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Anatomy and physiology

In healthy individuals without any pathological conditions of the airways, factors that determine PEF include:
  • the quality of the large airways
  • the volume of the lungs (a function of thoracic dimensions and the individual's stature)
  • the elastic properties of the lungs (the degree of stretch the lungs have been subjected to previously and the recoil ability of the lungs)
  • the power and co‐ordination of the expiratory muscles, primarily the abdominal muscles (related to lung inflation and the speed with which maximum alveolar pressure is reached)
  • the resistance of the instrument used to measure PEF (Cavill and Kerr [36], Chapman et al. [38]).
Any condition that alters any of the above factors could affect PEF. However, a reduction in one of these factors may be compensated for by an increase in one of the others, meaning that PEF may not alter, resulting in staff potentially underestimating the severity of the patient's condition (Dakin et al. [50], Hill and Winter [82]).
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