Pulmonary Vascular Disease

Pulmonary Vascular Disease

Encompasses a number of disorders including:  Congestion, Edema, Embolism, Infarct, Hypertension, and Diffuse Alveolar Damage.
 

• Pulmonary Congestion is an increase in blood within the vasculature of the lungs.  Like most disorders it can be either or acute or chronic. 
  • Acute pulmonary congestion is characterized by increased weight and redness within the lungs.
  • Microscopically the alveolar capillaries tend to be engorged with blood and may be associated with alveolar septal edema and/or focal intralveolar hemorrhage (red blood cells within the septum shown by arrow).
  • In chronic pulmonary congestion the septa are thickened and fibrotic and the alveolar spaces may contain hemosiderin-laden macrophages (heart failure cells).
  •  Chronic congestion is often called brown induration because of the brown color of the hemosiderin macrophages.
  •  Microscopically there may be variable interstitial fibrosis present. 
  • The pathogenesis of pulmonary congestion is most often related to left sided heart failure. 
  • Other causes are mitral valve disease and pulmonary veno-occlusive disease, circulatory collapse. 
  • Patients with this condition will experience dyspnea, orthopnea, and paroxysmal dyspnea.
  •   Heart failure cells (hemosiderin-laden macrophages) may actually be seen in the sputum as well.

   

• Pulmonary edema is characterized by the presence of transudate within the alveolar space (indicated by arrow). 
  • It can result from hemodynamic disturbances [increased capillary hydrostatic pressure due to heart failure or fluid overload] as well as direct increases in the permeability of the capillaries [due to inhaled or circulating toxins, radiation or oxygen toxicity].
  •  Other causes: lymphatic insufficiency due to lymphangitic carcinomatosis or silicosis, decreased interstitial pressure due to pneumothorax, decreased serum oncotic pressure (as in hypoproteinemia), and of course there are unknown pathogenesis associated with neurogenic conditions etc.
  • The histological picture seen in edema is very similar to that seen in chronic pulmonary congestion; this is probably due to the fact that the two events tend to occur together.

   

• Pulmonary embolism is due to a blood clot that occludes the large pulmonary arteries. 
  • The usual source of emboli is the deep veins of the leg (95% of time).
  •  Types of emboli:  thromboembolism (already discussed), bone marrow/ fat embolism (a result of a fracture of the long bones), air embolism, amniotic fluid embolism, foreign body embolism (talc powder from surgical gloves), and tumor embolism.  
    • Pulmonary embolism is typically a problem in people with some other underlying disorder such as cardiac disease or cancer, or who are immobilized for several days to weeks.
    •  It can also be linked to oral contraceptives and people who have experienced recent trauma (bone fractures etc.).

    
     

  • Symptoms of Emboli:
    • Patients who have a normal cardiovascular system, usually present with chest pain, cough, and respiratory distress due to ventilatory/perfusion imbalance.
       

• Results of emboli: 
  • A pulmonary embolism may also result in right heart failure and vascular sclerosis which will lead to pulmonary hypertension.
  •  Most emboli are silent and can cause sudden death; if the patient survives the clot it can result in infarction of the lungs.
  •  After the initial acute insult, emboli often resolve via contraction and fibrinolysis a process referred to as organization.
  •  In time capillary channels are formed creating a mini-lumen from one end of the thrombus to the other (recanalization). 

• This picture shows platelet groups with fibrin in a pre-mortem clot.  The pale layers of platelets mixed with fibrin against the dark layers of red cells produce a striation referred to as the Lines of Zahn.

• This picture shows the initial resorption of the thrombus and the beginning of recanalization. 

• The next slide is typical microscopic picture of recanalization.  Note the fenestrations that have formed in an effort to reestablish circulation

• Pulmonary infarcts is an area of ischemic necrosis caused by occlusion of an arterial supply or venous drainage in the lung.
  •  It is commonly the result of a pulmonary embolism in an individual that has underlying heart or lung disease.
  •  The infarcts have a characteristic wedge-shape (which can be viewed on x-ray) and are usually peripheral.
  •  They are classified as hemorrhagic infarcts (red in color) due to the presence of collateral blood supply. 
  • Infarcts are usually permanent and the end result is that the area will become fibrotic.
  • Microscopically one can see coagulate necrosis of lung parenchyma and alveolar hemorrhage.
  • Patient symptoms include: sudden pain, pleuritic chest pain (hurts when they breathe), hemoptosis, and fever.
  • Complications of pulmonary embolisms include ventilation-perfusion imbalance, right-sided heart failure, and pulmonary hypertension (especially if the person is “throwing” multiple clots).
  • The risk for deep venous thrombosis is usually in people who have been

