This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fundamental Concepts, Subject name: Anaesthesia
The physiological dead space is decreased by: 
Select and explain. 
A. Upright position, B. Positive pressure ventilation, C. Neck flexion, D. Emphysema
C: Neck flexion
Answer: C: Neck flexion 
Explanation: 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.