How are results of respiratory muscle strength assessment interpreted in pulmonary function testing?

Updated: May 14, 2020
  • Author: Kevin McCarthy, RPFT; Chief Editor: Nader Kamangar, MD, FACP, FCCP, FCCM  more...
  • Print


As many as 10 efforts are needed before consistency (two measurements within 10% of the highest measured pressure) is achieved in some patients. When respiratory muscle fatigue or neuromuscular disease is present, fatigue may set in before consistency is achieved. Adequate rest between efforts is important.

The range of normal values is broad, suggesting wide variations in respiratory muscle strength among normal values. This makes interpretation of low values difficult. Initial values should be compared to the lower limit of normal values for the patient's age.

In general, a PImax more negative than -80 cm water pressure and a PEmax more positive than +80 cm water pressure excludes important weakness of the respiratory muscles. Patients with a PEmax less than 50 cm water pressure may have difficulty generating sufficient cough to clear respiratory secretions.

In patients with ALS, a SNIF pressure less than 40 cm water was associated with a hazard risk for death of 9.1 (confidence interval [CI], 4-20.8) and the median mortality was 6 ± 0.3 months (95% CI, 2.5-8.5 mo).

Did this answer your question?
Additional feedback? (Optional)
Thank you for your feedback!