Prediction for the maximum inspiratory pressure value from the thoracic expansion measurement in Indonesian healthy young adults

Background The diaphragm is the primary muscle responsible for breathing. Weakness in the diaphragm will result in breathing difficulties. The micro-RPM (respiratory pressure meter) is a non-invasive testing device to measure respiratory muscle strength, which is not always feasible, while thoracic expansion measurements are easy to do. Aim This study constructs a prediction formula for a maximal inspiratory pressure (MIP) value from thoracic expansion measurements. Methods This study was quantitative with a cross-sectional design. Participants were healthy adults aged 20–40 years, with normal Mini-Mental State Examinations, body mass index, spirometry, and moderate activity levels. The tests performed were MIP and thoracic expansion measurements at three levels: axilla (L1), the fourth intercostal space (L2), and at processus xiphoideus (L3). The data were analyzed using an unpaired t-test and multivariate. Results The mean MIP for males (81.51 ± 13.90 cmH2O) was significantly greater than females (63.17 ± 15.89 cmH2O) (P = 0.0001). These findings were not different with the Chinese, Indian, Mangalorean, and Malaysian populations because they are all of Asian ethnicity. Thoracic expansion L2 (r = 0.463, P = 0.0001) and L3 (r = 0.502, P = 0.0001) were moderately correlated with MIP, whereas thoracic expansion L2, L3 combined with gender had a weak effect on MIP. The prediction formula was: MIP = 56.802 + 2.387 + L2 + 13.904 + Gender * and MIP = 53.289+ 3.561 + L3 + 9.504 + Gender *, * 0 = female; 1 = male. Conclusions A prediction formula for MIP can be made using the thoracic expansion variable with gender as a determinant factor. A quick and easy measurement of thoracic expansion can be used as a mean of screening respiratory muscle strength in patient care.