VITAL SIGN MONITOR FOR MEASURING BLOOD PRESSURE USING OPTICAL, ELECTRICAL AND PRESSURE WAVEFORMS

• US 20090018453A1
• Filed: 06/12/2008
• Published: 01/15/2009
• Est. Priority Date: 06/12/2007
• Status: Active Grant

• Current Assignee: Sotera Wireless Incorporated
• Original Assignee: Triage Wireless, Inc.
• Inventors: Dhillon, Marshal S., ZHOU, Zhou, Visser, Henk II, BANET, Matthew J., KOPOTIC, Robert J., Terry, Andrew S.
• Granted Patent: US 8,419,649 B2
• Time in Patent Office: Days
• US Class Current: 600/493
• CPC Class Codes: A61B 5/0022 Monitoring a patient using a global network, e.g. telephone networks, internet
• CPC Class Codes: A61B 5/02125 of pulse wave propagation time
• CPC Class Codes: A61B 5/02133 by using induced vibration of the blood vessel
• CPC Class Codes: A61B 5/0225 the pressure being controlled by electric signals, e.g. derived from Korotkoff sounds
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/0295 using plethysmography, i.e. measuring the variations in the volume of a body part as modified by the circulation of blood therethrough, e.g. impedance plethysmography
• CPC Class Codes: A61B 5/1118 Determining activity level
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/318 Heart-related electrical modalities, e.g. electrocardiography [ECG]
• CPC Class Codes: A61B 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: A61B 5/6824 Arm or wrist
• CPC Class Codes: A61B 5/721 using a separate sensor to detect motion or using motion information derived from signals other than the physiological signal to be measured
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61B 5/742 using visual displays A61B5/339 takes precedence

Abstract

A method and apparatus for continuous measurement of blood pressure, based on pulse transit time, which does not require any external calibration. This technique, referred to herein as the ‘composite technique’, is carried out with a body-won sensor that measures blood pressure and other vital signs, and wirelessly transmits them to a remote monitor. A network of disposable sensors, typically placed on the patient'"'"'s right arm and chest, connect to the body sensor and measure a time-dependent electrical waveform, optical waveform, and pressure waveform. The disposable sensors typically include an armband that features an inflatable bladder coupled to a pressure sensor, at least 3 electrical sensors (e.g. electrodes), and an optical sensor (e.g., a light source and photodiode) attached to a wrist-worn band.

Claims

1. A system for monitoring a patient'"'"'s vital sign, the system comprising:

a pressure-delivery system for applying a variable pressure to the patient'"'"'s arm;

a pressure sensor for measuring a time-dependent pressure waveform representing the pressure applied to the patient'"'"'s arm;

an optical sensor configured to attach to the patient and generate a time-dependent optical waveform representing a flow of blood within the patient;

an electrode system configured to attach to the patient and generate a time-dependent electrical waveform representing activity of the patient'"'"'s heart; and

a processing component programmed to;

i) determine a pulse transit time which is a measure of a separation in time of a first feature of the time-dependent electrical waveform and a second feature of the time-dependent optical waveform;

ii) determine a variation in the pulse transit time as a function of the pressure applied to the patient'"'"'s arm by the pressure-delivery system;

iii) determine from the time-dependent pressure waveform a first value of a preselected blood pressure parameter; and

iv) determine from the pressure-dependent variation of pulse transit time and the first value of the blood pressure parameter a relationship specifying how a selected blood pressure parameter varies as a function of pulse transit time.

2. The system of claim 1, wherein the relationship that is determined is a functional relationship.

3. The system of claim 1, wherein determining the relationship between the blood pressure parameter and pulse transit time comprises determining for each of a plurality of heartbeats a pulse transit time and a corresponding value for the blood pressure parameter.

4. The system of claim 1, wherein the processing component is programmed to determine the first value of the preselected blood pressure parameter from the time-dependent pressure waveform by extracting an oscillatory signal from the time-dependent pressure waveform and determining a pressure at which that oscillatory signal is at a maximum.

