NON-INVASIVE DETERMINATION OF THE CONCENTRATION OF A BLOOD SUBSTANCE

• US 20090024011A1
• Filed: 07/20/2007
• Published: 01/22/2009
• Est. Priority Date: 07/20/2007
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Huiku, Matti
• Granted Patent: US 8,412,296 B2
• Time in Patent Office: Days
• US Class Current: 600/323
• CPC Class Codes: A61B 5/14551 for measuring blood gases

Abstract

In order to provide a non-invasive and continuous concentration measurement with the technology of standard pulse oximeters, an a priori relationship is created, through an in-vivo tissue model including a nominal estimate of a tissue parameter indicative of the concentration of a blood substance. The a priori relationship is indicative of the effect of tissue on in-vivo measurement signals at a plurality of wavelengths, the in-vivo measurement signals being indicative of absorption caused by pulsed arterial blood. In-vivo measurement signals are acquired from in-vivo tissue at the plurality of wavelengths and a specific value of the tissue parameter is determined based on the a priori relationship, the specific value being such that it yields the effect of the in-vivo tissue on the in-vivo measurement signals consistent for the plurality of wavelengths. The specific value then represents the concentration of the substance in the blood.

Claims

1-30. -30. (canceled)

31. A method for determining concentration of a substance in blood of a subject, the method comprising:

creating an a priori relationship indicative of the effect of tissue on in-vivo measurement signals at a plurality of wavelengths, wherein the in-vivo measurement signals are indicative of absorption caused by blood of a subject;

acquiring the in-vivo measurement signals from in-vivo tissue at the plurality of wavelengths; and

determining, based on the a priori relationship, a specific value of a tissue parameter for which the effect of the in-vivo tissue on the in-vivo measurement signals is consistent for the plurality of wavelengths, the specific value representing concentration of a substance in the blood of the subject.

32. The method according to claim 31, wherein the creating includes creating the a priori relationship through an in-vivo tissue model including a nominal estimate of the tissue parameter.

33. The method according to claim 32, wherein

the creating includes creating the a priori relationship, in which the a priori relationship defines a predetermined parameter as a function of the in-vivo measurement signals;

and

the determining includes (i) defining a set of wavelength-specific values for the predetermined parameter and (ii) finding out the specific value of the tissue parameter, wherein the specific value renders the set of wavelength-specific values consistent.

34. The method according to claim 33, wherein the finding out includes conditionally altering the a priori relationship, thereby to find out the specific value of the tissue parameter.

35. The method according to claim 34, wherein the creating includes creating the a priori relationship, in which the predetermined parameter represents one of arterial oxygen saturation (SpO₂), fractional composition of a plurality of hemoglobin species in the blood of the subject, and a pseudo-isobestic signal.

36. The method according to claim 35, wherein

the creating includes creating the a priori relationship, in which the predetermined parameter represents arterial oxygen saturation (SpO₂);

and

a condition upon which the altering is conditional is whether the difference between the wavelength-specific values within the set is greater than a predetermined threshold, such that the altering is performed when the difference between the wavelength-specific values within the set is greater than the predetermined threshold and the altering is not performed when the difference between the wavelength-specific values within the set is not greater than the predetermined threshold.

37. The method according to claim 36, wherein the finding out includes selecting the nominal estimate as the specific value when the altering is not performed.

38. The method according to claim 34, wherein

the creating includes creating the a priori relationship, in which the predetermined parameter represents a pseudo-isobestic signal;

and

a condition upon which the altering is conditional is whether a quotient of two pseudo-isobestic signals is substantially the same as its theoretical equivalent, such that the altering is performed when the quotient is not substantially the same as its theoretical equivalent and the altering is not performed when the quotient is substantially the same as its theoretical equivalent.

39. An arrangement for determining concentration of a substance in blood of a subject, the arrangement comprising:

a first determination unit configured to store an a priori relationship indicative of the effect of tissue on in-vivo measurement signals at a plurality of wavelengths, wherein the in-vivo measurement signals are indicative of absorption caused by blood of a subject;

a measurement unit configured to acquire the in-vivo measurement signals from in-vivo tissue at the plurality of wavelengths; and

a second determination unit configured to determine, based on the a priori relationship, a specific value of a tissue parameter for which the effect of the in-vivo tissue on the in-vivo measurement signals is consistent for the plurality of wavelengths, the specific value representing concentration of a substance in the blood of the subject.

