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SMP - Cardiopulmonary Exam 2 > Lecture 29 - Resistance > Flashcards

Lecture 29 - Resistance Flashcards

1
Q

Condition for there to be flow through a tube?

A

Must be a pressure difference on either side

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2
Q

What does the pressure gradient through a tube determine? Explain.

A

Rate and pattern of flow

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3
Q

Stream lines of gas flow through tube at low flow? What flow does this correspond to?

A

Parallel => laminar flow

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4
Q

Stream lines of gas flow through tube at high flow? What flow does this correspond to?

A

Disorganized and disturbed => turbulent flow

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5
Q

Poiseuille’s Law? Under what conditions?

A

R = 8.η.L/π.r^4

η = viscosity
L = length

Condition: laminar flow

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6
Q

If the radius of an airway is halved, how will the resistance be affected?

A

Resistance increased 16 fold

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7
Q

Implication of Poiseuille’s Law in terms of blood transfusions?

A

To get blood in as fast as possible, use a short wide tube placed into a vein (e.g. dialysis lines, not central lines)

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8
Q

What determines whether flow will be laminar or turbulent?

A

Reynold’s number, Re

Re = 2.r.v.ρ/η

v = velocity
ρ = density
η = viscosity

Re > 2000 => probable turbulent flow
Re < 2000 => probable laminar flow

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9
Q

Is helium gas more likely to produce turbulent or laminar flow? Why?

A

Laminar because it has low density (less dense than N2)

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10
Q

How can we clinically reduce turbulent flow in the airways?

A

Replace N2 with helium gas in the mixture with O2

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11
Q

Why does inhaling helium gas make your pitch high?

A

Because less turbulent flow at the vocal cords

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12
Q

Equation for airway resistance?

A

R = Palv - Pmouth/flow rate

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13
Q

Palv at beginning of inhalation?

A

0 cm H2O

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14
Q

Palv during inhalation?

A

Decreases (negative) and then increases back to 0 cm H2O

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15
Q

Palv during at beginning of expiration?

A

0 cm H2O

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16
Q

Palv during expiration?

A

Increases (positive) and then decreases back to 0 cm H2O

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17
Q

Ppleura at beginning of inhalation?

A

-5 cm H2O

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18
Q

Is inspiratory flow positive or negative?

A

Negative

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19
Q

Is expiratory flow positive or negative?

A

Positive

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20
Q

Ppleura during inspiration?

A

Decreases as elastic recoil increases + further drop due to Raw to a value more negative than at resting state

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21
Q

Describe the cycles of volume, flow, intrapleural pressure, and alveolar pressure in regards to one another?

A
  • Flow and alveolar pressure are on same cycle
  • Volume and intrapleural pressure are on same cycle
  • Both are 1/2 a cycle apart
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22
Q

Where does most of the airway resistance occur? What does this mean?

A

In the 4th to 7th divisions of the airways => small airways disease is difficult to detect

23
Q

What airways diseases cause increase airway resistance? What do we call these?

A
  1. Asthma
  2. COPD: chronic bronchitis + emphysema

=> airway obstructive diseases

24
Q

Explain asthma.

A

Increase in inflammatory cells around airways causing them to narrow

25
Q

Explain chronic bronchitis.

A

Upper and lower airways are inflamed and produce a lot of mucus and pus, which impede on the respiratory cilia and narrow the airways

26
Q

Explain emphysema due to cigarette smoking.

A

Cigarette smoking deactivates an enzyme in lungs (anti-protease) that is responsible for keeping in check a protease that is responsible for getting to infections to allow WBCs to access them => protease attacks the elastic skeleton of the lung (parenchyma) => destruction of the alveolar walls + enlarged air sacs due to destruction of alveolar walls + damaged pulmonary capillaries by tearing, fibrosis, or thrombosis => compliance increases but there is no elasticity to keep airway open with expiration => airways close and have high resistance

27
Q

What are bronchi supported by?

A

Supported by radial traction of surrounding tissue

28
Q

How do bronchi change as the lungs expand?

A

Their caliber/diameter increases as lung expands

29
Q

Factors determining airway resistance?

A
  1. Different volumes cause airways to close/open affecting the resistance
  2. ANS innervation of smooth muscle
  3. Inflammation of bronchial walls increases Raw
  4. Density and viscosity of gas
30
Q

Describe the parasympathetic innervation of the airways.

A

Parasympathetic activity causes bronchoconstriction

31
Q

Describe the sympathetic innervation of the airways.

A

Sympathetic activity causes bronchodilation

32
Q

3 treatments for airway obstructive diseases?

A
  1. Beta-agonists to cause bronchodilation
  2. Steroids to decrease inflammation of bronchial walls
  3. Anti-cholinergic agents to inhibit the parasympathetic activity
33
Q

Describe the filling of two alveoli: 1 normal and 2 partially obstructed. What does this mean overall?

A
  1. Alveolus 2 takes longer to fill with air during inspiration because air first fills up alveolus 1 (path of least resistance)
  2. When we pause to hold our breath, both will be filled with the same amount of air (air from 1 will move to 2)
  3. Alveolus 2 takes longer to deflate during expiration because air first leaves alveolus 1 (path of least resistance)

=> Overall, alveolus 2 has a longer time constant to ventilate

34
Q

What happens to patients with airway obstructive diseases when they hyperventilate?

