Airway visualization by tantalum inhalation bronchography.

A novel technique for the generation of tantalum aerosols (aerodynamic mass median diameter, 5.8 mum; sigma g, +/-2.14) for inhalation bronchography via the mouth was applied in 26 anesthetized dogs. Ventilatory patterns during periods of aerosol inhalation were controlled by either bilateral electrophrenic stimulation of the diaphragm (EPS), or by intermittent, negative pressure at the body surface (INPV). We studied patterns of tracheobronchial deposition with regard to both the sites of particle deposition longitudinally along airways within lobes, and the topographic distribution of aerosol among the lung lobes. Bronchographic patterns were accordingly studied after inhalations by either (1) EPS and INPV in the supine posture with constant tidal volumes, but varied inspiratory flow (30 to 90 liter per min); or (2) EPS with constant tidal volume and peak inspiratory flow in the prine, right, and left lateral decubitus body positions. Under all airflow conditions, the aerosol was deposited on the surfaces of ciliated airways. Deposition was nearly entirely confined to subsegmental bronchi and above with vigorous inspirations, but extended distally to subsegmental bronchi in greater proportion with decreases in the inspiratory flow. Airways among the basal lung lobes were particularly subject to distal subsegmental and bronchiolar deposition with low rates of inspiratory airflow. Regionally, the aerosol was deposited preferentially in dependent lung lobes after inhalations with EPS in the right and left lateral decubitus positions, and in the basal lung lobes with EPS in the supine posture. A greater caudocranial uniformity in lobar aerosol distribution occurred with inhalations by INPV in the supine posture, and by EPS in the prone posture. The canine model strongly suggests that for clinical inhalation bronchography, nonhomogeneities in lobar deposition may be averted by inhalations in multiple body positions, and that deposition of the aerosol may be confined to ciliated airway surfaces by inertial impaction accompanying high rates of inspiratory airflow.