Concurrent Validity of a Low-Cost Manometer for Objective Assessments of Respiratory Muscle Strength.

Objective(s): This study examined the agreement in maximal expiratory (MEP) and inspiratory (MIP) pressure readings between two digital manometers: (1) the MicroRPM - the gold-standard manometer for respiratory muscle strength testing; and (2) the LDM - a low-cost, commercially available, alternative manometer.

Methods: Positive (MEP) and negative (MIP) pressures were simultaneously applied to the MicroRPM and LDM using a 3-liter syringe within a controlled laboratory setting. Pressure readings were compared, and agreement was analyzed using Lin's concordance correlation (ρ ). Agreement was interpreted as 'poor' if <0.90, 'moderate' if 0.90 - <0.95, 'substantial' if 0.95 - <0.99, and 'excellent' if ≥0.99. Twenty percent of the pressure trials were repeated by a second researcher to examine test-retest reliability.

Results: A total of 150 trials were completed, ranging from -167 to +208 cmH O. There was a median absolute difference of 0.3 cmH O in pressure readings between the MicroRPM and the LDM. Lin's concordance correlation revealed 'excellent' agreement between the LDM and MicroRPM devices, with test-retest reliability assessment revealing 'substantial-to-excellent' agreement between the LDM and MicroRPM devices, with a concordance correlation coefficient of ρ  = 0.999 (95% CI: 0.999-0.999).

Conclusions: There was a median difference of 1.0% in MEP and MIP pressure readings consistently observed between the LDM and MicroRPM. Despite these relatively small differences, excellent agreement between the two manometers was present. These data suggest the LDM may be a valid, lower cost alternative to the MicroRPM for objectively assessing respiratory strength in clinical practice; however, additional research is needed in healthy adults and in patient populations.

Level Of Evidence: NA Laryngoscope, 134:1831-1836, 2024.