<prompt> When VAQ is infinity, it meansDead spaceThe PO2 of alveolar air is 159 mmHg and PCO2 is 40 mmHgPaial pressure of O2 and CO are equalAtelectasis  <response>: -Ventilation perfusion ratio - normal 4lmin5lmin0.8 - AVQ INFINITY - Means Perfusion Q to lungs is zero that is blood supply to that area is hindered making it awasted ventilationin those alveoli. - This may be due to pulmonary embolism causing ed Physiological DEAD space . DEAD SPACE- Some of the air a person breathes never reaches the gas exchange areas but simply fills respiratory passages where gas exchange does not occur, - called so as its not useful for gas exchange. Physiologial total dead space anatomical dead space alveolar dead space non perfused non functioning Alveoli In Atelectasisventilation: perfusion ratio VAQ iszero. it is is the most common cause of a physiologic shunt. 