System for noninvasive hematocrit monitoring

• US 5,499,627 A
• Filed: 10/04/1994
• Issued: 03/19/1996
• Est. Priority Date: 10/06/1990
• Status: Expired due to Term

• Current Assignee: Fresenius Medical Care Holdings Incorporated (Fresenius Medical Care AG)
• Original Assignee: In-Line Diagnostics Corp.
• Inventors: Harris, David H., Steuer, Robert R.
• Primary Examiner(s): Sykes, Angela D.
• Application Number:
  US08/317,726
• Time in Patent Office: 532 Days
• Field of Search: 128/633-634, 128/664-667, 356/39-41
• US Class Current: 600/322
• CPC Class Codes: A61B 5/14535 for measuring haematocrit
• CPC Class Codes: A61B 5/14546 for measuring analytes not otherwise provided for, e.g. ions, cytochromes
• 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 5/14557 specially adapted to extracorporeal circuits
• CPC Class Codes: A61B 5/6826 Finger
• CPC Class Codes: A61B 5/6838 Clamps or clips
• CPC Class Codes: A61B 5/6843 Monitoring or controlling sensor contact pressure
• CPC Class Codes: A61M 1/361 before treatment
• CPC Class Codes: A61M 1/3612 after treatment
• CPC Class Codes: B07C 3/00 Sorting according to destination collating the pages of a book B42C1/00
• CPC Class Codes: G01N 2021/036 transformable, modifiable
• CPC Class Codes: G01N 21/0303 Optical path conditioning in cuvettes, e.g. windows; adapted optical elements or systems; path modifying or adjustment G01N21/031 - G01N21/15 take precedence

Abstract

A system for determining the hematocrit transcutaneously and noninvasively. Disclosed are a finger clip assembly and an earlobe clip assembly, each including at least a pair of emitters and a photodiode in appropriate alignment to enable operation in either a transmissive mode or a reflectance mode. At least two, and preferably three, predetermined wavelengths of light are passed onto or through body tissues such as the finger, earlobe, or scalp, etc. and the extinction of each wavelength is detected. Mathematical manipulation of the detected values compensates for the effects of body tissue and fluid and determines the hematocrit value. If a fourth wavelength of light is used which is extinguished substantially differently by oxyhemoglobin and reduced hemoglobin and which is not substantially extinguished by plasma, then the blood oxygen saturation value, independent of hematocrit, may be determined.

It is also disclosed how to detect and analyze multiple wavelengths using a logarithmic DC analysis technique. Then a pulse wave is not required. So this method may be utilized in states of low blood pressure or low blood flow.

Claims

1. A system for determining the hematocrit of the blood of a patient, the blood flowing in a pulsatile fashion in a body part of the patient or in an extracorporeal passageway in communication with the circulatory system of the patient so as to be subjectable to transcutaneous examination in the body part or to noninvasive examination in the extracorporeal passageway, the body part and the extracorporeal passageway defining a blood conduit and the system comprising:

(a) a blood conduit receiving means for receiving a blood conduit containing the flowing blood of the patient;

(b) emission means for directing radiation into the flowing blood within the blood conduit, said emission means being situated within said blood conduit receiving means, said radiation defining a directed radiation comprising;

(i) a first quantity of a radiation at a first radiation wavelength which, when directed into the flowing blood in the blood conduit,

(A) has a first extinguishment value which varies with the hematocrit in the flowing blood and

(B) has a second extinguishment value which varies with the plasma in the flowing blood, which second extinguishment value is at least ten times smaller than said first extinguishment value; and

(ii) a first quantity of radiation at a second radiation wavelength, distinct from said first wavelength, which, when directed into the flowing blood within the blood conduit,

(A) has a third extinguishment value which for varying hematocrit in the flowing blood is a non-fixed multiple of said first extinguishment value; and

(B) has a fourth extinguishment value which varies with the plasma in the flowing blood, which fourth extinguishment value is at least ten times greater than said second extinguishment value;

(c) detection means for detecting the portion of said directed radiation which passes through both the blood conduit and the flowing blood therein, said detection means being situated within said blood conduit receiving means, said detected portion of said directed radiation comprising;

(i) a second quantity of a radiation at the first radiation wavelength, and

(ii) a second quantity of a radiation at the second radiation wavelength;

(d) calculation means for determining the hematocrit of the patient by operating exclusively on the second quantities of the first and second radiation wavelengths.

