### Abstract

A method for the measurement of the hematocrit of blood flowing in small-bore glass tubes (H_{T}) is examined which relies upon a linear relationship between the difference in optical densities (ΔOD) at two isobestic wavelengths for oxy- and deoxyhemoglobin (546 and 520 nm) and the product of H_{T} and luminal diameter (D_{T}). The foundation for the technique has been shown to be firmly based upon the principles that: (1) The total optical density of blood flowing in a smallbore glass tube may be expressed as the sum of a pure absorption term (OD_{abs}), which is linear with H_{T}, and a nonlinear scattering term (B); and (2) at two closely spaced wavelengths, the scattering terms are approximately equal such that subtraction of the two total optical densities results in a term linearly proportional to the product of the difference in molecular extinction coefficients (Δε), hemoglobin concentration, and path length, D_{T}. These relationships were examined for the case of blood flowing in tubes ranging from 40 to 70 μm in luminal diameter and yielded a linear relationship of ΔOD = (ε_{546} - ε_{520})c_{cell} × H_{T}D_{T}, where c_{cell} is the mean corpuscular hemoglobin concentration. The slopes of these calibration curves, obtained for hemoglobin solutions and red cell suspensions, agreed with macrospectrophotometric values of Δε to within 2 and 12%, respectively. Simulation of a blanket application of the method to the measurement of H_{T} in these tubes revealed an accuracy of 11.6% (rms error) between values of H_{T} computed from the regression curve and those obtained by centrifugation. It is also shown that by choosing isobestic wavelengths with extinction coefficients in the ratio of 2:1, the scattering term may be computed from the relationship B = OD_{520} - ΔOD; and that variations in B attendant to red cell shape changes, as for example in the case of the sickling of Hb SS cells during deoxygenation, may be easily evaluated.

Original language | English (US) |
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Pages (from-to) | 42-55 |

Number of pages | 14 |

Journal | Microvascular Research |

Volume | 24 |

Issue number | 1 |

DOIs | |

Publication status | Published - Jul 1982 |

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### All Science Journal Classification (ASJC) codes

- Biochemistry
- Cardiology and Cardiovascular Medicine
- Cell Biology

### Cite this

*Microvascular Research*,

*24*(1), 42-55. https://doi.org/10.1016/0026-2862(82)90041-3