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22 spring: Physiology > exam 2 lecture 19 and 20 > Flashcards

exam 2 lecture 19 and 20 Flashcards

1
Q

1.The A-a gradient

A

The difference between the amount of O2 in the alveolar gas versus the arterial blood tells you if the lung is sick, or there’s not enough breathing going on

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2
Q

PaO2

A

pressure of oxygen gas dissolved in the arterial blood

mmHg

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3
Q

PaCO2

A

pressure of carbon dioxide dissolved in the arterial blood

mmHg

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4
Q

5 causes of hypoxemia

A
  1. Low inspired oxygen (decreased PiO2)•High altitude
  2. Hypoventilation•Not breathing enough (hold your breath)
  3. Diffusion limitation•Blood-gas barrier is too thick
  4. Shunt•Some blood is bypassing the lungs•“Hole in heart”
  5. Ventilation-perfusion (V/Q) inequality•The amount of ventilation isn’t matching the blood flow in the lungs
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5
Q

what causes low inspired oxygen?

A

decreased PiO2

high altitude

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6
Q

what causes hypoventilation

A

not breathing enough/holding your breath

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7
Q

what is a diffusion limitation

A

blood gas barrier is too thick (Fick’s law)

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8
Q

What causes a shunt

A

some blood is bypassing the lungs

hole in the heart

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9
Q

what causes V/Q mixmatch

A

the amount of ventilation isn’t matching the blood flow in the lungs

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10
Q

what causes of hypoxemia are problems with the lungs?

A
  1. Diffusion limitation•Blood-gas barrier is too thick
  2. Shunt•Some blood is bypassing the lungs•“Hole in heart”
  3. Ventilation-perfusion (V/Q) inequality•The amount of ventilation isn’t matching the blood flow in the lungs
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11
Q

what causes of hypoxemia are causes by problems not the lungs

A
  1. low inspired oxygen, decreased PiO2, high altitude
  2. Hypoventilation•Not breathing enough (hold your breath)
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12
Q

which one, PAO2 or PaO2, has to be bigger ?

A

PAO2 needs to be bigger to get air to move by diffusion from the alveoli to the arterial blood

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13
Q

what is the normal A-a gradient

A

5-10 mmHg

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14
Q
A

showing how O2 is lost from the atmosphere to the tissues

A-a gradient =5-10 mmHg

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15
Q

how to calculate PAO2

A

respiratory quotient (RQ) = relationship between O2 and CO2

mixed diet = 0.8

PAO2= FiO2(Patm-47) - (PaCO2/0.8)

= O2 going in and O2 going out

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16
Q

= is the amount of oxygen that enters the alveoli from the airways (PiO2) MINUS the amount oxygen leaving the alveoli into the capillary blood

A

PAO2

partial pressure of O2 in the alveolar

usually 100mmHg

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17
Q

PH20

A

47

pressure of H20 dissolved in the airways cause the body is warmer then the environment

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18
Q

___= [(PATM – PH2O) x FiO2] – (PACO2 / R)

A

PAO2

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19
Q

CO2 is so highly soluble that alveolar CO2 (PACO2) and arterial CO2 (PaCO2) are basically ___

A

the same.

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20
Q

what causes high A-a gradient?

A

lung problem

•If hypoxemia is caused by a problem with the lungs (pulmonary hypoxemia), then oxygen won’t transfer well from the alveolus to the blood, so the A-a gradient will be HIGH

  1. Diffusion limitation•Blood-gas barrier is too thick
  2. Shunt•Some blood is bypassing the lungs•“Hole in heart”
  3. Ventilation-perfusion (V/Q) inequality•The amount of ventilation isn’t matching the blood flow in the lungs
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21
Q

what causes of hypoxemia do not effect the A-a gradient?

A
  1. Low inspired oxygen (decreased PiO2)•High altitude
  2. HypoventilationNot breathing enough (hold your breath)
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22
Q

•If hypoxemia is caused by a problem with the lungs (pulmonary hypoxemia), then oxygen won’t transfer well from the alveolus to the blood, so the A-a gradient will be ___

A

high

  1. Diffusion limitation•Blood-gas barrier is too thick
  2. Shunt•Some blood is bypassing the lungs•“Hole in heart”
  3. Ventilation-perfusion (V/Q) inequality•The amount of ventilation isn’t matching the blood flow in the lungs
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23
Q

•If hypoxemia is just caused by decreased breathing effort (hypoventilation; don’t forget to breathe!) or the PiO2 is lower (high altitude) but the A-a gradient will be ___

A

normal

  1. Low inspired oxygen (decreased PiO2)•High altitude
  2. Hypoventilation•Not breathing enough (hold your breath)
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24
Q

why is A-a gradient normal with low PiO2

A

PiO2= FiO2(Patm-PH20)

at high altitude both PAO2 and PaO2 are decreased so the A-a gradient is normal

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25
Q

what is a common response to low PaO2

A

hyperventilation

decreased PaCO2

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26
Q

often ___ (hyperventilation in response to low PaO2)

A

decreased PaCO2

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27
Q

what effects CO2 in your blood

A

ventilation

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28
Q
A

PACO2=VCO2/VA

amount of CO2 directly effected by ventilation

the faster you breathe the less CO2

the slower you breath the more CO2

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29
Q

___ FiO2 alleviates hypoxemia because it leads to an increase in alveolar PO2

A

increasing

PAO2 = FiO2 (PATM – PH2O) – (PACO2/R)

PiO2= FiO2 (PATM – PH2O)

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30
Q

what happens to PCO2 with hypoventilation?

