This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Heart, Circulation, and Blood, Subject name: Physiology
Cyanosis is not seen in- 
Select and explain. 
A. CHF, B. COPD, C. CO poisoning, D. High altitude
C: CO poisoning
Answer: C: CO poisoning 
Explanation: Ans. is 'c' i.e., CO poisoing Hypoxic hypoxia (hypoxemia)Anemic hypoxiaStagnant hypoxiaHistotoxic hypoxiao Cyanosis presentCauses :* Hypoventilation as seen in interstitial lung disease & COPD* Cyanotic CHD* Reduced diffusion capacity* Right to left shunt, e.g. A V malformation* V/Q mismatch* High altitudeo Cyanosis absent Causes :* Anemia* CO poisoningo Cyanosis presento Causes :* CHF* Shock* Peripheral vasoconstrictiono Cyanosis absento Causes:* Cyanide poisoning