Study objective: A technique for assessing expiratory muscle strength is the measurement of maximal expiratory pressure (PEmax). Previous studies have shown that a tube-style mouthpiece yields greater PEmax values than a flange-style mouthpiece because the latter technique is limited by the strength of the buccal muscles. In individuals with weak muscles of exhalation, this limitation may not apply because the strength of their buccal muscles may exceed that of the respiratory muscles.
Design: A tube-style mouthpiece and flange-style mouthpiece were used to measure PEmax. The order of the mouthpiece used in testing was alternated between subjects and the greatest values obtained after three efforts were compared.
Setting: Department of Veterans Affairs Medical Center.
Participants: Fifty subjects with chronic spinal cord injury without acute medical illnesses recruited from veterans and the community.
Results: The mean difference between PEmaxtube and PEmaxflange was 20.7±26.4 cm H2O (p=0.0001). Differences were negligible in those with the weakest muscles of exhalation but were substantial even in some quadriplegic subjects.
Conclusion: Even in individuals with neuromuscular disorders, errors in assessment of expiratory strength occur when a flange-style mouthpiece is used, and we recommend that this technique be abandoned in the measurement of PEmax.