18 Pulmonary Circulation Flashcards
State the differences between pulmonary and systemic circulations
Pulmonary circulation
Heart:
- Thinner ventricular wall
- Lower pressure
Artery:
- Thinner arterial wall
- Shorter in distance
- Lower MAP (13 mmHg, 15% of systemic)
- More compliant
- Lower resistance (1.8, 10% of systemic)
- Lower volume (0.5L, 10% of systemic)
State the functions of pulmonary circulation
- Gas exchange
- Metabolism of vasoactive substances
- Filtration of blood (if small embolism, it can be metabolised)
Name examples of pulmonary shunts
- Bronchial circulation
- Foetal circulation
- Congenital defect (atrial and ventricular septal defect)
Describe the effect of increased cardiac output on pulmonary circulation
Due to the compliance of pulmonary arteries, increased blood flow will increase perfusion to the underperfused capillaries (towards the apex of the lungs; zone 1 and 2).
Increased cardiac output also causes us to breathe harder and quicker
*No oedema or increased pressure
Describe the effect of increasing ventilation on pulmonary circulation
Inspiration: reduces intra-alveolar blood flow
Expiration: reduces extra-alveolar blood flow
Describe the effect of hypoxaemia on pulmonary circulation
Hypoxia causes closure of oxygen sensitive K+ channel to induce depolarisation to open voltage gated Ca2+ channel and elicit smooth muscle constriction
Give one situation each to beneficial and pathological effects in high pulmonary resistance
Foetal life: blood flow through the lowest resistance circulation which is through the shunt: foramen ovale and ductus arteriosus
COPD: reduced alveolar ventilation and air trapping causes reduced oxygen. This increases vascular resistance and cause oedema and right ventricular hypertrophy leading to heart failure
What are the causes of pulmonary oedema
- Increased hydrostatic pressure due to mitral valve stenosis
- Hypoproteinaemia
- Infection
- Blocked lymphatics (cancer)
