Pulmonary Circulation Flashcards
2 blood supplies to the lungs
the bronchial and the pulmonary circulations
bronchial circulation is part of what circulation and where does it arise from?
The bronchial circulation is part of the systemic circulation
– arises from the aorta
where does the bronchial vascular bed supply oxygen to?
The bronchial vascular bed supplies oxygen and nutrients to the
smooth muscle and interstitial tissues of the lung
where does blood supplied in the smooth muscle and interstitial tissue of the lungs go to afterwards
It drains into pulmonary veins and returns back to the left ventricle
because it drains into pulmonary veins and returns back to the left ventricle what does that mean for venous return and gas exchange
– so pulmonary venous return is slightly greater than cardiac output
– it is also why gas exchange will never be perfect
what does pulmonary circulation distribute and where
The pulmonary circulation transports deoxygenated blood from right ventricle to the alveolar capillaries
– and returns oxygenated blood to the left atrium
pulmonary circulation receives what cardiac output and why
• Pulmonary circulation receives the whole of cardiac output as right
ventricular output must equal left
the pressure in the pulmonary circulation
low pressure system
right ventricular pressure
25/0 mmHg
Pulmonary artery pressure
25/10 mmHg
Pulmonary Pulse pressure
15 mmHg
Mean Pulmonary pressure
15 mmHg
• Pulmonary capillary pressure
~6 mmHg
Left atrial pressure (LAP)
~ 2 mmHg
how is systemic pressure measured
plethysmography
where is pulmonary capillary pressure measured
capillary wedge pressure
– is slightly higher than left atrial pressure
– used to estimate left atrial pressure
HOW is pulmonary capillary pressure measured
• Catheter put through right side into branch of pulmonary artery
– it wedges at the pulmonary capillaries and stops flow
what is resistance and pressure like during inhalation and why?
• As lung expands during inspiration, the extra-alveolar vessels are
pulled open
resistance is low, pressure is low
what is resistance and pressure like during expiration and why
lungs constrict during expiration, alveolar vessels smaller,
greater resistance and pressure
how are the shapes of the alveolar capillaries changed by blood pressure and air pressure and wht
distended by blood pressure
compressed by air pressure
due to its thin walls
why is there a difference between base and apex of lung
Given the height of the lung there is a difference in pressure between
the base and the apex
– it is ~30 cm in height, so this is ~22 mmHg of difference
– apex is -14 mmHg; base is +8 mmHg relative to cardiac leve
3 different zones of pulmonary blood flow
zone 1 - no flow
zone 2 - intermittent flow
zone 3 - continuous flow
zone 1 of pulmonary blood flow
capillary systolic pressure is less than alveolar leads to capillary collapse
– but only under abnormal conditions,
• e.g. very low pulmonary systolic pressure is there no flow at apex
PA > Pa > Pv
zone 2 of pulmonary blood flow
– capillary diastolic pressure less than alveolar
– in exercise, increased pulmonary arterial pressure means continuous flow in lung
Pa > PA > Pv
zone 3 of pulmonary blood flow
capillary diastolic pressure more than alveolar (most of lung).
Pa > Pv > PA
pulmonary resistance
low pressure - low resistance
darcy’s law
can take larger cardiac output w/o increasing resistance or pressure
pulmonary blood volume
500 ml
breathlessness - in heart failure
pulmonary congestion heart failure, ventricle pressure rises, pulmonary pressure rises reduced flow
how come pulmonary volume can increase w/o change in pressure or resistance
due to capillary recruitment and distension
how is pulmonary resistance controled
low neural/hormonal influence (SNS, PNS innervation)
little myogenic/metabolic effect like in other beds
oxygen - important factor
in pulmonary circulation hypoxia leads to …
constriction
pulmonary arteries constrict because of..
hypoxia
what does pulmonary arteries constriction in response to hypoxia control
capillary perfusion
shunting blood away from poorly ventilated areas
matching ventilation and perfusion
important factors of hypoxic disease
– COPD/high altitude cause hypoxic pulmonary vasoconstriction
– ultimately leads pulmonary hypertension and oedema
– may eventually lead to right heart failure
systemic circulation relates to …
starling forces
values in lungs are different
different pressure (hydrostatic pressure, mean interstitial pressure, colloid osmotic pressure) - bigger change in impact
what does low hydrostatic pressure mean
low capillary pressure - 6mm Hg
low lymphatic pumping mean
interstitial pressure lower: -8 mmHg
colloid osmotic pressure means
– leaky capillaries allow more colloid in interstitium: 15 mmHg
– plasma colloid the same: 26 mmHg
by what mechanisms do fluid in the alveoli leave?
active pumping of Na+ creating an osmotic gradient or
negative interstitial pressure sucks it out
cause of peripheral oedema
an imbalance in Starling forces or failure
to clear fluid leads to oedema
impact of interstitial oedema
increases the diffusion distance for O2 and
decreases lung compliance.
– if it reaches positive interstitial fluid pressure, fluid crosses alveolar
membranes giving alveolar oedema
– potentially fatal due to suffocation
major causes of pulmonary oedema
Rises in pulmonary capillary pressure
Increases in pulmonary capillary permeability
how does rise in pulmonary capillary pressure cause pulmonary oedema
left heart failure leads to failure of the circulation and pulmonary congestion
increasing capillary pressure
– high altitude causes hypoxic pulmonary vasoconstriction leading to HAPE
– in chronic conditions lymphatics can expand to compensate
increases in pulmonary capillary permeability
– damage to the capillary in conditions like pneumonia
– damage leads to leakiness and a decrease in the colloid osmotic pressure holding
fluid in the capillary
