Method for obtaining blood pressure data from optical sensor

• US 6,475,153 B1
• Filed: 05/10/2000
• Issued: 11/05/2002
• Est. Priority Date: 05/10/2000
• Status: Expired due to Term

• Current Assignee: LifeSync Corporation
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Lopez, Salvador, Ng, Richard, Olson, William, Khair, Mohammad, Ghaem, Sanjar
• Primary Examiner(s): Nasser, Robert L.
• Assistant Examiner(s): MALLARI, PATRICIA C
• Application Number:
  US09/568,781
• Time in Patent Office: 909 Days
• Field of Search: 600/485, 600/500-503
• US Class Current: 600/485
• CPC Class Codes: A61B 2562/0233 Special features of optical sensors or probes classified in A61B5/00
• CPC Class Codes: A61B 2562/0257 Proximity sensors
• CPC Class Codes: A61B 2562/046 in a matrix array
• CPC Class Codes: A61B 5/0015 characterised by features of the telemetry system
• CPC Class Codes: A61B 5/02007 Evaluating blood vessel condition, e.g. elasticity, compliance
• CPC Class Codes: A61B 5/021 Measuring pressure in heart or blood vessels A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/02438 with portable devices, e.g. worn by the patient
• CPC Class Codes: A61B 5/026 Measuring blood flow A61B3/1233, A61B3/1241 take precedence
• CPC Class Codes: A61B 5/0261 using optical means, e.g. infrared light
• CPC Class Codes: A61B 5/318 Heart-related electrical modalities, e.g. electrocardiography [ECG]
• CPC Class Codes: A61B 5/389 Electromyography [EMG]
• CPC Class Codes: A61B 5/681 Wristwatch-type devices
• CPC Class Codes: A61B 5/6843 Monitoring or controlling sensor contact pressure
• CPC Class Codes: A61B 5/7285 for synchronising or triggering a physiological measurement or image acquisition with a physiological event or waveform, e.g. an ECG signal A61B6/5205, A61B6/541, A61B8/5207, A61B8/543 take precedence
• CPC Class Codes: G08B 21/0453 worn on the body to detect health condition by physiological monitoring, e.g. electrocardiogram, temperature, breathing detecting, measuring or recording for diagnostic purposes A61B5/00
• CPC Class Codes: G08B 21/182 Level alarms, e.g. alarms responsive to variables exceeding a threshold
• CPC Class Codes: G08B 25/08 using communication transmission lines G08B13/19658, G08B21/0286, G08B25/016 take precedence

Abstract

An optical sensor generates blood pressure data by obtaining two dimensional images of the surface of the patient'"'"'s body, such as in the vicinity of the radial artery in the wrist area. Blood flow in the patient causes light to be reflected off a flexible reflective surface applied against the patient with a hold down pressure, and the scattering of light is sensed with a two-dimensional array of photo-detectors. The output of the photo-detectors during systolic and diastolic events is calibrated against known blood pressure measurements taken with a conventional air-cuff sphygmomanometer. Linear calibration relationships between output signal and blood pressure are obtained during calibration for some set of the photo-detectors. When blood pressure data is obtained from the patient, the linear calibration relationship between output signals and blood pressure is applied to the output signals from the set of photo-detectors, resulting in blood pressure data. The method provides for compensation for changes in hold down pressure and translation or rotation of the optical sensor relative to the patient. A preferred optical sensor arrangement for use in performing the method is also described.

Claims

1. A method for obtaining blood pressure data from a patient using an optical blood pressure sensor placed against a patient'"'"'s body, said sensor comprising a two-dimensional array of photo-sensitive elements, comprising the steps of:

(1) calibrating said optical sensor, said step of calibrating comprising the steps of obtaining at least one digitized two-dimensional calibration image of a portion of said patient'"'"'s body using said optical sensor, substantially simultaneously obtaining a blood pressure measurement form said patient, and comparing said blood pressure measurement to at least one portion of said at least one calibration image to thereby obtain a calibration relationship between said at least one portion of said at least one calibration image and said blood pressure measurement;

(2) subsequently obtaining a second digitized two-dimensional image of said portion of said patient'"'"'s body during a period in which said blood pressure data is to be obtained from said patient;

(3) applying said calibration relationship derived for said at least one portion of said at least one calibration to a corresponding portion of said second image to thereby derive said blood pressure data; and

(4) performing validation checking of output signals from multiple photosensitive elements corresponding to said portion of said calibration and second two-dimensional images.

10. The method of claim 1, further comprising the step of generating a multitude of digitized two-dimensional images over a data collection period of time and performing said step (3) for each of said multitude of images.

