Pulmonary Circulation Flashcards by Riki Sharma

What happens to pulmonary artery during low O2?

vasoconstriction (systemic results to vasodilation)

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Why does the pulmonary arteries vasoconstrict in areas with low O2?

To shunt blood in areas with more O2

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What things influence the rate of diffusion of gases?

pressure difference (air-blood)
Area of alveoli for diffusion
Thickness of alveoli tissue

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What is the diffusion equation?

Vgas = Area/ Thickness * Constant(P1-P2)

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Which condition is related to decreased area for gas exchange?

Emphysema

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Which condition is related to increased thickness?

Pulmonary fibrosis

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What does diffusion limitation mean?

The membrane is the largest obstacle in the alveoli in the gas exchange process (SUCH AS CO carbon monoxide)

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What does perfusion limitation mean?

The perfusion capacity limits the amount of chemical being exchanged (IE. N2O nitrous dioxide)

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Is O2 diffusion or perfusion limited?

normal person –> perfusion limited

disease –> diffusion

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How to measure diffusion lung function?

Diffusing capacity of CO:
Patient inhales small amount of CO –> measures CO exhaled –> compare with predicted

Healthy –> 75-140%
Disease –> <40%

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What happens to O2 exchange at rest vs. exercise?

At rest:
Blood flow slow –> more opportunity to migrate to blood from alveoli for a given time –> PaO2 reaches the same alveolar PaO2 quicker

At Exercise:
Blood flowing quicker –> less gas exchane happening for a given time –> neeed to travel a greater length in capillary to reach the same PaO2 as alveoli

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What increases alveolar vessel resistance?

Inspiration –> increased lung volume expands lung and elongates the vessels making them short but narrow

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What increases arteriolar resistance?

Expiration –> decreases lung volume

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When is the pulmonary resistance the lowest?

At functional residual capacity (FRC)

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What sound can be heard for PTN?

Loud P2 –> accentuated second heart sound at left upper sternal border

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What is cor pulmonale ?

Untreated pulmonary HTN that leads to high RVP, RV hypertrophy (dilation), elevated JVP, lower extremity edema, hepatomegaly

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What is the equation to calculate PA prressure?

PApressure = CO*PVR + LAP

so increase in CO [left to right shunts], PVR, or LAP [valve disease, CHF] can lead to PTN

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What are some secondary causes of PTN?

COPD
chronic pumlonary emboli
pulmonary fibrosis (scleroderma)
Sleep apnea or high altitude
HIV

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T or F: 1o PTN is rare

T: due to BMPR2 mutation that affects endothelial function

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What are the treatments for 1o PTN?

A) Bosetan –> antagonist endothelial-1 receptors
B) Sildenafil –> inhibits PDE-5 in smooth muscles of lungs

all PO –> leads to vasodilation

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What is normal for PaO2?

> 60 mmHg

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How to calculate the partial pressure of O2 in the alveoli?

PAO2 = PIO2 - (PaCO2/R) = 150 - (PaCO2/0.8)

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What is the A-a gradient?

difference between alveolar (A) and arterial (a) O2

10-15 mmHg (A-a gradient)

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What means if hypoxemic with normal A-a gradient?

Alveoli function good but not inhaling a lot of O2

due to hypoventilation or high altitude

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In what conditions will hypoxemia and high A-a gradient occur?

Alveoli not working, O2 not getting into blood | Fibrosis, Shunt, V/Q mismatch

T or F: CO2 is more sensitive than O2

F: O2 is

What happens in a diffusion limiting disease?

- hypoxemia - hypercapnea - alveolar destruction --> dead space --> further hypercapnia

In a normal lung, what is the V/Q ratio - (aka R)?

0.8

What does a VQ less than 1 mean?

Means Q higher than V (perfusion wasted; going to areas where there isnt enough O2)

What is a V/Q of 0 and how does it happen?

Means SHUNTING venous blood going to arterial without being oxygenated/ going an area of ventilation --> hypoxemia

What are the two types of shunting?

Anatomic - blood bypasses lungs/alveoli completely Physiologic - blood goes to non-functional alveoli --> ATELECTASIS

T or F: Shunting leads to hypercapnia along with hypoxemia

F: hypoxemia induces hyperventilation which keeps CO2 normal

What does it mean when V/Q is larger than 1?

DEAD SPACE: reduced perfusion relation to ventilation; ventilation is wasted where there isnt enough blood flow

What disease may result to a high V/Q?

Fribrosis --> damage alveolar vessels --> less perfusion

T or F: dead space commonly results to hypercapnia

T: less alveoles to take away CO2

How can DEAD Space lead to hypoxemia?

