CHEST-WALL MOTION DURING TIDAL BREATHING

We have used an automatic motion analyzer, the ELITE system, to study changes in chest wall configuration during resting breathing in five n ormal, seated subjects. Two television cameras were used to record the x-y-z displacements of 36 markers positioned circumferentially at the level of the third (S-1) and fifth (S-2) costal cartilage, correspond ing to the lung-apposed rib cage; midway between the xyphoid process a nd the costal margin (S-3), corresponding to the abdomen-apposed rib c age; and at the level of the umbilicus (S-4) Recordings of different s ubsets of markers were made by submitting the subject to five successi ve rotations of 45-90 degrees. Each recording lasted 30 s, and three-d imensional displacements of markers were analyzed with the Matlab soft ware. At spontaneous end expiration, sections S1-3 were elliptical but S-4 was more circular. Tidal changes in chest wall dimensions were co nsistent among subjects. For S1-2, changes during inspiration occurred primarily in the cranial and ventral directions and averaged 3-5 mm; displacements in the lateral direction were smaller (1-2 mm). On the o ther hand, changes at the level of S-4 occurred almost exclusively in the ventral direction. In addition, both compartments showed a ventral displacement of their dorsal aspect that was not accounted for by fle xion of the spine. We conclude that, in normal subjects breathing at r est in the seated posture, displacements of the rib cage during inspir ation are in the cranial, lateral outward, and ventral directions but that expansion of the abdomen is confined to the ventral direction.