Name the respiratory disorder in which the alveolar surface area involved in gas exchange is significantly reduced due to damage in the alveolar walls.

Which chronic disorder is characterized by damage to the alveolar walls,leading to a decrease in the respiratory surface area,and is primarily caused by cigarette smoking?

In this disease,the respiratory surface area decreases.

What is correct for emphysema?

Assertion $(A):$ $A$ person goes to high altitude and experiences 'altitude sickness' with symptoms like breathing difficulty and heart palpitations.
Reason $(R):$ Due to low atmospheric pressure at high altitude,the body does not get sufficient oxygen.
In the light of the above statements,choose the correct answer from the options given below.

What are the symptoms of $Altitude$ $Sickness$?