As such the overall value in the average human lung is closer to 0.8. Areas of lung below the heart have increased perfusion relative to ventilation due to gravity, reducing the V/Q ratio. The different ratios for different areas are due to the relation of the area to the heart. This means that ventilation exceeds perfusion towards the apex, and that perfusion exceeds ventilation towards the base. For example, when standing up straight, the ratio is roughly 3.3 in the apex of the lung, and only 0.63 in the base. However, the ratio varies depending on the part of the lung concerned. The ideal V/Q ratio would be 1 for maximally efficient pulmonary function. The perfusion (Q) of the lungs refers to the total volume of blood reaching the pulmonary capillaries in a given time period. In an average man, the ventilation rate is roughly 6L/min. This is calculated by multiplying the tidal volume (volume of air inhaled and exhaled in a single breath) by the respiratory rate. The ventilation rate (V) refers to the volume of gas inhaled and exhaled from the lungs in a given time period, usually a minute.
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