<prompt> The physiological dead space is decreased byUpright positionpositive pressure ventilationNeck flexionEmphysema  <response>: Dead space is defined as the volume of the airway that doesnot paicipate in gas exchange It is nothing but ventilation occurs but perfusion doesnot occur Anatomical Dead Space : from nasopharynx to respiratory bronchioles.average adult,normally 150ml Alveolar dead space : Alveoli that are ventilated but not perfused.usually it is absent Physiological or total dead space : Anatomical Alveolar dead space Factors that increase dead space : upright position neck extension advanced age positive pressure ventilation decreased pulmonary perfusion pulmonary emboli or pulmonary hypeension lung diseases emphysema or cystic fibrosis FACTORS THAT DECREASE DEAD SPACE : supine position , neck flexion , intubation Anatomical dead space is measured by single breath nitrogen test , physiological dead space is measured by modified bohrs equation. 