BODY-WORN SYSTEM FOR MEASURING CONTINUOUS NON-INVASIVE BLOOD PRESSURE (cNIBP)

• US 20100160798A1
• Filed: 12/30/2009
• Published: 06/24/2010
• Est. Priority Date: 06/12/2007
• Status: Active Grant

• Current Assignee: Sotera Wireless Incorporated (Foxconn Technology Co., Ltd.)
• Original Assignee: Sotera Wireless Incorporated (Foxconn Technology Co., Ltd.)
• Inventors: BANET, Matt, DHILLON, Marshal, McCOMBIE, Devin
• Granted Patent: US 8,602,997 B2
• Time in Patent Office: Days
• US Class Current: 600/490
• 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 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives

Abstract

The present invention provides a technique for continuous measurement of blood pressure based on pulse transit time and which does not require any external calibration. This technique, referred to herein as the ‘Composite Method’, is carried out with a body-worn monitor that measures blood pressure and other vital signs, and wirelessly transmits them to a remote monitor. A network of body-worn sensors, typically placed on the patient'"'"'s right arm and chest, connect to the body-worn monitor and measure time-dependent ECG, PPG, accelerometer, and pressure waveforms. The disposable sensors can include a cuff that features an inflatable bladder coupled to a pressure sensor, three or more electrical sensors (e.g. electrodes), three or more accelerometers, a temperature sensor, and an optical sensor (e.g., a light source and photodiode) attached to the patient'"'"'s thumb.

Claims

1. A method for monitoring a blood pressure value from a patient, comprising:

(a) applying a variable pressure to the patient'"'"'s arm using a pressure-delivery system;

(b) detecting a time-dependent pressure waveform representing the pressure applied to the patient'"'"'s arm;

(c) detecting a first time-dependent waveform comprising a first feature induced by the patient'"'"'s heartbeat with a first sensor configured to attach to the patient;

(d) detecting a second time-dependent waveform comprising a second feature induced by the patient'"'"'s heartbeat with a second sensor configured to attach to the patient;

(e) determining a pulse transit time from a separation in time between the first feature and the second feature;

(f) determining a variation in the pulse transit time as a function of the pressure applied to the patient'"'"'s arm;

(g) processing the variation in pulse transit time to determine a relationship between pulse transit time and blood pressure;

(h) digitally filtering a portion of the time-dependent pressure waveform to determine a processed pressure waveform;

(i) analyzing the processed pressure waveform to determine values for systolic blood pressure, diastolic blood pressure, and mean arterial pressure; and

(j) analyzing a pulse transit time, the relationship between pulse transit time and blood pressure, and blood pressure values determined from the processed pressure waveform to determine a blood pressure value when no pressure is applied to the patient'"'"'s arm with the pressure delivery system.

5. The method of claim 1, wherein step (g) further comprises processing the variation in pulse transit time to determine a relationship between pulse transit time and mean arterial pressure.

6. The method of claim 5, wherein step (g) further comprises processing the variation in pulse transit time with a mathematical model that estimates an effective mean arterial pressure in the patient'"'"'s arm that varies with pressure applied by the pressure-delivery system.

7. The method of claim 6, wherein the effective mean arterial pressure is the difference between the mean arterial pressure determined during step (i) and a pressure-induced blood pressure change.

8. The method of claim 7, wherein the pressure-induced blood pressure change is defined by the following equation or a mathematical derivative thereof:

Δ

MAP(P)=F×

(P_applied−

DIA_INDEX)

where Δ

MAP(P) is the pressure-induced blood pressure change, P_applied is pressure applied by the pressure-delivery system during inflation, DIA_INDEX is the diastolic pressure determined from the processed pressure waveform, and F is a mathematical constant.

9. The method of claim 1, wherein step (b) further comprises detecting the time-dependent pressure waveform representing the pressure applied to the patient'"'"'s arm while the pressure-delivery system is inflating.

10. The method of claim 9, wherein step (h) further comprises digitally filtering a portion of the time-dependent pressure waveform measured during inflation to determine a processed pressure waveform.

11. The method of claim 10, wherein step (h) further comprises digitally filtering a portion of the time-dependent pressure waveform measured during inflation with:

1) a digital bandpass filter; and

then

     2) a digital low-pass filter to determine the processed pressure waveform.

