Software compensation for lung volume in assessment of inspiratory muscle strength and endurance

BACKGROUND--To increase the sensitivity of measurements of maximal inspiratory pressure (MIP) as a test of inspiratory muscle strength and endurance, software was developed to correct for variation in lung volume. METHODS--Using a body plethysmograph to determine absolute lung volume during each manoeuvre, values for MIP were expressed as a percentage of the pressure "expected" from the unfatigued MIP/lung volume relation in each subject. RESULTS--The method reduced the variance in peak and average pressure during a series of 18 MIP manoeuvres of 10 seconds duration separated by rest intervals of 10 seconds. CONCLUSIONS--The correlation between average pressure and contraction number was improved significantly by the MIP/lung volume correction. This simple correction has many applications in measurements of the MIP.