Double-Slit Photometric Measurement of Velocity Profiles of Blood in Microvessels and Capillary Tubes

Citation

Baker, Mary (1972) Double-Slit Photometric Measurement of Velocity Profiles of Blood in Microvessels and Capillary Tubes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/DDWS-GF91. https://resolver.caltech.edu/CaltechETD:etd-12162005-112315

Abstract

The extreme blunting of velocity profiles for human blood, reported from double-slit photometric measurements, has been shown to be an artifact of the measuring technique. The velocities measured are actually an average of velocities throughout the tube. An equation developed to model this averaging predicts profiles which agree with experimental results. This model explains the increase in blunting with decreasing tube diameter previously reported even if the true profiles remain parabolic.

A trial and error method was chosen to extract information about the actual velocity distributions from double-slit measurements. Trial profiles were calculated using a τ versus γ^. relationship derived from bulk rheological measurements. The data of Barbee for τ_W versus ⩂ and for tube relative hematocrit were used. When these trial profiles were averaged with the model for double-slit averaging, they were consistent with double-slit measurements. Neither the calculated nor measured profiles gave any evidence of substantial blunting except for ⩂<2 sec^-1 where yield stress becomes important.

Although the continuum approach was used to calculate trial profiles, limitations in the continuum representation were evident from hematocrit considerations. No hematocrit distribution could be found that resulted in calculated profiles which produced both the correct volume flow rate and correct outflow hematocrit.

A simple correction procedure is described for calculating volume flow rates from double-slit centerline velocity measurements.

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