DUAL WAVELENGTH PHOTOMETER FOR ABSORBANCE DIFFERENCE MEASUREMENTS

• US 3,787,124 A
• Filed: 09/21/1972
• Issued: 01/22/1974
• Est. Priority Date: 09/21/1972
• Status: Expired due to Term

• Current Assignee: SLM Instruments Incorporated
• Original Assignee: George W. Lowy, Herbert M. Cullis, Paul Priarone
• Inventors: Lowy, George W., Priarone, Paul, Cullis, Herbert M.
• Primary Examiner(s): Wibert, Ronald L.
• Assistant Examiner(s): Evans, F. L.
• Application Number:
  US05/291,046
• Time in Patent Office: 488 Days
• Field of Search: 23/253R 356/51,96,97,184,186,188,205,212,95,93,182 250/218
• US Class Current: 356/434
• CPC Class Codes: G01N 21/314 with comparison of measurements at specific and non-specific wavelengths dual wavelength spectrometry G01J3/427

Abstract

A dual wavelength photometer for measuring the oxygenation characteristics of blood. Light is passed through two different filters on a rotating time-sharing wheel, one filter providing a reference wave length at which there is substantially no absorbance change as between oxygenated and deoxygenated blood, the other filter providing a wavelength at which there is maximum absorbance change. The two wavelengths are sequentially passed through a cuvette containing deoxygenated blood being treated at controlled rates with an oxygenating reagent and changes in absorbance are detected by a photomultiplier which generates corresponding signals. A time-shared difference-measuring circuit, synchronized with the rotating wheel, receives the signals and derives a resultant absorbance difference signal which is delivered to a recorder. The trace provided by the recorder shows the change in absorbance-difference with time as blood oxygenation proceeds.

Claims

1. A dual wavelength photometer comprising time-sharing duochromator means cyclically generating a reference beam of one wavelength and a measure beam of a second wavelength, a photosensitive device, means to direct said sequentially generated reference and measure beams toward said photosensitive device, means to support a sample in the path of the sequential beams reaching said photosensitive device whereby to generate respective sequential responses of said photosensitive device in accordance with the absorbances by the sample of the reference and measure beams, means to generate respective substantially concurrent steady signals having amplitudes in accordance with said responses, and means to measure the difference in the amplitudes of said steady signals, wherein the means to generate the respective steady signals and to measure the difference in their amplitudes comprises a differential amplifier, respective steady signal-generating amplifiers connected to the inputs of said differential amplifier, respective keyed circuit means alternately drivingly connecting the photosensitive device to said steady signal-generating amplifiers, means to key said keyed circuit means in synchronism with said sequentially generated reference and measure beams, and indicating means connected to the output of said differential amplifier.

2. The dual wavelength photometer of claim 1, and wherein each steady signal-generating amplifier is provided With a capacitor connected directly across its input and output terminals and with a discharge resistor connected in parallel with the capacitor through its keyed circuit means to allow the voltage drop across each steady signal-generating amplifier to adjust with changing amplitudes of its input pulses.

3. The dual wavelength photometer of claim 1, and wherein said duochromator means is of the rotary type and said keying means comprises a rotary disc member coupled to said rotary duochromator means, a light source on one side of said disc member, a second photosensitive device on the other side of said disc member, said disc member having an aperture located so as to become aligned with said light source and said second photosensitive device simultaneously with the generation of one of said beams, circuit means operatively connecting said second photosensitive device to one of said keyed circuit means, and means to operate the other keyed circuit means after a time delay corresponding to the phase angle spacing between the two beams.

4. The dual wavelength photometer of claim 3, and wherein the means to operate the other keyed circuit means comprises a timed signal generating circuit connected between said second photosensitive device and said other keyed circuit means, said timed signal generating circuit having means to generate an output signal at a time delay after excitation thereof corresponding to the phase angle spacing between the two beams.

5. The dual wavelength photometer of claim 1, and wherein the duochromator means comprises a light source, a rotating member located between said light source and said sample-supporting means, said rotating member having two spaced filters arranged to be alternately interposed between the light source and the sample-supporting means, one filter being arranged to pass only light of reference beam wavelength and the other filter being arranged to pass only light of measure beam wavelength, a calibration disc member rotatably engaged with said rotating member and having a window of predetermined optical density at the same radial distance from the axis of rotation of said rotating member as said filters, means to at times secure said calibration disc member to said rotating member with said window overlying one of the filters, and means to at other times hold the calibration disc member in a non-interfering position with respect to the optical path between said light source and the sample-supporting means.

6. The dual wavelength photometer of claim 5, and wherein said rotating member has a collar portion and said disc member is rotatably mounted on said collar portion.

7. The dual wavelength photometer of claim 1, and wherein said sample-supporting means comprises a transparent-walled titration cuvette having a top cover element, said top cover element having a downwardly concave bottom surface and being provided with titrant inlet conduit means connected to the outer portion thereof and fluid outlet conduit means connected to its center portion.

8. The dual wavelength photometer of claim 1, and wherein said reference beam is of a wavelength at which there is substantially no absorbance difference when passed through either oxygenated or deoxygenated blood and wherein said measure beam is of a wavelength at which there is substantially maximum absorbance difference when passed respectively through oxygenated and deoxygenated blood.

9. The dual wavelength photometer of claim 1, and means to admit a titrating reagent into said sample-supporting means so as to react with the sample while said beams are passing through the sample.

10. The dual wavelength photometer of claim 8, and means to admit an oxygenating reagent into said sample-supporting means so as to oxygenate the sample while said beams are passing through the sample.

11. The dual wavelength photometer of claim 1, and wherein the reference beam comprises light of 448 nm wavelength and the measure beam comprises light of 439 nm wavelengTh.

12. The dual wavelength photometer of claim 1, and wherein said time-sharing duochromator means comprises a light source, a rotating member located between said light source and said sample supporting means, said rotating member having two spaced filters arranged to be alternately interposed between the light source and the sample-supporting means, one of said filters being arranged to pass only light of reference beam wavelength and the other filter being arranged to pass only light of measure beam wavelength.

13. The dual wavelength photometer of claim 12, and wherein one filter is arranged to pass light only of 448 nm wavelength andthe other filter is arranged to pass only light of 439 nm wavelength.

14. The dual wavelength photometer of claim 1, and wherein said time-sharing duochromator means comprises a light source, a rotating member located between said light source and said sample-supporting means, said rotating member having two spaced filters arranged to be alternately interposed between the light source and the sample-supporting means, one filter being arranged to pass only light of reference beam wavelength and the other filter being arranged to pass only light of measure beam wavelength, and rotary drive means connected to said rotating member, and wherein said keying means comprises a rotary disc member coupled to said drive means, an auxiliary light source on one side of said disc member, a second photosensitive device on the other side of said disc member, said disc member having an aperture located so as to become aligned with said auxiliary light source and said second photo-sensitive device simultaneously with the interposition of one of said filters between the first-named light source and said sample supporting means, circuit means operatively connecting said second photosensitive device to one of said keyed circuit means, and means to operate the other keyed circuit means after a time delay corresponding to the spacing between the two filters.

15. The dual wavelength photometer of claim 14, and wherein the means to operate the other keyed circuit means comprises a timed signal-generating circuit connected between said second photosensitive device and said other keyed circuit means, said timed signal-generating circuit having means to generate an output signal at a time delay after excitation thereof corresponding to the spacing between the two filters.

16. The dual wavelength photometer of claim 1, and a logarithmic amplifier connected between said photosensitive device and said steady signal generating amplifiers.