A

increased

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31
Q

how to fix increased PCO2?

A

ventilation (needs to breathe faster)

increased CO2 is from hypoventilation

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32
Q

causes of hypoventilation

A

–Central respiratory depression (CNS disease, drugs)

–Abnormal respiratory muscle function

–Thoracic cage abnormalities

–Pleural space disease

–Upper airway obstruction

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33
Q

what happens to PO2 and PCO2 during hypoventilation and how do you fix it?

A

O2 decreases

CO2 increases

O2 fixed by giving more oxygen (increase FiO2)

PaO2= FiO2 (PATM – PH2O) - (PACO2/R)

CO2 fixed by ventilating patient and increasing breathe

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34
Q

explain diffusion limitation and how is causes hypoxemia

A

hemoglobin requires 0.25 seconds to get all O2, it normal takes hemoglobin 0.75 seconds to get across- plenty of time

if the walls become thickened (ficks law) it is harder for O2 to diffuse and it takes longer for hemoglobin to get full.

CO2 not effected cause it is 20x more soluble then O2

35
Q

what happens to A-a gradient with diffusion limitation

A

high

lots of O2 in the alveoli but none of it can get to the blood so big difference between A and a

36
Q

•Impaired diffusion generally results from an ___ – due to fluid or fibrosis in the interstitium (not in the alveolar lumen)

A

increase in the thickness of the blood gas barrier

37
Q

what happens to PaCO2 during diffusion limitation

A

usually normal

•PaCO2 does not increase until lesion is severe because it diffuses 20X more readily

38
Q

where is A-a gradient changed for diffusion limiations?

A
39
Q

where is A-a gradient increased for a shunt

A
40
Q

___ is when deoxygenated venous blood added to arterial circulation that has bypassed ventilated areas of lung

A

shunt

41
Q

what are two physiologic shunts?

A

bronchial circulation

coronary venous blood

42
Q

what are two pathologic shunts?

A

right to left cardiac shunt (VSD)

intrapulmonary- •Deoxygenated blood passes through normal pulmonary vasculature without contacting ventilated alveoli

43
Q

what cause of hypoxemia responds poorly to oxygen?

A

shunt

big shunt will skip lungs, doesn’t matter if you put a bunch of O2 into the lungs, the O2 will not get into the blood

44
Q
A

show how supplemental O2 will effect PaO2 with a shunt

big shunt= O2 does NOT help

little shunt = O2 helps

45
Q
A

CO2 is so soluble, as long as a small amount of blood gets to the lungs CO2 will diffuse easily

46
Q

V/Q mismatch will cause an A-a gradient to be ___

A

high

47
Q

___ responsible for most of the defective gas exchange (& resultant hypoxemia) in pulmonary disease

A

•V/Q mismatch

48
Q
A

gas flow

ventilation (L/min)

49
Q
A

blood flow

ml/min

50
Q

dead space ventilation

A

V/Q > 1

ventilation excessive relative to blood flow

breathing to fast or blood to slow

51
Q

venous admixture

A

perfusion (pulmonary capillary blood flow) excessive compared to ventilation

V/Q < 1

blood to fast, venous deoxygenated blood will mix with oxygenated blood cause it moved to quickly to gain O2 from alveoli

52
Q

what has V/Q <1

A

venous admixture

blood to fast to get enough oxygen

deoxygenated blood will mix with oxygenated blood

53
Q

what has V/Q >1

A

dead space ventilation

breathing normal but blood too slow

54
Q

what is the V/Q from a blocked airway

A

less then 1

too much Q not enough V

venous admixture

55
Q

what is the V/Q from a blood clot

A

greater than 1

dead space ventilation

too much V not enough Q

56
Q

what are some causes of venous admixture

A

V/Q less then 1

•Decreased V/Q (<1) = “intrapulmonary shunt”

–Occlusion of small airways (asthma, bronchitis)

–fluid filled alveoli (pulmonary edema)

–Collapsed alveoli (atelectasis)

57
Q

what are some causes of dead space ventilation

A

V/Q greater than 1

–emphysema (destruction of capillary alveolar interface

–reduced blood flow (emboli (blood clot), pulmonary hypertension)