2. A system as defined in claim 1, wherein said detection means detects the second quantity of the first radiation wavelength by:

(a) determining the intensity of the total first radiation wavelength;

(b) determining a first radiation wavelength pulsatile value representing the difference between the maximum and the minimum intensity of a pulsatile component of the first radiation wavelength;

(c) determining the ratio between the first radiation wavelength pulsatile value and the intensity of the total first radiation wavelength over a period of time; and

(d) determining a first mean ratio value over a period of time of the ratio between the first radiation wavelength pulsatile component and the average intensity of the first radiation wavelength.

3. A system as defined in claim 2, wherein said detection means detects the second quantity of the second radiation wavelength by:

(a) determining the intensity of the total second radiation wavelength;

(b) determining a second radiation wavelength pulsatile value representing the difference between the maximum and the minimum intensity of a pulsatile component of the second radiation wavelength;

(c) determining the ratio between the second radiation wavelength pulsatile value and the intensity of the total second radiation wavelength over a period of time;

(d) determining a second mean ratio value over a period of time of the ratio between the second radiation wavelength pulsatile component and the average intensity of the second radiation wavelength; and

(e) wherein the calculation means determines the hematocrit of the patient by operating exclusively on the second quantities of the first and second radiation wavelengths to determine the hematocrit of the patient by the ratio between the first mean ratio value and the second mean ratio value.

4. A system as defined in claim 1, wherein the detection means detects the second quantity of the first radiation wavelength by:

(a) determining the intensity of the total first radiation wavelength;

(b) determining a first radiation wavelength pulsatile value representing the true time derivative of a pulsatile component of the first radiation wavelength;

(c) determining the ratio between the first radiation wavelength pulsatile value and the intensity of the total first radiation wavelength over a period of time; and

(d) determining a first mean ratio value over a period of time of the ratio between the first radiation wavelength pulsatile component and the average intensity of the first radiation wavelength.

5. A system as defined in claim 4, wherein the detection means detects the second quantity of the second radiation wavelength by:

(a) determining the intensity of the total second radiation wavelength;

(b) determining a second radiation wavelength pulsatile value representing the true time derivative of a pulsatile component of the second radiation wavelength;

(c) determining the ratio between the second radiation wavelength pulsatile value and the intensity of the total second radiation wavelength over a period of time;

(d) determining a second mean ratio value over a period of time of the ratio between the second radiation wavelength pulsatile component and the average intensity of the second radiation wavelength; and

(e) wherein the calculation means determines the hematocrit of the patient by operating exclusively on the second quantities of the first and second radiation wavelengths to determine the hematocrit of the patient by the ratio between the first mean ratio value and the second mean ratio value.

6. A system as defined in claim 1, wherein the calculation means determines the hematocrit of the patient by associating the second quantities of the first and second radiation wavelengths with an empirically obtained value.

7. A system as defined in claim 1, wherein said calculation means determines the hematocrit of the patient by mathematically manipulating the second quantities of the first and second radiation wavelengths with a polynomial function to obtain a hematocrit.

8. A system as defined in claim 1, further comprising means for displaying the hematocrit.

9. A system as defined in claim 8, wherein the display means comprises a visually perceptible display.

10. A system as defined in claim 1, wherein the first radiation wavelength is in the range from 780 nanometers to 850 nanometers.

11. A system as defined in claim 1, wherein the first radiation wavelength is in the range from 520 nanometers to 600 nanometers.

12. A system as defined in claim 1, wherein the second radiation wavelength is in the range from 1200 nanometers to 1600 nanometers.

13. A system as defined in claim 1, wherein the flowing blood includes a competing biologic constituent relative to the hemoglobin in the flowing blood, wherein:

(a) said directed radiation further comprises a first quantity of a radiation at a third radiation wavelength, distinct from said first and second radiation wavelengths, and which, when directed into the flowing blood in the blood conduit,

(i) has a fifth extinguishment value which varies with the competing biologic constituent concentration in the flowing blood, said fifth extinguishment value being at least five times greater than said second extinguishment value; and

(ii) has a sixth extinguishment value which varies with the concentration of components other than the competing biologic constituent concentration in the flowing blood;

(b) said detected portion of said directed radiation further comprises a second quantity of a radiation at the third radiation wavelength; and

(c) wherein the calculation means mathematically operates on the second quantities of the first, second, and third radiation wavelengths to compensate for the effect of the competing blood constituent so as to determine a corrected hematocrit.

