P L6 - Pulm circulation Flashcards
2 types of circulation in lungs?
- Bronchial: Perfuses lung tissue
- Pulmonary: Perfuses alveoli
Is the pulmonary vascular bed fully perfused at resting cardiac output?
No
What happens when u move from supine to erect in regards to pulm circulation?
Results in 400ml of pulmonary blood vol being redistributed to systemic circulation
Primary function of pulm circulation?
To carry deoxygenated blood from the systemic circulation to the lungs.
Characteristics of pulm circulation?
- Non metabolic circulation (mainly involved in gas exchange)
- Small circulation (9-10%)
- Must maintain low pressure with changes in cardiac output
- It contains a fibrinolytic system (prevents build up of fibrin)
Secondary function of pulm circulation
- Blood reserve
- Renin- angiotensin system (regulates BP, fluid and salt balance – Angiotensin-2 causes vasoconstriction. ACE converts angiotensin-1 to 2.
- –> ACE is widely expressed in lung capillary blood vessels
Bronchial circulation - Type? what arteries does it arise from? What does it supply? where does it terminate? How many are there? How much of the total cardiac output?
- systemic circulation
- arises from the aorta and the intercostal A.
- Provides blood to bronchi, large BVs. hilar lymph nodes and visceral pleura
- Terminates at level of terminal bronchioles ———- Here it joins pulmonary capillaries and venules
- There are 3 main bronchial arteries – 2 in left and 1 in the right of the lung
- Forms 1-2% of total cardiac output
What are the pressures of the bronchial circulation similar to?
Since its a part of the systemic circulation it will have systemic blood pressures
What tissues of the lung does bronchial circ. supply?
Provides oxygen to the supporting tissues of the lung:
- Connective supporting tissue
- Septa
- Large and small bronchioles
- Large blood vessels
Where does bronchial circulation drain into?
Drains into right heart via bronchial veins and left side of heart via the bronchopulmonary veins
How is blood in the left atrium of the heart a venous admixture?
It contains 2% deoxygenated blood coming from the bronchopulmonary veins of the bronchial circulation
But is mostly made of oxygenated blood (98%)
Define gas transport:
Gas transport – Movement of O2 and CO2 for the purpose of replacing O2 thats been used up and excretion of CO2
How is pressure different in pulm and systemic circulation? (MAP, Arterial P, Venous P, systolic P, diastolic P)
Pressure is much higher in systemic circulation that in pulm circulation.
MAP (syst.) = 100 mmHg
MAP (pulm) = 14 mmHg
avg. arterial P. (pulm) = 12 mmHg vs. 30
avg. venous P. (pulm) = 8 mmHg vs. 10
systolic P (pulm) = 25 vs 120
Diastolic P (pulm) = 8. vs. 80
Why is resistance in pulm circulation lower than in systemic circ?
Since pressure gradient driving the flow is much lower in pulm. circ. than in systemic circ. and since cardiac output remains constant —> There needs to be a lower resistance in the pulmonary capillaries to allow for adequate flow rate (Flow = change in pressure/resistance)
The architecture of the normal pulmonary vasculature is designed to
* ensure a ______ compliance- ____ walls, _____ diameter
* _____ resistance network
* _______ for gas exchange
The architecture of the normal pulmonary vasculature is designed to
* ensure a high compliance- thin walls, large diameter
* low resistance network
* extensive surface area for gas exchange
Pulmonary arteries have:
a. ____ walls - _______ muscle and elastin
b. arteries are _____ but have a ______ diameter
c. arteries are very ______ and therefore have:
1)
2)
a. thin walls - less muscle and elastin
b. arteries are short but have a large diameter
c. arteries are very distensible
1) high arterial compliance
2) low resistance (Input pressure- output pressure/flow)
True or false:
1. Pulmonary veins are structurally similar to veins in systemic circ.
2. Do not branch
3. Veins move towards the airways
4. Pressure around pulmonary vein is more than alveolar pressure
5. have Intrinsic tendency to collapse
- True
- False - Have a pattern of branching like tracheobronchial tree
- False - move away
- F - Pressure around pulmonary vein is less than alveolar pressure (Extra-alveolar vessels)
- true
The pressure around pulmonary vein is _____ than alveolar pressure (Extra-alveolar vessels)
less
Do the pulm. veins have a tendency to collapse? What prevents this
Yes.
They’re Pulled open by traction by the lung parenchyma
Change in structure of pulmonary BVs from arteries –> capillaries (SM, Cells)
- Smooth Muscle decreases as you go from arteries to caps.
- In partially muscular arteries there are intermediate cells while in non-muscular arteries there are pericytes
- Capillaries are only one cell thick and their endothelial memb. fuses with those of the alveoli.