12. The method of claim 11, wherein step (i) further comprises analyzing the processed pressure waveform to determine a ratio between systolic and mean arterial blood pressure.

13. The method of claim 12, wherein step (j) further comprises processing the ratio between systolic and mean arterial blood pressure, pulse transit time, and the relationship between pulse transit time and blood pressure, to determine a systolic blood pressure value when no pressure is applied to the patient'"'"'s arm with the pressure delivery system.

14. The method of claim 11, wherein step (i) further comprises analyzing the processed pressure waveform to determine a ratio between diastolic and mean arterial blood pressure.

15. The method of claim 14, wherein step (j) further comprises processing the ratio between diastolic and mean arterial blood pressure, pulse transit time, and the relationship between pulse transit time and blood pressure, to determine diastolic blood pressure value when no pressure is applied to the patient'"'"'s arm with the pressure delivery system.

16. The method of claim 1, wherein the pressure-delivery system comprises a cuff comprising an inflatable bladder.

17. The method of claim 16, wherein the pressure-delivery system comprises a pneumatic system connected to the cuff and configured to inflate the cuff.

18. The method of claim 1, wherein step (a) is performed once every 4 hours or more.

19. The method of claim 1, wherein step (j) is performed once every 1 second or less.

20. The method of claim 19, wherein step (j) further comprises determining an average pulse transit time from a set of pulse transit times collected over a time period.

21. The method of claim 20, wherein the time period is between 10 and 120 seconds.

22. The method of claim 1, wherein both the first and second sensors are selected from the group comprising an optical sensor, a pressure sensor, an electrical impedance sensor, an ECG waveform sensor, and a transducer.

2. A method for monitoring a blood pressure value from a patient, comprising:

(a) applying a variable pressure to the patient'"'"'s arm using a pressure-delivery system;

(b) detecting a time-dependent pressure waveform representing the pressure applied to the patient'"'"'s arm during inflation of the pressure-delivery system;

(c) detecting a first time-dependent waveform comprising a first feature induced by the patient'"'"'s heartbeat with a first sensor configured to attach to the patient;

(d) detecting a second time-dependent waveform comprising a second feature induced by the patient'"'"'s heartbeat with a second sensor configured to attach to the patient;

(e) determining a pulse transit time from a separation in time between the first feature and the second feature;

(f) determining a variation in the pulse transit time as a function of the pressure applied to the patient'"'"'s arm during inflation of the pressure-delivery system;

(g) processing the variation in pulse transit time to determine a relationship between pulse transit time and blood pressure;

(h) digitally filtering a portion of the time-dependent pressure waveform measured during inflation to determine a processed pressure waveform;

(i) analyzing the processed pressure waveform to determine values for systolic blood pressure, diastolic blood pressure, and mean arterial pressure; and

(j) analyzing a pulse transit time, the relationship between pulse transit time and blood pressure, and blood pressure values determined from the processed pressure waveform to determine a blood pressure value when no pressure is applied to the patient'"'"'s arm with the pressure delivery system.

3. A method for monitoring a blood pressure value from a patient, comprising:

(a) detecting a time-dependent pressure waveform representing pressure applied to the patient'"'"'s arm during inflation of a pressure-delivery system;

(b) determining a pulse transit time between a first feature of a first time-dependent waveform and a second feature of a second time-dependent waveform, both the first and second waveforms measured from the patient;

(c) determining a variation in the pulse transit time as a function of the pressure applied to the patient'"'"'s arm during inflation of the pressure-delivery system;

(d) digitally filtering a portion of the time-dependent pressure waveform to determine a processed pressure waveform measured during inflation; and

(e) analyzing a pulse transit time and a calibration determined from the variation in pulse transit time and parameters extracted from the processed pressure waveform to determine a blood pressure value.

4. A method for monitoring a blood pressure value from a patient, comprising:

(a) detecting a time-dependent pressure waveform representing pressure applied to the patient'"'"'s arm during inflation of a pressure-delivery system;

(b) determining a pulse transit time between a first feature of a first time-dependent waveform and a second feature of a second time-dependent waveform, both the first and second waveforms measured from the patient;

(c) digitally filtering a portion of the time-dependent pressure waveform to determine a processed pressure waveform measured during inflation; and

(d) analyzing a pulse transit time and a calibration determined from a relationship between pulse transit time and blood pressure determined from parameters measured during inflation to determine a blood pressure value after inflation.