Gas Exchange Shunt Flashcards
What does PAO2 - PaO2 equal in normal individuals?
1.0kPa
What is the alveolar to arterial gap in common lung disease?
7.0kPa
What is pulmonary shunt?
Blood which enters systemic arterial system without passing through ventilated areas of lung
What are 2 normal shunts?
Bronchiole circulation
Coronary blood draining directly into left ventricle
What are 2 shunts associated with disease?
Congenital cardiac anomalies
Intrapulmonary shunt
What happens in intrapulmonary shunt?
PO2 and PCO2 fall in alveoli until they equilibrate with mixed venous PO2 and PCO2
No ventilation but continuous perfusion
What does CO depend on?
Size of shunt relative to size of area that is normally diffused
Is SaO2 saturation of Hb with O2 linearly related to PaO2?
No
What does the concentration of O2 in blood (CaO2) dependent on?
SaO2 and Hb
What is a consequence of a shunt?
Difference in PO2 between alveolar gas and arterial PO2
Arterial hypoxaemia and thus reduced O2 content in blood and reduced O2 delivery
What is alveolar PO2 determined by?
Balance between rate of addition of O2 to alveolus by ventilation and its removal by blood
What happens in exercise?
Skeletal muscles require more oxygen - extract more oxygen out of blood - blood returning to lungs have lower oxygen content and PO”
What happens with excercise in the present of a shunt?
Arterial blood O2 content reduces further with increasing O2 requirement
Lowers arterial PO2 upon venous mixing
Does hyperventilation help raise arterial PO2 in presence of a shunt?
Blood going through alveolus is fully saturated - no more room for oxygen through hyper ventilation
Hb saturation already at plateau
What is the only corrective mechanism for shunt available to the body?
Increased CO
Divert blood flow away from shunt (hypoxic pulmonary vasoconstriction)
