Excursion-volume relation of the right hemidiaphragm measured by ultrasonography and respiratory airflow measurements.

Background: Although real time ultrasonography has been used in the last decade to record diaphragmatic motion, the relation between diaphragmatic excursion and different inspired volumes (VT) has not been assessed by ultrasound.

Methods: Ten normal subjects were studied in the supine posture. Diaphragmatic excursion and VT were assessed simultaneously by M mode ultrasonography and respiratory airflow measurements at different inspired volumes. Ultrasound recordings of the movement of the right hemidiaphragm were carried out in the longitudinal plane subcostally. The transducer was held in a fixed position by a frame, built especially to eliminate any artefactual movement caused by outward motion of the anterior abdominal wall on inspiration.

Results: Mean (SD) maximal diaphragmatic excursion recorded was 6.0 (0.7) cm. Inspired volumes ranged from 15(5%) to 87(10%) of the subjects' inspiratory capacity. A linear relation between diaphragmatic excursion and VT was found in all subjects (r = 0.976-0.995). The regression line had a slope of 1.66 (0.24) cm/l. This slope had no correlation with either the height (r = 0.007) or weight (r = 0.143) of the subjects. In five subjects in whom diaphragmatic excursion could be recorded at volumes near total lung capacity, the relation between diaphragmatic excursion and VT became alinear at very high lung volumes.

Conclusions: The relation between diaphragmatic excursion and VT was linear between 15(5%) and 87(10%) of inspiratory capacity. Ultrasonography of the diaphragm is a simple technique that could be applied in the clinical investigation of patients with suspected abnormalities of diaphragmatic movement.