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USMLE > Respiratory - Physiology > Flashcards

Respiratory - Physiology Flashcards

1
Q

What is the inspiratory reserve volume?

A

Air that can still be breathed in after normal inspiration

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2
Q

What is the tidal volume?

A

Air that moves into lung with quiet inspiration, typically 500mL

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3
Q

What is the expiratory reserve volume?

A

Air that can still be breathed out after normal expiration

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4
Q

What is the residual volume?

A

Air in the lung after maximal expiration
Cannot be measured on spirometry

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5
Q

What is the inspiratory capacity?

A

IRV + TV

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6
Q

What is the functional residual capacity?

A

Volume of air in lung after normal expiration

(RV+ERV)

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7
Q

What is the Vital capacity?

A

Maximum volume of gas that can be expired after maximal inspiration
TV + IRV + ERV

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8
Q

What is the total lung capacity?

A

Volume of gas present in lungs after maximal inspiration
IRV + TV + ERV + RV

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9
Q

What lung volume(s) cannot be measured directly in a spirometer?

A

Any capacity with RV (including FRC, TLC) cannot be measured

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10
Q

What is physiological dead space?

A

Anatomic dead space of conducting airways and functional dead space in alveoli

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11
Q

What is the largest contributor of functional dead space?

A

Apex of health lung

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12
Q

How to calculate dead space

A

Vd = Vt x (PaCO2-PeCO2)/PaCO2

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13
Q

How to calculate alveolar ventilation?

A

Va = CO2 production/PACO2

As ventilation increases, PACO2 decreases

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14
Q

How to calclate minute ventilation?

A

(Vt-Vd) x RR

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15
Q

What are the tendencies of the lung and chest wall to do if there are no opposing forces?

A

Lung to collapse
Chest wall to spring outward

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16
Q

What happens to lung and chest wall pressures at FRC?

A

Inward pull of the lung is balanced by outward pull of chest wall

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17
Q

What is the system pressure at FRC?

A

Atmospheric pressure

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18
Q

What are the following pressures at FRC:

airway pressure
alveolar pressure
intrapleural pressure

A

Airway and alveolar pressure = 0
Intrapleural pressure = negative (prevent pneumothorax

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19
Q

What is compliance of the lung?

A

Change in lung volume for a given change in pressure

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20
Q

What conditions decrease compliance?

A

Pulmonary fibrosis
Pneumonia
Pulmonary edema

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21
Q

What conditions increase compliance?

A

Emphysema, normal aging

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22
Q

What is the structure of hemoglobin?

A

2 alpha and 2 beta (4 polypeptide subunits)

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23
Q

What are the two forms of hemoglobin and their affinity for O2?

A

Taut (low affinity)
Relaxed (high affinity)

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24
Q

What exhibits positive cooperativity and negative allostery?

A

Hemoglobin

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25
Q

What favors taut form over relaxed form? (5)

A
  1. Increased Cl-
  2. Increased H+
  3. Increased CO2
  4. Increased 2,3-BPG
  5. Increased temperature
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26
Q

What happens to the dissociation curve when taut form is favored?

A

Right shift, causing increased in O2 unloading

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27
Q

What is the structure of fetal hemoglobin? How is it different from adult form?

A

2 alpha 2 gamma subunits

Lower affinity for 2,3-BPG (higher affinity for O2)

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28
Q

What is methemoglobin? What does it have affinity for?

A

Oxidized form of hemoglobin (ferric, Fe3+)

Does not bind O2 as readily, but has increased affinity for cyanide

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29
Q

What is the normal state of iron in hemoglobin?

A

Ferrous, Fe2+

30
Q

To treat cyanide poisoning, nitrites are used. What is the mechanism for its action?

A

Oxidize hemoglobin to methemoglobin, which binds to cyanide, allowing cytochrome oxidase to function

31
Q

To treat cyanide poisoning, thiosulfate can be used. What is their mechanism of action?

A

Thiosulfate binds to cyanide to form thiocyante, which is renally excreted

32
Q

What is used to treat methemoglobinemia?

A

Methylene blue

33
Q

How does CO lead to toxicity?

A

CO binds to hemoglobin with 200x affinity than O2
Cause decrease oxygen-binding capacity with left shift in oxygen-hemoglobin dissociation curve

Decreased oxygen unloading in tissues

34
Q

Why does hemoglobin curve have sigmoidal shape?

A

Positive cooperativity
Tetrameric hemoglobin can bind 4 oxygen molecules and has higher affinity for each subsequent oxygen

35
Q

Why does myoglobin not show the same sigmoidal shape as hemoglobin?

A

Does not have positive cooperativity (monomeric)

36
Q

What is pulmonary hypoxic vasoconstriction?

A

Low PAO2 causes hypoxic vasoconstriction that shifts blood away from poorly ventilated region of lung

37
Q

What is the difference between perfusion and diffusion limited?

A

Perfusion limited - Gas equilibrates early along length of capillary

Diffusion only increase if blood flow increases

Diffusion limited - Gas does not equilibrate by the time blood reaches the end of capillary

38
Q

Examples of perfusion limited molecules

A

O2 (normal health), CO2, N2O

39
Q

Examples of diffusion limited molecules

A

O2 (emphysema, fibrosis), CO

40
Q

What is the consequence of pulmonary hypertension?

