Physiological Consequences of Elevated Pulmonary Artery Pressure

Question 1

What is the mechanism of inspiratory crackles?

Answer 1

• fibrosis or stiffness of lungs causes collapse on expiration, particularly at the bases
• on inspiration they pop open, causing a high-pitched crackling sound

Question 2

What is asbestosis?

Answer 2

• form of diffuse interstitial lung disease (DILD)
• progressive, diffuse inflammation and abnormal fibrosis of lung parenchyma
  
  • caused by indestructible asbestos bodies
• distrupts and damages A-C membrane
  
  • gas echange and mechanical defects
• presentation:
  
  • progressive exertional breathlessness and cough
  • clubbing, crepitations, +/- cyanosis

Question 3

How does chronic hypoxia lead to pulmonary hypertension?

Answer 3

• low V/Q units are compensated for by diverting blood from poorly ventilated alveoli
• constriction of precapillaries that supply those areas
• widespread leads to diversion to only a few vessels, thereby increasing the pulmonary pressure
• hypoxic vasoconstriction

Question 4

How does chronic inflammation lead to pulmonary hypertension?

Answer 4

• destruction and fibrosis of alveoli and vessels
  
  • e.g. fibrotic process of interstitial lung disease destroys vessels
• reduces the capillary bed
• increases pulmonary pressure

Question 5

What is the effect of pulmonary hypertension on right atrial and systemic venous pressures?

Answer 5

they will be increased

Question 6

What is the mechanism of the hypoxia and desaturation with exercise seen in patients with pulmonary emboli?

Answer 6

decreased perfusion of blood to alveoli

Question 7

What is the effect of increased systemic venous pressure on the systemic capillary bed?

Answer 7

• peripheral oedema
• ascities (fluid in the peritoneal cavity)
• pleural effusions

Question 8

What are the causes of pulmonary hypertension?

Answer 8

1. increased left atrial pressure
   
   • mitral stenosis, LVF
   • increased capillary leakage causing pulmonary oedema
2. increased pulmonary blood flow
   
   • L to R shunts, high flow states, excess central volume
   • relatively uncommon
3. increased pulmonary vascular resistance
   
   • vasoconstriction - low alveolar O2 (hypoventilation)
   • obstruction - embolism, primary pulmonary hypertension
   • obliteration - arteritis, emphysema, pulmonary fibrosis

Question 9

What is the mechanism of pulmonary hypertension causing right ventricular failure?

Answer 9

• pulmonary hypertension causes right ventricular dilation and hypertrophy
  
  • increased systemic venous pressure
    
    • increased hydrostatic pressure = fluid from systemic veins into tissues (peripheral oedema), peritoneal (ascites) and pleural spaces (effusion)
  • poor cardiac output
    
    • lassitude, breathlessness
    • RV pumps against higher P, tf O2’d venous return to LV decreases, CO decreases

Question 10

What is the normal range for bicarbonate on ABG?

Answer 10

21-27mmol/L