<prompt> In erect posture commonest site of foreign body in bronchus -Right posterior basalRight anterior basalLateral basalMedial basal  <response>: From Schwart, 7e The most common anatomic location for a foreign body is the right main stem bronchus or the rt. lower lobe.From Pretest Pretest has quoted Harrison, 14e, p 994 The right main stem bronchus is wider, shorter and vertically placed, and therefore the posterior segments of the right upper lobe if the pt. aspirated while supine are anatomically susceptible to aspiration pneumonia. The superior segments of the right lower lobe and left lower lobe if the pt. supine are also susceptible to aspiration pneumonia. These three segments are often referred to as the aspiration segments of the lung. The basilar segments of both lungs are susceptible to aspiration if the pts. aspirates while erect or sitting up.Inference : Segments involvedAspiration in Supine Position :RL upper lobe - posterior segmentRt. lower lobe - superior segmentLt. lower lobe - superior segmentAspiration in sitting or erection positionRt. basilar segments of lower lobe. 