A

If they breathe faster then the time constant of obstructed alveoli then these will not be fully ventilated and will have a V/Q imbalance (<1)

35
Q

Why are patients with airway obstructive diseases hypoxemic?

A

V/Q imbalance of obstructed alveoli

36
Q

Peak flow during expiration: effort dependent or independent?

A

Dependent

37
Q

Flow during expiration following peak flow: effort dependent or independent? What does this mean? Why?

A

Independent: after peak flow flow decreases back to 0 and the decelerating slope of this part of the curve is constant regardless of what the peak flow was

BECAUSE of the choke point, which limits flow

38
Q

Other name for choke point?

A

Equal pressure point

39
Q

What is the choke point worsened by? What does this mean?

A

Worsened by:

  1. Any increase in airway resistance => decrease in endobronchial pressure
  2. Reduced driving force (e.g. emphysema)
40
Q

Palv-Ppleu at the end of inspiration?

A

+ 8 cm H2O

41
Q

Describe the pressures in the alveoli and the pleural cavity during a force expiration and how it explains the choke point.

A

High positive pressure created by the recoil of the lung and the chest muscles so the Palv>Ppleura, but from the alveoli to the outside of the mouth the pressure decreases and there comes a point where positive Pairway this is a choke point that limits expiration

42
Q

Describe the flow-volume curve of respiration and the important points on it to note.

A
  • X-axis: volume
  • Y-axis: flow
  • Inspiration: bottom half and moving to the left
  • Expiration: upper half and moving to the right
  • Point on dotted line to the right of the curve: RV
  • Point on dotted line to the left of the curve: TLC
  • Between 2 points: vital capacity
43
Q

How is the flow-volume curve affected by a restrictive lung disease?

A

Lungs are less compliant and cannot get to the full TLC so the curve will be more narrow although peak flows are normal

44
Q

How is the flow-volume curve affected by an obstructive lung disease?

A

Peak flows are lower and the expiratory decelerating portion of the curve is convex due to the airways being narrowed

45
Q

How do the extrathoracic airways react to inspiration and expiration?

A
  1. Inspiration: negative pressure is experienced so they tend to collapse
  2. Expiration: positive pressure is experienced so they extend
46
Q

How is the flow-volume curve affected by an obstruction in the trachea outside of the thorax? What is this called? Classic example?

A
  1. Expiratory loop is normal
  2. Inspiratory loop is flattened as the peak flow is lower and constant for a certain period of time = obstruction of inspiratory flow

= VARIABLE EXTRATHORACIC OBSTRUCTION

Classic example: paralyzed vocal cords that collapse during inspiration OR intubated patient with tracheal tube causing inflammation and narrowing of airway

47
Q

What can you assume if there is an abnormality on only one phase (inspiration/expiration) of the flow volume curve?

A

Usually due to obstruction of main upper airway

48
Q

How is the flow-volume curve affected by an obstruction in the trachea inside of the thorax? What is this called?

A
  1. Inspiratory loop is normal
  2. Expiratory loop is flattened as the peak flow is lower and constant for a certain period of time = obstruction of expiratory flow

= VARIABLE INTRATHORACIC OBSTRUCTION

49
Q

How is the flow-volume curve affected by a FIXED obstruction in the trachea? What is this called?

A
  1. Inspiratory loop is flattened as the peak flow is lower and constant for a certain period of time = obstruction of inspiratory flow
  2. Expiratory loop is flattened as the peak flow is lower and constant for a certain period of time = obstruction of expiratory flow

= FIXED INTRA or EXTRATHORACIC OBSTRUCTION (cannot distinguish between the 2 with the curve)

50
Q

When you place an asthmatic patient who is having an asthma attack on a mechanical ventilator, how are the peak and plateau pressures affected? What about the difference between the 2?

A
  1. High peak pressure because asthma causes increased airway resistance and therefore peak pressure will be higher
  2. *Normal plateau pressure because asthma does not cause a problem with lung compliance
  3. Difference between peak and plateau pressures should be larger due to the high peak pressure
    * One could also argue that the plateau pressure is increased because: increased airway resistance => increased FRC => movement to the right to a less compliant portion on the compliance curve => less compliance = higher pressure => higher plateau pressure
51
Q

Are the alveolar membranes affected in chronic bronchitis?

A

NOPE

52
Q

Is the damage to the alveolar walls due to emphysema reversible?

A

NOPE

53
Q

Are expiratory peak flow and inspiratory peak flow equal in normal individuals?

A

It all depends on the force applied to inhale or exhale:

  • If you use your muscles to rapidly inhale a breath you will generate higher flow rates than if you passively exhale
  • However if you are using maximal effort to inhale and maximal efforts to exhale, you can generate much higher flow rates on exhalation than inhalation
54
Q

Why is only the deceleration curve of expiration affected in obstructive lung diseases? Aka why is the inspiratory curve shape normal (other than the low peak flow)?

A

In obstructive lung diseases the obstruction occurs in the intra thoracic airways:

  • On exhalation these airways narrow thus bringing out the obstruction
  • On inhalation the intrathoracic airways are pulled open and increase in diameter

SMP - Cardiopulmonary Exam 2 (15 decks)

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