Maximum static respiratory pressures in healthy elderly men and women: Issues of reproducibility and interpretation

Background: Respiratory muscle strength is assessed using the static pressure generated at the mouth during a maximal inspiratory or expiratory effort [PImax and PEmax, respectively (MSRPs)]. Interpretation of MSRPs relies upon comparison with 'normal' values, but MSRPs show very weak associations with predictors such as physical characteristics. The influence of habitual physical activity upon MSRPs remains undefined. Objectives: We examined measurement reproducibility, as well as the influence of physical characteristics and habitual physical activity upon MSRPs in healthy elderly people. Methods: MSRPs were assessed in 41 healthy subjects using a portable mouth pressure meter on two occasions, 1 week apart. Physical activity was assessed in 10 subjects by diary record. Pearson product-moment correlation coefficients were used to assess the association of MSRPs with other measured variables. Results: There was good measurement reproducibility of MSRPs, with coefficients of reproducibility of 10.2 and 12.8% for PImax and PEmax, respectively. MSRPs showed statistically significant negative correlations with age, but correlations with physical characteristics were poor, in contrast, MSRPs were highly correlated with physical activity. Conclusions: We conclude that MSRPs can be measured reproducibly and that they decline with advancing age. Physical characteristics are not good predictors of MSRPs; this may be due to a strong confounding influence of physical activity making interpretation of measurements problematic. We suggest that the poor predictive power of physical characteristics indicate that reference to 'normal' values be made with caution and that it may be more appropriate to consider functional interpretations of MSRPs based upon factors such as lung and chest wall elastance.