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USMLE > Respiratory - Physiology > Flashcards

Respiratory - Physiology Flashcards

(71 cards)

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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
What favors taut form over relaxed form? (5)
1. Increased Cl- 2. Increased H+ 3. Increased CO2 4. Increased 2,3-BPG 5. Increased temperature
26
What happens to the dissociation curve when taut form is favored?
Right shift, causing increased in O2 unloading
27
What is the structure of fetal hemoglobin? How is it different from adult form?
2 alpha 2 gamma subunits Lower affinity for 2,3-BPG (higher affinity for O2)
28
What is methemoglobin? What does it have affinity for?
Oxidized form of hemoglobin (ferric, Fe3+) Does not bind O2 as readily, but has increased affinity for cyanide
29
What is the normal state of iron in hemoglobin?
Ferrous, Fe2+
30
To treat cyanide poisoning, nitrites are used. What is the mechanism for its action?
Oxidize hemoglobin to methemoglobin, which binds to cyanide, allowing cytochrome oxidase to function
31
To treat cyanide poisoning, thiosulfate can be used. What is their mechanism of action?
Thiosulfate binds to cyanide to form thiocyante, which is renally excreted
32
What is used to treat methemoglobinemia?
Methylene blue
33
How does CO lead to toxicity?
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
Why does hemoglobin curve have sigmoidal shape?
Positive cooperativity Tetrameric hemoglobin can bind 4 oxygen molecules and has higher affinity for each subsequent oxygen
35
Why does myoglobin not show the same sigmoidal shape as hemoglobin?
Does not have positive cooperativity (monomeric)
36
What is pulmonary hypoxic vasoconstriction?
Low PAO2 causes hypoxic vasoconstriction that shifts blood away from poorly ventilated region of lung
37
What is the difference between perfusion and diffusion limited?
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
Examples of perfusion limited molecules
O2 (normal health), CO2, N2O
39
Examples of diffusion limited molecules
O2 (emphysema, fibrosis), CO
40
What is the consequence of pulmonary hypertension?
Cor pulmonale and subsequent RV failure (JVP, edema, hepatomegaly)
41
How to calculate diffusion of a gas
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
What is normal pulmonary artery pressure? What makes diagnosis of pulmonary hypertension?
Normal = 10-14 mmHg Pulm HTN = \>25 or \>35 during exercise
43
What does pulmonary hypertension results in?
arteriosclerosis, medial hypertrophy, intimal fibrosis of pulmonary arteries
44
What is primary pulmonary hypertension? Prognosis?
Inactivating mutation in BMPR2 gene The gene normally inhibits vascular smooth muscle proliferation poor prognosis
45
What is secondary pulmonary hypertension? (7)
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
How to calculate pulmonary vascular resistance?
Pulmonary Vascular Resistance = (Pressure of Pulmonary Artery - Left atrium) /Cardiac output
47
What affects resistance?
R = 8nl/pr^4 n=viscosity l=length r=radius
48
What is oxygen content?
O2 binding capacity x % saturation + dissolved O2 O2 Content = [1.34 x [Hgb] x % sat] + 0.0031PaO2
49
Normally 1g Hb can bind how many ml of O2?
1.34
50
Normal Hb amount in blood?
15 g/dL
51
Cyanosis results when deoxygenated Hb is more how many g/dL
5g/dL | (normal amount of Hb in blood is 15 g/dL)
52
What is the normal O2 binding capacity (ml O2/dL)?
20.1 mL O2/dL
53
As hemoglobin falls, what happens to the oxygen content, oxygen saturation and arterial PO2?
Oxygen content decreases Oxygen saturation and arterial PO2 do not
54
How to calculate oxygen delivery to tissue?
Cardiac output x O2 content of blood
55
What is the equation to calculate PAO2?
PAO2 = FIO2 x (Patm-Ph2o)-PaCO2/RQ Patm=760 Ph2o=47 RQ=0.8 ~ PAO2 = 150-PaCO2/0.8
56
What is the A-a gradient
PAO2 - PaO2 Normal is 10-15 mmHg
57
Give examples of increased A-a gradient?
Shunting V/Q mismatch fibrosis (impairs diffusion)
58
Examples of: Hypoxemia with Normal A-a gradient
High altitude Hypoventilation
59
Examples of: Hypoxemia and high A-a gradient
V-Q mismatch Diffusion limitation R to L shunt
60
Examples of: Hypoxia (decreased delivery to tissue)
Low cardiac output Hypoxemia Anemia CO poisoning
61
Examples of: ischemia (loss of blood flow)
Impeded arterial flow Reduced venous drainage
62
Which zone of the lung is V/Q highest or lowest?
V/Q highest in the apex (wasted ventilation) V/Q lowest in the base (wasted perfusion)
63
Where are ventilation and perfusion highest in the lung?
Both are highest in the base of the lung
64
What happens to V/Q as you exercise? Why?
Increase vasodilation of apical capillaries
65
When is V/Q = 0? V/Q = infinity?
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
What are the 3 forms of CO2 transported to the lung? Which is the highest?
1. Bicarbonate (90%) 2. Carbaminohemoglobin or HbCO2 (5%) Bound to N-terminus of globin (not heme) - favors taut (unloaded) form 3. Dissolved CO2
67
What is the haldane effect?
In lung, oxygenation promotes dissociation of H+ Towards CO2 formation -\> CO2 is released from RBC
68
What is the Bohr effect?
In peripheral tissue, high H+ from tissue shifts curve to right, unloading O2
69
What is the acute response to high altitude?
Increase ventilation Decreased PO2 and PCO2
70
What is the chronic response to high altitude? (5)
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
What happens to O2/CO2 during exercise?
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)

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