Respiratory Systems 15 - Pulmonary Circulation Flashcards
Compare arteries in the pulmonary and systemic circulation
- Arteries in the pulmonary circulation have a thinner wall and larger lumen
- This is because there are lower pressures generated by the right ventricle, as the lungs are close to the heart.
What percentage of blood volume and pressure does the pulmonary circulation contain?
- 10% volume
- 15% pressure
Compare the resistance in the systemic and pulmonary circulation
- Systemic circulation significantly higher resistance
- Pulmonary circulation 1/10th of the resistance
List the functions of pulmonary circulation
- Gas exchange
- Metabolism of vasoactive substances (contains ACE which makes angiotensin II a vasoconstrictor, and breaks down bradykinin a vasodilator)
- Filtration of the blood (eg.thrombosis/ airbubbles, elimination of small emboli. Local obstruction causes vasoconstriction)
Compare an embolus to an embolism
- Embolus is a mass within the circulation capable of causing obstruction
- Embolism is an event characterised by obstruction of a major artery
What is a pulmonary shunt?
A circumstance associated with bypassing the respiratory exchange surface
Give 3 examples of pulmonary shunts
- Bronchial circulation (from the aorta, returns in the pulmonary circulation so goes round left side of the heart twice)
- Foetal circulation (foramen ovale/ ductus arteriosus)
- Congenital defect (ventricular septal defect/atrial septal defect)
How would blood flow in the presence of an atrial septal defect?
- Initially blood would flow from the left side of the heart to the right side as the left side has stronger walls
- However, over time the right side would become stronger and blood would move from the right to the left side of the heart. This would be bad as deoxygenated blood is mixing with oxygenated blood
How would increasing cardiac output affect pulmonary vascular resistance?
- Pulmonary circulation is usually a low resistance high capacity circuit
- Increased cardiac output would increase pulmonary artery distention and increase perfusion of hypoperfused beds (top of the lung)
- There would be a small change in MAP, and minimal fluid leakage so pulmonary function would remain the same with no oedema
What would the effect on pulmonary vascular resistance be after increasing ventilation?
- Inspiration compresses alveolar vessels (by crushing them)
- Expiration compresses extraalveolar vessels (by changing intraplaural pressure)
What would the effect of hypoxaemia be on pulmonary vascular resistance?
- Systemic vascular response is vasodilation, while the pulmonary response is vasoconstriction
- This is due to ventillation perfusion matching (low ventillation of alveoli, so reduced blood supply)
When is the effect of hypoxia on pulmonary vascular resistance beneficial?
- In the foetus
- Blood flows through the path of least resistance
- High resistance in the pulmonary circuit means increased flow through shunts
- The first breath increases alveolar PO2 so the pulmonary vessels dilate
When is the effect of hypoxaemia on pulmonary vascular resistance bad?
- In COPD
- There is reduced alveolar ventillation, and as a result increased resistance in the pulmonary circuit
- This leads to pulmonary hypertension
- Right ventricular hypertrophy occurs leading to congestive heart failure
How does pulmonary fluid balance usually occur?
- There is steady fluid accumulation, as 1mmHg moves out of the capillary net
- This is drained by lymph vessels
- Oedema occurs if this is blocked.
Why does pulmonary oedema occur in left heart failure?
- The left side of the heart cant pump blood around the body, so blood builds up in the lungs
- This leads to hypertension in the lungs, the right side of the heart has to work harder
- Therefore there is increased plasma hydrostatic pressure and increased interstitial fluid
