โ Scribed by B. Chance; H.L. Liu; T. Kitai; Y.T. Zhang
No coin nor oath required. For personal study only.
Perturbations of scattering background for absorbance measurements by photon diffusion techniques complicate algorithms used for determining the concentration of blood and the saturation of hemoglobin in tissues. In order to better define these perturbations, we have undertaken a study of the effect of solutes, some of physiological importance, upon the scattering of three types of model systems: a lipid vessel suspension (Intralipid), a cell suspension (Baker's yeast), and a tissue (perfused liver). A simple formula relates absorbancy change to proportional changes of the input/output separation (\rho) and the square root of (\mu_{\mathrm{a}}) and (\mu_{\mathrm{s}}^{\prime}) in relation to a relevant model system. Thus, absorbance changes at (850 \mathrm{~nm}) and slopes and intercepts are measured as a function of (p); the absorption and reduced scattering coefficient, (\mu_{\mathrm{a}}) and (\mu_{\mathrm{s}}^{\prime}), are calculated. We studied each of these cases as a function of the perturbation induced by low-molecular-weight polyhydroxy solutes, generally sugars (mannitol, fructose, sucrose, and glucose), alcohols (propanediol and methanol), and electrolytes (sodium and potassium chloride). Dilatometric studies indicate volume changes of the solvent system and afford correction factors. The slopes are (\sim-1 \pm 0.5 \times 10^{-4} \mathrm{OD} / \mathrm{mm}) solute per centimeter separation of input/output per percent scatter (yeast or Intralipid) and indicate possible physiological detection of solutes in tissues in the millimolar range. The large optical effects of temperature upon the solute effect on model systems and of osmotic and perfusion pressures on the perfused liver further complicate the possibility of quantitative in vivo studies of these solutes. 1995 Academic Press, Inc.
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