System for noninvasive hematocrit monitoring

• US 6,681,128 B2
• Filed: 06/13/2001
• Issued: 01/20/2004
• Est. Priority Date: 10/06/1990
• Status: Expired due to Fees

• Current Assignee: Fresenius Medical Care Holdings Incorporated (Fresenius SE & Co. KGaA)
• Original Assignee: HEMA Metrics Incorporated
• Inventors: Harris, David H., Steuer, Robert R.
• Primary Examiner(s): Winakur, Eric F.
• Assistant Examiner(s): KREMER, MATTHEW J
• Application Number:
  US09/879,192
• Publication Number:
  US 20020038079A1
• Time in Patent Office: 951 Days
• Field of Search: 600/309-310, 600/322-323, 600/476, 600/473, 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 5/6816 Ear lobe
• 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: 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 determines heamtocrit 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 assed 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 plasmas, then the blood oxygen saturation value, independent of hematocrit, maybe 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 method for determining hematocrit of 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) selecting a first radiation wavelength that is isobestic for Hb and HbO₂ and not extinguished by non-hemoglobin components of the blood;

(b) selecting a second radiation wavelength that is isobestic for Hb and HbO₂ and extinguished by non-hemoglobin components of the blood;

(c) directing the first radiation wavelength into the blood conduit;

(d) directing the second radiation wavelength into the blood conduit;

(e) detecting the amount of steady state component of the first wavelength extinguished after passing through the blood conduit;

(f) detecting the amount of steady state component of the second wavelength extinguished after passing through the blood conduit;

(g) detecting the amount of pulsatile component of the first wavelength;

(h) detecting the amount of pulsatile component of the second wavelength;

(i) determining a ratio of the pulsatile component of the first wavelength to the steady state component of the first wavelength;

(j) determining a ratio of the pulsatile component of the second wavelength to the steady state component of the second wavelength;

(k) obtaining a mean value for the ratio of the pulsatile component of the first wavelength to the steady state component of the first wavelength over a period of time;

(l) obtaining a mean value for the ratio of the pulsatile component of the second wavelength to the steady state component of the second wavelength over a period of time; and

(m) determining the hematocrit by the ratio of the mean values obtained for the first and second wavelengths.

2. The method for determining the hematocrit of the blood of a patient of claim 1, further comprising the steps of:

(n) displaying the hematocrit.

3. The method for determining the hematocrit of the blood of a patient of claim 1, further comprising the steps of:

(n) selecting a third radiation wavelength;

(o) directing the third radiation wavelength into the blood conduit;

(p) determining a mean value for a ratio of pulsatile component of the third wavelength to steady state component of the third wavelength over a period of time; and

(q) calculating a corrected hematocrit value using a linear combination of the first, second and third wavelengths and their ratios.

4. The method for determining the hematocrit of the blood of a patient of claim 3, further comprising the steps of:

(r) display the corrected hematocrit value.

5. A system for determining hematocrit of 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) blood conduit receiving means for receiving a blood conduit containing the flowing blood of the patient;

(b) a first emitter positioned on said conduit receiving means for emitting a first radiation wavelength that is isobestic for Hb and HbO₂ and not extinguished by non-hemoglobin components of the blood;

(c) a second emitter positioned on said conduit receiving means for emitting a second radiation wavelength that is isobestic for Hb and HbO₂ and extinguished by non-hemoglobin components of the blood;

(d) means for directing the first radiation wavelength into the blood conduit;

(e) means for directing the second radiation wavelength into the blood conduit;

(f) means for detecting the amount of steady state component of the first wavelength extinguish after passing through the blood conduit;

(g) means for detecting the amount of steady state component of the second wavelength extinguished after passing through the blood conduit;

(h) means for detecting the amount of pulsatile component of the first wavelength;

(i) means for detecting the amount of pulsatile component of the second wavelength;

(j) means for determining a ratio of the pulsatile component of the first wavelength to the steady state component of the first wavelength;

(k) means for determining a ratio of the pulsatile component of the second wavelength to the steady state component of the second wavelength;

(l) means for obtaining a mean value for the ratio of the pulsatile component of the first wavelength to the steady state component of the first wavelength over a period of time;

(m) means for obtaining a mean value for the ratio of the pulsatile component of the second wavelength to the steady state component of the second wavelength over a period of time; and

(n) means for determining the hematocrit by the ratio of the mean values obtained for the first and second wavelengths.

6. The system for determining the hematocrit of the blood of a patient of claim 5, further comprising:

(o) means for displaying the hematocrit.

7. The system for determining the hematocrit of the blood of a patient of claim 5, further comprising:

(o) a third emitter positioned on said conduit receiving means for emitting a third radiation wavelength;

(p) means for directing the third radiation wavelength into the blood conduit;

(q) means for determining a mean value for a ratio of pulsatile component of the third wavelength to steady state component of the third wavelength over a period of time; and

(r) means for calculating a corrected hematocrit value using a linear combination of the first, second and third wavelengths and their ratios.

8. The system for determining the hematocrit of the blood of a patient of claim 7, further comprising:

(s) means for display the corrected hematocrit value.