Which of the following will decrease the physiologic dead space?

Neck flexion decreases the volume of anatomic dead space and thus the total or physiologic dead (which includes anatomic dead space) will decrease. Physiologic dead space includes those alveoli which do not receive perfusion, making it a wasted ventilation in those alveoli. Physiologic dead space increases in emphysema. Increase in tidal volume increases anatomic dead space & thus physiologic dead space In IPPV, the positive pressure ventilation increases alveolar pressure, which in turn compresses vessels. This will decrease the blood flow to some regions of the lung.