Mechanics of Breathing, Pulmonary Circulation

Question 1

Elastic force

Answer 1

Cause structures to snap back to equilibrium position after stretched or compressed. Due to collagen/elastin.

Question 2

Compliance

Answer 2

Distensibility of a system. The inverse of compliance. Change in volume/change in pressure.

Question 3

Transmural pressure

Answer 3

Pressure across alveolar wall. Intraalveolar pressure - intrapleural pressure.

Question 4

Hysteresis

Answer 4

Compliance of lung is different exhaling and inhaling. Exhaling, the lung is more compliant. This is due to the fact that surface tension in alveoli must be overcome during inhalation.

Question 5

How to calculate surface tension of alveoli?

Answer 5

Collapsing Pressure = 2T/r. This shows that a large alveolus experiences a weaker collapsing force than a smaller alveolus.

Question 6

How is surface tension in alveoli weakened?

Answer 6

Surfactant. A phospholipid. Important at birth.

Question 7

How does compliance of lung and chest wall system compare to their respective compliances.

Answer 7

Less, think of a balloon in a balloon.

Question 8

What is the volume present in lungs after a normal breath called?

Answer 8

Functional Residual Capacity.

Question 9

Is intrapleural pressure positive or negative?

Answer 9

Negative, created by elastic recoil lungs pulling in and elastic recoil chest wall bowing out.

Question 10

What does emphysema do to lung compliance?

Answer 10

Loss of collagen, so it increases compliance.

Question 11

What does fibrosis do to lung compliance?

Answer 11

Decreases compliance due to an increase in elastic tissue.

Question 12

Resistance equation

Answer 12

R=8µl/πr^4

Question 13

How to decrease airway resistance without altering airways?

Answer 13

Decrease viscosity of the air.

Question 14

Active muscles of inspiration?

Answer 14

External intercostals, accessories

Question 15

Active muscles of expiration?

Answer 15

Internal intercostals, abdominals

Question 16

Positive transmural pressure

Answer 16

Expanding pressure, keeps airways open.

Question 17

Negative transmural pressure

Answer 17

In people with emphysema, airway narrows with forced expiration.

Question 18

Resistance and pressure in pulmonary vessels?

Answer 18

Very low because walls are very thing and distensible. Also very low pressure.

Question 19

Pulmonary Systolic and Diastolic pressures?

Answer 19

25/10, due to low pressure from RV

Question 20

How to calculate pulmonary vascular resistance?

Answer 20

(mPAP-mLAP)/CO

Question 21

How is pulmonary blood flow regulated?

Answer 21

Arteriolar smooth muscle constriction.

Question 22

Most important mediator of pulmonary vasoconstriction?

Answer 22

Partial pressure of O2 in alveolar gas. If low PAO2, vasoconstrict, so blood can go to ventilated alveoli.

Question 23

Hypoxic Vasoconstriction

Answer 23

Low PAO2 causes vasoconstriction to better match V/Q.

Question 24

Mechanism of Pulmonary Vasoconstriction

Answer 24

Low PAO2, leads to inhibition of K channels in smooth muscles, leading to depolarization, leading to Ca influx and contraction.

Question 25

Role of NO

Answer 25

Relaxation

Question 26

Role of Endothelin?

Answer 26

Constriction via endothelin receptors

Question 27

Role of PGI2 and TXA2

Answer 27

Vasodilation by increasing cAMP.

Question 28

Causes and consequences of increased PVR.

Answer 28

Cause: high altidude, reduced barometric pressure, reduced partial pressure of O2.

Consequence. RV pressure overload and hypertrophy.

Question 29

Zone 1 Perfusion

Answer 29

PA>Pa>Pv. Pa is very low because of gravity, so it’s compressed. Physiologic dead space.

Question 30

Zone 2 Perfusion

Answer 30

Pa>PA>Pv. Pa is higher than PA, which is higher than Pv. Compresses end of capillary. Blood flow driven by Pa and PA difference.

Question 31

Zone 3 Perfusion

Answer 31

Pa>Pv>PA. Blood flow is highest, driven by Pa and Pv gradient.

Question 32

Anatomical Shunts

Answer 32

Blood from coronary arteries and bronchial arteries bypasses the lungs. This causes PaO2 to always be slightly less than PAO2. This accounts for 2% of blood.

Question 33

Right to left shunt

Answer 33

Blood passes the lungs without being oxygenated. Hypoxemia occurs that cannot be corrected with inspired oxygen.

Question 34

Does a right to left shunt cause great increase in PaCO2?

Answer 34

No, because chemoreceptors will increase ventilatory drive to rid the body of CO2. Chemoreceptors for O2 are not as sensitive.

Question 35

Left to right shunt

Answer 35

Oxygenated blood from left heart drains into right heart. ASD, VSD, patent ductus arteriosus. PO2 of right side of heart increased.