(XX.) Pneumotachography:
estimation of airway resistance
Physiology  - practical
Physiology department LF MU, 2015 © Michal Pásek

Pneumotachography is a method enabling estimation of airways resistance. It measures pressure
difference between two ends of tube through which the examined person breathes.
•Increased value of airways resistance indicates obstruction of the airways.

•Volume flow (Q) in rigid tube equals directly to pressure gradient between beginning and end of
the tube (DP=PA-PB), the fourth power of its radius (r) and indirectly to its length (l) and
viscosity of the fluid (h)
•
• p · DP · r4
•Q =
• 8 · l · h
•
•
•
•
•PA
•PB
•l
•r
•Poiseuille - Hagen law
•R is tube resistance against to gas flow
•=
•DP
•R

Resistance of airways
•
•Resistance of airways (Rd) results from inner friction between flowing gas and airways wall.
•
• p · rd4
•Rd =
• 8 · l · h
•DP
•Q
•=
•Small change of airways radius (rd) causes substantially bigger change of airways resistance to
air flow (Rd). Airways obstruction may be caused by chest compression, mucosal swelling, or smooth
muscles constriction in airways.

Principle of pneumotachograph
•DPp= Pp - Patm
•DPalv= Palv - Patm
•exp.
•insp.
•
•
•
•ΔPalv
•ΔPp
•ΔPatm
•
•Q
•Tube of pneumotachograph
•valve
•trachea
•lungs

•
Calculation of airways resistance
•DPp= Pp - Patm
•DPalv= Palv - Patm
•
•Q
•
•= Q =
•Pp-Patm
•Palv-Pp
•Rp
•Rd
•1
•DPalv
•[
•DPp
•Rd = Rp·
•]
•
•Rd
•Rp
•Tube of pneumotachograph
•valve
•trachea
•lungs

Pictures:
•Slide 5, 6 – Physiology and Neuroscience Practicals, Masaryk university 2013
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