58
Q

normal value for PACO2

A

38-44 mmHg

59
Q

normal value for PaO2

A

90-100 mmHg

60
Q

term for increase for CO2

A

hypercarbia

hypercapnia

61
Q

calculate PAO2

if room air and PACO2=48.3

if 100% O2

A

PAO2= FiO2(Patm-47) - (PACO2/0.8)

  1. 21(760-47) -(48.3/0.8)
  2. 73- 60.38

89.36 mmHg

1(760-47) -(48.3/0.8)

713-60.38

652.62

62
Q

what is the A-a gradient if

room air: PAO2 is 90, PaO2 is 59.8

100% O2= PAO2 653, PaO2 59.8

what does the A-a tell us?

A

A-a= 30.2

A-a= 593.2

abnormal= issue with lungs (shunt, V/Q or diffusion limitation)

63
Q

The effects of gravity mean that the more dependent (lower down) alveoli are ____ than the less-dependent alveoli

A

smaller and less ventilated

64
Q

explain

A

gravity causes alveoli at the bottom to be smaller (slinky)

gravity causes blood to pool at the bottom

leads to V/Q mixmatch

65
Q

what is hypoxic vasoconstriction?

A

when V/Q messed up the pulmonary arteries will become smaller in response to low alveolar O2, this reduction in blood flow(Q) will result in an increase in V/Q

not enough ventilation, blood flow will decrease to match

66
Q

explain pulmonary reflex to V/Q less then 1

A

decreased V will trigger pulmonary arteries to constrict so that V/Q increases

67
Q

explain pulmonary reflex to V/Q greater then 1

A

too much ventilation will cause pulmonary arteries to constrict to match V

68
Q

When the blood vessels sense a low oxygen tension (from hypoventilated alveoli, low V) THEY ____ thus reducing Q, which corrects the V/Q mismatch

A

vasocontrict

69
Q

explain hypocapnic bronchoconstriction

A

too little CO2

airways will close/constrict to allow CO2 to try to normalize

The airways bronchoconstrict in response to low alveolar CO2 causing decreased alveolar ventilation (V) → decrease V/Q ratio

70
Q

what can cause hypocapnia?

A

hyperventilating → breath off CO2

pulmonary embolus→ blood can’t get to lungs, CO2 can’t get out??

71
Q

how to correct local V/Q mixmatch?

A
72
Q

anesthesia will do what to the compensatory mechanisms for V/Q mixmatch?

A

turn them off!

73
Q

what is V/Q for the top and bottom?

A

top = greater than 1= dead space ventilation

bottom = less then 1 = venous admixture

74
Q

why does supplemental O2 help V/Q mixmatch for ventilated patient?

A

cancels out abnormal A-a, there is so much extra O2 that the V/Q will balance out

75
Q

what is a right to left shunt?

A

blood from deoxygenated (right side) is mixing with oxygenated (left side) without becoming oxygenated

•It means that blood from the de-oxygenated right side of the heart bypasses the lung and is shunted directly into the left side of the heart, so it dilutes the oxygenated blood with deoxygenated

76
Q
A

normal= hypoventilation or altitude

abnormal= shunt, V/Q or diffusion limitation

77
Q
A

responsive= low V/Q or diffusion limitation

non responsive= shunt

78
Q

what happens to PaCO2, A-a gradient and PaO2 on oxygen for all 5 causes of hypoxia?

A
79
Q

calculate A-a gradient if

A

PAO2= 0.3(760-47) - (45/0.8)

214- 56.25

158

A-a= 158-67= 91 abnormal

issue with lungs (shunt, v/q or diffusion)

her PaCO2 is also elevated→ hypoventilation

two things are going wrong

80
Q

hypoventilation does what to CO2?

what can cause this?

A

increases CO2

–Brain problem (anesthesia, brain disease)

–Diaphragmatic problem (exhaustion, injury)

–Lung problem? (has to be really REALLY severe)

81
Q

hyperventilation does what to CO2

what causes this?

A

decreases

–Fear or pain (increased resp rate)

–Hypoxia (low oxygen increases resp. rate)

–Acidemia (if the blood is too acidic from other problems, the patient will “blow off” the acidic CO2 to normalize blood pH)

82
Q

calculate A-a

what does this mean?

A

PAO2= FiO2(760-47) -(PaCO2/0.8)

  1. 21(760-47)- (60/0.8)
  2. 73-73
  3. 73

A-a= 76.73-70= 6.73

A-a normal and CO2 increased= hypoventilation issue

83
Q

PaCO2 when hypoventilating or hyperventilating

A

hyper= less then 40

hypo = greater than 40

PACO2= VCO2/VA

CO2 is so highly soluble that alveolar CO2 (PACO2) and arterial CO2 (PaCO2) are basically the same, so clinically they are used interchangeably

22 spring: Physiology (34 decks)

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