Pulmonary surfactant in health and human lung diseases: state of the art

Pulmonary surfactant is a complex and highly surface active material compos ed of lipids and proteins which is found in the fluid lining the alveolar s urface of the lungs. Surfactant prevents alveolar collapse at low lung volu me, and preserves bronchiolar patency during normal and forced respiration (biophysical functions). In addition, it is involved in the protection of t he lungs from injuries and infections caused by inhaled particles and micro -organisms (immunological, non-biophysical functions), Pulmonary surfactant can only be harvested by lavage procedures, which may disrupt its pre-existing biophysical and biochemical micro-organization. Th ese limitations must always be considered when interpreting ex vivo studies of pulmonary surfactant. A pathophysiological role for surfactant was first appreciated in premature infants with respiratory distress syndrome and hyaline membrane disease, a condition which is nowadays routinely treated with exogenous surfactant re placement. Biochemical surfactant abnormalities of varying degrees have bee n described in obstructive lung diseases (asthma, bronchiolitis, chronic ob structive pulmonary disease, and following lung transplantation), infectiou s and suppurative lung diseases (cystic fibrosis, pneumonia, and human immu nodeficiency virus), adult respiratory distress syndrome, pulmonary oedema, other diseases specific to infants (chronic lung disease of prematurity, a nd surfactant protein-B deficiency), interstitial lung diseases (sarcoidosi s, idiopathic pulmonary fibrosis, and hypersensitivity pneumonitis), pulmon ary alveolar proteinosis, following cardiopulmonary bypass, and in smokers. For some pulmonary conditions surfactant replacement therapy is on the hori zon, but for the majority much more needs to be learnt about the pathophysi ological role the observed surfactant abnormalities may have.