Method of validating and/or calibrating devices used for carrying out photometry of living tissues and a device for implementing said method

• US 5,891,025 A
• Filed: 02/24/1997
• Issued: 04/06/1999
• Est. Priority Date: 08/22/1994
• Status: Expired due to Fees

• Current Assignee: Johannes Buschmann
• Original Assignee: Johannes Buschmann
• Inventors: Falkowski, Reinhold, Buschmann, Johannes P.
• Primary Examiner(s): Peffley, Michael
• Assistant Examiner(s): WINAKUR, ERIC FRANK
• Application Number:
  US08/793,405
• Time in Patent Office: 771 Days
• Field of Search: 600/310, 600/322, 600/323, 600/331, 250/252.1, 356/41, 356/42, 356/243
• US Class Current: 600/331
• CPC Class Codes: A61B 5/14542 for measuring blood gases A61B5/14551 takes precedence
• CPC Class Codes: A61B 5/1464 specially adapted for foetal tissue
• CPC Class Codes: A61B 5/1495 Calibrating or testing of in-vivo probes
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction
• CPC Class Codes: G01N 21/3151 using two sources of radiation of different wavelengths G01N21/33 - G01N21/39 take precedence
• CPC Class Codes: G01N 33/4925 measuring blood gas content, e.g. O2, CO2 , HCO3

Abstract

The invention concerns a process for validation of devices for photometry of living tissue, which encompasses the following steps:

in vitro adjusting of a particular concentration of a substance to be detected in a bodily fluid;

transporting the bodily fluid which has been adjusted to a pre-determined concentration to at least one measuring cell;

transillumination of the bodily fluid; and

sensing of the light intensity of at least one spectral window for determination of at least one suitable parameter in the bodily fluid, which is contained in the measuring cell, by means of at least one emitter and at least one receiver;

thereby characterized,

that one actively and in a defined manner dynamically changes the effective absorption length through the bodily fluid, without using the bodily fluid for transmission of the forces, wherein the bodily fluid is found in the optical space between the emitter and the receiver; and

establishment of at least one relationship between the concentration on the one hand and the suitable parameter on the other hand. This process provides very precise results in the calibration of pulse oximeters. The invention concerns also the device for carrying out the process as well as appropriately calibrated pulse oximeters.

Claims

1. A process for in vitro validation of a photometric device, said method comprising:

(a) specifying a substance of a body fluid to be measured;

(b) adjusting a parameter of said substance of a body fluid in body fluid in vitro;

(c) providing adjusted body fluid from step (b) to a measuring area within a measuring cell such that at least some of said adjusted body fluid is between a radiation emitter and a radiation receiver, wherein at least one of said radiation emitter and radiation receiver is immersed within said body fluid, and wherein the mean light path between the radiation emitter and radiation receiver corresponds to the effective absorption length;

(d) transilluminating the body fluid in the measuring area;

(e) actively and in a defined manner periodically changing the effective absorption length through the body fluid between the radiation emitter and receiver, without using the body fluid as a medium for transmission of forces;

(f) detecting changes in light intensity of at least two spectral frequencies which are characteristic absorption frequencies for said substance of a body fluid to be detected, said changes constituting a ratio "Ω

" of said substance of a body fluid to be detected, wherein Ω

is defined with the following equation;

##EQU28## (g) determining a correlation between (i) said ratio Ω and

(ii) a parameter of said substance of a body fluid.

2. A process as in claim 1, wherein said parameter is concentration.

3. A process as in claim 1, wherein said parameter is saturation.

4. A process according to claim 1, wherein said photometric device is a pulse oximeter.

5. A process according to claim 1, wherein said validation is in vitro calibration of a pulse oximeter.

6. A process according to claim 1, wherein said body fluid is human blood and wherein said substance of a body fluid to be determined is oxygen.

7. A process according to claim 1, wherein said radiation emitter emits light in at least one red spectral region and at least one infrared spectral region.

8. A process according to claim 1, wherein the change in the effective absorption length is caused by changing the mean effective light path between emitter and receiver, with said emitter and receiver remaining stationary.

9. A process according claim 1, wherein said correlation is an evaluation of the relationship between (i) Ω

and (ii) oxygen saturation.

10. A process as in claim 9, wherein said oxygen saturation is the functional oxygen saturation (SaO_2func) according to the following equation:

##EQU29## and wherein the following equation is employed for calibration or after producing a calibration curve;

space="preserve" listing-type="equation">SaO.sub.2(func) =f(Ω

).

