Respiratory Mechanics

1. Inspiration

   Annotations:

   • Diaphragm is the most important inspiratory muscle, supplied by C3-5 (phrenic nerves). Abdo content move down and forwards Increased in chest cavity.External intercostal muscle aids in moving ribs up and forward Accessory muscles of inspiration does not really do much in normal inspiration. Involved mostly in forced inspiration. (exercise), Scalene muscles to elevate 2 ribs. Sternomastoids to raise sternum And the minor role is the alas nasi (flaring of nasal muscles) Small muscles of neck and head.
2. Expiration

   Annotations:

   • IT is a passive. The lungs go back to normal. Active expiration is found from exercise and it is aided by the abdominal wall muscles which is the most important muscle. The rectus abdominus, external and internal oblique and trnasverse muscles. Pushes diaphragm upwards. Internal intercostals: Opposite action to the external intercostals Neck and back muscles.

Annotations:

• Elasticity: Tendency to return to resting volume after distension. Partly due to the arragnement of tissue fibres of elastin and collagen.

1. Surface Tension

   Annotations:

   • Measure of the force acting to pull a liquid's surface molecules together at air-liquid interface. Accounts for 1/2 recoil of the lungsFollows Laplace Law.
2. Mechanics of Breathing

   Annotations:

   • Air deflation and inflation and pressure curve.
3. Surfactant

   Annotations:

   • maintains lung compliance and the low surface tension Secreted by Type II alveolar cells., Rapid turnover, depleted in regions with no blood flow. Consists of  90% DPPC 10% Proteins. SOme part are hydrophobic and hydrophillic, the repulsive force interfeure with hydrogen bonding between adjacent molecules of water. Therefore it lower surface tension and increased compliance, it stabilizes alveoli and keep alveoli dry.
4. Interdependence

   Annotations:

   • Alveolar are interconnected to each other, hence contribute to stability