Pulmonary Physiology 2 (9/25a) [Biomedical Sciences 1]

Question 1

Partial Pressure

Answer 1

Proportional to concentration in a gas mixture

The pressure a gas would exert if it occupied the entire volume of the mixture

The driving force for diffusion of gases

PA= alveolar pressure
Pa= arterial blood pressure
Pv= venous blood pressure

Pressure units are millimeters of mercury (mmHg)

Question 2

Partial Pressure Equation

Answer 2

Px = Pb * F

Px = partial pressure
Pb = barometric pressure
F = fractional concentration

Fractional concentration of oxygen in air is 21% (0.21)
PO2= (Pb - Pwater vapor)*0.21

Question 3

Why is PO2 of dry air 160?

Answer 3

PO2 = 760 mmHg * 0.21 = 160 mmHg

Question 4

Why is PO2 of tracheal air 150?

Answer 4

Pressure of water vapor is 47 mmHg

PO2= (760-47) * 0.21 = 150 mmHg

Question 5

Why is PAO2 100 mmHg?

Answer 5

Reflects balance between O2 entry to and exit from alveoli

Question 6

Why is PACO2 40 mmHg?

Answer 6

CO2 diffuses into alveoli from venous blood

Question 7

Why does PAO2 = PaO2 and PACO2 = PaCO2?

Answer 7

Arterial blood equilibrates with alveolar air under normal circumstances

Question 8

Diffusion Rate

Answer 8

Vx = DA (ΔP/Δx)

Vx = flow of gases per unit time
D = diffusion coefficient
A = surface area
ΔP = pressure gradient
Δx = thickness of the membrane

Question 9

As pressure gradient increases, diffusion will ___

Answer 9

increase

Question 10

As surface area increases, diffusion will ___

Answer 10

increase

Question 11

As membrane thickness increases, diffusion will ___

Answer 11

decrease

Question 12

Blood equilibrates within the first ____ of the length of the capillary

Answer 12

⅓

You could cut the length in half and the blood would still fully equilibrate

Normally, O2 equilibrates quickly, so PaO2 = PAO2

Question 13

In fibrosis, thickening of ___-___ ___ slows O2 exchange so PaO2 < PAO2

Answer 13

blood-gas barrier

Can have diffusion limitation

Question 14

How much oxygen is dissolved in plasma

Answer 14

Oxygen dissolved in the plasma is a really small component

• 2% of total O2 content
• Measured by PO2

If PaO2 = 100 mmHg, [O2]a = 0.3 mL O2 / 100 mL blood

• If CO=5 L/min, 15 mL O2/min delivered to tissues
• If resting metabolic rate= 250 mL O2/min, we have 4 sec before we are anoxic

Question 15

How much oxygen is bound to hemoglobin

Answer 15

98% of total O2 content

4 binding sites on each Hb molecule

Measured by % saturation (SaO2)

Question 16

Blood O2 Content

Answer 16

O2 Content = (Constant * [Hb] * % Saturation) + (Solubility * PO2)

O2 content = 20.3 mL O2 / 100 mL blood

Question 17

Oxy-Hemoglobin Dissociation Curve

Answer 17

relates SaO2 and PaO2

In areas of high PaO2, large changes in PaO2 correspond to small changes in SaO2 (EX: in the lungs)
-Allows better “loading” of O2 in the lungs

In areas of low PaO2, small changes in PaO2 correspond to large changes in SaO2 (EX: in the tissues)
-Allows better “unloading” of O2 in the tissues

Question 18

Oxy-Hb Curve - Affinity and P50

Answer 18

Decreased affinity = easier unloading of O2 to tissues

P50 defines affinity of Hb for O2, the PO2 at 50% Hb saturation

Normal P50 = 25 mmHg
-50% of Hb binding sites are occupied when PaO2 = 25 mmHg

Facilitates unloading of O2 to exercising tissues → increased oxygen release to muscle tissues

Question 19

Oxy-Hb Curve - Decreasing Affinity

Answer 19

Increased temperature and Bohr effect → decreases affinity of Hb for O2, shifting the curve to the right

Bohr effect → increased PCO2 and decreased pH can cause right shift

Increased P50 actually means decreased affinity, Hb will let go of O2 much more easily

EX: if P50=37 mmHg→ 50% of Hb binding sites are occupied when PaO2 = 37 mmHg, Need higher PaO2 to fill 50% of Hb binding sites, so Hb is less sticky to O2

