Two-dimensional ultrasound imaging of the diaphragm: quantitative values in normal subjects.

Introduction: Real time ultrasound imaging of the diaphragm is an under-used tool in the evaluation of patients with unexplained dyspnea or respiratory failure.

Methods: We measured diaphragm thickness and the change in thickness that occurs with maximal inspiration in 150 normal subjects, with results stratified for age, gender, body mass index, and smoking history.

Results: The lower limit of normal diaphragm thickness at end expiration or functional residual capacity is 0.15 cm, and an increase of at least 20% in diaphragm thickness from functional residual capacity to total lung capacity is normal. A side to side difference in thickness at end expiration of > 0.33 cm is abnormal. Diaphragm thickness and contractility are minimally affected by age, gender, body habitus, or smoking history.

Conclusions: This study confirms previous findings in much smaller groups of normal controls for quantitative ultrasound of the diaphragm and provides data that can be applied widely to the general population.