5. The system of claim 3, wherein the processing component is programmed to determine the first value of the preselected blood pressure parameter from the time-dependent pressure waveform by extracting an oscillatory signal from the time-dependent pressure waveform and fitting a predetermined function to an envelope of the oscillatory signal.

6. The system of claim 1, wherein the preselected blood pressure parameter and the selected blood pressure parameter are the same blood pressure parameters.

7. The system of claim 1, wherein the preselected blood pressure parameter is mean arterial pressure.

8. The system of claim 1, wherein the selected blood pressure parameter is mean arterial pressure.

9. The system of claim 1, wherein the processing component is further programmed to use the relationship to determine the value of the selected blood pressure parameter based on a measured pulse transit time for the patient, wherein the measured pulse transit time is obtained during a pressure free phase of operation phase in which the pressure-delivery system applies no pressure to the patient'"'"'s arm.

10. The system of claim 1, wherein the first feature of the time-dependent electrical waveform is a QRS complex and the second feature of the time-dependent optical waveform corresponds to a pressure pulse.

13. The method of claim 1, further comprising using the relationship to monitor the patient'"'"'s blood pressure based on measurements of pulse transit times for the patient when applying no pressure to the patient'"'"'s arm.

15. The system of claim 1, further comprising a housing unit that is configured to be worn in the patient'"'"'s arm and wherein said housing unit contains the pressure-delivery system, the pressure sensor, and the processing component.

11. A method of monitoring a patient'"'"'s vital sign, the method comprising:

applying a variable pressure to the patient'"'"'s arm;

measuring a time-dependent pressure waveform representing the pressure applied to the patient'"'"'s arm;

sensing a time-dependent optical signal which represents a flow of blood within the patient;

detecting a time-dependent electrical signal which represents activity of the patient'"'"'s heart;

determining a variation in a pulse transit time as a function of the pressure applied to the patient'"'"'s arm, wherein the pulse transit time is a measure of a separation in time of a first feature of the time-dependent electrical signal and a second feature of the time-dependent optical signal;

determining from the time-dependent pressure waveform a first value of a preselected blood pressure parameter; and

determining from the pressure-dependent variation of pulse transit time and the first value of the blood pressure parameter a relationship specifying how a selected blood pressure parameter varies as a function of pulse transit time.

12. The method of claim 11, wherein the relationship that is determined is a functional relationship.

14. The system of claim 11, wherein the first feature of the time-dependent electrical waveform is a QRS complex and the second feature of the time-dependent optical waveform corresponds to a pressure pulse.

16. A system for monitoring a patient'"'"'s vital sign, the system comprising:

a pressure-delivery system for applying a variable pressure to the patient'"'"'s arm;

a pressure sensor for measuring a time-dependent pressure waveform representing the pressure applied to the patient'"'"'s arm;

an optical sensor configured to attach to the patient and generate a time-dependent optical waveform representing a flow of blood within the patient;

an electrode system configured attach to the patient and generate a time-dependent electrical waveform representing activity of the patient'"'"'s heart; and

a processing component programmed to;

i) determine a pulse transit time when pressure is applied to the patient'"'"'s arm by the pressure system, wherein pulse transit time is a measure of a separation in time of a first feature of the time-dependent electrical waveform and a second feature of the time-dependent optical waveform;

ii) determine a variation in an amplitude of the optical waveform versus the pressure applied to the patient'"'"'s arm;

iii) fit a function to the variation in the amplitude of the optical waveform;

iv) determine a calibration value for a blood pressure parameter from the fitted function; and

v) use the calibration value for the blood pressure parameter and a subsequently measured pulse transit time obtained for the patient when no pressure is applied to the patient'"'"'s arm to determine the patient'"'"'s blood pressure at that subsequent time.