14. A system as defined in claim 13, wherein the third radiation wavelength is in the range from 900 nanometers to 1000 nanometers.

15. A system as defined in claim 14, wherein:

(a) said directed radiation further comprises a first quantity of a radiation at a fourth radiation wavelength, distinct from said first, second and third radiation wavelengths, which when directed into the flowing blood in the blood conduit,

(i) has a seventh extinguishment value which varies substantially with the oxyhemoglobin and reduced oxyhemoglobin concentrations in the flowing blood, and which

(ii) has an eighth extinguishment value, which is at least ten times smaller than said seventh extinguishment value for the plasma in the flowing blood;

(b) said detected portion of said directed radiation further comprises a second quantity of a radiation at the fourth radiation wavelength.

16. A system as defined in claim 15:

(a) wherein the calculation means is also capable of determining the patient'"'"'s blood oxygen saturation by the second quantities of the first, second, third, and fourth radiation wavelengths; and

(b) further comprising a display means wherein the display means is also capable of displaying a value of the blood oxygen saturation which is independent of hematocrit.

17. A system as defined in claim 15, wherein the fourth radiation wavelength is in the range from 600 nanometers to 700 nanometers.

18. A system as defined in claim 15, wherein the radiation generation means is situated opposite the radiation detection means, whereby the first, second, third, and fourth radiation wavelengths are transmitted through the blood conduit.

19. A system as defined in claim 15, wherein the radiation generation means is not situated opposite the radiation detection means, whereby the first, second, third, and fourth radiation wavelengths are reflected from the blood conduit.

20. A system as defined in claim 15:

(a) wherein the calculation means is also capable of determining the patient'"'"'s blood oxygen content by the second quantities of the first, second, third, and fourth radiation wavelengths; and

(b) further comprising a display means wherein the display means is also capable of displaying a value of the blood oxygen content.

21. A system as defined in claim 1, further comprising pressure means for squeezing at least some of the flowing blood out of the blood conduit while radiation having the first and second radiation wavelengths are being directed into the blood conduit.

22. A system as defined in claim 1, wherein the emission means comprises at least two light emitting diodes.

23. A system as defined in claim 1, wherein the emission means comprises at least two laser diodes.

24. A system as defined in claim 1, wherein the detection means comprises at least one photodetector.

25. A system as defined in claim 1, wherein the calculation means comprises a microprocessor and at least one analog to digital convertor.

26. A system for determining the hematocrit of the blood of a patient, the blood flowing in a pulsatile fashion in a body part of the patient or in an extracorporeal passageway in communication with the circulatory system of the patient so as to be subjectable to transcutaneous examination in the body part or to noninvasive examination in the extracorporeal passageway, the body part and the extracorporeal passageway defining a blood conduit, the system comprising:

(a) a blood conduit receiving means for receiving a blood conduit containing the flowing blood of the patient;

(b) first optical emitter means for directing radiation into the flowing blood within the blood conduit, said first optical emitter means being situated within said blood conduit receiving means, said radiation defining a first directed radiation comprising a first quantity of a radiation at a first radiation wavelength which, when directed into the flowing blood in the blood conduit is posessed of the following properties;

(i) a frequency that is near isobestic for oxyhemoglobin and reduced hemoglobin in the flowing blood;

(ii) a first extinguishment value which varies with the hematocrit in the flowing blood; and

(iii) a second extinguishment value which varies with the plasma in the flowing blood, which second extinguishment value is at least ten times smaller than said first extinguishment value;

(c) second optical emitter means for directing radiation into the flowing blood within the blood conduit, said second optical emitter emission means being situated within said blood conduit receiving means, said radiation defining a second directed radiation comprising a first quantity of radiation at a second radiation wavelength, distinct from said first wavelength, which, when directed into the flowing blood within the blood conduit is posessed of the following properties;

(i) a third extinguishment value which for varying hematocrit in the flowing blood is a non-fixed multiple of said first extinguishment value; and

