

It may be due to the lesser involvement of small airway as small airway obstruction may cause atelectasis resulting in the perfusion of poorly ventilated lung areas and development of hypoxemia. study is the presence of normal or near normal PaO2 in 80% of patients despite having moderate to severe emphysema on HRCT in 75% of patients. Blood flow is also reduced due to compression by the overinflated alveolar walls. The reduced perfusion causes modest V/Q mismatch and explains the lack of correlation with extent of emphysema. also reported reduced pulmonary capillary blood volume across all spectrum of emphysema. measured blood volume on the basis of positron emission tomography scan and found lower tissue density and peripheral vascular volume within lungs in emphysematous patients. Severe V/Q mismatch does not develop in COPD patients as the destruction of the alveolar surface is associated with a reduction in perfusion also.

COPD is a shunt since the alveoli are being destroyed despite being adequately perfused correct?
