Design-based sampling and quantitation of the respiratory airways

Design-based quantitation of the nasal cavity, larynx and tracheobronchial conducting airways after exposure to inhaled toxicants requires complete measurement of all respiratory airways or appropriate sampling followed by morphometric measurements. In vivo imaging (MRI or CT) of the nasal cavity, larynx and conducting airways provides anatomical detail of all the airways down to the distal airways. Since inhaled toxicants show predictable deposition patterns in the airways, identification and sampling of conducting airways becomes essential in a precise toxicological evaluation. Lengths, diameters and luminal surface areas can be directly measured on fixed specimens using a steromicroscope. Estimates of cell numbers, extracellular matrix volumes and vessel/nerve lengths per airway or epithelial basal laminar surface are estimated stereologically. Selected airways are cut into smaller pieces using a "fractionator" for uniform sampling of the airways. Cell numbers are estimated using a "disector." Volumes are estimated using point probes, while length and surface areas are estimated by isotropically oriented sections with plane and line probes; an approach free of assumptions of shape, size or spatial orientation. True biological variance and the average sampling variance of the stereological measurement define the minimal sampling required to achieve precise estimates of the nasal cavity, larynx and conducting airways.