Pleura Physiology PDF

Pleura Def: Double-walled sac of serous membrane enclosing lung. Formed of two layers: 1) Parietal pleura: Part of pleura that lines thoracic cavity 2) Visceral pleura: Part that covers firmly the outer surface of the lung INNERVATION OF PLEURA: 1) Parietal layer:  Innervated by...

Pleura Def: Double-walled sac of serous membrane enclosing lung. Formed of two layers: 1) Parietal pleura: Part of pleura that lines thoracic cavity 2) Visceral pleura: Part that covers firmly the outer surface of the lung INNERVATION OF PLEURA: 1) Parietal layer:  Innervated by somatic fibers  Highly sensitive to irritation and inflammation. 2) Visceral pleura:  innervated by autonomic fibers  insensitive to irritation and inflammation. Def:  Narrow cavity between the two layers of pleura.  Filled with "pleural fluid," -1- Def: Fluid in pleural space. Serous fluid secreted by the pleura. Normal value: Normal volume: 10-20 mL. Composition: Similar in composition to plasma but: 1) Protein (< 1.5 g/dl) 2) Contains macrophages (75%), lymphocytes, neutrophils 3) pH: alkaline relative to plasma Dynamics of pleural fluid: 1) Formation: Formed by hydrostatic pressure in systemic vessels of pleural membranes Average rate of 0.6 mL/hour 2) Absorption: Absorbed at a similar rate by osmotic pressure in parietal pleural lymphatic system & pleural vessels leaving only 10-20 mL of fluid in the pleural sac. FORCES KEEPING PLEURAL SPACE FREE OF FLUID & GASES 1) Balance of: a) Hydrostatic pressure (filtration force) b) Oncotic pressure (reabsorption force) 2) Extensive lymphatic vessels (drainage of excess filtering fluid). Main absorption through parietal lymphatics -2- Def: Abnormal excess fluid in the pleural space occurs When production of pleural fluid exceeds reabsorption. Causes: 1) ↑ Hydrostatic pressure as in heart failure. 2) ↓ Plasma oncotic pressure as in liver failure. 3) ↑ Capillary permeability:  Due to inflammation (e.g., pneumonia, malignancy). Diagnosis: 1) Chest x-rays:  Show an area of effusion  Arising from diaphragm & filling the lower portion. 2) Needle aspiration:  And fluid analysis can help. Treatment: 1) Fluid drainage. 2) Treatment of the cause. 3) In some cases:  Surgery may be necessary. -3- Def: Negative pressure in the pleural cavity. Causes of negative intrapleural pressure: 1) Lack of air in the pleural cavity. 2) Continuous tendency of lung to recoil against chest's tendency to expand. Elastic recoil of lung is helped by: a) Elastic tissue in bronchial wall & Lung b) Surface tension of fluid lining alveoli Normal values of I.P.P. (usually negative pressure): 1) -3 mmHg at the end of normal expiration. 2) -6 mmHg at the end of normal inspiration. 3) -30 mmHg in forced inspiration with closed glottis (Muller's experiment). 4) +40 mmHg in forced expiration with closed glottis (Valsalva's maneuver). SIGNIFICANCE OF THE NEGATIVITY OF I.P.P. Responsible for negativity of intrathoracic pressure, which: 1) Helps expansion of the lung during inspiration & prevents its collapse during expiration. 2) ↑ Venous return (suction of blood) to the heart. 3) ↑ Lymphatic drainage. MEASUREMENT OF I.P.P: 1) Direct:  By inserting a needle connected to a manometer. 2) Indirect:  By intra-esophageal balloon connected to a mercury manometer. -4- Def: Disease in which air enters the pleural space causing partial or full lung collapse. CAUSES OF PNEUMOTHORAX 1) Spontaneous (simple) pneumothorax:  Can be further subdivided into: a) Primary spontaneous pneumothorax in absence of underlying lung disease b) Secondary spontaneous pneumothorax Due to underlying lung disease 2) Traumatic pneumothorax: Can result from any kind of trauma to the chest. TYPES OF PNEUMOTHORAX: 1) Open pneumothorax: An injury creates a hole in the chest wall allowing air from the environment to enter the pleural cavity May be due to: a) Penetrating trauma b) Iatrogenic: as in lung biopsy Pleural cavity I.P.P = Atmospheric pressure -5- 2) Closed pneumothorax: Air from the lung itself leaks into the pleural space through a tear in the lung tissue May be due to: a) Fractured rib end tears the lung b) Occurs spontaneously in some individuals. Pleural cavity I.P.P < Atmospheric pressure 3) Tension pneumothorax: The pleural injury acts as a one-way valve, allowing air to enter during inspiration but not escape during expiration. With each inhalation, more air gets trapped inside the chest, leaving less space for the lungs to expand. Pleural cavity (IPP) > Atmospheric pressure -6- MANIFESTATIONS OF PNEUMOTHORAX: 1) Sudden chest pain. 2) Shortness of breath. 3) Shallow & Rapid breathing. 4) Shock & cyanosis. 5) Fast heart rate. 6) Low oxygenation of body tissues. 7) If bilateral, this condition is fatal. 8) If tension pneumothorax  Mediastinal shift : Affected lung collapses medially, Pushing heart & mediastinum in opposite direction Causing the other lung to compress Compress the heart Congested neck veins WHY TENSION PNEUMOTHORAX IS LIFE-THREATENING? Marked increased pressure inside chest can compress the heart  lead to collapse of blood vessels that drain to the heart  ↓ venous return & cardiac output. If untreated, cardiovascular collapse will occur, leading to cardiac arrest. TREATMENT OF PNEUMOTHORAX: 1) Chest tube (intercostal drain): The most definitive initial treatment. 2) Oxygen therapy. 3) In open pneumothorax: Initial treatment with three-sided occlusive dressing. 4) Surgery may be required to repair the hole. -7-