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Software compensation for lung volume in assessment of inspiratory muscle strength and endurance
D K McKenzie1, S C Gandevia, R B Gorman
1Department of Respiratory Medicine, Prince of Wales Hospital, Sydney, Australia.
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.