Detection of impaired intrapulmonary convective mixing by aerosol bolus dispersion in patients with emphysema.

The broadening of an inhaled aerosol bolus (aerosol bolus dispersion) during respiration provides a noninvasive, nonradioactive, and easy to perform technique which is a measure of the extent of convective gas mixing processes in the lung and symmetry of ventilation during the breathing cycle. In this study, this technique was evaluated for the ability to detect ventilation inhomogeneities in pulmonary emphysema (PE). An aerosol bolus undergoes changes in shape between its inspiration and expiration. In comparison with the inhaled bolus, the exhaled bolus is more spread because of convective mixing and may have a shift in the location of the mode caused by asymmetries of filling and emptying of lung units. We hypothesized that in PE these changes differ from healthy subjects and are related to lung health. Twenty nine patients with PE inhaled 25 ml boluses containing 0.9 micron monodisperse aerosol particles into volumetric lung depths of 200, 400, 600, and 800 cm3. The control group were 79 healthy subjects. As each bolus was expired, we measured bolus dispersion (volumetric width at one-half aerosol concentration peak height) and mode shift. In patients with PE exhaled boluses were significantly broader than those exhaled by normal subjects at all volumetric lung depths. At a lung depth of 800 cm3, patients showed a bolus dispersion that was 52% greater than that of healthy subjects (p < 0.0001) and they exhaled the bolus mode earlier (p < 0.0001). Aerosol bolus parameters were not influenced by anthropometric data. Pulmonary function parameters indicating obstruction showed a weak negative correlation with aerosol bolus parameters (R2 < 0.4). The bolus parameters appeared to be supplemental to conventional lung function tests and significantly indicated marked ventilation asymmetry and altered convective gas transport in pulmonary emphysema. The results support the use of the aerosol bolus dispersion test in assessing peripheral parenchymal lung injury.