Capacity of PImax and SNIP for the Diagnosis of Respiratory Muscle Weakness

Introduction: Chronic respiratory diseases and neuromuscular disorders are associated with respiratory muscle weakness, one of the main causes of development of respiratory failure. In patients with suspected respiratory muscle weakness, maximal inspiratory pressure (PImax), maximal expiratory pressure (PEmax), sniff nasal inspiratory pressure (SNIP) or forced vital capacity (FVC) measurement in seated and supine position are diagnostic methods of such pathology. This study’s aim is to determine diagnostic accuracy for respiratory muscle weakness when PImax and SNIP separately and in combination. Material and methods Descriptive cross-sectional study, in which the value of the PImax, PEmax and SNIP have been collected, alongside seated and supine position FVC spirometry testing between January and June 2021 in a tertiary university hospital. Results: Sample size was 100 patients. Mean age was 56.8 years (+/− 17.6) and 53% were male. Pathological threshold of PImax were one-third of reference values based on sex and age. SNIP value less than 35% of normal value according to the sex and age of the patients was considered pathological. Patients that were referred to a specialized laboratory for assessment of possible respiratory muscle weakness showed diagnosis in 18% by PImax, 57% by SNIP and 16% by PImax plus SNIP. Conclusions: Individualized assessment of the PImax and SNIP tends to overdiagnose respiratory muscle weakness, hence that both tests should be regarded not as interchangeable but as complementary for diagnosis.