ABSTRACT
There is now both functional and morphological evidence that disease in the peripheral airways is the earliest manifestation of chronic obstructive pulmonary disease (COPD) and that inflammation and fibrosis in the small airways may be the most important anatomical causes of mild to moderately severe airflow obstruction. Therefore gas exchange disturbances are expected to be present in COPD, and this is widely recognized to occur on the basis of alveolar ventilation/perfusion (VA/Q) inequality, a phenomenon whereby a considerable range of local airway obstruction occurs leading to reduced local ventilation and hence to regions of low VA/Q ratio. As the disease progresses, VA/Q inequality increases, leading to impairment of O2 and CO2 arterial blood tensions. Arterial blood gases are of great importance in assessing the prognosis and the need for long-term oxygen treatment. We will first review some of the methodological problems related to O2 and CO2 evaluation, and then describe the abnormalities observed in stable COPD.
