To evaluate respiratory muscle strength in healthy Korean children in order to establish the criteria for normal reference values for future applications. In contrast with the other parameters for testing pulmonary function, normal values for respiratory muscle strength in healthy Korean children have not been assessed to date.

We conducted a complete survey of 263 students at Sinmyung Elementary School in Yangsan, Gyeongsangnam-do, and measured their height and body weight, performed pulmonary function tests, and evaluated maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) as measures of respiratory muscle strength. We excluded the subjects with respiratory or cardiovascular diseases that could affect the results. The subjects were children aged 8–12 years, and they consisted of 124 boys and 139 girls.

The MIP and MEP values (mean±standard deviation) for the entire subject group were 48.46±18.1 cmH₂O and 47.95±16 cmH₂O, respectively. Boys showed higher mean values for MIP and MEP in every age group. Korean children showed lower mean values for MIP and MEP compared to those in previous studies conducted in other countries (Brazil and USA).

Our results showed that boys generally have greater respiratory muscle strength than girls. We found a significant difference between the results of our study and those of previous studies from other countries. We speculate that this may be attributed to differences in ethnicity, nutrition, or daily activities.

To determine the abnormal pulmonary function value in Korean Duchenne muscular dystrophy (DMD) patients, we performed a comparative analysis of the patients' pulmonary function value expressed as % of the overseas reference data and Korean healthy children and adolescent reference data.

We performed pulmonary function test (PFT) in a total of 27 DMD patients. We compared the patients' FVC% and FEV1% of the overseas reference data with those of the Korean children and adolescent reference data. Also, we compared the patients' MIP% and MEP% of the prediction equation data with those of the Korean children and adolescent reference data.

Age of the subjects ranged from 8 to 16 years (12.03±2.27 years). The mean maximal expiratory pressure (MEP), maximal inspiratory pressure (MIP), vital capacity (VC), forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), and peak cough flow (PCF) were 36.93±9.5 cmH₂O, 45.79±17.46 cmH₂O, 1.4±0.43 L, 1.45±0.45 L, 1.40±0.41 L, and 206.25±61.21 L/min, respectively. The MIP%, MEP%, and FVC% of the Korean children and adolescent reference data showed statistically significant higher values than those of the prediction equation data.

We observed a clear numeric difference between Korean DMD patients' pulmonary function value expressed as % of the overseas data and inland data. To perform a precise assessment of respiratory function and to determine appropriate respiratory therapy, pulmonary function values of Korean DMD patients should be interpreted taking into account the inland normal pulmonary function test data.