Pulmonary surfactant is a complex and highly surface active material composed of
lipids and
proteins which is found in the fluid lining the alveolar surface of the lungs.
Surfactant prevents alveolar collapse at low lung volume, and preserves bronchiolar patency during normal and forced respiration (biophysical functions). In addition, it is involved in the protection of the 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. These 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 replacement. Biochemical
surfactant abnormalities of varying degrees have been described in
obstructive lung diseases (
asthma,
bronchiolitis,
chronic obstructive pulmonary disease, and following
lung transplantation), infectious and suppurative
lung diseases (
cystic fibrosis,
pneumonia, and human immunodeficiency virus),
adult respiratory distress syndrome, pulmonary oedema, other diseases specific to infants (chronic
lung disease of prematurity, and
surfactant protein-B deficiency),
interstitial lung diseases (
sarcoidosis,
idiopathic pulmonary fibrosis, and
hypersensitivity pneumonitis),
pulmonary alveolar proteinosis, following
cardiopulmonary bypass, and in smokers. For some pulmonary conditions
surfactant replacement
therapy is on the horizon, but for the majority much more needs to be learnt about the pathophysiological role the observed
surfactant abnormalities may have.