Inhaled particle deposition and body habitus.

As a result of the intrapleural pressure gradient that exists in the human lung, both ventilation and particle deposition increase from apex to base. Since the intrapleural gradient varies with the height of the subject, it was decided to compare regional particle deposition in tall, short, and obese subjects to ascertain whether it was influenced by height and weight. Surprisingly, deposition in the vertical plane was not significantly influenced by the height of the subject when corrected for ventilated lung volume. In addition, it was shown that in obese subjects there was increased deposition in the middle zones relative to the apices and bases. This finding persisted after correction for ventilated lung volume and differential attenuation resulting from non-uniform thickness of the fat layer in the obese subject's chest. In the tall and short groups there was a consistent pattern in the concentric deposition of particles with there being a gradient from the central or hilar region to the periphery of the lungs, with the latter showing the most deposition.