Small airways, lung function and aviation

The anatomy, physiology and functional assessment of small airways and their relevance to aviation is reviewed. Small airways normally contribute little to lung function, and they can become extensively and irreversibly damaged, or even closed, before clinical deterioration is evident. Small airways disease does, however, produce typical and reproducible changes in spirogram, flow volume, and closing volume measurements. Minor abnormalities of respiratory function, inconsequential at sea level, can substantially reduce arterial oxygen saturation at high altitude. Aircrew with pulmonary disease could also be severely affected by loss of pressure, causing significant hypoxia. Stress during flight may exacerbate airways obstruction, especially in asthmatics. The hypoxia resulting from these situations could seriously compromise in-flight performance. Peak flow, FEV1, and FVC measurements are recommended for civilian air crew prior to employment and at routine intervals thereafter.