Pulmonary circulation

Question 1

Systemic capillaries

Answer 1

-high pressure
-capillaries receiving blood from left ventricle/aorta and return to right side of the heart through veins

Question 2

Pulmonary capillaries

Answer 2

-low pressure
-receive blood from right ventricle/pulmonary artery and return oxygenated blood to left atrium
-extensive branching to facilitate gas exchange

Question 3

Resistance of pulmonary capillaries

Answer 3

-low resistance, capillaries are highly distensible and compressible (7x more compliant than systemic) to accommodate changes in right heart output

Question 4

Total blood volume in pulmonary capillaries

Answer 4

~10%

Question 5

Contraction and relaxation of pulmonary capillaries

Answer 5

-responds to neural or humoral factors to alter resistance and determine contraction and relaxation

Ex. exercise: vascular resistance decreases (pressure increase). Capillary bed from 70ml at rest to 250ml to maximize gas exchange

Question 6

Lung blood sources

Answer 6

-lungs receive blood from 2 sources:
1.Bronchial circulation
2. Pulmonary circulation

Question 7

Bronchial circulation

Answer 7

-part of systemic system (so High pressure!)
-provides nourishment and arterial perfusion from trachea to terminal bronchioles

Question 8

Where does bronchial circulation arise?

Answer 8

Comes from aorta or intercostal arteries

Question 9

How much cardiac output does bronchial circulation receive?

Answer 9

1% of cardiac output

Question 10

Mix of systemic and pulmonary circulation

Answer 10

• 1/3 of venous blood returns to right atrium via azygous vein
• 2/3 to pulmonary vein and left atrium, which mixes with O2 rich blood

Question 11

Pulmonary circulation

Answer 11

-receives total (100%) output from right ventricle for gas exchange (reoxygenate the blood and release CO2)
-provides perfusion to structures distal of terminal bronchioles; nutrients from mixed venous blood

Question 12

Pressure of pulmonary circulation

Answer 12

-low pressure, high volume

Question 13

Gas exchange properties

Answer 13

1.Presence of oxygen in alveoli
2. Flow of blood to pulmonary capillaries

Question 14

Optimal gas exchange ratio

Answer 14

Alveolar ventilation (oxygen) (V)/ Pulmonary perfusion/flow (blood) (Q)
**optimal=1 but normal average=0.8

Question 15

VQ mismatch

Answer 15

-where there is an inadequate amount of V or Q

Question 16

What influences Blood flow distribution (Q)?

Answer 16

-influenced by gravity
-results in a vertical gradient dependent on the position of the animal
- volume  pressure  flow is mostly higher in caudal/ventral regions compared to cranial/dorsal regions

Question 17

Blood flow distribution (Q) exception in horses

Answer 17

-flow is actually higher in the dorsal region of lungs instead of the ventral region of other animals

Question 18

Reason for blood flow distribution exception in horses

Answer 18

Hypothesized that a large vertical lung height and the dorsal distance relative to the heart requires higher pulmonary arterial pressure (Pa) to drive blood flow (Pa in horse is higher than Pa in dog)
- Minimizes the effect of gravity

Question 19

Intense exercise in a race horse

Answer 19

-huge increase in pulmonary pressure (more than 60mm Hg vs 35mm Hg in other species)
- can result in capillary rupture (exercise-induced pulmonary hemorrhage)

Question 20

Gravity, alveolar size, and alveolar ventilation

Answer 20

-transpulmonary pressure drives distention
-greater the pressure, greater the pull, larger the alveoli=greater ventilation
-therefore larger alveoli more dorsally will have greater ventilation

Question 21

Respiratory zones

Answer 21

-3 conceptual zones affected by pressures in the lungs
-Zone 1,2,3

Question 22

Factors that effect respiratory zones

Answer 22

1.Arterial pressure (Pa)
2.Alveolar pressure (PA)
3. Venous pressure (Pv)

Question 23

Respiratory zone 1

Answer 23

PA > Pa > Pv

Large alveoli (large transpulmonary pressure)
-results in reduced blood flow due to compressed capillary from alveoli

High ventilation (V), low blood flow (Q) = V/Q ratio is very high

Question 24

Pathology of Respiratory zone 1

Answer 24

-does not normally exist in healthy lungs (physiological dead space)
- can theoretically occur near the apex/dorsal region

Ex. pulmonary embolism or late-stage COPD involving capillary damage or emphysema

Question 25

Wasted ventilation

Answer 25

-respiratory zone 1
-lots of gas (V) but not enough blood flow (Q) to facilitate gas exchange

Question 25

Respiratory zone 2

Answer 25

Pa> PA > Pv

-alveoli open and filled with air
-sufficient systole pressure forces deoxygenated blood into capillaries towards alveoli to facilitate gas exchange

**Results in appropriate amount of oxygen and blood flow= best functioning zone of the lung where blood flow (Q) closely matches with ventilation (V) V/Q= ~1 (or 0.8)

Question 26

Optimal gas exchange

Answer 26

-respiratory zone 2
-balance of alveolar ventilation and pulmonary blood flow

Question 27

Respiratory zone 3

Answer 27

Pa > Pv > PA
- Alveoli is small (low transpulmonary pressure)
- High blood flow
- High perfusion (Q), low ventilation (V)
**Results in V/Q ratio is very small
- Partially functioning zone of the lung, could theoretically occur near the caudal/ventral area

Question 28

Pathological examples resulting in respiratory zone 3

Answer 28

-Pulmonary hypertension (high Pa) or bronchoconstriction/atelectasis (low PA)

Question 29

Wasted perfusion

Answer 29

-respiratory zone 3
-lots of blood flow (Q) but not enough gas (V) to facilitate gas exchange

Question 30

Modification examples to V/Q zones

Answer 30

-boundaries between the zones are dependent on physiological conditions (**Not fixed anatomical landmarks)

Examples:
1.low blood pressure (Eg. Hemorrhage reduce Pa) will increase zone 1
2. high blood pressure (pulmonary hypertension; increase Pa) will increase zone 3
3. Forceful inspiration will shift zone 3 to zone 2 by expanding the alveoli (increase PA). Will also see a small shift from zone 2 to zone 1.
4. Exercise: increase in cardiac output results in increase in Pa (zone 1 to zone 2), coupled with forceful respiration (PA) (zone3 to zone 2)
**Maximize zone 2 to support aerobic demand
5.Change in anatomical position will influence V/Q capacities

Question 31

Shunt vs. dead space

Answer 31

Shunt: zone 3; V/Q «1
Dead space: zone 1; V/Q&raquo_space;1
**whereas health zone= zone 2= V/Q=1

Question 32

V/Q»1

Answer 32

-ventilation exceeds blood flow so oxygen present but no blood flow to facilitate gas exchange

Question 33

V/Q«1

Answer 33

-blood flow exceeds ventilation (primarily due to obstruction) so blood flow there but no oxygen

Question 34

VQ mismatch

Answer 34

-results in hypoxemia (low oxygen in systemic blood)

Question 35

Right to Left shunt

Answer 35

-the pneumonic region (collapsed alveoli) receives no ventilation so blood flow through that region does not pick up any oxygen
- the blood from this region mixes with oxygenated blood from healthy alveoli which reduces overall PO2 returning to the heart

**Results in deoxygenated blood leaving from the right ventricle returning to the heart/left ventricle as still poorly oxygenated blood= hypoxemia

Question 36

Does oxygen supplementation improve hypoxemia?

Answer 36

-no because there is no way to overcome the obstructed alveoli (even if more oxygen is supplied)