Measuring apparatus

• US 5,647,359 A
• Filed: 03/31/1994
• Issued: 07/15/1997
• Est. Priority Date: 04/01/1993
• Status: Expired due to Term

• Current Assignee: Terumo Kabushiki Kaisha
• Original Assignee: Terumo Kabushiki Kaisha
• Inventors: Kurio, Masaru, Kohno, Hiromasa
• Primary Examiner(s): Sykes, Angela D.
• Application Number:
  US08/221,234
• Time in Patent Office: 1,202 Days
• Field of Search: 128/633-4, 128/664-7, 128/692, 356/39-41
• US Class Current: 600/341
• CPC Class Codes: A61B 5/1459 invasive, e.g. introduced into the body by a catheter A61B5/1464 takes precedence

Abstract

Light components are radiated into a blood vessel from light-emitting diodes (17, 18) for emitting light components having different wavelengths through an optical fiber. Bight components reflected by the blood upon radiation into the blood vessel are received by a photo transistor (19) to detect their reflected light intensities. For example, a minimum value of the reflected light intensity of the light component from the light-emitting diode (18) is obtained from the reflected light intensities detected within a predetermined period of time. A measurement value is calculated using this minimum value and a minimum value of the reflected light intensity of the light component from the corresponding light-emitting diode (17).

Claims

1. A measuring apparatus comprising:

radiating means for radiating light having first and second wavelengths different from each other in blood;

detecting means for detecting reflected light intensities from the blood upon radiation of the light having the first and second wavelengths;

minimum value detecting means for detecting a minimum value of the reflected light intensity of one of the light having the first and second wavelengths detected by said detecting means within a predetermined period of time; and

calculating means for calculating an oxygen saturation on the basis of the minimum value detected by said minimum value detecting means and a minimum value of the reflected light intensity of the other light corresponding to the minimum value detected by said minimum value detecting means.

2. An apparatus according to claim 1, wherein said radiating means radiates the light in the blood from a distal end of a catheter through an optical fiber.

3. An apparatus according to claim 2, wherein said detecting means guides the light incident on the distal end of said catheter to a photosensor through an optical fiber.

4. An apparatus according to claim 1, wherein said minimum value detecting means sequentially calculates differences between reflected light intensities of two points adjacent on a time axis within the predetermined period of time to express calculated differences as signs, and defines, as the minimum value, a central one of five points having a pattern of "-, -, +, +" of the reflected light intensities.

5. An apparatus according to claim 1, wherein said calculating means comprises:

parameter calculating means for calculating a parameter representing a variation of the reflected light intensities which corresponds to one of the light components having the first and second wavelengths within a first predetermined period of time;

means for obtaining a smallest value of the minimum values calculated by said minimum value detecting means within a second predetermined period of time; and

reference value calculating means for calculating a reference value from the parameter and the smallest value,

wherein the oxygen saturation is obtained on the basis of the minimum values which are within a predetermined range from the reference value.

6. An apparatus according to claim 5, wherein the reference value is determined on the basis of the smallest value and changed in accordance with a current reference value and the smallest value when the parameter is within the second predetermined period of time.

7. An apparatus according to claim 5, wherein said calculating means calculates the oxygen saturation as follows:

##EQU3## for a₀ =141.2

a₁ =-23.10

a₂ =-51.38

a₃ =14.72

where M2 is an average value of the minimum values which are within a predetermined range from the reference value, and M1 is an average value of the reflected light intensity of the light of another wavelength.

8. A measuring apparatus comprising:

detecting means for detecting a signal intensity from a probe inserted into a blood vessel;

extremum detecting means for calculating a minimum value and/or a maximum value of the signal intensity detected by said detecting means within a first predetermined time period;

measuring means for calculating a measurement value on the basis of the minimum value and/or the maximum value;

calculating means for calculating a smallest value of the minimum values and/or a largest value of the maximum values in a second predetermined time period;

reference intensity signal determining means for determining a reference intensity signal on the basis of the smallest value and/or the largest value; and

parameter calculating means for calculating a parameter for evaluating a degree of reliability of the measurement value measured by said measuring means, on the basis of the smallest value and/or the largest value, and the reference intensity signal.

9. An apparatus according to claim 8, wherein the signal intensity detected by said detecting means is an intensity of light reflected by the blood upon radiation of light into the blood by radiating means.

10. An apparatus according to claim 8, wherein said extremum detecting means sequentially calculates differences between reflected light intensities of two points adjacent on a time axis within a third predetermined period of time to express calculated differences as signs, and defines, as the minimum value, a central one of five points having a pattern of "-, -, +, +" of the reflected light intensities.

11. An apparatus according to claim 8, wherein the measurement value calculated by said measuring means is one of the oxygen saturation in the blood, a blood flow rate, and a measurement value obtained by measuring living body information on the basis of a signal from a sensor located near a blood-side end of an optical fiber.

12. An apparatus according to claim 8, further comprising alarming means for alarming the degree of reliability of a measurement value based on the parameter calculated by said parameter calculating means.

13. A measuring apparatus comprising:

detecting means for detecting a signal intensity from a probe inserted into a blood vessel;

extremum detecting means for calculating a minimum value and/or a maximum value of the signal intensity detected by said detecting means within a first predetermined period of time;

calculating means for calculating a smallest value of the maximum value and/or largest values of the maximum values in a second predetermined period of time;

variation parameter calculating means for calculating a changing parameter representing a degree of change of the reflected light intensity in the second predetermined period of time;

reference intensity signal determining means for determining a reference intensity signal on the basis of the smallest value and/or the largest value and the variation parameter; and

parameter calculating means for calculating a parameter for evaluating a degree of reliability of a measurement value, on the basis of the smallest value and/or the largest value, and the changing parameter and the reference intensity signal.

14. An apparatus according to claim 13, wherein said variation parameter calculating means defines a standard deviation, a variation coefficient, or a function thereof as the variation parameter.

15. An apparatus according to claim 14, wherein said reference signal calculating means updates the reference value to a new reference value in accordance with a predetermined function when the variation parameter falls within a predetermined range, and does not update the reference value when the variation parameter falls outside the predetermined range.

16. An apparatus according to claim 13, wherein the measurement value calculated by said measuring means is one of the oxygen saturation in the blood, a blood flow rate, and a measurement value obtained by measuring living body information on the basis of a signal from a sensor located near a blood-side end of an optical fiber.

17. A measuring apparatus comprising:

an optical fiber for transmitting light into a blood vessel;

radiating means, connected to said optical fiber, for radiating the light into blood;

reflected light intensity detecting means, connected to said optical fiber, for detecting a reflected light intensity from the blood;

minimum value detecting means for detecting a minimum value of the reflected light intensity detected by said reflected light intensity detecting means in a first predetermined period of time;

smallest value calculating means for calculating a smallest value (MIN) of the minimum values within a second predetermined period of time longer than the first predetermined period of time;

variation parameter calculating means for calculating a variation parameter (CV2) representing a degree of variation of the reflected light intensity within the first predetermined period of time;

parameter calculating means for combining the smallest value (MIN) and the variation parameter (CV2), and a reference intensity signal (BL) determined by the smallest value and the variation parameter, and calculating a plurality of parameters for evaluating a degree of reliability of a separately calculated measurement value; and

evaluating means for calculating one parameter for evaluating the degree of reliability of the measurement value from a sum total (SRP) of the plurality of parameters.