Assessment of diaphragmatic levels on plain chest radiograph--a new approach.

Background: The aim of this study was to provide an alternate simple linear measurement of diaphragmatic levels from a relatively fixed position, the lung apex, on chest radiographs.

Study Design: 526 consecutive posteroanterior (PA) chest radiographs of Nigerian adult subjects reported as normal were evaluated. The 'Lung apex to diaphragmatic apex' (LATDA) distances in centimeters for both hemidiaphragms were obtained from the chest radiographs.

Results: There were 210 males and 316 females ranging in age from 15 to 85 years. The mean ranges of LATDA values on the right were 21.2 cm to 23.8 cm and 20.8 cm to 22.7 cm, with total means of 22.9 cm and 21.5 cm in males and females respectively. On the left, the ranges were 23.1cm to 25.5 cm and 21.6 cm to 23.5 cm with total means of 24.4 cm and 22.6 cm in males and females respectively. Left LATDA was higher in 95% of subjects and higher LATDA values represent lower hemidiaphragms while low LATDA values indicate elevated hemidiaphragms. LATDA measurements were statistically higher in males for all age groups. Mean differences between right and left LATDA were 1.5 cm and 1.2 cm in males and females respectively.

Conclusion: From this study, the lower limits of normal LATDA values in females and males are 16 cm and 18 cm while upper limits are 28 cm and 30 cm respectively. A "rule of twos" that could be applied to routine use in clinical practice is suggested thus: Left LATDA value is 2 cm higher than right LATDA value and LATDA values in males are 2 cm higher than in females.