A

Cor pulmonale and subsequent RV failure (JVP, edema, hepatomegaly)

41
Q

How to calculate diffusion of a gas

A

Vgas = A/T x Dk(P1-P2)
A=area
T=thickness
Dk(P1-P2) = difference in partial pressure

A is increased in emphysema
T is increased in pulmonary fibrosis

42
Q

What is normal pulmonary artery pressure?
What makes diagnosis of pulmonary hypertension?

A

Normal = 10-14 mmHg
Pulm HTN = >25 or >35 during exercise

43
Q

What does pulmonary hypertension results in?

A

arteriosclerosis, medial hypertrophy, intimal fibrosis of pulmonary arteries

44
Q

What is primary pulmonary hypertension?
Prognosis?

A

Inactivating mutation in BMPR2 gene

The gene normally inhibits vascular smooth muscle proliferation

poor prognosis

45
Q

What is secondary pulmonary hypertension? (7)

A
  1. COPD
  2. mitral stenosis (increased resistance)
  3. recurrent thromboemboli (decreased cross-sectional area of pulmonary vascular bed)
  4. autoimmune disease (systemic sclerosis, inflammation -> intimal fibrosis, medial hypertrophy)
  5. Left to right shunt (increased shear stress leading to endothelial injury)
  6. sleep apnea
  7. living in high altitude (hypoxic vasoconstriction)
46
Q

How to calculate pulmonary vascular resistance?

A

Pulmonary Vascular Resistance = (Pressure of Pulmonary Artery - Left atrium) /Cardiac output

47
Q

What affects resistance?

A

R = 8nl/pr^4

n=viscosity
l=length
r=radius

48
Q

What is oxygen content?

A

O2 binding capacity x % saturation + dissolved O2

O2 Content = [1.34 x [Hgb] x % sat] + 0.0031PaO2

49
Q

Normally 1g Hb can bind how many ml of O2?

50
Q

Normal Hb amount in blood?

51
Q

Cyanosis results when deoxygenated Hb is more how many g/dL

A

5g/dL

(normal amount of Hb in blood is 15 g/dL)

52
Q

What is the normal O2 binding capacity (ml O2/dL)?

A

20.1 mL O2/dL

53
Q

As hemoglobin falls, what happens to the oxygen content, oxygen saturation and arterial PO2?

A

Oxygen content decreases

Oxygen saturation and arterial PO2 do not

54
Q

How to calculate oxygen delivery to tissue?

A

Cardiac output x O2 content of blood

55
Q

What is the equation to calculate PAO2?

A

PAO2 = FIO2 x (Patm-Ph2o)-PaCO2/RQ

Patm=760
Ph2o=47
RQ=0.8

~ PAO2 = 150-PaCO2/0.8

56
Q

What is the A-a gradient

A

PAO2 - PaO2

Normal is 10-15 mmHg

57
Q

Give examples of increased A-a gradient?

A

Shunting
V/Q mismatch
fibrosis (impairs diffusion)

58
Q

Examples of: Hypoxemia with Normal A-a gradient

A

High altitude

Hypoventilation

59
Q

Examples of: Hypoxemia and high A-a gradient

A

V-Q mismatch
Diffusion limitation
R to L shunt

60
Q

Examples of: Hypoxia (decreased delivery to tissue)

A

Low cardiac output
Hypoxemia
Anemia
CO poisoning

61
Q

Examples of: ischemia (loss of blood flow)

A

Impeded arterial flow
Reduced venous drainage

62
Q

Which zone of the lung is V/Q highest or lowest?

A

V/Q highest in the apex (wasted ventilation)
V/Q lowest in the base (wasted perfusion)

63
Q

Where are ventilation and perfusion highest in the lung?

A

Both are highest in the base of the lung

64
Q

What happens to V/Q as you exercise? Why?

A

Increase vasodilation of apical capillaries

65
Q

When is V/Q = 0? V/Q = infinity?

A

V/Q = 0 - ventilation problem (airway obstruction - shunt)
Even 100% O2 does not improve PO2

V/Q = infinity - blood flow obstruction (physiologic dead space)
Assuming < 100% dead space, 100% O2 improves PO2

66
Q

What are the 3 forms of CO2 transported to the lung? Which is the highest?

A
  1. Bicarbonate (90%)
  2. Carbaminohemoglobin or HbCO2 (5%)
    Bound to N-terminus of globin (not heme) - favors taut (unloaded) form
  3. Dissolved CO2
67
Q

What is the haldane effect?

A

In lung, oxygenation promotes dissociation of H+
Towards CO2 formation -> CO2 is released from RBC

68
Q

What is the Bohr effect?

A

In peripheral tissue, high H+ from tissue shifts curve to right, unloading O2

69
Q

What is the acute response to high altitude?

A

Increase ventilation
Decreased PO2 and PCO2

70
Q

What is the chronic response to high altitude? (5)

A
  1. Increase EPO (increase hematocrit/Hgb)
  2. Increase 2,3 BPG (release more O2)
  3. Increase mitochondrial
  4. Increase renal excretion of bicarb (can augment by use of acetazolamide) to compensate for respiratory alkalosis
  5. Chronic hypoxic pulmonary vasoconstriction results in RVH
71
Q

What happens to O2/CO2 during exercise?

A

Increase CO2 production, O2 consumption
Increase ventilation rate to meet O2 demand

V/Q ration from apex to base more uniform
Increase pulmonary blood flow from increased CO

Decrease pH from lactic acidosis

No change in PaO2 and PaCO2 (increased venous CO2 content and decreased venous O2 content)

USMLE (13 decks)

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