Pulmonary perfusion & V/Q

Question 1

Pulmonary vs Systemic circulation

Answer 1

Purpose:
P = Heart –> Lungs O2 and CO2
S= Heart –> body delivery and waste pick up

Pulmonary
Shorter vessels
Decreased pressure
Larger diameter = less resistance
Limited ability to control regional distribution of blood
Blood flow markedly affected by gravity

Question 2

What physiological variation can cause Pulmonary volume to shift from normal?

Answer 2

• high thoracic pressure = expels blood out

posture (supine → erect will decrease by 1/10)

increased systemic vascular tone forces blood into pulmonary circulation

Question 3

features of Zone 1

Answer 3

No blood flow in cardiac cycle

Avl cap pressure never exceeds alv air pressure (arterioles crushed)

High PO2 and Low PCO2

PA> Pa > Pv

Question 4

features of Zone 2

Answer 4

Intermittent blood flow as PA pressur peaks

Pa> PA > PV

Question 5

features of Zone 3

Answer 5

Continuous blood flow

Pa> PV > PA

Question 6

What does V and Q stand for?

Answer 6

V = alveolar Ventilation (VA)

Q= Perfusion (CO)

Question 7

what is the purpose of hypoxic pulmonary vasoconstriction?

Answer 7

to improve V/Q matching**

decreased Blood flow to poorly ventilated Alveloi and redirects blood to ventilated alveoli

Question 8

What is the normal value of V/Q?

Answer 8

0.8

Question 9

How does the V/Q ratio change throughout 3 zone model?

Answer 9

progressively decreases from Z 1 –> 3

Question 10

What is the V/Q ratio?

Answer 10

the relationship between the amount of air reaching the alveoli and the amount of blood flowing through the capillaries surrounding those alveoli.

Question 11

What are the origins of a High V/Q ratio?

Answer 11

Pulmonary embolism (blood clot in lung, but V normal)

Pulmonary Vascular Disease

Localised Vascular Compression

Question 12

What are the consequences of high V/Q ratio?

Answer 12

increased VD (less air participating in gas exchange)

Hypoxemia

increased A-a gradient (O not as efficiently transferred)

Hypocapnia

Question 13

What is actually happening in High V/Q ratio?

Answer 13

More air is reaching the alveoli than there is blood flow to pick up the oxygen.

Question 14

What is the origin of low V/Q ratio?

Answer 14

Airway obstructions:
Asthma
COPD
Penumonia

Alveolar collapse

Pulmonary Edema

Neuromuscular

Question 15

What actually occurs in a low V/Q ratio?

Answer 15

enough blood flowing past alveoli, but not enough air reaching to oxygenate

Question 16

What are the consequences of Low V/Q ratio?

Answer 16

Hypoxemia
Hypercapnia (high CO2)
increased A-a gradient
increased work of breathing

Question 17

What effect does gravity have on pressures in the lung?

Answer 17

Uneven ventilation and perfusion (due to gravitational gradient in Ppul)

Alveoli on apex = stretched = less compliant

Alveoli on base = squashed due to gravity = better ventilated as has more compliance.

Question 18

what impact does exercise have on pulmonary blood flow?

Answer 18

Increased blood flow by 4-7 fold

Increased Pulmonary blood flow = increased SA for diffusion

Improved V/Q

Question 19

Why does PV have a lower PO2?

Answer 19

decreased time in pulmonary circulation
decreased oxygenation

Question 20

What is a shunt?

Answer 20

Alveoli are perfused but NOT ventilated

Question 21

What is the impact of a shunt on VQ?

Answer 21

V/Q= 0, decreased PAO2, increased PACO2

Question 22

What is the impact of a pulmonary Embolism on VQ?

Answer 22

Effect on V/Q: V/Q of the affected alveolus = infinity (dead space), decreased PAO2, increased PACO2

Question 23

What is a pulmonary embolism?

Answer 23

Foreign fragments (tumour, thrombus) block a blood vessel

Question 24

What are the 4 starling pressures?

Answer 24

Capillary Hydrostatic Pressure (HPcap)

Capillary Oncotic pressure (OPcap)

Interstitial fluid pressure (HPif)

Interstitial oncotic pressure (OPif)

Question 25

Which Starling pressures favour filtration?

Answer 25

HPcap, OPif and HPif

Question 26

Which Starling pressures favour reabsoprtion?

Answer 26

just OPcap

Question 27

How does LSHF cause a pulmonary Oedema?

Answer 27

LV failure --> backflow into LA and Pul Circulation --> increased HPcap --> favours filtration --> Pulmonary Oedema

Question 28

How can pneumonia cause pulmonary oedemas?

Answer 28

Infection --> inflammation --> increased pul capillary permeability --> protein and fluid leakage

Question 29

What is the purpose of Hypoxic pulmonary vasconctriction?

Answer 29

Défense against Shunts Promotes blood flow to areas of lung that are better ventilated.

Question 30

What is the impact of lower pressure in Systole and Diastole in the PA on the RV?

Answer 30

decreased afterload (less pressure to overcome = preserves RV contractility, SV and mechanical efficiency)

Question 31

Describe the systemic and pulmonary Pressure and Resistance.

Answer 31

Systemic - high P and R = so can get blood to all tissues Pulmonary = low P and R = efficient due to short route and needs to protect delicate lung tissue

Question 32

What is the impact of hypoxia on Pulmonary Vs Systemic Vasculature?

Answer 32

Pulmonary - Hypoxic Pulmonary Vasoconstriction - if HPV becomes widespread = increased PA pressure and RSHF Systemic - Hypoxic systemic vasodilation - = drop in BP, circulatory shock

Question 33

How does chronic pulmonary disease lead to RSHF and Peripheral oedema?

Answer 33

CPD --> chronic hypoxia in lungs --> HPV --> becomes widespread --> increased Res --> increases afterload --> RV hypertrophy to compensate --> overworked RV = RSHF --> blood back flows --> oedema

Question 34

Why is blood flow more pulsatile in capillaries in zone 2?

Answer 34

due to the cyclical pumping of the heart. Unique pressures of Zone 2 make pulsatile nature more pronounced

Question 35

Why does a patient with Haemorrhage have Zone 2 --> zone 1?

Answer 35

Decreased Blood Volume:   Reduced Pulmonary Arterial Pressure

Question 36

What factor can lead to the formatiom of a oedema?

Answer 36

Increased Hydrostatic pressure (hr failure, venous insufficiency, DVT) Decreased colloid osmotic pressure increased capillary permeability lymphatic obstruction (lymphedema)

Question 37

which areas of the lungs are best a) ventilated b) perfused

Answer 37

a- base of lungs b- bases of lungs