11. The method of claim 10, further comprising the step of applying a Kalman filter to said digitized two-dimensional images.

12. The method of claim 10, further comprising the step of applying a finite impulse response filter to at least one of said multitude of two-dimensional images.

13. The method of claim 10, further comprising the steps of measuring gating window parameters and performing said step (3) for said multitude of two-dimensional images obtained during a gating window.

14. The method of claim 10, further comprising the step of estimating arterial compliance from a rate of change of skin displacement determined from sequential images in said multitude of two-dimensional images.

15. The method of claim 10, further comprising the step of measuring pulse rate from sequential images in said multitude of two-dimensional images over a measured interval of time.

16. The method of claim 10, further comprising the step of averaging said blood pressure data from said multitude of two-dimensional images.

17. The method of claim 1, further comprising the step of measuring a first hold-down pressure being applied between said optical sensor and said patient during said calibrating step, measuring a second hold down pressure being applied between said optical sensor and said patient during the obtaining of said second image, comparing said first hold down pressure with said second hold down pressure, and scaling said blood pressure data in accordance with said comparison between said first and second hold down pressures.

18. The method of claim 10, wherein said array comprises a two-dimensional array of photo-detectors detecting scattering patterns from light transmitted from a radiation source nominally oriented normal to the patient'"'"'s body at said location.

19. The method of claim 18, wherein said light source comprises a source of coherent electromagnetic photo-radiation.

20. The method of claim 1 wherein a computing platform incorporated into said optical pressure sensor performs step (3).

21. The method of claim 1 wherein a computing platform remote from said optical pressure sensor performs step (3).

22. The method of claim 21, wherein said optical blood pressure sensor further comprises a wireless transceiver for sending output data from said array to a remote base unit incorporating said computing platform.

23. The method of claim 22, wherein said remote base unit further comprises a wireless transceiver for sending configuration or data acquisition commands to said optical blood pressure sensor.

24. The method of claim 1, wherein said optical blood pressure sensor further comprises a machine-readable storage medium containing a set of instructions for performing step (3).

25. The method of claim 1, wherein said array comprises a charge-coupled device.

26. The method of claim 1, wherein said sensor is incorporated into a device adapted to be worn around the wrist of a patient.

27. The method of claim 1, wherein said step of calibrating further comprises the steps of making a plurality of blood pressure measurements of said patient during systolic and diastolic events and substantially simultaneously obtaining a plurality of two-dimensional images from said array, and deriving a calibration relationship between said blood pressure measurements and signal outputs from a plurality of photo-sensitive elements in said array from said plurality of two-dimensional images.

31. The method of claim 25, wherein said step of generating a calibration relationship comprises the steps of making a plurality of blood pressure measurements of said patient during systolic and diastolic events and substantially simultaneously obtaining a plurality of two-dimensional images from said array, and deriving a calibration relationship between said blood pressure measurements and signal outputs from a plurality of photo-sensitive elements in said array from said plurality of two-dimensional images.

32. The method of claim 1, further comprising incorporating said sensor into a device adapted to be worn around the wrist of a patient.

2. A method for obtaining blood pressure data from a patient using an optical blood pressure sensor placed against a patient'"'"'s body, said sensor comprising a two-dimensional array of photo-sensitive elements, comprising the steps of:

(1) calibrating said optical sensor, said step of calibrating comprising the steps of obtaining at least one digitized two-dimensional calibration image of a portion of said patient'"'"'s body using said optical sensor, substantially simultaneously obtaining a blood pressure measurement form said patient, and comparing said blood pressure measurement to at least one portion of said at least one calibration image to thereby obtain a calibration relationship between said at least one portion of said at least one calibration image and said blood pressure measurement;

(2) subsequently obtaining a second digitized two-dimensional image of said portion of said patient'"'"'s body during a period in which said blood pressure data is to be obtained from said patient;

(3) applying said calibration relationship derived for said at least one portion of said at least one calibration to a corresponding portion of said second image to thereby derive said blood pressure data;

(4) generating a multitude of digitized two-dimensional images over a data collection period of time and performing said step (3) for each of said multitude of images; and

(5) measuring blood flow rate from sequential images in said multitude of two-dimensional images over a measured interval of time.

