[Normal value of the tracheal bifurcation angle and correlation with left atrial volume]

We evaluated the mean value and the variability range of the tracheal bifurcation angle by patient gender, age, height, weight, build, body area and max transverse diameter of the chest under normal conditions. We also evaluated tracheal bifurcation angle changes in orthostatism and recumbency, as well as in the different respiratory phases. Finally, we investigated the statistical correlation between the tracheal bifurcation angle value and the left atrial volume, to eventually derive either value from the other.

We reviewed 700 high-voltage radiographs of the chest performed in 500 patients with normal echocardiographic findings from 1986 to 1990. To analyze the relationships with the left atrium, 100 patients with echocardiographically enlarged atrium were submitted to high-voltage radiography. The tracheal bifurcation angle was measured directly.

Mediastinal radiographs nearly always depict the trachea and extraparenchymal bronchi adequately. The tracheal bifurcation angle should be measured continuing and joining the upper and lower parabronchial contours. A 4-degree deviation is accepted between the upper or interbronchial and lower or carinal angles since the angles formed by parallel segments have the same value. Under normal conditions the absolute mean value of the tracheal bifurcation angle was 79.7 degrees and the range 37-105 degrees.

In normal patients the mean value of the tracheal bifurcation angle: is independent of age and gender; depends on build; is related to the max transverse diameter of the chest and to body area; exhibits no major radiographic changes in orthostatism versus recumbency; exhibits no major radiographic changes in expiration versus inspiration; is correlated with left atrial volume, but the value is not statistically significant.