Differences in Diaphragmatic and Chest Wall Excursion During Quiet Breathing According to Body Position: Dynamic Analysis by MRI

Background and Purpose: The diaphragm is the largest contributor to respiration but is highly influenced by position. Therefore, despite understanding the importance of “positioning” in respiratory physiotherapy, research on diaphragmatic excursion between body positions remains insufficient. This study examined the differences in diaphragm and chest wall excursion between supine, prone, and left and right side-lying positions to investigate the most suitable position for ventilation. Methods: Diaphragmatic excursion, as well as the lateral and anteroposterior diameters of the chest walls of 40 healthy adults (20 males and 20 females), was dynamically imaged during quiet breathing in 4 positions using magnetic resonance imaging, and the amount of excursion was calculated. The Friedman test was used for statistical analysis to compare differences in diaphragmatic and chest wall excursions. Results: The median age was 21.0 years, the median BMI was 20.8 kg/cm 2 , and all pulmonary function values were normal and within the reference values based on Japanese predicted normal values. The diaphragm and chest wall exhibited significantly greater excursion in the prone position than in other positions ( P < .001). In the side-lying position, the anteroposterior diameter excursion of the lower chest wall on the unloaded side was significantly greater ( P < .005). However, there was no significant difference between the side-lying and supine positions ( P > .05). Conclusions: Diaphragmatic and chest wall excursion during quiet breathing was found to be significantly greater in the prone position than in other positions. This suggests that the prone position is the optimal “positioning” for increased ventilation and may contribute to the prevention of respiratory complications.