Composition of human pulmonary surfactant varies with exercise and level of fitness

We have tested the hypothesis that the composition of alveolar surfactant varies with pattern of breathing and level of fitness. We examined three major components of surfactant, surfactant protein A (SP-A), disaturated phospholipids (DSP), and cholesterol (CHOL) in bronchoalveolar lavage (BAL) fluid from 12 healthy men before and after exercise. Fitness was assessed as work load/heart rate ([kpm · min^-1]/[HR · HRmax^-1]) achieved during cycling for 30 min at 90% theoretical maximal heart rate. Using a bronchoscope, four 20-ml vols of 0.15 M NaCl at 37° C were instilled and then recovered from first a right upper and then a right lower lobe segmental bronchus. As we found no differences in the BAL from upper and lower lobes, the fluid was combined. We found a direct relationship between CHOL and DSP (r(s) = 0.84, p < 0.001), SP-A and CHOL (r(s) = 0.40, p < 0.025), and between SP-A and DSP (r(s) = 0.44, p < 0.025). The change in the ratios CHOL/DSP, SP- A/CHOL, and SP-A/DSP immediately after exercise was correlated with fitness (r(s) = -0.56, p < 0.025; r(s) = 0.75, p < 0.005; r(s) = 0.62, p < 0.025, respectively). We conclude that the composition of surfactant can change rapidly with exercise in a manner related to fitness, and we suggest that this is consistent with the existence of at least two pools of tissue surfactant of different composition supplying the alveolar compartment.