(ii) a fourth extinguishment value which varies with the plasma in the flowing blood, which fourth extinguishment value is at least ten times greater than said second extinguishment value;

(d) third optical emitter means for directing radiation into the flowing blood within the blood conduit, said third optical emitter emission means being situated within said blood conduit receiving means, said radiation defining a third directed radiation comprising a first quantity of a radiation at a third radiation wavelength distinct from said first and second radiation wavelengths and which, in combination with one of the first or second radiation wavelengths, is independent of hematocrit, and which, when directed into the flowing blood in the blood conduit is posessed the following properties;

(i) a fifth extinguishment value which varies with the competing biologic constituent concentration in the flowing blood, said fifth extinguishment value being at least five times greater than said second extinguishment value; and

(ii) a sixth extinguishment value which varies with the concentration of components other than the competing biologic constituent concentration in the flowing blood;

(e) photodetection means for detecting the portion of said first, second and third directed radiation which passes through both the blood conduit and the flowing blood therein, said photodetection means being situated within said blood conduit receiving means, said detected portions comprising;

(i) a second quantity of a radiation at the first radiation wavelength,

(ii) a second quantity of a radiation at the second radiation wavelength,

(iii) a second quantity of a radiation at the third radiation wavelength; and

(f) positioning means for holding the first optical emitter means, the second optical emitter means, the third optical emitter means, and the photodetection means such that the radiation path from the first, second, and third optical emitter means to the photodetection means are approximately equal;

(g) calculation means for the following;

(i) mathematically operating on the second quantities to the first, second, and third radiation wavelengths such that the spatial, geometric, and tissue variations are eliminated in each wavelength

(ii) mathematically operating on the second quantities of the first, second, and third radiation wavelengths to compensate for the effect of the competing blood constituent, and

(iii) determining the hematocrit of the patient; and

(h) display means for providing a visually perceptible indication of the hematocrit.

27. A system as defined in claim 26, further comprising fourth optical emitter means for directing radiation into the flowing blood within the blood conduit, said fourth optical emitter means being situated within said blood conduit receiving means, said radiation defining a fourth directed radiation and comprising:

(a) a first quantity of a radiation at a fourth radiation wavelength which, when directed into the flowing blood within the blood conduit,

(i) has a seventh extinguishment value which varies substantially with the oxyhemoglobin and reduced oxyhemoglobin concentrations in the flowing blood, and which

(ii) has an eighth extinguishment value, which is at least ten times smaller than said seventh extinguishment value for the plasma in the flowing blood;

(b) wherein the photodetection means detects the portion of said fourth directed radiation which passes through both the blood conduit and the flowing blood therein, said detected portion of said fourth radiation wavelength comprising a second quantity of the fourth radiation wavelength.

28. A system as defined in claim 27:

(a) wherein the calculation means mathematically operates on the second quantity of the fourth radiation wavelength to determine the patient'"'"'s blood oxygen saturation; and

(b) wherein the display means displays a value of the blood oxygen saturation which is independent of hematocrit.

29. A system as defined in claim 27:

(a) wherein the calculation means mathematically operates on the second quantity of the fourth radiation wavelength to determine the patient'"'"'s blood oxygen content; and

(b) wherein the display means displays a value of the blood oxygen content.

30. A system for determining the desired biologic constituent concentration of the blood of a patient, the blood flowing in a pulsatile fashion in a body part of the patient or in an extracorporeal passageway in communication with the circulatory system of the patient so as to be subjectable to transcutaneous examination in the body part or to noninvasive examination in the extracorporeal passageway, the body part and the extracorporeal passageway defining a blood conduit, the system comprising:

(a) a blood conduit receiving means for receiving a blood conduit containing the flowing blood of the patient;

(b) emission means for directing radiation into the flowing blood within the blood conduit, said emission means being situated within said blood conduit receiving means, said radiation defining a directed radiation comprising;

(i) a first quantity of a radiation at a first radiation wavelength which, when directed into the flowing blood within the blood conduit,

(A) has a first extinguishment value which varies with the desired biologic constituent concentration in the flowing blood and

(B) has a second extinguishment value which varies with the concentration of components other than the desired biologic constituent in the flowing blood, which second extinguishment value is at least ten times smaller than said first extinguishment value; and

