Comparison of two methods of measurement of maximal respiratory pressures in health and cystic fibrosis

Introduction: Respiratory muscle strength can be assessed by static mouth measurements of maximal inspiratory pressure (Pimax) and maximal expiratory pressure (Pemax). Impaired respiratory muscle strength is common in neuromuscular and obstructive pulmonary disease such as Cystic Fibrosis (CF). Maximal respiratory pressures can easily be measured with a portable manometer on the bedside and in the community. Our objective was to compare maximal respiratory pressures as measured by standard laboratory equipment and the portable mouth pressure meter Micro RPM. Methods: Pimax and Pemax were assessed in 296 healthy subjects and patients with CF with the Micro RPM and standard laboratory equipment. The Micro RPM measures and digitally displays maximal respiratory pressures after averageing over a one second period. Standard laboratory equipment consisted of a differential pressure transducer, whose amplified signals were analyzed by Lab-VIEW software. Each subject performed at least five reproducible maneuvers after familiarizing with the equipment. Results: The Micro RPM accurately measured maximal inspiratory and maximal expiratory pressures both in healthy individuals as well as in patients with CF. Mean difference (standard deviation) of the methods was 1.37 (17.73) cm H2O for Pimax maneuvers and 1.84 (9.09) cm H2O for Pemax maneuvers. Conclusions: The Micro RPM can reliably and accurately measure maximal respiratory mouth pressures and its use could be applied both in the clinical and the research setting.