Method for measuring blood oxygen content under low perfusion

• US 8,275,434 B2
• Filed: 12/30/2008
• Issued: 09/25/2012
• Est. Priority Date: 03/10/2005
• Status: Active Grant

• Current Assignee: Shenzhen Mindray Bio-Medical Electronics Co., Ltd. (Excelsior Union Ltd.)
• Original Assignee: Shenzhen Mindray Bio-Medical Electronics Co., Ltd. (Excelsior Union Ltd.)
• Inventors: Zhang, Xu, Ye, Jilun
• Primary Examiner(s): WINAKUR, ERIC FRANK
• Application Number:
  US12/346,565
• Publication Number:
  US 20090112074A1
• Time in Patent Office: 1,365 Days
• Field of Search: 600/310, 600/322, 600/323, 600/336
• US Class Current: 600/323
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/7242 using integration

Abstract

A method for measuring blood oxygen content under low perfusion, which is used in a device for measuring blood oxygen content, includes the steps of: initializing the device that is applied with power; collecting and processing data with a driving circuit of light emitting device, a bias circuit, a gain circuit and an A/D sampling circuit, which are controlled under a cone control module; calculating blood oxygen saturation based on the collected data with a data processing module which integrates the collected data in a period of time with an area integration method; and outputting from a communication functional module results of the blood oxygen saturation or pulse rate calculated with the data processing module. The method further includes a decision step of deciding the two results acquired from the data processing module with the waveform method and the integration method respectively based on the intensity of the measured signal and generating the final measured result, performed by a decision unit included in the device. By adopting the above method, the disturbance to effective signal by noise can be eliminated. As a result, the measuring accuracy of blood oxygen content under low perfusion can be improved without increasing the production cost for the measuring device.

Claims

1. A method for measuring blood oxygen content under low perfusion, the method comprising:

receiving signals from a light-receiving device representing intensities of two different wavelengths of light attenuated by body tissue;

converting the signals, using an analog-to-digital converting circuit, into digital data;

collecting, in a memory of a patient monitoring device, the data representative of the intensities of light over a period of time that includes more than one cycle, wherein the collected data is cyclical to indicate blood pulsing through the body tissue;

integrating, by a microprocessor, the collected data in the memory over the period of time that includes more than one cycle using an area integration method that determines an area between the collected data and a normalized value of the collected data; and

determining, by the microprocessor, based at least in part on the integration of the collected data, a first value of blood oxygen saturation.

2. The method of claim 1, further comprising:

fitting an envelope waveform to the collected data;

determining a maximum value and a minimum value of the envelope waveform; and

calculating a second value of the blood oxygen saturation with a waveform method based on the maximum value and the minimum value of the envelope waveform.

3. The method of claim 2, further comprising:

deciding between the first value of blood oxygen saturation based on the integration and the second value of blood oxygen saturation based on the envelope waveform; and

outputting, from the patient monitoring device, a final measured result of the blood oxygen saturation based on the decision.

4. The method of claim 3, wherein a precondition for the decision is:

A=a*A₁+(1−

a)*A₂,

where “

A₁”

is the second value of the blood oxygen saturation based on the envelope waveform, “

A₂”

is the first value of the blood oxygen saturation based on the integration, “

A”

is the final measured result of the blood oxygen saturation, and “

a”

ranges from 1 to 0.

5. The method of claim 1, wherein collecting the data comprises:

passing two lights through end parts of tissues, wherein one is red light, and the other is infrared light; and

detecting the two lights after they pass through the end parts of tissues.

6. The method of claim 5, wherein integrating the collected data comprises:

respectively integrating the collected data of the two lights to calculate the ratio of integration result of the red light to that of the infrared light for replacing the ratio of alternating current (AC) peak value of the intensity of the red light Red_AC to the AC peak value of the intensity of the infrared light Ir_AC received during the period of time.