Where are pericytes and intermediate cells present? What are their functions?
– In partially muscular arteries there are intermediate cells while in non-muscular arteries there are pericytes
- Intermediate cells are thought to be located between muscle cells and pericytes and are believed to have contractile properties
- Pericytes play a role in structural integrity and communication with smaller vessels
Pulmonary BVs can be located in 2 regions which are?
Regarding both of them say:
– where they’re located
– How their diameter changes with lung inflation
Intra-acinar vessels are associated with respiratory bronchioles, alveolar ducts and
alveolar walls, i.e., airways involved in gas exchange.
└diameter of capillaries that populate the alveolar septal walls tends to
decrease with lung inflation
Extra-alveolar vessels are tethered to lung parenchyma and distend and/or lengthen
with lung inflation.
How may inspiration cause increased resistance in capillaries?
Inspiration - inflates alveoli - puts pressure on capillaries and compresses them thus increasing resistance
Accounts for 40% of resistance
pulmonary capillaries - surrounded by very small area of _______ and primarily by ________
pulmonary capillaries - surrounded by very small area of interstitial fluid and primarily by air filled alveoli
diameter of capillaries and capillary blood flow is determined by the relationship between _______and_______
blood pressure and alveolar pressure
(inc. blood P = inc. flow, Inc. alv. P = dec. flow – due to increased resistance)
as blood flow increases (inc. cardiac output), resistance ________
Explain why/how this trend occurs
decreases
This occurs due to:
- Increase in capillary recruitment
- Use of capillary reserve
- Due to the distensibility of arteries, arterioles and capillaries (they expand more as blood flow increases)
influence of lung expansion on blood flow
- large vessels are expanded by decrease in pressure
- capillaries may be compressed by expansion of the alveoli
3 factors that contribute to resistance in the pulmonary circulation?
- Vessels have smooth muscle that is relaxed (increased diameter)
- As blood flow increases, resistance decreases due to capillary recruitment, use of capillary reserve and distensibility of the arterial vessels
- Lung expansion: As lungs expand:
—— greater vessels expand due to a decrease in pressure decreasing resistance
—— Capillaries may be compressed due to expansion of alveoli thus increasing resistance.
Explain How an increase or decrease in lung volume affects resistance in extra-alveolar and alveolar blood capillaries.
LOW LUNG VOL.;
– The extra alveolar vessels are compressed as tissues surrounding them are compressed thus there’s an increase in resistance in these vessels. A change in intrapleural Pressure affects the radius of these vessels. A more -ve intrapleural P (goes from -4 to -6 during inspiration) pulls open these vessels decreasing resistance. So thus at low lung volumes theres an increased resistance in these vessels.
– The vessels surrounding the alveoli however are distended as they are not being compressed by the expanded alveoli and thus have low resistance.
HIGH LUNG VOL:
– At high lung vol (during inspiration) The intrapleural pressure is more -ve and the tissues surrounding the extra-alveolar vessels are less compressed thus these vessels become slightly distended thus decreasing resistance in these vessels.
– However at high lung volumes, the alveoli become inflated and compress the capillaries surrounding the alveoli - thus increasing resistance in them
THEREFORE BOTH HIGH AND LOW LUNG VOLUMES HAVE THE EFFECT OF INCREASING RESISTANCE IN THE PULMONARY BLOOD VESSELS.
At what lung volume will resistance in the pulm. capillaries be optimal?
At both high and low lung volumes theres resistance in alveolar and extra-alveolar capillaries respectively.
There is thus least resistance in pulm capillaries at FRC (functional residual capacity).
What law can we use to understand the movement of fluid/flux of fluid across compartments in the lung.
Starling’s law
What is the flux of fluid determined by according to starlings law?
(1) Capillary Hydrostatic,
(2) Tissue Hydrostatic,
(3) Capillary Oncotic,
(4) Tissue Oncotic Pressures
Hydrostatic pressure? What can it be altered by?
Hydrostatic – Pressure that any fluid exerts within a given space – can be altered by gravity.
Oncotic pressure (colloid osmotic pressure) is the _______ pressure resulting from the difference within the ____ between the ____ and
__________.
Oncotic pressure (colloid osmotic pressure) is the osmotic pressure resulting from the difference within the ECF between the protein contents of plasma and interstitial fluid.
