BACKGROUND: Respiratory muscle interaction is further profoundly affected by a number of pathologic conditions. Hyperinflation may be particularly severe in chronic obstructive pulmonary disease(COPD) patients, in whom the functional residual capacity(FRC) often exceeds predicted total lung capacity(TLC). Hyperinflation reduces the diaphragmatic effectiveness as a pressure generator and reduces diaphragmatio contribution to chest wall motion Ultrasonography has recently been shown to be a sensitive and reproducible method of assessing diaphragmatic excursion. This study was performed to evaluate how differences of diaphragmatic excursion measured by ultrasonography associate with normal subjects and COPD patients. METHODS: We measured diaphragmatic excursions with ultrasonography on 28 healthy subjects(16 medical studentz 12 age-matched control) and 17 COPD patientc Ultrasonographic measurements were performed during tidal breathing and maxima] respiratory efforts approximating vital capacity breathing using Aloka KEC-620 with 3.5 MHz transducen Measurements were taken in the supine posture. The ultrasonograpbic probe was positioned transversely in the midclavicular line below the right subcostal margin After detecting the right hetnidiaphragm in the B-mode the ultrasound beam was then positioned so that it was approximately parallel to the movement of middle or posterior third of right diaphragm. Recordings in the M-inodc at this position were made throughout the test Measurements of diaphragmatio excursion on M-mode tmcing were calculated by the average gap in 3 times-respiration cycle. Pulmonary functicn test(SensorMedics 2800), maximal inspiratory(Plmax) and expiratory mouth pressure(PEmax, Vitalopower KH-101, Chest) were measured in the seated posture. RESULTS: During the tidal breathing, diaphragmatic excursions were recorded 1.5 +/-0.5cm, 1.7+/-0.5cm and 1.5 +/- 0.6cm in medical students, age-matched control group and COPD patients, respectively. Diaphragm excursions during maximal respiratory efforts were significantly decreased in COPD patients (3.7+/-1.3cm) when compared with medical students, age-matched control group(6.7+/-1.3cm, 5.8+/-1.2cm, p<0.05). During maximal respiratory efforts in control subjects, diaphragm excursions were cowelatal with FEV1, FEV1/FVC, PEF, PIF, and height. In COPD patients, diaphragm excursions during maximal respiratory efforts were correlated with PEmax(maxinIal expiratory pressure), age, and %FVC. In multiple regression analysis, The combination of PEmax and age was an independent marker of diaplngnt excursions during maximal respiratory efforts with COPD patients. CONCLUISON: COPD subjects had smaller diaplragmatic excursions during maximal respintoty efforts than control subjects. During maximal respiratory efforts in COPD patients, diaphragm excursions were well correlated with PEmax. Those results suggest that diaphragm excursions during rnaximel respiratory efforts with COPD patients may be valuable at predicting the pulnionmy function.