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SF3- EXAM 2 > Gas Exchange > Flashcards

Gas Exchange Flashcards

1
Q

How is ventilation calculated?

A

RR x CO

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2
Q

What is an average/ normal ventilation?

A

6000 ml/min or 6L/min

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3
Q

Boyle’s Law

A

States that when temperature s constant, pressure and volume are inversely related

P1V1=P2V2

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4
Q

Dalton’s law

A

The total pressure exerted by a gas mixture is the sum of the pressures exerted by the individual gases that make it that mixture

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5
Q

Henry’s Law

A

States that the amount of a gas absorbed by a liquid to which it is not chemically combined is directly proportional to the positive pressure of the gas in the liquid.

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6
Q

Composition of Alveolar Air- in comparison to atmospheric air

A
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7
Q

What is the significance of slow replacement of alveolar air?

A
  • Prevents sudden changes in gas composition in the alveolar air and subsequent concentration in blood
  • Maintains respirtory control mechanisms which are dependent on stability of tissue oxygenation, carbon dioxide concentration and pH when respiration is temporarily interrupted
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8
Q

What are primary gases found in inspired air?

A

N2

O2

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9
Q

Immediately, upon entry to respiratory passage, air is humidified with __________.

A

Water vapor

NOTE: Total pressure in alveoli cannot exceed barometric pressure; therefore, other gases are diluted

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10
Q

What are the partial pressure of oxygen and carbon dioxide dependent on?

A
  • Rate of absorption of O2 into the blood
  • Rate of entry of new O2 into the lungs
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11
Q

What is the normal alveolar PO2?

A

104 mm Hg

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12
Q

What’s the normal alveolar ventilation?

A

4.2 L/min

NOTE: There is a 4-fold increase in VA required during exercise

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13
Q

The composition of expired air is determined by the ______ and ___________.

A

Dead space and alveolar volumes

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14
Q

What does the first portion of expelled air contain?

A

Dead space air, which is air that has been humidified and does not participate in gas exchange

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15
Q

What does the second portion of expelled air contain?

A

A gradual mixing of dead space with alveolar air until all dead space is washed out and only alveolar air is being expelled

NOTE: For pulmonary tests, collect last amount of air for pure sample of alveolar gas

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16
Q

Total pulmonary ventilation is greater than alveolar ventilation because of __________.

A

Dead space

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17
Q

A portion of tidal volume that remains in the upper conducting airways and does not participate in gas exchange.

A

Dead space volume

NOTE: Anatomical dead space is determined by the size and number of airways the gas occupies. While, physiological dead space usually occurs indiseased lungs.

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18
Q

What areas are considered to have physiological dead space?

A
  • Ventilated alveoli with no perfusion
  • Over-ventilated areas relative to the amount of perfusion
  • Sites of no gas exhange
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19
Q

Fowler’s Method of Dead Space Measurement

A
  1. Subject takes a single breath of 100% O2 and then exhales into a tube that continuously measures the [N2] in the expired gas.
  2. Anatomic dead space containing 100% O2 and 0% N2 empties first followed by alveolar emptying.
  3. Alveolar emptying results is a rise in [N2] and a decline in [O2] until a plateau is reached (indicates alveolar gas only).
  4. The volume with initially 0% N2 plus 50% of the rising N2 volume is equal to the anatomic dead space.
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20
Q

Fick’s Law

A

States that the diffusion of a gas across a sheet of tissue is directly related to the surface area of the tissue, the diffusion constant for that gas, and the partial pressure difference of the gas on each side of the tissue and is inversely proportional to tissue thickness

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21
Q

Partial pressure of a gas

A

The partial pressure of a gas is equal to the fraction of the gas in gas mixture times the barometric pressure

  • O2 = 21% of Barometric pressure
  • N2= 79% of Barometric pressure
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22
Q

How can PO2 be changed?

A
  • Fraction of inspired oxygen (air mask)
  • Changes in Barometric pressure
  • Supplemental O2
  • Travel to high altitudes (decreases PO2)
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23
Q

What are the partial pressire in the alveolar air determined by?

A
  • Alveolar ventilation
  • O2 consumption
  • CO2 production
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24
Q

Ideal Alveolar Gas Equation

A
  • PAO2= The partial pressure of oxygen in the alveolus
  • PIO2= Inspired partial pressure of oxygen which is equal to the FIO2 times the difference between the barometric pressure and pressure of H2O
  • PACO2= The alveolar gas carbon dioxide tension
  • R= Respiratory exchange ratio= 0.8
    • Ratio of CO2 excreted to the oxygen taken up by the lungs
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25
Q

What does a respiratory exhange ratio of 0.8 indicate?

A

That there is more O2 consumed than CO2 produced

REMEMBER: The ratio is CO2/O2

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26
Q

Compartmental Values for Respiratory Gases

27
Q

Alveolar Carbon Dioxide Equation

A

FACO2 is a function of cellular metabolism

28
Q

The fraction of CO2 in alveolus is the function CO2 production from _______ and the rate of elimation by the lungs.

A

Cellular metabolism

29
Q

Relationship between alveolar ventilation and PACO2

A

If you double your VA; halve your PACO2

If you halve your VA; double your PACO2

30
Q

Why is CO2 ventilation increased during exercise?

A

There is an increase in metabolic activity, meaning more CO2 is being produced. To maintain a normal CO2, ventilation must increase

31
Q

Hypercapnia

A

Increased arterial PCO2.

*Hypercapnia is 2nd to hypoventilation

32
Q

Ventilation is best in ______ regions when considering body position.

A

Dependent

NOTE: Body position changes ventilation such that ventilation per unit volume is best in lower depedent regions of the lung compared with upper regions

33
Q

Distribution of alveiolar ventilation

34
Q

What are the changes in ventilation (in a single breath) for reduced compliance and increased airway resistance?

