STRUCTURAL-CHANGE OF THE ACINUS DURING GROWTH ASSESSED BY SINGLE-BREATH TRACER GAS WASHOUTS

In the present investigation we wanted to study the functional and str uctural development of the acinus, using a vital capacity (VC) single- breath tracer gas washout test, modified so that the subject inspired helium (He) and sulfurhexafluoride (SF6) in oxygen. We used as indices of ventilation the slopes of N-2(S-N2), He(S-He), and SF6(S-SF6) as w ell as (S-SF6 - S-He), which may be considered an index of acinar mixi ng linked to acinar structure. We studied two populations: Population I - 49 children and adolescents (8 - 18 years of age); and Population II - 18 non-smoking adults (22 - 48 years of age). Age and vital capac ity (VC) were correlated in Population I, but not in Population II. In both populations there was a significant decrease of S-N2, S-SF6, and S-He as a function of VC. Growth and VC changes were determinants of these decreases in Population I, while only changes in VC were signifi cant determinants in Population II. For each gas, the regression lines of slope versus VC for Populations I and II were not significantly di fferent; we therefore suggest that the decrease in slope in Population I is mainly due to an increase in lung volume during growth. (S-SF6 - S-He) was not correlated with VC in Population I and was negatively c orrelated with VC in Population II (P < 0.01). This discrepancy implie s that a child will have a smaller (S-SF6 - S-He) than an adult at com parable VC. Since the magnitude of (S-SF6 - S-He) values are related t o acinar branching asymmetry, our results suggest that asymmetry of th e acinus increases with lung growth and maturation. (C) 1996 Wiley-Lis s, Inc.