Differences between systemic and pulmonary capillaries:
a. pulmonary capillary pressure is ______ ( ___ mm. Hg.)
b. lung interstitial pressure more ______ ( ____ mm.Hg.)
c. pulmonary capillaries- _______ to proteins interstitial colloidal osmotic pressure _____ ( ____ mm. Hg.)
d. alveolar walls _______
e. blood passes though capillaries in ____ sec (time of one cardiac cycle at rest)
a. pulmonary capillary pressure low ( 7mm. Hg.)
b. lung interstitial pressure more negative (-8mm.Hg.)
c. pulmonary capillaries- “leaky” to proteins interstitial colloidal osmotic pressure high (14mm. Hg.)
d. alveolar walls thin and weak
e. blood passes though capillaries in 0.8 sec (time of one cardiac cycle at rest)
Fluid is kept in capillaries due to _________ and_______
opposing capillary hydrostatic and oncotic pressures
Alveolar Hydrostatic & Alveolar Oncotic Pressures are very important – true or false
False – they are negligible
What are the outward and inward forces involved in filtration pressure? What are their values?
Net outward forces:
– Interstitial oncotic pressure = - 14 mmHg
– INterstitial hydrostatic pressure = -8 mmHg
– Capillary hydrostatic pressure = 7 mmHg
Total = 29 mmHg
Net inward forces:
– Plasma oncotic pressure = - 28 mmHg
What is the net filtration pressure?
Net filtration pressure = 1 mmHg
What happens to the interstitial fluid in the lungs?
Some of it evaporated during respiration
Most of it carried away by the lymph nodes in the lungs.
What is pulmonary oedema – where can it occur in the lung?
Build up of water in the lung
– Alveolar pulm oedema is water in alveoli
– Interstitial pulm. oedema is water in the interstitium
What can pulm oedema be the result of
Cardiogenic reasons:
– Heart failure (example: R. side heart failure due to hypertension possibly due to lack of O2)
Non-cardiogenic reasons;
– Infection (like pneumonia)
– High altitude
What does pulm. oedema mainly impair?
Gas exchange
What is the ventilation perfusion ratio in humans?
0.84 (4.2 L/min// 5 L/min – where 4.2 is the ventilation occuring and 5 is the perfusion)
Physiological shunt —>
Physiological dead space —>
Physiological shunt —> Perfusion without ventilation (blood reaches the lung but no gas exchange occurs)
Physiological dead space —> Ventilation without perfusion (Gas reaches the membrane but doesnt cross the memb. into the blood)
What is pulmonary flow dependent on?
- Pulm. vascular resistance
- Pressure gradient
- Gravity
- PaO2
Where is intrapleural pressure more -ve? (base/apex)
- What are the values of IP at base, apex and at level of heart?
Where are the alveoli smaller? base/apex?
Where can the alveoli distend more during inspiration?
Why is this so? explain in terms of hydrostatic pressure and where it’s more?
More -ve at apex (-10)
IP increases as you move down the lung:: at level of heart = -5mmHg
At base of lung = -2.5 mmHg
Alveoli are smaller are the base and larger at the apex thus they can distend more at the base than they can at the apex.
Alveoli are smaller at the base of the lung due to increased hydrostatic pressure exerted at the base of the lung
As you move down the lung (towards the base) what trend would you expect to see in the ventilation and perfusion?
Where is blood perfusion more and why?
As you move down the lung::
– Increased ventilation
— Increased blood perfusion
Blood perfusion is more due to an increased gravitational force
Would the V/Q ratio be high or low for the following:
– Gas > perfusion
– Gas < perfusion
high
low
_____ Pressure needs to be lower than ____ pressure for sufficient perfusion
(alveolar/arterial)
alveolar, arterial
Explain the relationship between the flow in terms of the pulm. arterial pressure and the alveolar pressure in the different zones of the lung.
Zone 1: Alveolar P always greater than pulm. P – NO FLOW
Zone 2: Pulm P. greater than alveolar P during systole and alveolar P greater than pulm. P during diastole – thus – INTERMITTENT FLOW
Zone 2: Pulm. blood P. always greater than alveolar P. –> CONTINUOUS FLOW.
How do the following change as you move from the apex to the base of the lung?
- Intrapleural P
- Mean pulm. arterial pressure
- Perfusion values (Q)
- Intrapleural P::
> -10 –> -5 –> -2.5 - Mean pulm. arterial pressure::
> 4 –> 15 –> 26 mmHg - Perfusion values (Q)::
> 0.56 –> 5 –> 10.3
What are the V/Q values at base and apex of lung and what is the avg. value.
What does this mean in terms of the amt of ventilation and perfusion occuring?
Base: 0.63
Apex: 3.4
Avg: 0.8
More perfusion than ventilation
Is there more ventilation or perfusion occuring in the lungs?
More perfusion
Does vasoconstriction as a result of alveolar hypoxia occur in a linear or non-linear fashion?
Non-linear
What is normal oxygen partial P in alveoli and below what level is the alveolar constriction mexchanism activated?
normal = 104 mmHg
Below = 70 mmHg
