Ventilation‐perfusion in health & disease

Posted by e-Medical PPT Thursday, May 7, 2015
Distribution of ventilation Distribution of ventilation
•Spatial & anatomical variation
•Rate of alveolar filling
•Rate of alveolar emptying

Clinical relevance Clinical relevance
Perfusion is poor & pulsatile at apex
Pa& Pv proportionately increases from top to bottom
PA changes minimally with gravity
Pressures are max at bottom
Pulmonary edema starts at bottom
Redistribution of blood flow to apex –antler’s horn

Understanding V/Q relationships Understanding V/Q relationships
Consider lung as single unit
– Relationships between PAO2, PACO2, alveolar ventilation & pulmonary blood flow
–Alveolar gas equation
Consider lung as multiple units of varying V/Q
–Clinical consequences in health & disease

Alveolar PO and PCO Alveolar PO2 and PCO2
Determined by the ratio between ventilation and blood flow: V/Q
PO2and PCO2 are inversely related through alveolar ventilation
Increasing V/Q produces higher PAO2and lower PACO2
Decreasing V/Q produces lower PAO2and higher PACO2

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