Ensemble-Averaged Measurement of Stochastic Motion By Current-Modulating of VCSEL Wavelength

An in-vivo method for measuring at least one blood parameter, the method comprising:

• a. operating a VCSEL in n Hz/m nm wavelength-fluctuation mode (n≥2) by varying an amount of electrical current delivered to the VCSEL to cause at least n distinct m nm wavelength-increase-decrease events per second where for each wavelength-increase-decrease event, an increase in an effective wavelength of the VCSEL of at least m nm is followed by a decrease of the effective wavelength of the VCSEL of at least m nm, a value of n being at least 2 and a value of m being at least 0.5, the time-dependence of an instantaneous amount of current defining a function I(t), the time-dependence of an instantaneous effective wavelength of the VCSEL being λEFFECTIVE(t);
• b. illuminating skin containing occluded blood by the VCSEL that is operating in n Hz/m nm wavelength-fluctuation mode to generate an optical response of light scattered by red blood cells (RBCs) within the occluded blood;
• c. receiving at least some of the RBC-scattered light into photodetector(s) to generate an electrical representation of the optical signal;
• and
• d. sampling the electrical representation of the optical signal to obtain a sample point set Sample_Point_Set={(st1,MV(st1)), (st2,MV(st2)),) . . . (stP, MV(stP)),} of sample points, each sample point (sti,MV(sti)) being an ordered pair where measurement value MV(sti) describes the optical signal at a different respective sampling-time sti;
• e. classifying each sample point (sti,MV(sti)) of the sample point set Sample_Point_Set, according to an instantaneous effective-wavelength λEFFECTIVE(sti) of the VCSEL at its sampling time sti, into a VCSEL-wavelength category Cat(j) selected from a plurality of VCSEL-wavelength categories {Cat1 . . . CatQ};
• f. for each given VCSEL-wavelength category Catj of the plurality of VCSEL-wavelength categories {Cat1 . . . CatQ} forming, from the sample points classified into the given VCSEL-wavelength category Cat(j), a respective VCSEL-wavelength-category-specific sample point set VCSEL_wavelength_specific_sample_points(Cat(j)) of sample points {(s(1_CAT(j),MV(st1_CAT(j)), (st2_CAT(j),MV(st2_CAT(j)), . . . }
• g. for each given VCSEL-wavelength category Catj of the plurality of VCSEL-wavelength categories {Cat1 . . . CatQ}, processing its VCSEL-wavelength-category-specific sample point set VCSEL_wavelength_specific_sample_points(Cat(j)) to compute therefrom a VCSEL-wavelength-category-specific RBC-motion-descriptive signal Catj (RBC-motion) describing relative motion of the RBCs of the occluded blood from which the light of the VCSEL is scattered;
• i. averaging the RBC-motion-descriptive signals {Cat1(RBC-motion) . . . CatQ (RBC-motion)} to compute a multi-category-averaged RBC-motion-descriptive signal;
• and
• j. computing the blood parameter from the multi-category-averaged RBC-motion-descriptive signal.