VITAL SIGN MONITOR FOR CUFFLESSLY MEASURING BLOOD PRESSURE USING A PULSE TRANSIT TIME CORRECTED FOR VASCULAR INDEX

• US 20090018422A1
• 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: KOPOTIC, Robert J., DHILLON, Marshal S., ZHOU, Zhou, Visser, Henk II, BANET, Matthew J., Terry, Andrew S.
• Granted Patent: US 8,574,161 B2
• Time in Patent Office: Days
• US Class Current: 600/324
• CPC Class Codes: A61B 2562/08 Sensors provided with means for identification, e.g. barcodes or memory chips
• 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 5/02125 of pulse wave propagation time
• CPC Class Codes: A61B 5/0285 Measuring or recording phase velocity of blood waves
• CPC Class Codes: A61B 5/352 Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: A61B 5/7475 User input or interface means, e.g. keyboard, pointing device, joystick

Abstract

A method and apparatus for measuring a patient'"'"'s blood pressure featuring the following steps: 1) measuring a time-dependent optical waveform with an optical sensor; 2) measuring a time-dependent electrical signal with an electrical sensor; 3) estimating the patient'"'"'s arterial properties using the optical waveform; 4) determining a pulse transit time (PTT) from the time-dependent electrical signal and the time-dependent optical waveform; and 5) calculating a blood pressure value using a mathematical model that includes the PTT and the patient'"'"'s arterial properties.

Claims

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

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) analyze the time-dependent optical waveform to determine a vascular index representing properties of the patient'"'"'s blood circulatory system;

iii) determine a first estimate of a value of a blood pressure parameter from a measured pulse transit time for the patient; and

iv) use the vascular index to modify the first estimate of the value of the blood pressure parameter.

2. The system of claim 1, wherein the processing component is programmed to modify the first estimate of the value of the blood pressure parameter by adding a correction factor to the first estimate, wherein in the correction factor is determined by the vascular index.

3. The system of claim 2, wherein the correction factor is linearly proportional to the vascular index.

4. The system of claim 2, wherein the correction factor is equal to (VI−

Age)*MVI+BVI, where VI is the vascular index, Age is an age of the patient, and MV1 and BV1 are real numbers.

5. The system of claim 1, wherein the processing component is programmed to analyze the time-dependent optical waveform by:

bandpass filtering the time-dependent optical waveform to generate a filtered waveform;

computing a derivative of the filtered waveform to generate a derivative waveform; and

computing the vascular index from characteristics of a waveform derived from the derivative waveform.

6. The system of claim 5, wherein the waveform that is derived from the derivative waveform is characterized by a plurality of features each having a corresponding value and computing the vascular index involves using the values of the plurality of features.

7. The system of claim 6, wherein the processing component is further programmed to analyze the time-dependent optical waveform by filtering the derivative waveform to generate the derived waveform.

8. The system of claim 5, wherein the derivative that is used to generate the derivative waveform is the second derivative.

9. 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.

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

generating a time-dependent optical waveform from a flow of blood within the patient;

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

analyzing the time-dependent optical waveform to determine a vascular index representing properties of the patient'"'"'s blood circulatory system;

measuring 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;

determining a first estimate of a value of a blood pressure parameter from the measured pulse transit time; and

using the vascular index to modify the first estimate of the value of the blood pressure parameter.

11. The method of claim 10, wherein using the vascular index to modify the first estimate of the value of the blood pressure parameter involves adding a correction factor to the first estimate, wherein in the correction factor is determined by the vascular index.

12. The method of claim 11, wherein the correction factor is linearly proportional to the vascular index.

13. The method of claim 11, wherein the correction factor is equal to (VI−

Age)*MVI+BVI, where VI is the vascular index, Age is an age of the patient, and MV1 and BV1 are real numbers.

14. The method of claim 10, wherein analyzing the time-dependent optical waveform involves:

bandpass filtering the time-dependent optical waveform to generate a filtered waveform;

computing a derivative of the filtered waveform to generate a derivative waveform; and

computing the vascular index from characteristics of a waveform derived from the derivative waveform.

15. The method of claim 14, wherein the waveform that is derived from the derivative waveform is characterized by a plurality of features each having a corresponding value and computing the vascular index involves using the values of the plurality of features.

16. The method of claim 14, further comprising filtering the derivative waveform to generate the derived waveform.

17. The method of claim 14, wherein the derivative that is used to generate the derivative waveform is the second derivative.

18. The method of claim 14, 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.

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

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) analyze the time-dependent optical waveform to determine a vascular index representing properties of the patient'"'"'s blood circulatory system; and

iii) use the vascular index and a measured pulse transit time for the patient to determine a value of a blood pressure parameter for the patient.

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

generating a time-dependent optical waveform from a flow of blood within the patient;

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

analyzing the time-dependent optical waveform to determine a vascular index representing properties of the patient'"'"'s blood circulatory system;

determining 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; and

using the vascular index and a measured pulse transit time for the patient to determine a value of a blood pressure parameter for the patient.