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

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

⅓

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
Q

Abnormalities in blood gases are processed by

A

respiratory centers in medulla and pons

26
Q

Increased ventilatory drive in response to abnormal blood gases

A

Exhalation of more CO2 → PaCO2 returns to normal

Inhalation of more O2 → PaO2 returns to normal

27
Q

Hypoxemia vs Anemia

A

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
Q

Ventilation and Perfusion

A

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
Q

Ventilation and perfusion gradients due to gravity

A

Ventilation: base→ apex

Blood flow: base→ apex

30
Q

Shunt (airway obstruction)

A

Perfusion is normal, but ventilation is zero

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

31
Q

Dead space (pulmonary embolism)

A

Ventilation is normal, but perfusion is zero

32
Q

Distribution of Perfusion

A

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
Q

Distribution of Ventilation

A

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
Q

Flow of blood through zones

A

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

35
Q

When V/Q is high

A

ventilation is greater than flow

blood coming out of lung looks more like atmospheric/inspired air

36
Q

When V/Q is low

A

ventilation is less than flow

blood coming out of lung looks more like venous blood

37
Q

Zone 1 (V/Q)

A

(closer to apex)

V lower
Q lowest
V/Q highest (3)
PaO2 130
PaCO2 28
38
Q

Zone 2 (V/Q)

A 
V mid
Q mid
V/Q mid (0.8)
PaO2 100
PaCO2 40
39
Q

Zone 3 (V/Q)

A

(closer to base)

V higher
Q highest
V/Q lowest (0.6)
PaO2 89
PaCO2 42
40
Q

Pulmonary system exchanges oxygen and carbon dioxide between ___ and ___

A

cells and environment

41
Q

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

A

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
Q

Ventilation and moderate exercise

A

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
Q

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

A

hypoxemia

Unit 1 (24 decks)

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