<prompt> The physiological dead space is decreased by:Upright positionPositive pressure ventilationNeck flexionEmphysema  <response>: Ans. is c i.e., Neck flexion FactorEffectPosture UprightincreaseSupinedecreasePosition of airway Neck extensionincreaseNeck flexiondecreaseAgeincreaseArtificial airwaydecreasePositive pressure ventilationincreaseAnticholinergic drugsincreasePulmonary perfusion Pulmonary emboliincreaseHypotensionincreaseEmphysemaincrease Factors affecting dead space. 