3. A method for obtaining blood pressure data from a patient using an optical blood pressure sensor placed against a patient'"'"'s body, said sensor comprising a two-dimensional array of photo-sensitive elements, comprising the steps of:

(1) calibrating said optical sensor, said step of calibrating comprising the steps of obtaining at least one digitized two-dimensional calibration image of a portion of said patient'"'"'s body using said optical sensor, substantially simultaneously obtaining a blood pressure measurement form said patient, and comparing said blood pressure measurement to at least one portion of said at least one calibration image to thereby obtain a calibration relationship between said at least one portion of said at least one calibration image and said blood pressure measurement;

(2) subsequently obtaining a second digitized two-dimensional image of said portion of said patient'"'"'s body during a period in which said blood pressure data is to be obtained from said patient; and

(3) applying said calibration relationship derived for said at least one portion of said at least one calibration to a corresponding portion of said second image to thereby derive said blood pressure data;

wherein said portion of said calibration image comprises a single location in said calibration, wherein said calibration relationship is obtained for said single location in said calibration image, and wherein said corresponding portion in said second image comprises said single location in said calibration image.

4. A method for obtaining blood pressure data from a patient using an optical blood pressure sensor placed against a patient'"'"'s body, said sensor comprising a two-dimensional array of photo-sensitive elements, comprising the steps of:

(1) calibrating said optical sensor, said step of calibrating comprising the steps of obtaining at least one digitized two-dimensional calibration image of a portion of said patient'"'"'s body using said optical sensor, substantially simultaneously obtaining a blood pressure measurement form said patient, and comparing said blood pressure measurement to at least one portion of said at least one calibration image to thereby obtain a calibration relationship between said at least one portion of said at least one calibration image and said blood pressure measurement;

(2) subsequently obtaining a second digitized two-dimensional image of said portion of said patient'"'"'s body during a period in which said blood pressure data is to be obtained from said patient; and

(3) applying said calibration relationship derived for said at least one portion of said at least one calibration to a corresponding portion of said second image to thereby derive said blood pressure data;

wherein said portion of said calibration image comprises a set of locations in said calibration image having substantially different image intensity values, and wherein said calibration relationship is performed for said set of locations.

5. A method for processing output signals from a two-dimensional array of photo-sensitive elements to generate blood pressure data, said two-dimensional array of photo-sensitive elements incorporated into an optical blood pressure sensor adapted to be placed on the surface of a patient and obtain optical information as to movement of the patient'"'"'s body in response to blood flow in the patient, comprising the steps of:

generating a calibration relationship between output signals from a set of at least one of said photo-sensitive elements to known blood pressure measurements;

obtaining, via said optical blood pressure sensor, a two-dimensional image of the surface of a patient'"'"'s body during a period in which blood pressure information is sought for said patient;

digitizing said two-dimensional image to thereby obtain a two-dimensional array of digital output values, said output values including output values for said set of at least one of said photo-sensitive elements; and

applying said calibration relationship to a portion of said array of digital output values corresponding to said set of at least one of said photo-sensitive elements to thereby derive said blood pressure data;

wherein said set of at least one of said photo-sensitive elements comprises a single photo-sensitive element in said array.

6. A method for obtaining blood pressure data from a patient using an optical blood pressure sensor placed against a patient'"'"'s body, said sensor comprising a two-dimensional array of photo-sensitive elements, comprising the steps of:

(1) calibrating said optical sensor, said step of calibrating comprising the steps of obtaining at least one digitized two-dimensional calibration image of a potion of said patient'"'"'s body using said optical sensor, substantially simultaneously obtaining a blood pressure measurement form said patient, and comparing said blood pressure measurement to at least one portion of said at least one calibration image to thereby obtain a calibration relationship between said at least one portion of said at least one calibration image and said blood pressure measurement;

(2) subsequently obtaining a second digitized two-dimensional image of said portion of said patient'"'"'s body during a period in which said blood pressure data is to be obtained from said patient;

(3) applying said calibration relationship derived for said at least one portion of said at least one calibration to a corresponding portion of said second image to thereby derive said blood pressure data; and

(4) compensating for rotation or translation of said optical sensor relative to said patient occurring between the obtaining of said calibration and second images.

7. The method of claim 6, wherein said step of compensating comprises the step of applying an algorithm to said calibration and second images to determine a translation or rotation of said at least one portion of said calibration and second two-dimensional images, and generating a new set of calibration relationships according to said translation or rotation.

8. The method of claim 6, wherein said step of compensating is initiated in response to said applying preformed in step (3) in the event that a digitized value of an output signal from a photo-sensitive element corresponding to said at least one portion of said calibration image differs from a digitized value of an output signal from said photo-sensitive element for said second image by a predetermined threshold amount.

