37 Pathophysiology of Pulmonary Vascular Disease

Question 1

Pulmonary vascular disease

• Characterized by…
• This causes…
• Can be caused by disorders that…

Answer 1

• Characterized by…
  
  • Narrowing or occlusion of the pre-capillary pulmonary arteries
• This causes…
  
  • An increase in pulmonary vascular resistance, which leads to an abnormally high pulmonary artery pressure (pulmonary hypertension)
• Can be caused by disorders that…
  
  • Affect only the pulmonary vasculature (intrinsic)
  • Result from diseases that damage the airways and/or parenchyma of the lungs (extrinsic)

Question 2

Intrinsic pulmonary vascular disease

Answer 2

• Idiopathic pulmonary arterial hypertension
• Chronic thromboembolic pulmonary hypertension
• Pulmonary hypertension associated with collagen vascular diseases
• HIV
• Left to right shunts

Question 3

Alterations in respiratory mechanics

Answer 3

• Intrinsic pulmonary vascular disease does not affect the pulmonary parenchyma or the airways
• Elastic recoil, compliance, and airway resistance are typically normal

Question 4

Alterations in gas exchange:
Narrowing or occlusion of pulmonary arteries leads to…

Answer 4

• Redistribution of pulmonary blood flow
• An abnormally large degree of mismatching between ventilation and perfusion

Question 5

Alterations in gas exchange:
V/Q regions, PaO2, minute ventilation, and PaCO2

• V/Q regions
• PaO2 and PA-aO2
• Minute ventilation and PaCO2

Answer 5

• V/Q regions
  
  • These diseases produce high V/Q regions
    
    • Since blood flow is decreased or stopped to lung units that remain normally ventilated
  • This blood must be diverted to other regions of the lungs, which will then have too much perfusion for the amount of ventilation (i.e. low V/Q)
• PaO2 and PA-aO2
  
  • The low V/Q units will cause the PaO2 to fall and the PA-aO2 to increase
• Minute ventilation and PaCO2
  
  • High V/Q units increase the amount of alveolar and physiologic dead space
  • This increases the minute ventilation required to maintain a normal PaCO2
  • Patients with pulmonary vascular disease usually increase minute ventilation so that PaCO2 remains normal or even decreases

Question 6

Alterations in gas exchange

• PaO2 with exercise
• The mechanism

Answer 6

• PaO2 with exercise
  
  • Like emphysema and interstitial lung disease, disorders of the pulmonary vasculature are often associated with a fall in PaO2 with exercise
• The mechanism
  
  • With a large decrease in the surface area available for diffusion, exercise causes…
    
    • An increase in capillary blood velocity
    • A decrease in the time available for equilibration between the PaO2 of alveolar gas and capillary blood

Question 7

Pulmonary function tests

• Lung and chest wall mechanics
• Lung volumes and flow rates
• PFT findings
• DLCO
• Surface area of the alveolar-capillary interface

Answer 7

• Lung and chest wall mechanics
  
  • Intrinsic pulmonary vascular disease does not alter lung or chest wall mechanics
• Lung volumes and flow rates
  
  • Lung volumes and flow rates measured by pulmonary function testing are usually normal
• PFT findings
  
  • Patients with pulmonary vascular damage from parenchymal lung disease will, of course, have PFT findings typical of the underlying disease
• DLCO
  
  • Both intrinsic and extrinsic pulmonary vascular diseases reduce the DLCO
• Surface area of the alveolar-capillary interface
  
  • This is because vascular narrowing and occlusion decrease the surface area of the alveolar-capillary interface

Question 8

Alterations in cardiovascular function

• Pulmonary vascular disease causes…
• This can lead to…
• …which is manifested clinically by…

Answer 8

• Pulmonary vascular disease causes…
  
  • Pulmonary hypertension
• This can lead to…
  
  • Increased right ventricular afterload
  • Right ventricular failure
• …which is manifested clinically by…
  
  • Peripheral edema
  • Hepatomegaly
  • Jugular venous distention

Question 9

Alterations in cardiovascular function

• Right ventricular failure can reduce left ventricular output in two ways
• Both of these processes…

Answer 9

• Right ventricular failure can reduce left ventricular output in two ways
  
  • Impaired RV systolic function reduces the amount of blood pumped to the left heart
  • RV dilation, when severe, can reduce LV size and compliance
• Both of these processes…
  
  • Reduce LV preload, which can lead to a drop in cardiac output and even hypotension

Question 10

Pathophysiology of dyspnea and exercise intolerance

• Intrinsic pulmonary vascular disease leads to symptoms primarily through its effects on…
• With increased activity, cardiac output and blood flow through the lungs…
• Since vascular resistance is high, this leads to…
• RV dysfunction leads to…

Answer 10

• Intrinsic pulmonary vascular disease leads to symptoms primarily through its effects on…
  
  • Cardiovascular function
• With increased activity, cardiac output and blood flow through the lungs…
  
  • Increases
• Since vascular resistance is high, this leads to…
  
  • A further increase in pulmonary artery pressure
  • Increased RV afterload
  • Precipitated or worsened RV failure
• RV dysfunction leads to…
  
  • Inadequate LV preload
  • Prevention of cardiac output from increasing sufficiently to meet the metabolic demands of the body
  • Dyspnea and exercise intolerance