17. The system of claim 16, wherein the blood pressure parameter is systolic blood pressure.

18. The system of claim 16, wherein the function is a linear function.

19. The system of claim 16, wherein the first feature of the time-dependent electrical waveform is a QRS complex and the second feature of the time-dependent optical waveform corresponds to a pressure pulse.

20. The system of claim 16, further comprising a housing unit that is configured to be worn in the patient'"'"'s arm and wherein said housing unit contains the pressure-delivery system, the pressure sensor, and the processing component.

21. A method of monitoring a patient'"'"'s vital sign, the method comprising:

applying a variable pressure to the patient'"'"'s arm;

measuring a time-dependent pressure waveform representing the pressure applied to the patient'"'"'s arm;

sensing a time-dependent optical waveform representing a flow of blood within the patient;

detecting a time-dependent electrical waveform representing activity of the patient'"'"'s heart;

determining a pulse transit time when applying pressure to the patient'"'"'s arm, wherein pulse transit time is a measure of a separation in time of a first feature of the time-dependent electrical waveform and a second feature of the time-dependent optical waveform;

determining a variation in an amplitude of the optical waveform versus the pressure applied to the patient'"'"'s arm;

fitting a function to the variation in the amplitude of the optical waveform;

determining a calibration value for a blood pressure parameter from the fitted function; and

using the calibration value for the blood pressure parameter and a subsequently measured pulse transit time obtained for the patient when no pressure is applied to the patient'"'"'s arm to determine the patient'"'"'s blood pressure at that subsequent time.

22. A system for measuring a patient'"'"'s vital sign, the system comprising:

a pressure-delivery system for applying a variable pressure to the patient'"'"'s arm;

a pressure sensor for measuring a time-dependent pressure waveform representing the pressure applied to the patient'"'"'s arm;

an optical sensor configured to attach to the patient and generate a time-dependent optical waveform representing a flow of blood within the patient; and

a processing component programmed to;

i) determine a variation in an amplitude of the optical waveform versus the pressure applied to the patient'"'"'s arm;

ii) fit a function to the variation in the amplitude of the optical waveform; and

iii) determine a value for a blood pressure parameter from the fitted function, wherein the determined value is a systolic blood pressure for the patient.

23. The system of claim 22, wherein the function is a linear function.

24. The system of claim 22, wherein the processing component is further programmed to limit the pressure applied to the patient by the pressure-delivery system to a value that is less than the patient'"'"'s systolic blood pressure.

25. The system of claim 22, further comprising a housing unit that is configured to be worn in the patient'"'"'s arm and wherein said housing unit contains the pressure-delivery system, the pressure sensor, and the processing component.

26. A method of measuring a patient'"'"'s vital sign, the system comprising:

applying a variable pressure to the patient'"'"'s arm;

measuring a time-dependent pressure waveform representing the pressure applied to the patient'"'"'s arm;

sensing a time-dependent optical waveform representing a flow of blood within the patient;

determining a variation in an amplitude of the optical waveform versus the pressure applied to the patient'"'"'s arm;

fitting a function to the variation in the amplitude of the optical waveform versus the pressure applied to the patient'"'"'s arm; and

determining a value for a blood pressure parameter from the fitted function, wherein the determined value is a systolic blood pressure for the patient.

27. A system for monitoring a patient'"'"'s vital sign, the system comprising:

a pressure-delivery system for applying a variable pressure to the patient'"'"'s arm;

a pressure sensor for measuring a time-dependent pressure waveform representing the pressure applied to the patient'"'"'s arm;

an optical sensor configured to attach to the patient and generate a time-dependent optical waveform representing a flow of blood within the patient; and

a processing component programmed to;

i) determine from a time-dependent pressure waveform acquired from the pressure sensor a value of a first blood pressure parameter for the patient;

ii) determine a variation in an amplitude of the optical waveform versus the pressure applied to the patient'"'"'s arm;

iii) fit a function to the variation in the amplitude of the optical waveform; and

iv) determine from the fitted function a value for a second blood pressure parameter for the patient.