Question 20

3 Modes of carbon dioxide transport

Answer 20

Dissolved in plasma
- 5% of total

Bound to hemoglobin

• Binds at a different site than O2
• 3% of total

Chemically modified form

• Protons (H+) and bicarbonate (HCO3-)
• 92% of total

Question 21

Transport of CO2

Answer 21

Where PCO2 is high (EX: tissues), reaction goes to the right

Where PCO2 is low (EX: lungs), reaction goes to the left

When bicarbonate levels rise, chloride shift occurs

Question 22

Hypoxemia

Answer 22

PaO2 < 80 mmHg

Sensed by peripheral chemoreceptors in carotid and aortic bodies

Less sensitive than central chemoreceptors

Causes

• Breathing hypoxic gas
• Hypoventilation
• Diffusion limitation (fibrosis)
• Ventilation/perfusion is not matched (most common and important in lung disease)

Question 23

Hypoventilation

Answer 23

PaO2 and PAO2 fall, PaCO2 rises

Decreased ventilatory drive (brain damage, drugs)

Paralysis/weakness of ventilatory muscles

Damage to chest wall

Question 24

Hypercapnia

Answer 24

PaCO2 > 45 mmHg

Sensed by central chemoreceptors in brain stem

Very sensitive to pCO2 and pH of cerebrospinal fluid

Most important regulator of ventilation

Question 25

Abnormalities in blood gases are processed by

Answer 25

respiratory centers in medulla and pons

Question 26

Increased ventilatory drive in response to abnormal blood gases

Answer 26

Exhalation of more CO2 → PaCO2 returns to normal Inhalation of more O2 → PaO2 returns to normal

Question 27

Hypoxemia vs Anemia

Answer 27

If normal O2 content is 20 mL / 100 mL blood and normal [Hb]=15 Hypoxemia → PaO2=60 mmHg, SaO2 = 90% → O2 = 19 mL O2 / 100 mL blood Anemia → [Hb]=10 → 13.9 mL O2 / 100 mL blood - O2 content is much more affected by [Hb] - Anemia can have a huge effect on oxygen content even with normal PaO2 and SaO2

Question 28

Ventilation and Perfusion

Answer 28

Ventilation (V) → air in L/min Perfusion (Q) → cardiac output in L/min V/Q defines the relationship between air flow and cardiac output -Normal V/Q is 4/5 → 0.8

Question 29

Ventilation and perfusion gradients due to gravity

Answer 29

Ventilation: base→ apex Blood flow: base→ apex

Question 30

Shunt (airway obstruction)

Answer 30

Perfusion is normal, but ventilation is zero Blood goes through lung region, but no gas exchange → it is just like venous blood

Question 31

Dead space (pulmonary embolism)

Answer 31

Ventilation is normal, but perfusion is zero

Question 32

Distribution of Perfusion

Answer 32

Pulmonary blood flow affected by: 1) Gravity - Flow at bases > flow at apex 2) Pressure in - Pulmonary artery (Pa), Pulmonary vein (Pv), Alveoli (PA) Capillaries in apex are underperfused/overventilated, while those in base are overperfused/underventilated

Question 33

Distribution of Ventilation

Answer 33

Ventilation is also affected by gravity, but not as much as perfusion is Alveoli at apex are pulled open at rest → very small increase in volume during inspiration Alveoli at base → much larger increase in volume during inspiration

Question 34

Flow of blood through zones

Answer 34

Mixed venous blood→ base→ zone 3→ zone 2→ zone 1→ apex→ inspired air

Question 35

When V/Q is high

Answer 35

ventilation is greater than flow blood coming out of lung looks more like atmospheric/inspired air

Question 36

When V/Q is low

Answer 36

ventilation is less than flow blood coming out of lung looks more like venous blood

Question 37

Zone 1 (V/Q)

Answer 37

(closer to apex) ``` V lower Q lowest V/Q highest (3) PaO2 130 PaCO2 28 ```

Question 38

Zone 2 (V/Q)

Answer 38

``` V mid Q mid V/Q mid (0.8) PaO2 100 PaCO2 40 ```

Question 39

Zone 3 (V/Q)

Answer 39

(closer to base) ``` V higher Q highest V/Q lowest (0.6) PaO2 89 PaCO2 42 ```

Question 40

Pulmonary system exchanges oxygen and carbon dioxide between ___ and ___

Answer 40

cells and environment

Question 41

Increased minute ventilation to account for needed increase in O2 and CO2 during exercise

Answer 41

REST - VO2 250 mL/min - VCO2 240 mL/min - Minute ventilation 5 L/min EXERCISE - VO2 5000 mL/min - VCO2 3000 mL/min - Minute ventilation 100 L/min

Question 42

Ventilation and moderate exercise

Answer 42

Phase 1: fast -Probably neural in origin Phase 2: primary Phase 3: steady state Ventilation increased in proportion to VO2 and VCO2 → maintains constant PaCO2 → Well matched to oxygen consumption and carbon dioxide production

Question 43

In pathological conditions, defects in V/Q are a major cause of ___

Answer 43

hypoxemia