A

Normal- 97%

Reduced compliance- 80%

Increased resistance - 50%

36
Q

How is the ventilation/ perfusion ratio determined for a single alveolus?

A

Ratio is equal to alveolar ventilation divided by the capillary blood flow

37
Q

How is the ventilation/ perfusion ratio determined for an entire lung?

A

Total alveolar ventilation divided by the cardiac output

38
Q

Ventilation- Perfusion mismatching increases with _______ and _________.

A

Age and lung disease

39
Q

In patients with cardiopulmonary disease, misamtcing of ventilation and perfusion, is the most common cause of ____________.

A

Arterial hypoxemia

40
Q

Distribution of Ventilation and Perfusion in the upright lung

41
Q

In cases of severe emphysema, V/Q ratio is ___________ (low/high). In cases of chronic bronchitis, V/Q ratio is (low/high).

A
  • High V/Q in emphysema due to low perfusion
    • Capillaries are ablated, secondary to alveolar wall deteriotation
  • Low V/Q in chronic broncitis due to high perfusion and low ventilation

NOTE: A normal V/Q does not necessarily indicate a healthy lung because of compensatory mechanisms

42
Q

High PO2 environment at apex of the lung affects the distribution of _____________.

A

Pulmonary tuberculosis

*Tuberculosis bacillus thrives in O2- rich environments

43
Q

Overall V/Q in the normal lung is _________.

44
Q

At the apex of the lung, what happens to the ventilation to perfusion ratio?

A

V/Q will be greater than one due to an increased ventilation relative to little perfusion in pulmonary circulation due to gravity

45
Q

At the base of the lung, what happens to the ventilation to perfusion ratio?

A

V/Q wil be less than one due to the perfusion being greater than ventilation

46
Q

What are the pressure ratios for alveoli, arteries, and veins, in each zone of perfusion?

A
  • Zone 1
    • ​PA > Pa > Pv
    • Blood vessels can become completely collapsed by alveolar pressure (PA) and blood does not flow through these regions.
  • Zone 2
    • Pa > PA > Pv
    • Blood flows in pulses.
    • At first there is no flow because of obstruction at the venous end of the capillary bed.
    • Pressure from the arterial side builds up until it exceeds alveolar pressure and flow resumes.
  • Zone 3
    • ​Pa > Pv > PA
    • Blood flow follows a pressure gradient
    • Results in distension of the blood vessels and lowering resistance.

Alveoli =PA

Arteries =Pa

Veins =Pv

47
Q

Zone 1 of perfusion does not exist normally. When can it be reached?

A
  • When a subject is mechanically ventilated
  • Physiological condtion that significantly reduce Pa pressure
    • Hemorrhage
  • Under conditions of decreased arterial pressure
48
Q

Which zone of perfusion has blood existing that is most reflective of PaO2?

49
Q

Which zone of perfusion has the best blood, follows a pressure gradient and has no collapsed capillaries?

50
Q

Regional differences in ventilation and perfusion in the normal upright lung

51
Q

The difference between PAO2 and PaO2 is termed _____

A

AaO2

NOTE: A=alveolar and a = arterial. In normal subjects there is little to no difference between the two.

52
Q

Oxygenated and deoxygenated blood mixing causes a reduction in the ______.

53
Q

An _______ (increase/decrease) in AaO2 is the hallmark of inefficient or abnormal gas exhange.

54
Q

Thebesian vessels that supply the ____ drain directly into the arterial circulation, rather than the coronary sinus in the right atrium.

A

Left ventricle

55
Q

Low PaO2 is known as ________

A

Arterial hypoxemia

NOTE: An abnormal PaO2 can occur in the presence or absence of an abnormal AaDO2. However, the relationship between the PaO2 and AaDO2 is useful in determining the cause of the abnormal PaO2 and predicting the response to supplemental oxygen therapy.

56
Q

What is the normal AaDO2?

A

Less than 15mm Hg

NOTE: Value for the AaDO2 increases 3 mmHg per decade of life, making less than 25 mmHg the upper limit of normal

57
Q

What is the most common cause of hypoxemia?

A

V/Q mismatch

58
Q

Stages of impaired gas exhange

59
Q

Lung mechanisms of arterial hypoxemia

A

Diffusion deficits

Shunt

Ventilation/ Perfusion Mismatch

Alveolar hypoventilation

60
Q

What is the V/Q ratio in cases of a physiological shunt?

A

V/Q= 0

  • Complete block of airway; all ventilation diverted to adjacent alveolus
  • Perfusion is equally distributed between both units
  • Results: Mixed venous blood with no gas exhange- it remains mixed venous
61
Q

Disease states associated with hypoxia

A
  • Congenital heart defects
  • Anatomic shunts
  • Tetralogy of Fallot
    • Pulmonary valve stenosis
    • Ventricular septal defect
    • Overriding aorta
  • Guillain- Barre syndrome
    • Diaphragm doesn’t generate a great force, results in decreased minute ventilation
62
Q

What factors determine alveolar O2?

A

The balance between the rate of O2 uptake and the rate of O2 replenishment by ventilation

63
Q

AaDO2 results of hypoventilation

A

Normal because both PAO2 and PaO2 are decreased

64
Q

Causes of hypoventilation

A
  1. Respiratory center deficit
  2. Interference with nerve
  3. Dislocation of cervical spin, disruption of nerves to diaphragm
  4. Anterior horn cell problem
  5. Neuritis
  6. Neuromuscular Junction/paralysis or affect of anesthesia
  7. Muscle atrophy

SF3- EXAM 2 (11 decks)

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