Describe the factors that affect airways resistance
Candidates who used a structured approach of using formulae that describe resistance fluid
flow scored well. Poiseuille’s law describes the determinates of resistance to laminar fluid flow
and provides a useful answer structure. The most common mistakes were confusion between
resistance and compliance as well as failure to describe turbulent as well as laminar flow.
The question asked specifically for airways resistance, and the candidates would have probably not earned any marks if they discussed other contributing elements (eg. inertance, tissue resistance and the effect of gas compression). Ergo, only airway stuff is listed here:
A main determinant of airway resistance is whether the flow is laminar or turbulent. This depends on the Reynolds number, which is a dimensionless metric determined by:
Thus, the factors which affect airway resistance are:
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