Abstract
Flow of blood into the microcirculation becomes progressively slower until, in the finest vessels, the average velocity approaches zero. The pressure gradient also falls progressively until it too approaches zero.
The effect of pressure gradient on blood flow may be studied in tubes of any convenient size; in this report a tube 0.55 mm in diameter was used.
Owing to the great variability in flow resistance of samples prepared in identical fashion from different subjects, simple viscosity measurements at a single pressure gradient will produce only an array of viscosities. An innovation was adopted: two pressure gradients, one of which was the lowest practicable and the other two and one-half times greater, were employed to produce a basis for an “internal comparison”. The ratio between the two apparent viscosities is a dimensionless number that characterizes the sample.
By our method all Newtonian liquids of whatever viscosity must yield a ratio of 2.5. Our experimental samples, which were 87% red cell suspensions, produced a range of ratios from 1.6 to 9.7.
Normal subjects and patients with diseases other than cancer had ratios above 4.0, In marked contrast, patients with cancer occupied the range below 3.9.
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