(ii) a first quantity of a radiation at a second radiation wavelength, distinct from said first wavelength, which, when directed into the flowing blood within the blood conduit,

(A) has a third extinguishment value which for varying concentrations in the flowing blood of the desired blood constituent is a non-fixed multiple of said first extinguishment value and

(B) has a fourth extinguishment value which varies with the concentration of components other than the desired biologic constituent in the flowing blood, which fourth extinguishment value is at least ten times greater than said second extinguishment value;

(c) detection means for detecting the portion of said directed radiation which passes through both the blood conduit and the flowing blood therein, said detection means being situated within said blood conduit receiving means, said detected portion of said directed radiation comprising;

(i) a second quantity of a radiation at the first radiation wavelength, and

(ii) a second quantity of a radiation at the second radiation wavelength; and

(d) calculation means for determining the desired biologic constituent concentration by operating exclusively on the second quantities of the first and second radiation wavelengths.

31. A system as defined in claim 30, wherein said detection means detects the second quantity of the first radiation wavelength by:

(a) determining the intensity of the total first radiation wavelength;

(b) determining a first radiation wavelength pulsatile value representing the difference between the maximum and the minimum intensity of a pulsatile component of the first radiation wavelength;

(c) determining the ratio between the first radiation wavelength pulsatile value and the intensity of the total first radiation wavelength over a period of time; and

(d) determining a first mean ratio value over a period of time of the ratio between the first radiation wavelength pulsatile component and the average intensity of the first radiation wavelength.

32. A system as defined in claim 31, wherein the detection means detects the second quantity of the first radiation wavelength by:

(a) determining the intensity of the total first radiation wavelength;

(b) determining a first radiation wavelength pulsatile value representing the true time derivative of a pulsatile component of the first radiation wavelength;

(c) determining the ratio between the first radiation wavelength pulsatile value and the intensity of the total first radiation wavelength over a period of time; and

(d) determining a first mean ratio value over a period of time of the ratio between the first radiation wavelength pulsatile component and the average intensity of the first radiation wavelength.

33. A system as defined in claim 32, wherein said detection means detects the second quantity of the second radiation wavelength by:

(a) determining the intensity of the total second radiation wavelength;

(b) determining a second radiation wavelength pulsatile value representing the difference between the maximum and the minimum intensity of a pulsatile component of the second radiation wavelength;

(c) determining the ratio between the second radiation wavelength pulsatile value and the intensity of the total second radiation wavelength over a period of time;

(d) determining a second mean ratio value over a period of time of the ratio between the second radiation wavelength pulsatile component and the average intensity of the second radiation wavelength; and

(e) wherein the calculation means determines the desired biologic constituent concentration of the patient by operating exclusively on the second quantities of the first and second radiation wavelengths to determine the desired biologic constituent concentration of the patient by the ratio between the first mean ratio value and the second mean ratio value.

34. A system as defined in claim 33, wherein the detection means detects the second quantity of the second radiation wavelength by:

(a) determining the intensity of the total second radiation wavelength;

(b) determining a second radiation wavelength pulsatile value representing the true time derivative of a pulsatile component of the second radiation wavelength;

(c) determining the ratio between the second radiation wavelength pulsatile value and the intensity of the total second radiation wavelength over a period of time;

(d) determining a second mean ratio value over a period of time of the ratio between the second radiation wavelength pulsatile component and the average intensity of the second radiation wavelength; and

(e) wherein the calculation means determines the desired biologic constituent concentration of the patient by operating exclusively on the second quantities of the first and second radiation wavelengths to determine the desired biologic constituent concentration of the patient by the ratio between the first mean ratio value and the second mean ratio value.

35. A system as defined in claim 30, wherein the calculation means determines the desired biologic constituent concentration of the patient by associating the second quantities of the first and second radiation wavelengths with an empirically obtained value.

36. A system as defined in claim 30, wherein said calculation means determines the desired biologic constituent concentration of the patient by mathematically manipulating the second quantities of the first and second radiation wavelengths with a polynomial function to obtain the desired biologic constituent concentration.

