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

1
Q

Partial Pressure

A

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)

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2
Q

Partial Pressure Equation

A

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

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3
Q

Why is PO2 of dry air 160?

A

PO2 = 760 mmHg * 0.21 = 160 mmHg

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4
Q

Why is PO2 of tracheal air 150?

A

Pressure of water vapor is 47 mmHg

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

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5
Q

Why is PAO2 100 mmHg?

A

Reflects balance between O2 entry to and exit from alveoli

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6
Q

Why is PACO2 40 mmHg?

A

CO2 diffuses into alveoli from venous blood

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7
Q

Why does PAO2 = PaO2 and PACO2 = PaCO2?

A

Arterial blood equilibrates with alveolar air under normal circumstances

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8
Q

Diffusion Rate

A

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
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9
Q

As pressure gradient increases, diffusion will ___

A

increase

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10
Q

As surface area increases, diffusion will ___

A

increase

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11
Q

As membrane thickness increases, diffusion will ___

A

decrease

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12
Q

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

A

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

Normally, O2 equilibrates quickly, so PaO2 = PAO2

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13
Q

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

A

blood-gas barrier

Can have diffusion limitation

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14
Q

How much oxygen is dissolved in plasma

A

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
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15
Q

How much oxygen is bound to hemoglobin

A

98% of total O2 content

4 binding sites on each Hb molecule

Measured by % saturation (SaO2)

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16
Q

Blood O2 Content

A

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

O2 content = 20.3 mL O2 / 100 mL blood

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17
Q

Oxy-Hemoglobin Dissociation Curve

A

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

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18
Q

Oxy-Hb Curve - Affinity and P50

A

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

19
Q

Oxy-Hb Curve - Decreasing Affinity

A

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

20
Q

3 Modes of carbon dioxide transport

A

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
21
Q

Transport of CO2

A

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

22
Q

Hypoxemia

A

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)
23
Q

Hypoventilation

A

PaO2 and PAO2 fall, PaCO2 rises

Decreased ventilatory drive (brain damage, drugs)

Paralysis/weakness of ventilatory muscles

Damage to chest wall

24
Q

Hypercapnia

A

PaCO2 > 45 mmHg

Sensed by central chemoreceptors in brain stem

Very sensitive to pCO2 and pH of cerebrospinal fluid

Most important regulator of ventilation

25
Abnormalities in blood gases are processed by
respiratory centers in medulla and pons
26
Increased ventilatory drive in response to abnormal blood gases
Exhalation of more CO2 → PaCO2 returns to normal Inhalation of more O2 → PaO2 returns to normal
27
Hypoxemia vs Anemia
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
28
Ventilation and Perfusion
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
29
Ventilation and perfusion gradients due to gravity
Ventilation: base→ apex Blood flow: base→ apex
30
Shunt (airway obstruction)
Perfusion is normal, but ventilation is zero Blood goes through lung region, but no gas exchange → it is just like venous blood
31
Dead space (pulmonary embolism)
Ventilation is normal, but perfusion is zero
32
Distribution of Perfusion
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
33
Distribution of Ventilation
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
34
Flow of blood through zones
Mixed venous blood→ base→ zone 3→ zone 2→ zone 1→ apex→ inspired air
35
When V/Q is high
ventilation is greater than flow blood coming out of lung looks more like atmospheric/inspired air
36
When V/Q is low
ventilation is less than flow blood coming out of lung looks more like venous blood
37
Zone 1 (V/Q)
(closer to apex) ``` V lower Q lowest V/Q highest (3) PaO2 130 PaCO2 28 ```
38
Zone 2 (V/Q)
``` V mid Q mid V/Q mid (0.8) PaO2 100 PaCO2 40 ```
39
Zone 3 (V/Q)
(closer to base) ``` V higher Q highest V/Q lowest (0.6) PaO2 89 PaCO2 42 ```
40
Pulmonary system exchanges oxygen and carbon dioxide between ___ and ___
cells and environment
41
Increased minute ventilation to account for needed increase in O2 and CO2 during exercise
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
42
Ventilation and moderate exercise
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
43
In pathological conditions, defects in V/Q are a major cause of ___
hypoxemia