28. The system of claim 27, wherein the first blood pressure parameter is mean arterial pressure.

29. the system of claim 27, wherein the second blood pressure parameter is systolic blood pressure.

30. The system of claim 27, wherein the processing component is further programmed to cause the pressure-delivery system to perform an inflation phase during which the pressure-delivery system applies an increasing amount of pressure on the patient'"'"'s arm as a function of time and to obtain the acquired time-dependent pressure waveform during the inflation phase.

31. The system of claim 27, further comprising a housing unit that is worn on the patient'"'"'s arm, wherein said housing unit housing the pressure-delivery system, the pressure sensor, and the processing component.

32. A method of monitoring a patient'"'"'s vital sign, the method comprising:

applying a variable pressure to the patient'"'"'s arm;

measuring a time-dependent pressure waveform representing the pressure applied to the patient'"'"'s arm;

sensing a time-dependent optical waveform representing a flow of blood within the patient;

determining from the time-dependent pressure waveform a value of a first blood pressure parameter for the patient;

determining a variation in an amplitude of the optical waveform versus the pressure applied to the patient'"'"'s arm;

fitting a function to the variation in the amplitude of the optical waveform; and

determining from the fitted function a value for a second blood pressure parameter for the patient.

33. The system of claim 32, wherein the first blood pressure parameter is mean arterial pressure.

34. the system of claim 32, wherein the second blood pressure parameter is systolic blood pressure.

35. A system for monitoring a patient'"'"'s vital sign, the system comprising:

a pressure-delivery system for applying a variable pressure to the patient'"'"'s arm;

a pressure sensor for measuring a time-dependent pressure waveform representing the pressure applied to the patient'"'"'s arm;

an optical sensor configured to attach to the patient and generate a time-dependent optical waveform representing a flow of blood within the patient;

an electrode system configured to attach to the patient and generate a time-dependent electrical waveform representing activity of the patient'"'"'s heart; and

a processing component programmed to;

i) determine a pulse transit time for the patient which is a measure of a separation in time of a first feature of the time-dependent electrical waveform and a second feature of the time-dependent optical waveform;

ii) cause the pressure-delivery system to enter an inflation phase of operation;

iii) perform a calibration during the inflation phase of operation to determine a calibration value of a preselected blood pressure parameter;

iv) use the calibration value to establish a functional relationship for determining the value of a selected blood pressure parameter as a function of measured pulse transit time for the patient; and

v) during a pressure-free phase of operation, use the functional relationship to determine values of the selected blood pressure parameter based on measured values of pulse transit time for the patient.

36. The system of claim 35, wherein the preselected blood pressure parameter is mean arterial blood pressure.

37. The system of claim 35, wherein the selected blood pressure parameter is systolic blood pressure.

38. A method of monitoring a patient'"'"'s vital sign, the method comprising:

applying a variable pressure to the patient'"'"'s arm;

measuring a time-dependent pressure waveform representing the pressure applied to the patient'"'"'s arm;

sensing a time-dependent optical waveform representing a flow of blood within the patient;

detecting a time-dependent electrical waveform representing activity of the patient'"'"'s heart;

causing the pressure-delivery system to enter an inflation phase of operation;

performing calibration measurements of the patient'"'"'s blood pressure during the inflation phase of operation to determine a calibration value of a preselected blood pressure parameter;

using the calibration value to establish a functional relationship for determining the value of a selected blood pressure parameter as a function of measured pulse transit time for the patient; and

during a pressure-free phase of operation, using the functional relationship to determine values of the selected blood pressure parameter based on measured values of pulse transit time for the patient, wherein pulse transit time is a measure of a separation in time of a first feature of the time-dependent electrical waveform and a second feature of the time-dependent optical waveform.