Describe the PHYSICAL PRINCIPLES that are involved in the flow of blood through a dialysis circuit, and, in the movement of solutes across a dialysis membrane.

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College Answer

This question required candidates to describe the physical principles of blood flow
through a dialysis circuit and the movement of solute across a dialysis membrane.
While most candidates were able to allude to important factors contributing to the
flow of a fluid through a hollow tube, few did so in a systematic way and only some
provided relevant formulae showing the relationship between pressure, fluid viscosity
and tube resistance. A short discussion proceeding to flesh out the factors that
determine blood viscosity, circuit pressures and practical examples was expected.
Some candidates discussed convective processes extensively, which was not
required in this question focussed on dialysis. Most candidates were able to describe
the physical chemistry involved in diffusion across a semipermeable membrane in
basic terms, however few provided sufficient details of these important principles.
Very few candidates went on to properly discuss electrochemical forces affecting
solute and water movement across a membrane or the factors that influence the
performance of dialytic therapies in practical application.
Syllabus: A2c, R2e, D1, 2b,c
Recommended sources: Basic Physics and Measurement in anaesthesia, Davis and
Kenny, various sections. Also Review of Medical Physiology, Ganong, chp 2, 32