![]() ![]() Collateral ventilation in the obstructed segments prevents absorption atelectasis and subsequent shunt formation by keeping the alveoli ventilated.Presentation on theme: "The 3-compartment lung model described by Riley and Cournand151,152 represents gas exchange in the lung in regard to the matching of alveolar gas volume."- Presentation transcript:ġ The 3-compartment lung model described by Riley and Cournand151,152 represents gas exchange in the lung in regard to the matching of alveolar gas volume (V̇A) and perfusion (Q̇T), shunt (Q̇S), and dead space (VD). The factor that prevents the development of shunt is collateral ventilation. The shunt is an uncommon mechanism of hypoxemia in COPD patients. However, emphysema severity on quantitative chest computed tomography scan did not predict hypoxemia. In the COPD gene study, female sex, higher body mass index, lower FEV1 were independent risk factors for hypoxemia development in patients with moderate to very severe COPD. 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? ![]()
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