11.

11. A process for in vitro validation of a photometric device, said method comprising:

(a) specifying a substance of a body fluid to be measured;

(b) adjusting a parameter of said substance of a body fluid in body fluid in vitro;

(c) providing adjusted body fluid from step (b) to a measuring area such that at least some of said adjusted body fluid is between a radiation emitter and a radiation receiver, wherein the mean light path between the radiation emitter and radiation receiver corresponds to the effective absorption length;

(d) transilluminating the body fluid in the measuring area;

(e) actively and in a defined manner periodically chancing the effective absorption length through the body fluid between the radiation emitter and receiver, without using the body fluid as a medium for transmission of forces;

(f) detecting changes in light intensity of at least two spectral frequencies which are characteristic absorption frequencies for said substance of a body fluid to be detected, said chances constituting a ratio "Ω

" of said substance of a body fluid to be detected, wherein Ω

is defined with the following equation;

##EQU30## (g) determining a correlation between (i) said ratio Ω and

(ii) a parameter of said substance of a body fluid, wherein the change in the effective absorption length is caused by changing the physical distance between said emitter and receiver.

12. A process for in vitro validation of a photometric device, said method comprising:

(a) specifying a substance of a body fluid to be measured;

(b) adjusting a parameter of said substance of a body fluid in body fluid in vitro;

(c) providing adjusted body fluid from step (b) to a measuring area such that at least some of said adjusted body fluid is between a radiation emitter and a radiation receiver, wherein the mean light path between the radiation emitter and radiation receiver corresponds to the effective absorption length;

(d) transilluminating the body fluid in the measuring area;

(e) actively and in a defined manner periodically changing the effective absorption length through the body fluid between the radiation emitter and receiver, without using the body fluid as a medium for transmission of forces;

(f) detecting chances in light intensity of at least two spectral frequencies which are characteristic absorption frequencies for said substance of a body fluid to be detected, said changes constituting a ratio "Ω

" of said substance of a body fluid to be detected, wherein Ω

is defined with the following equation;

##EQU31## (g) determining a correlation between (i) said ratio Ω and

(ii) a parameter of said substance of a body fluid, wherein the change in the effective absorption length is caused by displacement of at least part of said body fluid in the mean effective light path between said radiation emitter and radiation receiver by an optically neutral displacement body which is more transparent at the spectral frequency at which changes in light intensity are being measured than said body fluid containing said substance to be detected and wherein said displacement body is moved between at least a first position and a second position.

13. A process according to claim 12, wherein said displacement body is a diffuse glass wedge.

14. A process according to claim 12, wherein said displacement body is a rotating optical transparent disc with varying thickness.

15. A process according to claim 12, wherein light scattering particles are dispersed in a coating layer associated with said emitter and/or receiver, and wherein said particles are selected from the group consisting of glass beads and titanium oxide.

16. A process according to claim 15, wherein said displacement body is periodically moved, generating a pulsatile variation in effective absorption length through said body fluid containing said substance to be measured.

17. A process for in vitro validation of a photometric device, said method comprising:

(a) specifying a substance of a body fluid to be measured;

(b) adjusting a parameter of said substance of a body fluid in body fluid in vitro;

(c) providing adjusted body fluid from step (b) to a measuring area such that at least some of said adjusted body fluid is between a radiation emitter and a radiation receiver, wherein the mean light path between the radiation emitter and radiation receiver corresponds to the effective absorption length;

(d) transilluminating the body fluid in the measuring area;

(e) actively and in a defined manner periodically changing the effective absorption length through the body fluid between the radiation emitter and receiver, without using the body fluid as a medium for transmission of forces;

(f) detecting changes in light intensity of at least two spectral frequencies which are characteristic absorption frequencies for said substance of a body fluid to be detected, said changes constituting a ratio "Ω

" of said substance of a body fluid to be detected, wherein Ω

is defined with the following equation;

##EQU32## (g) determining a correlation between (i) said ratio Ω and

(ii) a parameter of said substance of a body fluid, wherein at least one of said emitter and receiver is provided with an optically transparent layer for reducing the effective non-pulsatile absorption length of the body fluid.

