Respiratory movements

Result from change in the dimensions and therefore volume of the thoracic cavity. The resulting change in pressure results in inspiration and expiration. The chest can increase in diameter in three dimensions to increase the volume of the thorax:

• Vertical
• Transverse
• Anteroposterior

The vertical diameter is increased mainly by:

• Contraction and flattening of the thoracic diaphragm.
  
  
• Raising of the ribs by external intercostals.
  

The transverse diameter is increased by:
Ribs swinging outwards ( bucket handle movement) Elevation of the ribs Elevation of the sternum This is achieved mainly by the contraction of the external intercostals muscles

The anteroposterior diameter of the thorax is increased by:

• Raising of the ribs.
• Raising of the sternum
  
  

Note: Movement at the costovertebral joints through the long axes of the necks of the ribs results in raising and lowering their anterior ends- the “pump handle movement.”

During expiration:

• Elastic recoil of the lungs
  
  
• Reduction in intra thoracic volume by decrease in all three diameters.
  
  
• Increase in intra thoracic pressure

Accessory muscles of respiration: Required in forced ventilation

a) All muscles attached to the ribs and sternum such as scalene muscles and sternocleidomastoid muscles in the neck

b) Pectoralis major and minor, subclavius and serratus anterior on the chest wall

c) Abdominal wall muscles.

d) Internal intercostal muscles