At a different functioning alveoli: ventilation becomes lower and perfusion become higher (lots of blood is directed to vessels getting ventilation) --> MIMICS SHUNTING (V/Q less than 1) --> blood has less than 99% oxygenated blood

What kind of V/Q mismatch does pulmonary edema result to?

lower than 1 --> fluid in alveoli reduces ventilation capacity --> leads to hypoxemia

How to determine underlying mechanism of inadequate gas exchange (ie. shunt, V/Q mismatch, or dead space)?

Look at: 1. response to 100% O2 2. Hypercapnia

T or F: In cases of shunting, 100% O2 does not improve condition (ie. hypoxemia).

T: poor ventilation not resolved at non-functional alveoli

T or F: Dead space and V/Q mismatch will correct with 100% O2

``` T Dead space (questionable) ```

T or F: 100% O2 does not corrects VQ mismatch in pulmonary edema

F: corrects it because, the affected alveoli still have some ventilation gas exchange capacity and so increasing O2 means blood is getting more O2 and hypoxemia is resolved

What are causes of elevated PaCO2?

- increased production (fever) - decreased ventilation (hypoventilation) - increased dead space

What is the equation of PaCO2?

PaCO2 = CO2 production/ (Tidal Volume - Dead Space) Alveolar ventilation = Tidal volume - dead space

Why doesnt hypercapnia result in shunting/VQ mismatch?

Hyperventilation (due to hypoxemia) happens which results to CO2 clearance

Which part of the apex has the least blood flow and ventilation?

Apex

From bottom to top of the lungs, does blood flow or ventilation decrease more quickly?

Blood Flow so the VQ greatest at the apex (top) and low at the base

T or F: during exercise the VQ ratio approaches 1

Where is the hydrostatic pressure of vessels the greatest in the lungs?

At the base (bottom)

T or F: alveolar pressure is gravity dependent

F: stays the same

What is the Bohr effect?

When acid (H+) increases in the blood which allows Hb to take the taut form (less O2 affinity) and release O2 to tissues more easily --> more O2 off-loading per given paO2

What does chronic hypoxia induce?

Release of erythropotein from the kidneys to increase Hct and Hb, pulmonary HTN, cor pulmonale, higher release of 2,3- BPG

Which molecule impacts the cerebral blood flow at the normal range?

CO2 (high cause vasodilation)

In which disease states CO2 and oxygenation require monitoring?

COPD --> may induce hypoventilation (respiratory depression) ALS -->respiratory muscle failure Pneumonia --> may hypoventilate

Why is ventilation different throughout the lungs?

The imbalance in ventilation results from the fact that intrapleural pressure is different in the various regions - -> blood more at the base - -> lung at the base stretched causing more neg intrapleural pressure at apex

T or F: Apical alveoli are more fully expanded than those at the bases

T | Bc less pressure to keep it open

What is the pressure change between expiratory and inspiratory during normal breathing?

decrease of intrapreural pressure by 3 cm H2O | ie. -10 --> -13

Where is ventilation and perfusion highest?

Base of the lung

T or F: pulmonary arterial pressure increases from base to apex

F: apex to base it increases

From where does the PA enters the lung?

At the hilum, branching off from pulmonary trunk

T or F: is pulmonary venous pressure dependent on height

Where is VQ highest, and lowest?

Ventilation --> TOP (high VQ --> less PaCO2, high PaO2 but very little perfusion) Perfusion --> BOTTOM (low VQ --> less O2 --> high perfusion and high ventilation)

What is an intrapulmonary (physiologic) shunt?

venous blood goes through unventilated alveoli, cardiac shunt, shunt channels in lungs

Is the pulmonary circulation high flow and low pressure and resistance?

Yes

When is the arteriole resistance highest?

At low lung volumes (RV) the small arterioles are narrow (like the airways) and this increases the arteriolar resistance to blood flow [ie.EXPIRATION]

When is the capillary resistance highest?

At large lung volumes (TLC) the expanded alveoli stretch the capillaries and cause a high resistance in them [IE. INSPIRATION]

What is PVR consist of?

capillary resistance AND arteriole resistance

Where is PVR lowest?

FRC

Why does the lung vasocontrict its vessels in areas of hypoxemia?

This mechanism is important for shifting blood flow away from lung areas which are not being ventilated.

How is high altitude pulmonary edema occur?

Hypoxia --> leads to hypoxic arterial vasoconstriction --> one side leads arteriolar vasoconstriction and one side the arteriole receives more blood --> capillary hypertension --> pulmonary edema