Breathing patterns influence aerosol deposition sites in excised dog lungs

Abstract

Particles' suspended in inhaled air can deposit on lung surfaces. The amount deposited in different lung regions is determined by distribution of ventilation and local efficiency of particle collection. We examined how the pattern of ventilation influences sites of aerosol deposition in excised dog lungs. The lungs breathed a 99mTc-labeled aerosol according to one of three patterns: slow-deep (f less than 25/min, VT greater than 0.35 TLC); rapid-shallow (f greater than 65/min, VT less than 0.26 TLC); and slow-shallow (f = 8.4/min, VT = 0.1 TLC). After exposure, lungs were inflated, dried, and sliced transversely at 1-cm intervals. Distribution of deposited aerosol in each slice was measured by 1) gamma camera, 2) autoradiography, and 3) dissection of each slice into pieces whose activity, weight, and airway content were recorded. Our results indicate that a) total deposition decreases as f increases, b) slow-deep breathing produces uniform deposition throughout the lung, but with little aerosol collection in large airways, c) rapid-shallow ventilation results in enhanced large-airway deposition and marked heterogeneity in deposition distribution, and d) slow-shallow breathing enhances small-airway deposition. The deposition distributions characteristic of different breathing patterns were apparent on the visual displays from the gamma camera and autoradiographs. These techniques showed particle retention changing across lobar divisions, as a function of distance from the hilum, and across the lungs in both the caudal-to-cranial and dorsal-to-ventral directions.