Summary: PO2 and PCO2 of lung units varies along the line between the two fixed points - mixed venous blood (lowest O2 and highest CO2 ) and inspired gas (highest O2 and lowest CO2 ) Ventilation perfusion mismatch is responsible for the hypoxaemia seen in pulmonary oedema, chronic obstructive airways disease, pulmonary embolism and interstitial lung disease.
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