LARGE LUNGS AND GROWTH-HORMONE - AN INCREASED ALVEOLAR NUMBER

Previous physiological studies suggest that increased lung growth in p atients with acromegaly is associated with either a normal or above no rmal pulmonary transfer factor, These findings can be interpreted to s uggest either alveolar hypertrophy or hyperplasia as the mechanism for lung growth in this condition, Since the ventilated airspaces retain normal elastic properties, we wanted to determine whether the mechanis m for lung growth in acromegaly is the result of an increased alveolar number rather than size. Measurements of pulmonary distensibility (K) (an index of alveolar size), elastic recoil, single-breath carbon mon oxide transfer factor and carbon monoxide transfer coefficient (Kco), pulmonary capillary blood volume and alveolar membrane diffusing capac ity, together with chest width, were compared in nonsmoking, acromegal ic and normal men and women, with and without an increased lung size. Pulmonary transfer factor was normal for all groups studied, regardles s of lung size, However, Kco was inversely related to total lung capac ity (% predicted) for all subjects and Kco (% predicted) was inversely related to chest width in men, Pulmonary capillary blood volume (% pr edicted) was inversely related to total lung capacity (% predicted) fo r subjects with large lungs, Pulmonary distensibility (K), membrane di ffusing capacity and elastic recoil were within the normal range. Thes e findings suggest normal alveolar size, alveolar membrane surface are a and mechanical function in subjects with large lungs, They also sugg est that Kco may not be a reliable guide to the interpretation of the mechanism of lung growth in individuals with disproportionately large lungs, and may be reduced because not all the alveoli are perfused, Th e normal values for pulmonary distensibility found in all our individu als with large lungs, including acromegalics, suggest that lung growth has been achieved by an increased alveolar number rather than size, H owever, morphometric studies of the lungs of nonsmoking, acromegalic s ubjects without lung disease, are required to substantiate this findin g.