9. A method for obtaining blood pressure data from a patient using an optical blood pressure sensor placed against a patient'"'"'s body, said sensor comprising a two-dimensional array of photo-sensitive elements, comprising the steps of:

(1) calibrating said optical sensor, said step of calibrating comprising the steps of obtaining at least one digitized two-dimensional calibration image of a portion of said patient'"'"'s body using said optical sensor, substantially simultaneously obtaining a blood pressure measurement form said patient, and comparing said blood pressure measurement to at least one portion of said at least one calibration image to thereby obtain a calibration relationship between said at least one portion of said at least one calibration image and said blood pressure measurement;

(2) subsequently obtaining a second digitized two-dimensional image of said portion of said patient'"'"'s body during a period in which said blood pressure data is to be obtained from said patient; and

(3) applying said calibration relationship derived for said at least one portion of said at least one calibration to a corresponding portion of said second image to thereby derive said blood pressure data;

wherein said portion of said calibration image comprises a set of locations in said calibration image having substantially the same image intensity values, wherein said calibration relationship is obtained for said set of locations.

28. A method for processing output signals from a two-dimensional array of photo-sensitive elements to generate blood pressure data, said two-dimensional array of photo-sensitive elements incorporated into an optical blood pressure sensor adapted to be placed on the surface of a patient and obtain optical information as to movement of the patient'"'"'s body in response to blood flow in the patient, comprising the steps of:

generating a calibration relationship between output signals from a set of at least one of said photo-sensitive elements to known blood pressure measurements;

obtaining, via said optical blood pressure sensor, a two-dimensional image of the surface of a patient'"'"'s body during a period in which blood pressure information is sought for said patient;

digitizing said two-dimensional image to thereby obtain a two-dimensional array of digital output values, said output values including output values for said set of at least one of said photo-sensitive elements; and

applying said calibration relationship to a portion of said array of digital output values corresponding to said set of at least one of said photo-sensitive elements to thereby derive said blood pressure data;

wherein said set of at least one of said photo-sensitive elements comprises a set of photo-sensitive elements having substantially similar output signals at said known blood pressure measurement.

29. The method of claim 28, wherein said calibration relationship comprises a linear scaling relationship between blood pressure and a digitized output signal from said set of at least one of said photo-sensitive elements.

30. The method of claim 28 further comprising the step of scaling said blood pressure data in accordance with a change in the hold down pressure applied between said optical sensor and said patient from an initial, calibration hold down pressure and a hold down pressure when said two-dimensional image is obtained.

33. The method of claim 28, further comprising the step of generating a multitude of digitized two-dimensional images over a data collection period of time and performing said steps of digitizing and applying for each of said multitude of images.

34. The method of claim 33, further comprising the step of applying a Kalman filter to said digitized two-dimensional images.

35. The method of claim 33, further comprising the step of applying a finite impulse response filter to at least one of said multitude of two-dimensional images.

36. The method of claim 33, further comprising the steps of measuring gating window parameters and obtaining said multitude of two-dimensional images during a gating window.

37. The method of claim 33, further comprising the step of estimating arterial compliance from a rate of change of skin displacement determined from sequential images in said multitude of two-dimensional images.

38. The method of claim 33, further comprising the step of measuring pulse rate from sequential images in said multitude of two-dimensional images over a measured interval of time.

39. The method of claim 33, further comprising the step of averaging said blood pressure data from data obtained from said multitude of two-dimensional images.

40. The method of claim 28, wherein said array comprises a charge-coupled device.

41. The method of claim 28, wherein said array comprises a two-dimensional array of photo-detectors detecting scattering patterns from light transmitted from a radiation source nominally oriented normal to the patient'"'"'s body at said location.

42. The method of claim 41, wherein said light source comprises a source of coherent electromagnetic photo-radiation.

43. The method of claim 28, wherein said step of applying is performed by a computing platform incorporated into said optical blood pressure sensor.

44. The method of claim 28, wherein at least one of said step of applying is performed in a computing platform remote from said optical blood pressure sensor.

45. The method of claim 43, wherein said optical blood pressure sensor further comprises a wireless transceiver for sending output data from said array to a remote base unit incorporating said computing platform.

46. The method of claim 45, wherein said optical blood pressure sensor further comprises a wireless transceiver for sending output data from said array to a remote base unit incorporating said computing platform.

47. The method of claim 46, wherein said remote base unit further comprises a wireless transceiver for sending configuration or data acquisition commands to said optical blood pressure sensor.

52. The method of claim 28, further comprising incorporating said sensor into a device adapted to be worn around the wrist of a patient.

