THE UPPER LIMIT OF ALVEOLAR-CAPILLARY RECRUITMENT IN A YOUNG MAN WITHLUNG GROWTH IMPAIRMENT

In order to obtain further insight into the adaptive mechanisms relati ng to gas exchange in anatomically small lungs, tests of mechanical lu ng function and gas exchange were made in an active young man, whose l ung growth had been severely impaired due to pectus excavatum develope d in childhood. We found our patient to have small (total lung capacit y, 59% of predicted) but mechanically normal lungs. He had a normal ca rdiac output, a normal single-breath diffusing capacity (100% pred), a nd a high diffusion coefficient (148% pred) associated with a high pul monary capillary blood volume (131% pred) at rest. Pulmonary distensib ility (K) and elastic recoil were normal. During steady-state exercise he was unable to recruit further reserves of pulmonary capillaries, b ut this was not reflected in a plateau for oxygen consumption, which w as presumably the result of an increased pulmonary capillary blood flo w rather than volume. The recruitment of pulmonary capillary reserves in this young man has enabled him to maintain a normal maximum exercis e capacity. In addition, the high stroke volume and a haemoglobin leve l in the high normal range (176 g.l-1) may have maintained his maximal exercise function, despite fewer alveolar units. This study suggests that, contrary to previous findings, loss of a major proportion of lun g tissue need not impair exercise capacity. Patients with either small lungs or following pneumonectomy may benefit from physical training s ufficient to optimize both an increase in cardiac output and recruitme nt of their existing alveolar capillary reserves.