed pressure waveform data representing each of the plurality of pressure waveforms;

producing noise data which is representative of noise contained in the pressure waveforms;

correcting the noise data by a function which may vary from pressure waveform to pressure waveform and which is a substantially fixed value during each pressure waveform;

correcting the sensed pressure waveform data based on the noise data to produce corrected pressure waveform data;

deriving a plurality of parameters from the corrected pressure waveform data; and

determining a blood pressure value based upon the parameters.

4. The method of claim 3 wherein the function is a gain.

5. A non-invasive blood pressure measurement device, the measurement device comprising:

means for applying pressure to an artery so that the artery exhibits pressure data;

first sensing means for sensing the pressure data, the pressure data including data for a plurality of bears;

second sensing means for sensing noise data;

signal producing means connected to the first and second sensing means for producing output signals corresponding to the sensed pressure data; and

processing means for receiving the output signals from the signal producing means, for deriving a plurality of parameters using sensed pressure corrected to remove noise, the noise adjusted with a gain having a substantially fixed value during each beat, the gain being variable from beat to beat, and for determining a blood pressure value using the derived parameters.

6. The measurement device of claim 5 wherein the first sensing means includes:

a first transducer having a sensing surface;

a first flexible diaphragm for being positioned over the underlying artery; and

first interface means between the first flexible diaphragm and the sensing surface of the transducer for transmitting pressure pulses from the diaphragm to the transducer.

7. The measurement device of claim 6 wherein the second sensing means includes:

a second diaphragm which is responsive to pressure applied to the artery;

a second transducer; and

second interface means between the second diaphragm and the second transducer for transmitting pressure from the diaphragm to the second transducer.

8. The measurement device of claim 7 wherein the first and second sensing means arc mounted on a sensor interface assembly which is pivotally connected to a housing.

9. A non-invasive blood pressure measurement system comprising:

means for applying pressure to an artery;

means for sensing pressure from the artery over time while the pressure is applied to the artery to generate pressure data, the pressure data including data for a plurality of beats;

means for sensing noise associated with applying pressure;

means for adjusting the noise with a gain having a substantially fixed value during each beat, the gain changing between beats;

means for deriving a pressure value based upon a waveform analysis of the pressure data as corrected with the noise data.

10. A method of determining blood pressure, the method comprising:

applying pressure to an artery;

sensing pressure over time while pressure is applied to the artery to generate pressure waveform data for pressure waveforms representing a plurality of beats;

sensing noise over time;

correcting the noise by a gain which may vary from beat to beat and which is a substantially fixed value during each beat;

correcting the waveform data to remove the corrected noise;

detecting onset of the beats from the waveform data;

extracting waveform parameters using a detected onset of one of the beats; and

determining a blood pressure value based upon the waveform parameters.

11. A method for determining blood pressure of an artery having a pulse, the method comprising:

applying pressure to the artery;

sensing pressure data produced by the artery, the pressure data including data for a plurality of beats;

correcting the pressure data by removing noise components associated with motion artifacts, the noise components adjusted with a gain having a substantially fixed value during each beat, the gain variable from beat to beat;

deriving a plurality of parameters from the corrected pressure data; and

determining a blood pressure value based upon the plurality of parameters and a stored set of coefficients.

12. A device for external measurements of blood pressure in an underlying artery surrounded by tissue of a patient, the device comprising:

first sensing means for sensing blood pressure pulses in the underlying artery;

second sensing means for sensing noise associated with motion artifacts;

means for adjusting the noise with a gain having a substantially fixed value during each pulse, the gain changing between pulses;

means for applying a variable pressure to the artery; and

means for calculating blood pressure from the sensed blood pressure pulses corrected to remove the adjusted noise, based upon shape of the sensed pressure pulses within the underlying artery.

13. The device of claim 12 wherein the first sensing means includes:

a first transducer having a sensing surface;

a first flexible diaphragm for being positioned over the underlying artery; and

first interface means between the first flexible diaphragm and the sensing surface of the first transducer for transmitting pressure pulses from the first flexible diaphragm to the first transducer.

14. The device of claim 13 wherein the second sensing means includes:

a second transducer having a sensing surface;

a second flexible diaphragm; and

second interface means between the second flexible diaphragm and the sensing surface of the transducer for transmitting pressure from the second flexible diaphragm to the second transducer.

15. A method of generating adjusted pressure waveform data representing blood pressure pulses in an artery, the method comprising:

sensing a range of pressures applied to the artery and generating pressure data that represents the sensed pressures;

sensing the blood pressure pulses in the artery and generating pulse data that represents the sensed blood pressure pulses;

calculating relative gain values representing the relative gain between the pressure data and the pulse data at various points in time;

adjusting the pressure data with a function based on the relative gain values, the function varying between pulses and held substantially constant during each pulse; and

generating adjusted pressure waveform data by subtracting the adjusted pressure data and the pulse data.

16. The method of claim 15 wherein the function is a gain.

17. The method of claim 16 and further comprising:

deriving a plurality of parameters from the adjusted pressure waveform data; and

determining a blood pressure value based upon the plurality of parameters.

18. A non-invasive blood pressure measurement device, the measurement device comprising:

means for applying pressure to an artery so that the artery exhibits pressure data;

first sensing means for sensing the pressure data, the pressure data including data for a plurality of beats, wherein the first sensing means includes;

a first transducer having a sensing surface;

a first flexible diaphragm for being positioned over the underlying, artery; and

first interface means between the first flexible diaphragm and the sensing surface of the transducer for transmitting pressure pulses from the diaphragm to the transducer;

second sensing means for sensing noise data;

signal producing means connected to the first and second sensing means for producing output signals corresponding to the sensed pressure data; and

processing means for receiving the output signals from the signal producing means, for deriving a plurality of parameters using sensed pressure corrected to remove noise, the noise adjusted with a gain having a substantially fixed value during each beat, and for determining a blood pressure value using the derived parameters.

19. The measurement device of claim 18 wherein the second sensing means includes:

a second diaphragm which is responsive to pressure applied to the artery;

a second transducer; and

second interface means between the second diaphragm and the second transducer for transmitting pressure from the diaphragm to the second transducer.

20. The measurement device of claim 19 wherein the first and second sensing means are mounted on a sensor interface assembly which is pivotally connected to a housing.