48. A method for processing output signals from a two-dimensional array of photo-sensitive elements to generate blood pressure data, said two-dimensional array of photo-sensitive elements incorporated into an optical blood pressure sensor adapted to be placed on the surface of a patient and obtain optical information as to movement of the patient'"'"'s body in response to blood flow in the patient, comprising the steps of:

generating a calibration relationship between output signals from a set of at least one of said photo-sensitive elements to known blood pressure measurements;

obtaining, via said optical blood pressure sensor, a two-dimensional image of the surface of a patient'"'"'s body during a period in which blood pressure information is sought for said patient;

digitizing said two-dimensional image to thereby obtain a two-dimensional array of digital output values, said output values including output values for said set of at least one of said photo-sensitive elements; and

applying said calibration relationship to a portion of said array of digital output values corresponding to said set of at least one of said photo-sensitive elements to thereby derive said blood pressure data;

wherein said calibration relationship comprises a linear scaling relationship between blood pressure and a digitized output signal from said set of at least one of said photo-sensitive elements;

wherein said calibration relationship comprises a plurality of linear scaling relationships between said known blood pressure and a plurality of output signals from a plurality of individual photo-sensitive elements in said array, said linear scaling relationships of the form y^s,d(n, m)=a_n,m^s,d X(n, m)+b_n,m^s,d, where Y^s,d is blood pressure for systolic and diastolic events, (n, m) are one or more individual photo-sensitive elements in an n by m array of such elements, X(n, m) is an output signal value and a_n,m^s,d and b_n,m^s,d are calibration coefficients during systolic and diastolic events for each photo-sensitive element, determined during calibration of the array.

49. A method for processing output signals from a two-dimensional array of photo-sensitive elements to generate blood pressure data, said two-dimensional array of photo-sensitive elements incorporated into an optical blood pressure sensor adapted to be placed on the surface of a patient and obtain optical information as to movement of the patient'"'"'s body in response to blood flow in the patient, comprising the steps of:

generating a calibration relationship between output signals from a set of at least one of said photo-sensitive elements to known blood pressure measurements;

obtaining, via said optical blood pressure sensor, a two-dimensional image of the surface of a patient'"'"'s body during a period in which blood pressure information is sought for said patient;

digitizing said two-dimensional image to thereby obtain a two-dimensional array of digital output values, said output values including output values for said set of at least one of said photo-sensitive elements;

applying said calibration relationship to a portion of said array of digital output values corresponding to said set of at least one of said photo-sensitive elements to thereby derive said blood pressure data; and

performing validation checking of output signals from multiple photo-sensitive elements corresponding to said portion of said two-dimensional image.

50. A method for processing output signals from a two-dimensional array of photo-sensitive elements to generate blood pressure data, said two-dimensional array of photo-sensitive elements incorporated into an optical blood pressure sensor adapted to be placed on the surface of a patient and obtain optical information as to movement of the patient'"'"'s body in response to blood flow in the patient, comprising the steps of:

generating a calibration relationship between output signals from a set of at least one of said photo-sensitive elements to known blood pressure measurements;

obtaining, via said optical blood pressure sensor, a two-dimensional image of the surface of a patient'"'"'s body during a period in which blood pressure information is sought for said patient;

digitizing said two-dimensional image to thereby obtain a two-dimensional array of digital output values, said output values including output values for said set of at least one of said photo-sensitive elements;

applying said calibration relationship to a portion of said array of digital output values corresponding to said set of at least one of said photo-sensitive elements to thereby derive said blood pressure data;

generating a multitude of digitized two-dimensional images over a data collection period of time and performing said steps of digitizing and applying for each of said multitude of images; and

measuring blood flow rate from sequential images in said multitude of two-dimensional images over a measured interval of time.

51. A method for processing output signals from a two-dimensional array of photo-sensitive elements to generate blood pressure data, said two-dimensional array of photo-sensitive elements incorporated into an optical blood pressure sensor adapted to be placed on the surface of a patient and obtain optical information as to movement of the patient'"'"'s body in response to blood flow in the patient, comprising the steps of:

generating a calibration relationship between output signals from a set of at least one of said photo-sensitive elements to known blood pressure measurements;

obtaining, via said optical blood pressure sensor, a two-dimensional image of the surface of a patient'"'"'s body during a period in which blood pressure information is sought for said patient;

digitizing said two-dimensional image to thereby obtain a two-dimensional array of digital output values, said output values including output values for said set of at least one of said photo-sensitive elements;

applying said calibration relationship to a portion of said array of digital output values corresponding to said set of at least one of said photo-sensitive elements to thereby derive said blood pressure data; and

compensating for rotation or translation of said optical sensor relative to said patient occurring between the obtaining of said calibration relationship and said two-dimensional image.