37. A system as defined in claim 30, wherein the desired biologic constituent comprises red blood cells.

38. A system as defined in claim 30, wherein the desired biologic constituent comprises hematocrit.

39. A system as defined in claim 30, wherein the desired biologic constituent comprises hemoglobin.

40. A system as defined in claim 30, wherein the first radiation wavelength has a first extinguishment value substantially the same amount for oxyhemoglobin and for reduced hemoglobin in the flowing blood and has a second extinguishment value, which is at least ten times smaller than said first extinguishment value for the plasma in the flowing blood.

41. A system as defined in claim 30, wherein the first radiation wavelength is in the range from about 780 nanometers to about 850 nanometers.

42. A system as defined in claim 30, wherein the first radiation wavelength is in the range from about 520 nanometers to about 600 nanometers.

43. A system as defined in claim 30, wherein the second radiation wavelength has a third extinguishment value substantially the same amount for oxyhemoglobin and for reduced hemoglobin in the flowing blood and has a fourth extinguishment value, which is approximately the same as said third extinguishment value for the plasma in the flowing blood.

44. A system as defined in claim 30, wherein the second radiation wavelength is in the range from about 1200 nanometers to about 1600 nanometers.

45. A system as defined in claim 30, wherein the flowing blood includes a competing biologic constituent relative to the hemoglobin in the flowing blood, wherein:

(a) said directed radiation further comprises a first quantity of a radiation at a third radiation wavelength, distinct from said first and second radiation wavelengths, and which, when directed into the flowing blood in the blood conduit,

(i) has a fifth extinguishment value which varies with the competing biologic constituent concentration in the flowing blood, said fifth extinguishment value being at least five times greater than said second extinguishment value; and

(ii) has a sixth extinguishment value which varies with the concentration of components other than the competing biologic constituent concentration in the flowing blood;

(b) said detected portion of said directed radiation further comprises a second quantity of a radiation at the third radiation wavelength;

(c) said system further comprising calculation means for mathematically operating on the second quantities of the first, second, and third radiation wavelengths

(i) such that the spatial, geometric, and tissue variations are eliminated in each radiation wavelength; and

(ii) to compensate for the effect of the competing biologic constituent.

46. A system as defined in claim 45, wherein the third radiation wavelength is extinguished approximately the same amount by oxyhemoglobin and reduced hemoglobin in the flowing blood and is substantially extinguished by plasma in the flowing blood.

47. A system as defined in claim 45, wherein the third radiation wavelength is in the range from about 900 nanometers to about 1000 nanometers.

48. A system as defined in claim 45, wherein:

(a) said directed radiation further comprises a first quantity of a radiation at a fourth radiation wavelength, distinct from said first, second and third radiation wavelengths, which when directed into the flowing blood in the blood conduit has the following properties;

(i) a seventh extinguishment value which varies substantially with the oxyhemoglobin and reduced oxyhemoglobin concentrations in the flowing blood, and which

(ii) an eighth extinguishment value, which is at least ten times smaller than said seventh extinguishment value for the plasma in the flowing blood;

(b) said detected portion of said directed radiation further comprises a second quantity of a radiation at the fourth radiation wavelength;

(c) and said calculation means further;

(i) mathematically operates on the second quantity of the fourth radiation wavelength such that the spatial, geometric, and tissue variations are eliminated in the fourth radiation wavelength, and

(ii) determines a blood oxygen saturation value which is independent of hematocrit by mathematically operating on the second quantities of the first, second, third, and fourth radiation wavelengths.

49. A system as defined in claim 48, wherein the fourth radiation wavelength is in the range from about 600 nanometers to about 700 nanometers.

50. A system as defined in claim 45, wherein:

(a) said directed radiation further comprises a first quantity of a radiation at a fourth radiation wavelength, distinct from said first, second and third radiation wavelengths, which when directed into the flowing blood in the blood conduit,

(i) has a seventh extinguishment value which varies substantially with the oxyhemoglobin and reduced hemoglobin concentrations in the flowing blood, and which

(ii) has an eighth extinguishment value, which is at least ten times smaller than said seventh extinguishment value for the plasma in the flowing blood;

(b) said detected portion of said directed radiation further comprises a second quantity of a radiation at the fourth radiation wavelength;

(c) and said calculation means further;

(ii) mathematically operates on the second quantity of the fourth radiation wavelength such that the spatial, geometric, and tissue variations are eliminated in the fourth radiation wavelength; and

(ii) determines a blood oxygen saturation value which is independent of hematocrit by mathematically operating on the second quantities of the first, second, third, and fourth radiation wavelengths.

