When fluid or air make it into the pleural cavity this can cause a restriction that makes it impossible for the lungs to completely expand. Pleurisy, pleural effusions, pneumothorax and hemothorax are three disease processes that involve the pleural cavity..
The pleural space contains mostly air, although there is a small amount of pleural fluid. The fluid is used as a lubricant to allow the two layers of membranes to easily rub against each other to aid in inspiration. When the muscles of respiration contract, this pulls the pleural cavity outward creating a negative pressure that expands to the lungs. This allows for air to be drawn in. I discussed how we breathe in this post.
There are not connections between the pleural cavity of the right and left lung, and it is for this reason if you have air in the right lung (collapsed lung or pneumothorax) it will not effect the other lung.
Pleurisy: This is usually a complication of some other disease, and generally causes pain with inspiration. Likewise, it can precede a pleural effusion. According to Egan's Fundamentals of Respiratory Care, it's characterized by "fibrinous exudate on the pleural surface." It can also produce a rub on inspiration.
Rub: This is a grating sound on inspiration.
Pleural effusion: This is when fluid accumulates in the pleural cavity that surrounds the lungs. The only way fluid can increase in the pleural cavity is if more is produced than is reabsorbed by the body. The only way for this to happen is if there is an underlying disease process.
There are two types of pleural effusions. Yet first we must define oncotic pressure and hydrostatic pressure.
Oncotic pressure: This is pressure exerted by proteins in the pleural space (or blood) that pulls water into this area. This pressure must be balanced with hydrostatic pressure in order for the fluid in the pleural space to stay at a normal, healthy level.
Hydrostatic pressure: Also called fluid statics. It's a pressure that drives fluid out of the cavity.
Transudative causes: This is when either the oncotic or hydrostatic pressure increases and causes water to accumulate in the plueral spaces. This can be caused by:
- Congested heart failure
- Liver cirrhosis
- Pulmonary embolism
- Lung cancer
- Fungal or Viral infections
- Systemic Lupas
- Rheumatoid arthritis
- Pulmonary embolism
- Atelectisis due to lack of ability of lungs to expand
- Dyspnea (feeling of air hunger)
- Increased sputum production
- Lack of chest movement
- Diminished or absent breath sounds over effusion
- Vocal fremitis is absent
- Percussion of chest wall is flat
- Egophany may on effected side
- Medistinal shift away from the fluid
- Tracheal shift away from the fluid
References: Egans Fundamentals of Respiratory Care