Ventilation perfusion, compensation, local control of arterioles/bronchioles by O and CO2

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Biomedical Science
BMS 420
Charles Miller

26 November V and P are essential elements in normal lung function but V:P ratio of ~.8 is not necessarily a dictation of normal V and P! V:P varies in lung (.63 – 3.3) P in alveoli = P in arterial blood CO2 CO2 P O2in alveoli >O2 in arterial blood V:P mismatch spectrum No Q (PA blocked) V:Q = ∞ No V (shunt) V:Q = 0 Regional differences in ventilation perfusion disappear with exercise Alveolar dead-space ventilation without compensation V Perfusion to lung stops while ventilation continues;Q → ∞ The alveolar gas assumes the composition of inspired air V́ Perfusion of other lung increases, causing ↓ Q́ Compensation: bronchiolar constriction ↑P , ↓ P , and ↑ pH around smooth muscle causes bronchiolar constriction, diverting O2 CO2 airflow to “normal” airways In response to ↓ blood flow, alveolar type II pneumocytes produce
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