Pulmonary Circulation and Pulmonary Embolism Flashcards
1
Q
Describe blood supply to lungs
A
- Bronchial: bronchial arteries from systemic circulation supply smooth muscle in airways, nerves and interstitial tissue, 2% of LH output, blood drains to LA via PV
- Pulmonary circulation: PA comprising CO from RH, supplies dense capillary network around alveoli, returns blood to LA via PV
2
Q
Describe bronchial circulation
A
- Arises from aorta and supplies trachea and bronchi
- Nourishes pulmonary vessels, interstitial, pleura
- Drains into azygos vein and pulmonary veins
- Also has a role in regulation of temp and humidity in airways
3
Q
Describe pulmonary circulation
A
- Right to left
- Low pressure, low resistance circuclation
- Contrasts with systemic circulation- high pressure, high resistance circulation
- Considerable room for adaptation enabling large increases in CO accommodated without increasing pressure/ resistance within circulation
4
Q
What is the equation for vascular resistance?
A
(P1-P2)/ blood flow
- Resistance 10x greater in systemic than pulmonary
5
Q
What are the influences on pulmonary vascular resistance?
A
- Mediator, e.g. serotonin (arterial vasoconstriction) and histamine (venoconstriction)
- Intravascular pressures
- Lung volumes
6
Q
Describe intravascular pressure
A
- Fall in pulmonary vascular resistance as pulmonary arterial or venous pressure rises
- Two adaptations- recruitment and distension
7
Q
What are the effects of recruitment and distension?
A
- Recruitment- increase number of perfused capillaries in response to a stimulus
- Distension- individual capillary segments get bigger
8
Q
Describe pulmonary vascular resistance and lung volumes
A
- Extra-alveolar vessels pulled open as lung expands- low resistance at lung volumes and vice versa
- Capillaries- squashed as alveolar press. rises and resistance rises
- Calibre reduced at large lung volumes due to stretching/thinning of alveolar walls- hence vascular resistance rises
9
Q
How is blood flow distributed in the lung?
A
- Unequal throughout lung
- Blood flow decreases from bottom to apices
- Explained by hydrostatic pressure differences within the blood vessels
10
Q
How are ventilation and perfusion controlled locally?
A
- Ventilation in alveoli matches perfusion through capillaries
- If vent decreases in group of alveoli, PCO2 increases and PO2 decreases
- blood flowing here not oxygenated
- Decreased tissue PO2 around under-ventilated alveoli- constricts arteries and diverts blood to better ventilated alveoli
- Ventilation perfusion mismatch
11
Q
What are the non-respiratory functions of pulmonary circulation?
A
- Filter: vital function in protecting systemic arterial circulation from emboli
- Mediator metabolism: ACE involved in converting Ang I to Ang II
12
Q
What is pulmonary hypertension?
A
- mean pulmonary artery press >25mmHg at rest or >30mmHg on exercise
- In health mean PA is 15mmHg
- Associated with an increase in pulmonary vascular resistance
- Ultimately may lead to RH failure
13
Q
What are the causes of pulmonary hypertension?
A
- Group 1- pulmonary arterial hypertension which includes familial and associated with conditions
- Group 2- secondary to heart disease (huge group)
- Group 3- secondary to lung conditions (big group)
- Group 4- chronic thromboembolic PH (small group)
- Group 5- mixed bag of rarities
14
Q
Describe group 1 causes of pulmonary hypertension
A
- Disease of small arteries per se, characterised by vascular proliferation and remodelling
- Increased PVR due to vasoconstriction, remodelling of vessel wall and thrombosis in situ
- Respond to new vasodilator
15
Q
Describe group 2 and 3 causes of pulmonary hypertension
A
- Cause PH secondary to underlying condition
- Heart disease causes post-capillary disease
- Lung conditions can cause pulmonary hypertension due to combination of hypoxia, vasoconstriction and destruction of vascular bed (E.g. emphysema)
