Alveolar and tissue surfactant pool sizes in humans

The amounts of surfactant in human lung tissue and in the alveolar pool have not been extensively reported. We used 24 human lungs from persons over the age range of 13 mo to 80 yr to investigate whether the amount of saturated phosphatidylcholine (Sat-PC) in the human lung changed with age. Lung lavages also were obtained from 10 lungs at autopsy for measurements of the alveolar Sat-PC and surfactant protein-A (SP-A) concentrations. We found that (mean +/- SEM) lung Sat-PC/body weight (28.4 +/- 2.2 mumol/kg), Sat-PC/lung protein (0.060 +/- 0.005 mumol/mg), and Sat-PC/lung deoxyribonucleic acid (DNA) (0.23 +/- 0.01 mumol/mg) did not vary significantly with age. The amounts of alveolar Sat-PC (1.9 +/- 0.2 mumol/kg) and SP-A (105 +/- 15 micrograms/kg) were lower than previous estimates in other species. The relatively small surfactant pools in the human may make the lung more susceptible to injuries that interfere with surfactant function.