The movement of air into and out of the lungs is carried out by creating a pressure gradient between the lungs and the atmosphere. The pressure within the lungs is less than the atmospheric pressure so, there is a negative pressure in the lungs with respect to atmospheric pressure. The puncture in the chest affects this pressure gradient maintained by the lungs and thus, may cause cessation of breathing

For efficient exchange of gases, respiratory surface must have certain characteristics such as
(i) it must be thin, moist and permeable to respiratory gases.
(ii) it must be large.
(iii) it must be highly vascular.
Only alveolar region has these characteristics. Thus, diffusion of gases occurs in this region only.

In male, the lateral movements of thorax constitutes 25% of breathing, while the abdominal movement accounts for 75% breathing. Thus, it regarded as abdominal breathing.
In women, particular in pregnant women, the entire breathing is through lateral movements of the thorax. thus, breathing in women is regarded as thoracic.
The VC is higher in men than in women and in the young ones than in the old persons.

The foul air follows the route given below
Alveoli\(\rightarrow \)Alveolar ducts\(\rightarrow \)Bronchioles\(\rightarrow \)Bronchi\(\rightarrow \)Trachea\(\rightarrow \)Larynx\(\rightarrow \)Glottis\(\rightarrow \)Pharynx\(\rightarrow \)Internal nares\(\rightarrow \)Nasal chambers\(\rightarrow \)External nares\(\rightarrow \)Atmosphere.
The tidal volume increases 4-10 times during excitment and activity.

A person sleeping in such room gets carbon monoxide poisonong.CO combines with Hb more readily than oxygen forming carboxyhaemoglobin.This reduce the amount of free Hb available for carrying O₂ .Thus, the tissue is starved of O₂ .this is the reason why it is not advisable to sleep in closed rooms warmed with coals