The value of multiple tests of respiratory muscle strength

Abstract

Background: Respiratory muscle weakness is an important clinical problem. Tests of varying complexity and invasiveness are available to assess respiratory muscle strength. The relative precision of different tests in the detection of weakness is less clear, as is the value of multiple tests. Methods: The respiratory muscle function tests of clinical referrals who had multiple tests assessed in our laboratories over a 6-year period were analysed. Thresholds for weakness for each test were determined from published and in-house laboratory data. The patients were divided into three groups: those who had all relevant measurements of global inspiratory muscle strength (group A, n = 182), those with full assessment of diaphragm strength (group B, n = 264) and those for whom expiratory muscle strength was fully evaluated (group C, n = 60). The diagnostic outcome of each inspiratory, diaphragm and expiratory muscle test, both singly and in combination, was studied and the impact of using more than one test to detect weakness was calculated. Results: The clinical referrals were primarily for the evaluation of neuromuscular diseases and dyspnoea of unknown cause. A low maximal inspiratory mouth pressure (PImax) was recorded in 40.1% of referrals in group A, while a low sniff nasal pressure (Sniff Pnasal) was recorded in 41.8% and a low sniff oesophageal pressure (Sniff Poes) in 37.9%. When assessing inspiratory strength with the combination of all three tests, 29.6% of patients had weakness. Using the two non-invasive tests (PImax and Sniff Pnasal) in combination, a similar result was obtained (low in 32.4%). Combining Sniff Pdi (low in 68.2%) and Twitch Pdi (low in 67.4%) reduced the diagnoses of patients with diaphragm weakness to 55.3% in group B. 38.3% of the patients in group C had expiratory muscle weakness as measured by maximum expiratory pressure (PEmax) compared with 36.7% when weakness was diagnosed by cough gastric pressure (Pgas), and 28.3% when assessed by Twitch T10. Combining all three expiratory muscle tests reduced the number of patients diagnosed as having expiratory muscle weakness to 16.7%. Conclusion: The use of single tests such as PImax, PEmax and other available individual tests of inspiratory, diaphragm and expiratory muscle strength tends to overdiagnose weakness. Combinations of tests increase diagnostic precision and, in the population studied, they reduced the diagnosis of inspiratory, specific diaphragm and expiratory muscle weakness by 19-56%. Measuring both PImax and Sniff Pnasal resulted in a relative reduction of 19.2% of patients falsely diagnosed with inspiratory muscle weakness. The addition of Twitch Pdi to Sniff Pdi increased diagnostic precision by a smaller amount (18.9%). Having multiple tests of respiratory muscle function available both increases diagnostic precision and makes assessment possible in a range of clinical circumstances.

Pulmonary function in adolescents with ataxia telangiectasia

“…It has been recognized that PI max and PE max testing may overdiagnose muscle weakness and additional tests, albeit more invasive (i.e., sniff maneuvers or measurement of cough gastric pressure) may be more useful in increasing diagnostic accuracy. 27 Nevertheless, the consequence of expiratory muscle weakness in A-T is potentially significant. Expiratory muscle weakness may be associated with impaired clearance of airway secretions, contributing to the increased risk of pulmonary complications during respiratory illness in this population.…”

Maximal respiratory pressure in healthy 20 to 89 year-old sedentary individuals of central São Paulo State

“…The evaluation of respiratory muscle strength through maximal respiratory pressure (MRP) has been used since the 1960s and 70s because of its important diagnostic and prognostic role in neuromuscular 10 , lung 11 and cardiovascular 12 disease. It is a quick, simple, practical, low-cost and non-invasive method [13][14][15] for the evaluation of both healthy individuals and individuals with certain chronic diseases 2 .…”

Postoperative Phrenic Nerve Palsy, A Cause Of Prolonged Mechanical Ventilation In Trans-Sternal Thymectomy

“…With bilateral disease, vital capacity may fall to 50% of predicted 18 . Maximal inspiratory pressures fall to 80% and 30% of predicted, with unilateral and bilateral paralysis, respectively 19 .…”