Saline aerosol bolus dispersion. II. The effect of conductive airway alteration

In a companion study (Verbanck S, Schuermans D, Vincken W, and Paiva M, J A ppl Physiol 90: 1754-1762, 2001), we investigated whether saline aerosol bo lus tests could also be used to detect proximal, as opposed to peripheral, airway alterations. We studied 10 never-smokers before and after histamine challenge, obtaining, for various volumetric lung depths (VLD), saline bolu s-derived indexes computed by discarding aerosol concentrations below eithe r 50% of the exhaled bolus maximum (halfwidth, H) or below cutoffs ranging from 5 to 25% (standard deviation, sigma (5%)-sigma (25%)) and skew (sk(5)- sk(25%)). Multiple-breath N-2 washout-derived indexes of conductive (S-cond ) and acinar (S-acin) ventilation inhomogeneity were also determined. After histamine, S-cond significantly increased (P = 0.008) whereas Sacin remain ed unaffected, indicating purely conductive airway alteration. Consistent w ith this observation, sk(5%) (or sk(25%)) was increased to the same extent at all VLD, and sigma (5%) was increased preferentially at low VLD. By cont rast, H and sigma (25%) displayed preferential increases at high VLD, a pat tern similar to that induced by peripheral alterations. The present work sh ows that proximal airway alteration can be reliably identified by saline bo lus tests only if these include measurements at low and high VLD and if bol us dispersion is quantified as a standard deviation with a low cutoff.