Maximal inspiratory pressure: does the choice of reference values matter?

Abstract

Background: Single-point measurements of maximal inspiratory pressure (MIP) are frequently used to suggest inspiratory muscle weakness. Although there is substantial disparity among predicted MIP according to specific regression equations, it remains unclear whether those discrepancies impact on the diagnosis of inspiratory muscle weakness in clinical practice. Methods: 1729 consecutive subjects (50.1% males, aged 18 to 94) who underwent MIP measurements in a reference laboratory. MIP was predicted according to the most cited MIP reference values. Diagnosis/suspicion of neuromuscular disease in a subject with restriction by body plethysmography indicated a “high” pre-test probability of weakness. Results: Prevalence of weakness ranged from 33.4 % ( Enright et al. ) to 66.9 % ( Neder et al.). Black and Hyatt, Neder et al., and Bruschi et al. agreed well in indicating weakness (κ values ranging from 0.74 to 0.80; p Enright et al., Harik-Khan et al., Wilson et al. had a high pre-test likelihood of weakness. Absolute MIP values at which most equations agreed to indicate weakness in both genders were 2 O ( 2 O (40-80 yrs) and 2 O(> 80 yrs). Conclusion: Prevalence of inspiratory muscle weakness is influenced by the reference values used for MIP prediction. Some specific regression equations are more closely related to clinical and physiological features suggestive of inspiratory muscle weakness than others.