51. A system as defined in claim 50, wherein the fourth radiation wavelength is in the range from about 600 nanometers to about 700 nanometers.

52. A method for determining the hematocrit of the blood of a patient, the blood flowing in a pulsatile fashion in a body part of the patient or in an extracorporeal passageway in communication with the circulatory system of the patient so as to be subjectable to transcutaneous examination in the body part or to noninvasive examination in the extracorporeal passageway, the body part and the extracorporeal passageway defining a blood conduit and the method comprising the steps of:

(a) placing the blood conduit within a blood conduit receiving means with the flowing blood in the blood conduit;

(b) directing radiation into the flowing blood within the blood conduit using a radiation generation means situated within the blood conduit receiving means, said radiation defining a directed radiation comprising;

(i) a first quantity of a radiation at a first radiation wavelength which, when directed into the flowing blood within the blood conduit,

(A) is extinguished substantially the same amount by oxyhemoglobin and reduced hemoglobin in the flowing blood and

(B) is extinguished by the plasma in the flowing blood in a first manner; and

(ii) a first quantity of radiation at a second radiation wavelength which, when directed into the flowing blood within the blood conduit,

(A) is extinguished substantially the same amount by oxyhemoglobin and reduced hemoglobin in the flowing blood and

(B) is extinguished by the plasma in the flowing blood in a second manner substantially different from said first manner;

(c) detecting the portion of said directed radiation which passes through both the blood conduit and the flowing blood therein with a radiation detection means situated within said conduit receiving means, said detected portion of said directed radiation comprising;

(i) a second quantity of a radiation at the first radiation wavelength being detected by steps comprising;

(A) determining the extinguishment of the total first radiation wavelength;

(B) determining a first radiation wavelength pulsatile value representing the difference between the maximum and the minimum extinguishment of a pulsatile component of the first radiation wavelength;

(C) determining the ratio between the first radiation wavelength pulsatile value and the extinguishment of the total first radiation wavelength over a period of time; and

(D) determining a first mean ratio value over a period of time of the ratio between the first radiation wavelength pulsatile component and the average extinguishment of the first radiation wavelength, and

(ii) a second quantity of a radiation at the second radiation wavelength; and

(d) operating on the second quantities of the radiations at the first and second radiation wavelengths to determine the hematocrit of the patient.

53. A system for determining the hematocrit of the blood of a patient, the blood flowing in a pulsatile fashion in a body part of the patient or in an extracorporeal passageway in communication with the circulatory system of the patient so as to be subjectable to transcutaneous examination in the body part or to noninvasive examination in the extracorporeal passageway, the body part and the extracorporeal passageway defining a blood conduit and the system comprising:

(a) a blood conduit receiving means for receiving a blood conduit containing the flowing blood of the patient;

(b) emission means for directing radiation into the flowing blood within the blood conduit, said emission means being situated within said blood conduit receiving means, said radiation defining a directed radiation comprising;

(i) a first quantity of a radiation at a first radiation wavelength which, when directed into the flowing blood in the blood conduit,

(A) is extinguished substantially the same amount by oxyhemoglobin and reduced hemoglobin in the flowing blood and

(B) is extinguished by the plasma in the flowing blood in a first manner; and

(ii) a first quantity of a radiation at a second radiation wavelength which, when directed into the blood flowing within the blood conduit,

(A) is extinguished substantially the same amount by oxyhemoglobin and reduced hemoglobin in the flowing blood and

(B) is extinguished by the plasma in the flowing blood in a second manner substantially different from said first manner;

(c) detection means for detecting the portion of said directed radiation which passes through both the blood conduit and the flowing blood therein, said detection means being situated within said blood conduit receiving means, said detected portion of said directed radiation comprising;

(i) a second quantity of a radiation at the first radiation wavelength, and

(ii) a second quantity of a radiation at the second radiation wavelength;

(d) calculation means for determining the hematocrit of the patient by operating on the second quantities of the first and second wavelengths, wherein the calculation means includes means for determining the logarithmic intensity ratio of the second quantities of the first and second radiation wavelengths.