![]() Gravity also affects the intrapleural pressure, causing the intrapleural pressure to be increased at the base relative to the apex. Conversely, the blood flow at the apex is generally lower, which results in decreased perfusion. This increased pressure results in distension of the pulmonary blood vessels at the base and an increase in blood flow and perfusion. The blood pressure at the base of the lungs is higher than the blood pressure at the apex because of the weight of the column of blood. Gravity also plays a significant role in determining the V/Q ratio. ![]() For this reason, the overall average value for V/Q is approximately 0.8.V/Q is lowest at the base of the lung (where it is approximately 0.63).V/Q is highest at the apex of the lung (where it is approximately 3.3).Both ventilation and perfusion increase from the apex to the base of the lungs, perfusion, however, rises at a greater rate. The V/Q ratio, however, varies in different regions of the lung partially because of the proximity of the heart to the region of the lung. ![]() The ventilation/perfusion ratio (V/Q ratio) is a ratio used to the efficiency and adequacy of the matching of these two variables. Ventilation (V) refers to the flow of air into and out of the alveoli, while perfusion (Q) refers to the flow of blood that reaches the alveoli via the capillaries. ![]() To ensure that enough oxygen is provided by ventilation to saturate the blood fully requires that ventilation and perfusion of the lungs are adequately matched. ![]()
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