Determination of normal values for an isocapnic hyperpnea endurance test in healthy individuals

Respiratory Muscle Endurance (RME) is an alternative way to assess respiratory muscle impairment but normal values are lacking to use this test in a clinical perspective. Our objective was then to determine reference values of RME in healthy subjects. We recruited 161 healthy subjects (25-80 years old) who were distributed within 5 groups with a 10-year range. We measured vital capacity (VC) and maximal respiratory pressure (MIP, MEP). The RME test consisted of isocapnic hyperpnea at increasing levels of ventilation until exhaustion to determine Tlim (expressed in minutes and as percentage of maximal voluntary ventilation, MVV). A significant difference between age-groups was observed for both VC and MEP expressed as percentage of predicted value. Mean Tlim was 21.8±5.9min [95% confidence interval 20.9-22.8], 74.4±15.9% of predicted MVV [95% CI 71.8-76.9]. Tlim was similar among age groups. Tolerance to the RME test was excellent. This study provides normal values of RME in a large age range of healthy subjects and demonstrates that RME is preserved in the elderly.