Mechanisms determining residual volume of the lungs in normal subjects.

residual volume of the lungs in normal subjects. J. Appl. Ph ysiol. 23(2) : 22 I-227. I g67.-Differences between the terminal portions of the flow-volume and volume-time curves of young and old normal subjects during forced expirations indicate that different mechanisms set the lower limit to lung volume in these two age groups. Most young subjects reach the limit quickly (2-4 set); no further volume change occurs in spite of continued effbrt. Most old subjects reach the limit more slowly (I O-I 5 set) and some continue to expire with decreasing flow as long as the effort is maintained. When external pressures assisting expiration were suddenly applied at or near RV, spiro-grams of young individuals showed sudden decrements of lung volume, while those of some old subjects were virtually unin-fluenced. In the former, the static balance of muscle and recoil forces, mainly in the chest Iwall, sets the limit to expiration, and