7. The method of claim 6, wherein the determination of the first value of blood oxygen saturation depends at least in part on a forgetting factor λ

that ranges from 0 to 1, and the ratio of the AC peak value Red_AC to Ir_AC of the two lights at a current time is

8. The method of claim 7, wherein the value of the forgetting factor λ

is 0.8.

9. The method of claim 1, wherein the period of time for integration is approximately 2-3 seconds.

10. A patient monitoring device for measuring blood oxygen content under low perfusion, the device comprising:

a sensor to receive signals from a light-receiving device representing intensities of two different wavelengths of light attenuated by body tissue; and

a data processing circuit to;

convert the signals, using an analog-to-digital converting circuit, into digital data;

collect, in a memory of a patient monitoring device, the data representative of the intensities of light over a period of time that includes more than one cycle, wherein the collected data is cyclical to indicate blood pulsing through the body tissue;

integrate, by a microprocessor, the collected data in the memory over the period of time that includes more than one cycle using an area integration method that determines an area between the collected data and a normalized value of the collected data; and

determine, by the microprocessor, based at least in part on the integration of the collected data, a value of blood oxygen saturation.

11. The device of claim 10, further comprising:

a gain circuit to amplify signals received from the sensor;

an analog-to-digital converter to convert the amplified signals to digital signals; and

a control circuit to control the gain circuit and the analog-to-digital converter.

12. The device of claim 11, further comprising:

a driving circuit under the control of the control circuit; and

a light emitting device driven by the driving circuit to emit a red light and an infrared light into the body tissue for detection by the sensor.

13. The device of claim 12, wherein the data processing circuit integrates the collected data by:

respectively integrating the collected data of the two lights to calculate the ratio of integration result of the red light to that of the infrared light for replacing the ratio of alternating current (AC) peak value of the intensity of the red light Red_AC to the AC peak value of the intensity of the infrared light Ir_AC received during the period of time.

14. The device of claim 13, wherein the data processing circuit makes the determination of the value of blood oxygen saturation based at least in part on a forgetting factor λ

that ranges from 0 to 1, and the ratio of the AC peak value Red_AC to Ir_AC of the two lights at a current time is

15. The device of claim 14, wherein the value of the forgetting factor λ

is 0.8.

16. The device of claim 10, further comprising a communication circuit to output the value of blood oxygen saturation.

17. A system for measuring blood oxygen content under low perfusion, the system comprising:

means for receiving signals from a light-receiving device representing intensities of two different wavelengths of light attenuated by body tissue;

means for converting the signals, using an analog-to-digital converting circuit, into digital data;

means for collecting the data representative of the intensities of light over a period of time that includes more than one cycle, wherein the collected data is cyclical to indicate blood pulsing through the body tissue;

means for integrating, by a microprocessor, the collected data in the memory over the period of time that includes more than one cycle using an area integration method that determines an area between the collected data and the normalized value of the collected data; and

means for determining, by the microprocessor, based at least in part on the integration of the collected data, a first value of blood oxygen saturation.

18. The system of claim 17, further comprising:

means for passing two lights through end parts of tissues, wherein one is red light, and the other is infrared light; and

means for detecting the two lights after they pass through the end parts of tissues.

19. The system of claim 18, wherein integrating the collected data comprises:

respectively integrating the collected data of the two lights to calculate the ratio of integration result of the red light to that of the infrared light for replacing the ratio of alternating current (AC) peak value of the intensity of the red light Red_AC to the AC peak value of the intensity of the infrared light Ir_AC received during the period of time.

20. The system of claim 19, wherein the determination of the first value of blood oxygen saturation depends at least in part on a forgetting factor λ

that ranges from 0 to 1, and the ratio of the AC peak value Red_AC to Ir_AC of the two lights at a current time is

21. The system of claim 20, wherein the value of the forgetting factor λ

is 0.8.

22. The system of claim 17, wherein the period of time for integration is approximately 2-3 seconds.