• Pulmonary hypertension is defined as a pulmonary pressure of greater than ¼ of the systemic pressure. 
  • It is mostly secondary manifestation of recurrent thromboemboli, congenital or acquired heart disease, or some sort of obstructive disorder (COPD), but there can be other causes.
  • One of the most common etiologies is the unknown etiology.
  • An example was given of a drug on the market that resulted in pulmonary hypertension and death.  The drug was Fen-Fen.
  •  Primary Pulmonary hypertension rarely occurs but when it does it is found in young females.
    •  Secondary pulmonary hypertension must always be ruled out before a diagnosis of primary pulmonary hypertension is made.
  •   To some extent early lesions are reversible. 
  • The major complication of pulmonary hypertension is cor pulmonale (right heart failure due to pulmonary hypertension).
  •  Pathology (see picture):
    • Small arteries and arterioles are the most commonly affected vessels.
    •  These vessels undergo a thickening of the media and fibrosis of the intima. (in the picture shown the intima is also thickened)
    • Artheromatous plaque formation is indicative of severe pulmonary hypertension.
    • These vessels do not recanalize because there have been changes to the actual wall of the vessels; damage is irreversible at this point.
    • This picture above shows a plexiform vessel in which small capillaries have infiltrated the vessel in an attempt to reestablish flow.  This indicates end stage pulmonary hypertension.

     

• Diffuse alveolar Damage (also called “shock lung”, “wet lung” etc.), is the anatomic correlate to Acute/Adult Respiratory Distress Syndrome (ARDS); is a result of microvascular endothelial injury, although alveolar epithelial cell injury may also be important. 
  • Usually arises from pulmonary infection especially viral infections (i.e. SARS, avian flu). [Remember that the characteristic of viral pneumonia is interstitial pnemonitis].
  • Is usually the result of continued infection with a viral agent (in diseases like SARS and bird flu this symptom which should take a few weeks, can happen the next day).
  • Can also be caused by aspiration of toxins, drug reactions/overdose, autoimmune reactions, trauma (shock etc.), or septicemia or other organ system disease such as acute hemorrhagic pancreatitis.
  •   Pathology:
    • The gross appearance of the lung is heavy, and edematous with areas of hemorrhage, atelectasis and consolidation. 
    • Microscopically the characteristic feature is the appearance of hyaline membrane (see arrow) with alveolar type II cell hyperplasia. 
      • Hyaline membrane disrupts air exchange.
    • Edema, congestion and variable cellular infiltrates may also be seen.

§         As was mention before SARS shows rapid progression to the ARDS stage. A throwback to Micro… this disease is a coronavirus.

• More than half of the patients infected with this virus will die.
• When you hear of individuals dying from ARDS usually is a result of progression to this hyaline membrane phase.

Atelectasis:

• Atelectasis is a condition defined by the collapse or incomplete expansion of the alveolar air spaces. 
• It can be either acquired or primary. 
• Primary atelectasis implies that there has never been adequate expansion of the alveoli while acquired can be thought of as loss of normal expansion of the alveoli.
•  Primary atelectasis is seen in very immature infants in whim respiratory centers of the brain a respiratory muscles are poorly established. 
• Acquired atelectasis occurs primarily in adults and can be secondary to stasis after surgery, obstruction, compression, or loss of surfactant.
  • Obstruction atelectasis is the consequence of complete obstruction of an airway by a tumor, foreign body, or mucus plug. 
    • In time it leads to resorption of the oxygen trapped in the affected alveoli. 
    • As a result, the blood supply to these alveoli is not oxygenated.
  • Compression atelectasis is more common and results when the pleural cavity is partially or completely filled by some type of exudates (fluid, blood, air, tumor etc.). 
    • May also be due to an inability to fully expand the lungs.  An example is loss of surfactant which may occur in ARDS or chemical pneumonitis. 
    • Respiratory distress is a result of a deficiency of pulmonary surfactant which is needed to reduce surface tension in the lungs.  Fetal surfactant is produced after 35 weeks of gestation and thus premature infants are at risk of developing respiratory distress.

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