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Physiology > Lecture 24 - Respiratory Physiology #3 > Flashcards

Lecture 24 - Respiratory Physiology #3 Flashcards

1
Q

What is the PO2 and PCO2 in dry inspired air?

A

PO2 = 160 mmHg
PCO2 = 0 mmHg

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2
Q

What is the PO2 and PCO2 in humidified tracheal air?

A

PO2 = 150 mmHg
PCO2 = 0 mmHg

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3
Q

What is the PO2 and PCO2 in systemic arterial blood?

A

PaO2 = 100 mmHg
PaCO2 = 40 mmHg

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4
Q

What is the PO2 and PCO2 in mixed venous blood?

A

PvO2 = 40 mmHg
PvCO2 = 46 mmHg

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5
Q

Describe the relationship between alveoli and capillaries.

A

Very thin space between alveoli and capillaries.

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6
Q

In normal conditions, how long does it take for PO2 to reach 100% during exercise?

A

0.25 seconds

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7
Q

If the rate of oxygen diffusion is decreased, how does the body compensate?

A

Increase breathing rate

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8
Q

What occurs in pulmonary edema?

A
  • Alveoli are filled with fluid.
  • Gas exchange cannot occur since the fluid displaces the air.
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9
Q

What happens in interstitial fibrosis?

A

There is a thickening of the diffusion membrane due to alveolar inflammation and scar tissue formation on the alveolar walls.

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10
Q

What happens when the diffusion membrane is thickened (Fick’s law)?

A

Increasing membrane thickness decreases the ventilation across alveolus.

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11
Q

How soluble is oxygen?

A

Not very - only 0.003mL of oxygen dissolves in 100mL of plasma for every 1mmHg of partial pressure.

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12
Q

How much of the oxygen transported in blood is dissolved?

A

An insignificant fraction, <1%.

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13
Q

How much oxygen is transported by hemoglobin?

A

99%

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14
Q

What property of blood is useful for oximetry?

A

Blood is red when oxygenated and turns purple when deoxygenated.

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15
Q

When Hb combines with oxygen it turns…

A

Red

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16
Q

What is % saturation?

A

% of all the hemoglobin molecules that are bound to oxygen.

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17
Q

How many heme proteins are in hemoglobin?

A

4

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18
Q

What does oxygen bind to in the heme protein?

A

Iron

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19
Q

Oxygen combines with heme…

A

Loosely and reversibly

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20
Q

How many molecules of oxygen can bind to each hemoglobin?

A

4 oxygen molecules.

Hb has 4 heme proteins that each have one iron molecule that can bind oxygen.

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21
Q

How much Hb is in each red blood cell?

A

A lot

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22
Q

Describe the relationship between saturation and partial pressure.

A

Not linear - more of an S shape.

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23
Q

What are the physiological advantages of having an S shape relationship in the hemoglobin dissociation curve?

A

The flat portion of the curve is better for oxygen loading and the steep portion of the curve is better for unloading.

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24
Q

Which part of the oxygen dissociation curve is used in the lungs? Why is it useful there?

A

The flat portion. At higher levels of PO2, there is not a significant change in hemoglobin saturation. It stays near 100% between 60 and 100 mmHg. This allows for oxygen loading.

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25
Q

Which part of the oxygen dissociation curve is important for function at high altitudes?

A

The flat portion. Because there is no significant change in saturation, the body can still load Hb adequately in areas with lower PO2 in the atmosphere.

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26
Q

Which part of the oxygen dissociation curve is used in the tissues? Why is it useful there?

A

The steep portion. At PO2 between 30-50 mmHg, there is a big change in hemoglobin saturation. It drops from 90% to 50%, which allows oxygen to be unloaded into the tissues.

27
Q

A right shift accentuates the…

A

unloading capacity.

28
Q

A right shift ____ the affinity of Hb for oxygen.

A

decreases.

29
Q

In a right shift:

At a given pressure, ____ oxygen is bound to Hb (so ____ is released to the tissues).

A

At a given pressure, LESS oxygen is bound to Hb (so MORE is released to the tissues).

30
Q

When does a right shift occur?

A
  • Higher temperatures
  • Lower pH

(exercise)

31
Q

A right shift occurs at the level of …

A

the tissues.

32
Q

A left shift accentuates the…

A

loading capacity.

