The pulmonary artery and bronchus travel together and there are 3 basic regions where the relationship is best visualised
In the upright position, the ratio of the size of the pa to the bronchus is 1.2:1, in the mid lung zone it is 1:1, and in the upper lungs it is .8 :1
Ashley Davidoff MD
Ashley Davidoff MD TheCommonVein.net bronchus segmental normal