These extremes are mainly hypothetical legitimate V/Q ratios in the areas between the shunted areas and the dead spaces are what are used clinically.The anatomic dead space is measured by Fowler’s method. SHUNTED AREA: A shunted area is an area with perfusion (Q) but no ventilation (V).ĭEAD SPACE: the opposite of a shunt, dead space is an area with ventilation (V) but no perfusion (Q). When standing the bases have a lower V/Q ratio than the rest of the lung, this is because the blood that is pulled down by gravity compresses the alveoli and make them harder to inflate. They sit upon the convex surface of the diaphragm, separating the left lung from the stomach, spleen and left lobe of the liver, and the right lung from the right lobe of the liver. The apices of the lungs are the area most superior of the organ, stretching to about the area just above the sternal end of the first rib.īASES: The bases of the lungs are broad and concave. This is due to the effect of gravity on blood. When the V/Q is < 0.8, it means perfusion exceeds ventilation. Things that may cause this are aspiration, blockage of bronchi by a foreign object, pneumonia, severe asthma, pulmonary edema, or COPD.ĪPICES (top): When a person is standing, the apices of the lungs have a higher V/Q ratio than the bases of the lungs. When the V/Q is > 0.8, it means ventilation exceeds perfusion. Things that may cause this are a blood clot, heart failure, emphysema, or damage to the pulmonary capillaries. Therefore the Normal V/Q ratio is 4/5 or 0.8. Disruptions of V and Q are how pulmonary embolisms, pneumonia, and other lung pathologies kill patients.Ī normal V (alveolar ventilation)value is around 4 L/minute.Ī normal Q (perfusion)value is around 5 L /minute.

This means that some of the blood in the bottom of the lung is not oxygenated and some of the air in the top of the lung does not have its oxygen extracted. This concept is critical. There is more air in the top of the lung, and there is more blood in the bottom of the lung (because of gravity). The diagram to the right can be simplified as follows. This is due to two main reasons: gravity and air. In the normal lung, the V and the Q are not equal, the normal ratio is about 0.8. Q = the amount of blood that reaches the alveoli through the capillary beds

V = the amount of air that reaches the alveoli through the alveolar duct In respiratory physiology, the V/Q ratio refers to the ratio of ventilation to perfusion.

Physiologic dead space in emphysema