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Pulmonary Ventilation Distribution

  • Empirical studies have shown that the rate of pulmonary ventilation is not uniform throughout the lung. Rather, it appears that gravity exerts a moderate influence on the distribution of pulmonary ventilation resulting in increased ventilation in lower regions of the lung. Consequently, when standing upright the lung apex tends to have the poorest ventilation whereas the lung base displays the greatest ventilation. However, the influence of gravity appears to be greater on blood, resulting in a steeper vertical gradient of pulmonary blood flow distribution. As a result, although the lung apex has the least total ventilation, it's ventilation-perfusion ratio is the greatest whereas the lung base displays the lowest ventilation-perfusion ratio as described in ventilation-perfusion ratio distribution.