L20. Physiological Consequences of Elevated Pulmonary Artery Pressure

Question 1

What do abnormalities in pulmonary circulation often lead to?

Answer 1

Increased leakage of fluid across the capillaries into the interstitial space as a result of increased pressure in the pulmonary arteries

Question 2

What are the three major mechanisms to disturb the pulmonary vasculature?

Answer 2

1. Inflammation and fibrotic processes that physically destroy the wall
2. Reactive vasoconstriction (a compensation for V/Q mismatch)
3. Obstruction of the vessels from within (clots)

Question 3

What is a common cardiac consequence of pulmonary hypertension?

Answer 3

Increase in right heart pressure leading to right ventricular hypertrophy, increase in systemic venous pressure and eventually right heart failure

Question 4

What are the common cardiac findings of pulmonary hypertension

Answer 4

Sinus tachycardia
Right ventricular heaves
High JVP with v waves
Low S2 and 4th heart sound 
Pulmonary systolic ejection murmurs

Question 5

What are the ways to examine if there is pathology in the pulmonary vasculature?

Answer 5

No specific examination available (by exclusion)
Investigation: CT angiogram with injection of dyes
V/Q Scan where radioactive particles distribute around the lungs vs. the distribution in the blood.

Question 6

What is the main reason for the V/Q scan?

Answer 6

Distinguish prime abnormalities (alveolar vs. capillary)

Question 7

What are the consequences of pulmonary hypertension on the right atrium?

Answer 7

Increase in pressure

Question 8

What are the consequences of pulmonary hypertension on the systemic venous pressure?

Answer 8

Increase in pressure

Question 9

What are the consequences of increased systemic venous pressure?

Answer 9

The systemic capillary bed (tissues) is overwhelmed with pressure and fluid will leak into the tissues = peripheral oedema
Ascites (accumulation of fluid in the peritoneum)
Pleural effusions

Question 10

What are the major causes of pulmonary hypotension?

Answer 10

Increased in pulmonary vascular resistance

1. Vasoconstriction (compensation and hypoventilation)
2. obstruction (embolism)
3. Obliteration (inflammation)

Also increased left arterial pressure (back up of pressure)
And largely increased pulmonary blood flow

Question 11

Describe respiratory acidosis and the compensation mechanism

Answer 11

Due to CO2 retention (thus high CO2) - hypoventilation
and compensated for by bicarbonate retention to bring the pH back up to near normal (a renal mechanism: takes several days to act)

Question 12

Describe metabolic acidosis and the compensation mechanism

Answer 12

Due to increased production of acid (lactic acid in exercise) or loss of base (diarrhoea) and shows a normal or decreased CO2 levels.
Compensation is by hyperventilation to remove more CO2 and achieve a low CO2 to bring pH back to near normal

Question 13

Describe respiratory alkalosis and the compensation mechanism

Answer 13

Due to a low CO2 (hyperventilation) and is compensated for by hyperventilation to bicarbonate excretion to get rid of the base and bring the pH back down to near normal (a renal compensation which takes days to occur)

Question 14

Describe metabolic alkalosis and the compensation mechanism

Answer 14

Due to an increase in HCO3 or a loss of acid and is only limitedly compensated for by hypoventilation to retain CO2 acid levels. This is because too much hypoventilation leads to hypoxia.