Effect of Cystic Fibrosis on Inhaled Aerosol Boluses

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Abstract
An aerosol bolus undergoes changes in shape between its inspiration and expiration. In comparison with the inhaled bolus, the exhaled bolus, the exhaled bolus is more spread because of convective mixing, may have a shift in the location of the mode caused by asymmetries of filling and emptying of lung units, and contains fewer particles because of particle deposition. We hypothesized that the extent of these changes is related to lung health. To examine this, 11 patients with cystic fibrosis (CF) and 11 healthy subjects inhaled 70 cm3 boluses containing 1 .mu.m monodisperse particles that were inspired to volumetric penetrations (Vp) of 100 to 700 cm3. As each bolus were expired, we measured spreading (volumetric width at one-half aerosol concentration peak height), modal shift, and particle deposition. Patients with CF exhaled boluses that were broader than those exhaled by normal subjects at all penetrations examined. At a Vp of 600 cm3, patients had a mean bolus half-width that was 68% greater than that of healthy subjects (p < 0.0001), and they exhaled the bolus mode 20% earlier (p < 0.0002). Particle deposition was increased compared with that in normal subjects at all Vp. For example, mean deposition at a Vp of 60 cm3 was 46.2 .+-. 2.6% (SE) for the patients versus 25.8 .+-. 1.6% for the normal subjects (p < 0.0001). Among the patients with CF, pulmonary function parameters indicating obstruction were significantly correlated with bolus spreading and aerosol deposition: the percent predicted FEV1/FVC was inversely correlated with spreading (r = -0.88, p < 0.0004) and deposition (r = -0.84, p < 0.0008). We conclude that bolus spreading and deposition are increased in proportion to the severity of obstructive lung diseases such as cystic fibrosis.