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Yenlilalion/Perfusion

RESPIRATORY PHYSIOLOGY

A. Conditions with Iow ventilation/perfusion ratio

B. Conditions with high ventilation/pcrfusion ratio

no perfusion iphysiologic dead space)    hypo perfusion

Ventilation or biood flow/unit lung vol

Both ventilation and blood flow are gravity dependent and decrease from bottom to top ot lung. Gradient of blood flow is steeper than that of ventilat»on, so ventilation/perfusion ratio increases u|) lung

Figurę 5.16 Ventilation/Perfusion (Va/Qc) Relationships-

•avity affects not only capillary perfusion (see Figurę 5.15) but alve-    bul Iow blood flow), whereas the opposite is true at the bases. In a

ir \cntilation as wefl. In an erect person the ratio of yentilation to    normal lung the average Va/Qc is approximately 1

- rfusion (Va/Qc) is grealer than 1 at the apices (i.e., high ventilation

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