In an open pneumothorax, the major effect of mediastinal shift is to
ExplanationA. Inspiration in a lateral position during spontaneous ventilation causes more negative pleural pressure on the dependent side of the open pneumothorax. The relatively higher pressure on the nondependent side causes a downward shift of the mediastinum during inspiration. The reverse happens on expiration, and the mediastinum shifts upward. This results in an ineffective respiratory exchange, but the major effect is by decreasing the contribution of the dependent lung to the tidal volume.
