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Table 1 Summary of the clinical tests used in the assessment of respiratory muscle strength [63]

From: Ventilator-induced diaphragm dysfunction: translational mechanisms lead to therapeutical alternatives in the critically ill

 TestThreshold valuesAdvantagesDisadvantages
Volitional TestsMaximum static inspiratory pressure (PImax)Male < − 45 cm H2OFemale < − 30 cm H2OEasy to perform.Normal values are availableDifficult interpretation.Lack of specificity
Maximum static transdiaphragmatic pressure (PI,di,max)Male < 40 cm H2O (2)Female < 30 cm H2OEasy to perform. Well tolerated by patients.Wide normal range.Limited usefulness in clinical practice.Limited normal data
Sniff transdiaphragmatic pressure (Sniff Pdi)Male < 100 cm H2O (2)Female < 70 cm H2ORequires little practice. It is relatively reproducible.Range of normal valuesTechnical limitationsVariability.
Maximum sniff pressures (nasal)Male < 50 cm H2OFemale < 45 cm H2O
Maximum cough pressureMale < 130 cm H2OFemale < 95 cm H2ONormal ranges availableLimited validation in critically ill patient.
Nonvolitional testsTwitch transdiaphragmatic pressure (PdiTw)Male and female < 18 cm H2OMeasurement specific for the diaphragm and is not influenced by the central nervous systemRequires considerable skill.Uncomfortable for patients
Diaphragm excursion (DE)< 10 cmProvides both morphological and functional information in real time. Allows repeated measurements over time and monitoring recoveryLearning curve.Inter-observer variations.Availability.Reproducibility
Inspiratory diaphragm thickening fraction (TFdi)< 20%