BODY-WORN PULSE OXIMETER

• US 20100324389A1
• Filed: 09/14/2009
• Published: 12/23/2010
• Est. Priority Date: 06/17/2009
• Status: Active Grant

• Current Assignee: Sotera Wireless Incorporated
• Original Assignee: Sotera Wireless Incorporated
• Inventors: MOON, Jim, BANET, Matt, DHILLON, Marshal, McCOMBIE, Devin
• Granted Patent: US 8,437,824 B2
• Time in Patent Office: Days
• US Class Current: 600/324
• 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 5/022 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 5/0245 by using sensing means generating electric signals, i.e. ECG signals
• CPC Class Codes: A61B 5/1116 Determining posture transitions
• CPC Class Codes: A61B 5/1118 Determining activity level
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: A61B 5/681 Wristwatch-type devices
• CPC Class Codes: A61B 5/6824 Arm or wrist
• CPC Class Codes: A61B 5/6826 Finger
• CPC Class Codes: A61B 5/6838 Clamps or clips
• 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 5/746 Alarms related to a physiological condition, e.g. details of setting alarm thresholds or avoiding false alarms alarms per se G08B

Abstract

The invention provides a body-worn system that continuously measures pulse oximetry and blood pressure, along with motion, posture, and activity level, from an ambulatory patient. The system features an oximetry probe that comfortably clips to the base of the patient'"'"'s thumb, thereby freeing up their fingers for conventional activities in a hospital, such as reading and eating. The probe secures to the thumb and measures time-dependent signals corresponding to LEDs operating near 660 and 905 nm. Analog versions of these signals pass through a low-profile cable to a wrist-worn transceiver that encloses a processing unit. Also within the wrist-worn transceiver is an accelerometer, a wireless system that sends information through a network to a remote receiver, e.g. a computer located in a central nursing station.

Claims

1. A method for monitoring a patient, comprising:

(a) measuring a first time-dependent signal by detecting radiation emitted by a first radiation source after it passes through a portion of the patient;

(b) measuring a second time-dependent signal by detecting electrical signals from the patient using at least two electrodes, and processing the electrical signals with an electrical circuit to form the second time-dependent signal;

(c) measuring a time-dependent motion signal with at least one motion sensor;

(d) processing the first and second time-dependent signals to determine a transit time corresponding to a single heartbeat in a collection of heartbeats;

(e) processing multiple transit times, each corresponding to a heartbeat within the collection of heartbeats, with a first algorithm to identify a portion of the first time-dependent signal that may be affected by motion;

(f) analyzing the time-dependent motion signal to estimate if the portion of the first time-dependent signal is affected by motion;

(g) applying a mathematical filter that processes both the portion of the first time-dependent signal and a numerical template representing a pre-determined portion of a time-dependent signal if it is determined that the portion of the first time-dependent signal is affected by motion;

(h) determining a filtered version of at least a portion of the first time-dependent signal with the mathematical filter; and

(i) processing the filtered version of the first time-dependent signal to determine a oxygen saturation value for the patient.

4. The method of claim 1, wherein step (e) further comprises determining a transit time that has a high or low value that lies outside a pre-determined range.

5. The method of claim 4, wherein step (e) further comprises applying a statistical filter to the multiple transit times to determine the transit time that lies outside a pre-determined range.

6. The method of claim 5, wherein the statistical filter comprises taking an average and standard deviation of the multiple transit times, and determining transit times that fall outside the average by more than a multiple of one standard deviation.

7. The method of claim 1, wherein step (f) further comprises comparing an amplitude of the time-dependent motion signal to a pre-determined value to estimate if the portion of the first time-dependent signal is affected by motion.

8. The method of claim 1, wherein step (f) further comprises comparing a power value from a frequency-domain spectrum calculated from the time-dependent motion signal to a pre-determined value to estimate if the portion of the first time-dependent signal is affected by motion.

9. The method of claim 1, wherein step (g) further comprises applying a matched filter that processes both the portion of the first time-dependent signal and a numerical template representing a pre-determined portion of a time-dependent signal if it is determined that the portion of the first time-dependent signal is affected by motion.

10. The method of claim 9, wherein the numerical template is a pre-determined value stored in a computer memory.

11. The method of claim 9, wherein the numerical template is determined prior to step (a) by measuring a first time-dependent signal by detecting radiation emitted by a first radiation source after it passes through a portion of the patient.

12. The method of claim 1, wherein step (a) further comprises measuring a third time-dependent signal by detecting radiation emitted by a second radiation source after it passes through a portion of the patient.

13. The method of claim 12, wherein step (i) further comprises extracting AC and DC components from the first and third time-dependent signals.

14. The method of claim 13, wherein step (i) further comprises determining an oxygen saturation value for the patient by calculating a mathematical ratio that includes the AC and DC components extracted from the first and third time-dependent signals.

15. The method of claim 14, wherein both the first and third time-dependent signals each comprise a pulse, and a single ratio is calculated for the pulse.

16. The method of claim 14, wherein both the first and third time-dependent signals each comprise a pulse, and a single ratio is calculated for a portion of the pulse.

2. A signal processing method comprising:

(a) measuring multiple transit times from portions of a first and second time-dependent signal, the first time-dependent signal measured with an optical sensor, and the second time-dependent signal measured with an electrical sensor;

(b) measuring a time-dependent motion signal with a motion sensor;

(c) collectively processing the multiple transit times and the time-dependent motion signal to determine if the first time-dependent signal is affected by motion; and

(d) filtering the first time-dependent signal depending on the processing done in (c).

3. A method of determining oxygen saturation and blood pressure values for a patient, comprising:

(a) measuring multiple transit times from portions of a first and second time-dependent signal, the first time-dependent signal measured with an optical sensor, and the second time-dependent signal measured with an electrical sensor;

(b) measuring a time-dependent motion signal with a motion sensor;

(c) processing the multiple transit times and the time-dependent motion signal to determine if the first time-dependent signal is affected by motion;

(d) filtering the first time-dependent signal depending on the processing done in (c) to determine a filtered time-dependent signal; and

(e) determining oxygen saturation and blood pressure values for a patient using the filtered time-dependent signal.