33
Q

A left shift ____ the affinity of Hb for oxygen.

34
Q

In a left shift:

At a given pressure, ____
oxygen is bound to Hb (so
____ is picked up in the
lungs).

A

At a given pressure, MORE
oxygen is bound to Hb (so
MORE is picked up in the
lungs).

35
Q

When does a left shift occur?

A
  • Lower temperatures (lungs are cooler than the body)
  • Increases in pH (less CO2 in lungs so less acidic)
36
Q

What are 3 contributors to oxygenation?

A
  1. Oxygen uptake - how much in alveolus? how much uptake into arterial blood?
  2. Oxygen content - how much in arterial blood?
  3. Oxygen delivery - blood flow / cardiac output?
37
Q

What percentage of room air is oxygen?

38
Q

What is the alveolar gas equation used for?

A

Used to calculate the maximum oxygen pressure in the alveolus at a given time.

39
Q

PaO2 should be (smaller than / equal to / larger than) PAO2 if everything is working properly.

A

Almost equal.

40
Q

Alveolar oxygen equation

A

PAO2 = FiO 2 x (PB - P H2O) – (PaCO2/0.8)

41
Q

What is FiO2?

A

Fraction of inspired oxygen.

42
Q

What is PB?

A

Barometric pressure

= 760mmHg at sea level
= 670mmHg in Calgary

43
Q

What is PH2O?

A

Water vapour pressure

= 47mmHg at body temp

44
Q

What should PaCO2 be if ventilation is normal?

45
Q

What is PAO2 at sea level vs in Calgary when oxygen is 21%?

A

100mmHg at sea level
80mmHg in Calgary

46
Q

How can you estimate PAO2 at sea level?

A

Oxygen percentage multiplied by 5

ex. 21 x 5 = 105 mmHg

47
Q

Under anesthesia, patients breathe what percentage of oxygen?

48
Q

What is hypoxemia?

A

The condition when the oxygen
saturation (%) of arterial blood is low.

49
Q

What is hypoxia?

A

When the oxygen levels are low at the level of the tissues themselves (may be due to low oxygen levels or to low delivery).

50
Q

How can you measure hypoxemia?

A
  • Arterial blood gas sample (most accurate)
  • Pulse oximeter
51
Q

What are 5 causes of hypoxemia?

A
  1. Low inspired oxygen.
  2. Hypoventilation.
  3. Diffusion impairment.
  4. Ventilation/Perfusion mismatch.
  5. Right-to-left shunt (e.g. cardiac defect).
52
Q

How do you choose a site for blood sampling?

A
  • A blood sample is collected
    “downstream” from a tissue
    bed.
  • Analysis will reflect the
    metabolism and gas levels at
    that location only.
  • You need to think about what
    you are interested in (the
    lungs or the body).
53
Q

An arterial blood sample will give an indication of oxygenation at the level of…

A

the lungs.

54
Q

What is the A-a gradient?

A

A measure of the ability of the lungs to load oxygen and the blood to pick it up.

Used to assess the difference between oxygen in the alveoli and the oxygen in the arteries. Ideally, there should be no difference.

55
Q

A larger difference in the A-a gradient indicates…

A
  • The inability of the lung to oxygenate blood
  • The presence of venous admixture (V/Q mismatch)
56
Q

What is the formula for A-a gradient?

A

A-a gradient = PAO2 – PaO2

57
Q

What is a normal value for the A-a gradient?

58
Q

What can be done if the A-a gradient is abnormal?

A
  • Increase inspired oxygen to increase levels in alveoli
  • Ventilate patient to remove CO2 (if severe hypercapnia is a problem)
59
Q

What is the formula for oxygen content?

A

Content = (1.34 x Hb x O2 Sat %) + (PO2 x 0.003)

60
Q

Oxygen content definition

A

The total amount of oxygen that is carried in the blood is a combination of its dissolved and Hb-bound components.

61
Q

What is the normal arterial blood oxygen content?

A

~20 mL of oxygen/dL of arterial blood

62
Q

What is the normal venous blood oxygen content?

A

Normal venous blood carries 15 mL/ dL.

63
Q

What is the formula for oxygen delivery?

A

DO2 = Cardiac Output x Arterial O2 Content

Physiology (52 decks)

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