Respiratory muscular strength in children with mucopolysacaridosis: comparison with predictive equations.

Background: Mucopolysaccharidoses (MPS) are rare metabolic diseases that impair respiratory function leading to respiratory failure. This study aimed to compare maximal inspiratory and expiratory pressures (MIP and MEP) obtained in children with MPS and compare with predicted values from previous studies involving healthy children.

Methods: This is a cross-sectional study, in which the chest deformity was evaluated; MIP, MEP through digital manometer, and lung function through spirometry. MIP and MEP were compared with five different predict equations and with a control group of healthy children. Agreement between respiratory muscle weakness regarding absolute values of MIP and MEP in relation to predictive values by the equations included in the study were assessed by Kappa coefficient.

Results: MPS group was composed of 22 subjects. 45.5% had pectus carinatum, 36.4% pectus excavatum, and presented lower MIP (37.14±36.23 cmH2O) and MEP (60.09±22.3 cmH2O) compared with control group (22 healthy subjects) (MIP: 91.45±35.60; MEP: 95.73±22.38). Only the MEP equations proposed by Tomalak et al. were close to those found in our MPS children (P=0.09). In the MPS group it was observed a weak agreement between inspiratory weakness through absolute and predicted values in only two equations: Tomalak et al. and Domenèch-Clar et al. (for both: k=0.35, P value =0.03); and for MEP a moderate agreement was found using all predictive equations.

Conclusions: In MPS children MRP data should not be normalized using the reference equations for healthy ones, is more coherent to longitudinally follow absolute pressures and lung volumes in this group.