18. A process for in vitro validation of a photometric device, said method comprising:

(a) specifying a substance of a body fluid to be measured;

(b) adjusting a parameter of said substance of a body fluid in body fluid in vitro;

(c) providing adjusted body fluid from step (b) to a measuring area such that at least some of said adjusted body fluid is between a radiation emitter and a radiation receiver, wherein the mean light path between the radiation emitter and radiation receiver corresponds to the effective absorption length;

(d) transilluminating the body fluid in the measuring area;

(e) actively and in a defined manner periodically changing the effective absorption length through the body fluid between the radiation emitter and receiver, without using the body fluid as a medium for transmission of forces;

(f) detecting changes in light intensity of at least two spectral frequencies which are characteristic absorption frequencies for said substance of a body fluid to be detected, said chances constituting a ratio "Ω

" of said substance of a body fluid to be detected, wherein Ω

is defined with the following equation;

##EQU33## (g) determining a correlation between (i) said ratio Ω and

(ii) a parameter of said substance of a body fluid, further comprising dispersing color neutral plastic scattering particles in the body fluid to increase the scattering properties of said body fluid for better tissue imitation, wherein said scattering particles have approximately the specific density of the body fluid.

19. A device for in vitro validation of a photometric device by a method comprising:

(a) specifying a substance of a body fluid to be measured;

(b) adjusting the concentration parameter of said substance of a body fluid in body fluid in vitro;

(c) providing adjusted body fluid from step (b) to a measuring area such that at least some of said adjusted body fluid is between a radiation emitter and a radiation receiver, wherein at least one of said radiation emitter and a radiation receiver are immersed in said body fluid and wherein the mean light path between the radiation emitter and radiation receiver corresponds to the effective absorption length;

(d) transilluminating the body fluid in the measuring area;

(e) actively and in a defined manner periodically changing the effective absorption length through the body fluid between the radiation emitter and receiver, without using the body fluid as a medium for transmission of forces;

(f) detecting changes in light intensity of at least two spectral frequencies which are characteristic absorption frequencies for said substance of a body fluid to be detected, said changes constituting a ratio "Ω

" of said substance of a body fluid to be detected, wherein Ω

is defined with the following equation;

##EQU34## (g) determining a correlation between (i) said ratio Ω and

(ii) a parameter of said substance of a body fluid;

said device for in vitro validation of a photometric device comprising;

at least one device for adjusting the parameter of a substance of a body fluid to be measured;

at least one measuring area;

a transport device, with which the body fluid with the adjusted concentration is brought into said measuring area;

at least one radiation emitter and at least one radiation receiver provided in said measuring area;

means for periodically varying the mean effective light path between the radiation emitter and at least one radiation receiver, without using the body fluid as a medium for transmission of forces on the emitter and/or receiver; and

a device which converts a read-out of a light intensity as detected by means of said radiation receiver at at least one spectral frequency into the form of at least one parameter, which light has traveled from said radiation emitter to said radiation receiver through the body fluid, and brings about a correlation between (i) the concentration and (ii) the parameter.

20. A device according to claim 19, wherein an optical displacement body with variable thickness is provided in the optical path between the emitter and receiver and is provided with means for moving between a first and a second position for actively and in a defined manner periodically changing the effective absorption length through the body fluid between the radiation emitter and receiver, without using the body fluid as a medium for transmission of forces.

21. A process for in vitro validation of a photometric device, said method comprising:

(a) specifying a substance of a body fluid to be measured;

(b) adjusting a parameter of said substance of a body fluid in body fluid in vitro;

(c) providing adjusted body fluid from step (b) to a measuring area within a measuring cell such that at least some of said adjusted body fluid is between a radiation emitter and a radiation receiver, wherein said radiation emitter and radiation receiver are immersed within said body fluid, and wherein the mean light path between the radiation emitter and radiation receiver corresponds to the effective absorption length;

(d) transilluminating the body fluid in the measuring area;

(e) actively and in a defined manner periodically changing the effective absorption length through the body fluid between the radiation emitter and receiver, without using the body fluid as a medium for transmission of forces;

(f) detecting changes in light intensity of at least two spectral frequencies which are characteristic absorption frequencies for said substance of a body fluid to be detected, said changes constituting a ratio "Ω

" of said substance of a body fluid to be detected, wherein Ω

is defined with the following equation;

##EQU35## (g) determining a correlation between (i) said ratio Ω and

(ii) a parameter of said substance of a body fluid.