40. The arrangement according to claim 39, wherein the a priori relationship is created through an in-vivo tissue model including a nominal estimate of the tissue parameter.

41. The arrangement according to claim 40, wherein

the first determination unit is configured to store the a priori relationship, in which the a priori relationship defines a predetermined parameter as a function of the in-vivo measurement signals;

and

the second determination unit is configured to (i) define a set of wavelength-specific values for the predetermined parameter and (ii) find out the specific value of the tissue parameter, wherein the specific value renders the set of wavelength-specific values consistent.

42. The arrangement according to claim 41, wherein the second determination unit is further configured to conditionally alter the a priori relationship, thereby to find out the specific value of the tissue parameter.

43. The arrangement according to claim 42, wherein the predetermined parameter represents one of arterial oxygen saturation (SpO₂), fractional composition of a plurality of hemoglobin species in arterial blood, and a pseudo-isobestic signal.

44. The arrangement according to claim 42, wherein the second determination unit is configured to alter the a priori relationship when a difference between the wavelength-specific values within the set is greater than a predetermined threshold and not to alter the a priori relationship when the difference fails to be greater than the predetermined threshold.

45. The arrangement according to claim 43, wherein

the predetermined parameter represents a pseudo-isobestic signal;

and

the second determination unit is configured alter the a priori relationship when a quotient of two pseudo-isobestic signals fails to be substantially the same as its theoretical equivalent and not to alter the a priori relationship when the quotient is substantially the same as its theoretical equivalent.

46. The arrangement according to claim 39, wherein the first determination unit, the measurement unit, and the second determination unit reside in a single patient monitoring device.

47. An apparatus for determining concentration of a substance in blood of a subject, the apparatus comprising:

an interface unit configured to download an a priori relationship indicative of the effect of tissue on in-vivo measurement signals at a plurality of wavelengths, wherein the in-vivo measurement signals are indicative of absorption caused by blood of a subject;

a signal reception unit configured to receive in-vivo measurement signals acquired from in-vivo tissue at the plurality of wavelengths; and

a determination unit configured to determine, based on the a priori relationship, a specific value of a tissue parameter for which the effect of the in-vivo tissue on the in-vivo measurement signals is consistent for the plurality of wavelengths, the specific value representing concentration of a substance in the blood of the subject.

48. A sensor for determining concentration of a substance in blood of a subject, the sensor being attachable to a subject and comprising:

an emitter unit configured to emit radiation through tissue of the subject at at least three wavelengths;

a detector unit configured receive the radiation and to produce in-vivo measurement signals for the at least three wavelengths, wherein the in-vivo measurement signals are indicative of absorption caused by blood of the subject; and

a memory unit configured to store an a priori relationship indicative of an estimated effect of the tissue on the in-vivo measurement signals at the at least three wavelengths.

49. A memory unit for determining concentration of a substance in blood of a subject, the memory unit storing an a priori relationship indicative of an estimated effect of in-vivo tissue on in-vivo measurement signals at at least three wavelengths, wherein the memory unit is accessible for at least one entity configured to determine, based on the a priori relationship, a specific value of a tissue parameter for which the effect of the in-vivo tissue on the in-vivo measurement signals is consistent for the at least three wavelengths.

50. A computer program product for determining concentration of a substance in blood of a subject, the computer program product comprising:

a first program product portion configured to receive an a priori relationship indicative of the effect of tissue on in-vivo measurement signals at a plurality of wavelengths, wherein the in-vivo measurement signals are indicative of absorption caused by blood of a subject;

a second program product portion configured to receive in-vivo measurement signals acquired from in-vivo tissue at the plurality of wavelengths; and

a third program product portion configured to determine, based on the a priori relationship, a specific value of a tissue parameter for which the effect of the in-vivo tissue on in-vivo measurement signals is consistent for the plurality of wavelengths, the specific value representing concentration of a substance in the blood of the subject.