V'/Q' = Ventilation Perfusion Ratio

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How to Read a Blood - Gas Distribution Curve

						Anitha Mittapalli
						BME 403


VENTILATION-PERFUSION RATIO

	The commonest cause of Hypoxemia is referred to as the
ventilation-perfusion inequality, which occurs when the ventilation and
blood flow are mismatched in the lung, impairing  O2 and CO2 transfer.
This situation is best explained via the ventilation-perfusion ratio(
Va/Q).
	This ratio comes in handy when the concentration of O2 in any lung
unit is to be determined(as well as other gases) and thus is important in
the subject of pulmonary gas exchange.  Ideally, the ventilation
/perfusion ration is uniformly distributed.  During exercise, this ratio
increases since VA and Q both increase. Here, VA represents ventilation
and Q represents blood flow.  This is one of the reasons for its
importance in pulmonary gas exchange.
	From the web page,
http://www.meddan.luc.edu/lumen/MedEd/Medicine/PULMONAR/F1IVA.HTM
it was stated that the ventilation/perfusion inequality is the most common
clinical cause of arterial hypoxemia.  Ideally  both the ventilation and
blood flow should match, that is ventilation has to be distributed in the
blood flow or perfusion while the perfusion should also be distributed to
ventilated areas.  Thus it is very important that the regions which
require high ventilation should also have high blood flows.  Similarly,
regions with low vent. should have low Q.
	The ventilation-perfusion equation states:
Va/Q=8.63*r*(CaO2-CvO2)/PaCO2.

TEST  QUESTION:
1.Two physiological problems caused from Va and Q mismatch are:
_____________             _____________;
Answer:  hypoxemia , Hypercapnia

email: mittapal@aludra.usc.edu.

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