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CPR 2 > Airflow And. Airways DLA > Flashcards

Airflow And. Airways DLA Flashcards

1
Q

Why is their effort independence in flow volume loops?

A

This is due to dynamic airway compression

  • during forced expiration
  • intrapleural pressure at or above alveolar pressure
  • Causes dynamic collapsing of the lung airways
  • Associated with wheezing of COPD
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2
Q

When are flow volume loops made?

A

Measured during forced breathing

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3
Q

What causes the effort-dependent loops portion of the flow volume loops?

A

Due to:
-Vel and force of muscle contraction

  • elastic recoil lung
  • Airway patency
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4
Q

What causes the effort independent portion of the flow volume loop?

A

Despite varying effort of exhalation, later parts of curves take same path

Due to:
-Elastic recoil of lung

-Airway resistance (EPP dynamic compression & airway resistance with lung vol)

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5
Q

Why is it impossible to breach flow-volume loop?

A
  • Impossible to breach flow volume loop - I.e. starting slow and then exhaling forcefully result in same path decline
  • Something limits expiratory flow over most of lung volume

-Dynamic compression of airways increases resistance to airflow and effectively limits flow during expiration I.e. no matter how hard you try to exhale the flow is limited by the collapsed airways

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6
Q

What is the transmural Pressure formula?

A

PTA= Paw-Pp

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7
Q

What is the trans pulmonary pressure (PL)?

A

PL= PA- PI

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8
Q

What is the preinspiration phase of the breathing cycle?

A

Airway pressure everywhere is 0(no flow)

Intrapleural pressure -5 P (IP), there is a +5 cm H2O holding airways open

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9
Q

What is the role of inspiration in the breathing cycle?

A

Chest wall expands, diaphragm flattens, intrapleura P(IP) and alveolar pressure PA fail by 2, and air flows into the lungs. Pressure drops along the airway, and so at a point further it is -1. Pressure +6 holding airway open

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10
Q

What are the occurrences of end inspiration of breathing cycle?

A

Flow is 0. Slightly higher intrapleural pressure PIP.

All of the above - airflow driven by PA and PATM gradient

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11
Q

What is the role of forced expiration and intrapleural pressure in breathing cycle?

A

Forced expiration, intrapleural pressure increases to +30 (diaphragm and thorax). Lung elastic recoil adds 18 cm H2O pressure to the lungs. As air flows down this steep gradient pressure the airway pressure falls way below the intrapleural pressure PIP causing the airways to collapse above the EPP and airway resistance to increase dramatically

Effective= PA-PIP

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12
Q

What is dynamic compression of the airway ?

A

Process that results in effort independence of the flow-volume loop

Effort independence region of flow volume loop: Dynamic compression results in resistance to air flow as intrapleural pressure increases. Thus any extra effort not result in increased air flow due to this “valve”

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13
Q

What is Equal Pressure Point (EPP)?

A

Point at which pressure inside the airway equals pressure outside (intrapleural pressure).

Dynamic airway c9mpression starts after the equal pressure point( EPP)

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14
Q

Summarize EPP

A

EPP= when pleural pressures= airway pressures

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15
Q

Summarize Dynamic airway compression

A

Above EPP, upstream towards mouth,there is dynamic airway compression

  • decreased radius, increased resistance, thus radius restricts airflow
  • occurs at lower lung volumes
  • results in effort independent portion of the flow-volume loop
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16
Q

What is the significance of EPP?

A

Pressure gradient from alveoli to mouth drives air movement during exhalation.

Note: pleural pressures no longer subatomic, but positive during forced expiration

At certain point airway pressure= pleural prrsssure. This is the equal pressure point

As expiration continues the EPP will travel down into the lung

Upstream from EPP (towards alveoli) airways remain open

Downstream from EPP unsupported airways collapse. Larger airways suppo4ted by cartilage

17
Q

Summarize the function of forced expiration

A

Upon forced expiration airways collapse and act as a valve rate limiting flow through the airways

-As lung volume declines resistance increases, due to decrease in structural support at low lung volumes (I.e. the inflated lung is more rigid and the floppy airways are held open by this rigidity)

  • Therefore, more effort does not produce more flow
    • And thus the effort-independent portion of the flow-volume loop
18
Q

Summarize dynamic compression of the airways

A

Limits air flow in normal subjects during forced expiration

-May occur in diseased lungs at relatively low expiratory flow rates, thus reducing exercise ability

During dynamic compression, flow is determined by alveolar pressure minus pleural pressure (not mouth) and is therefore independently effort

Is exaggerated in some lung diseases by reduced elastic recoil and loss of radial traction on airways

19
Q

Compare elastic recoil and compliance of the lung

A

Normal lungs- EPP
Dynamic compression/restriction typically in airways with cartilage.

High lung compliance I.e. low elasticity e.g. emphysema, COPD

EPP lower down respiratory tree- dynamic compression also lower down tree

  • Decreased elastic recoil pressure (ERP) of lung (+2 vs +10)
  • Airway pressures less (+32 vs +40)
  • EPP further down respiratory treee
20
Q

Explain pathology of emphysema

A

In pathological states of high lung compliance eg emphysema, the elastic recoil force of the lung is reduced

During a maximal expiration,

  • PIP+ 30
  • Elastic recoil pressure of the alveoli now +2 vs +10
  • thus, pressure gradient from the Alveoli to the outside is less steep and the TAP along the airway is less

Consequently the EPP is going to occur to at higher lung volumes

At a PA of +32 and a PIP of +30 most of the airways are going to be compressed early in expiratory flow. This explains why patients with emphysema find it so diff8cult to breathe out

21
Q

Summarize Airway generation

A

Airway resistance decreases dramatically down respiratory tree

Even though radius falls significantly

22
Q

When is air resistance highest?

A

Highest in medium sized bronchi; low in very small airways

Contraction of bronchial smooth muscle narrows airways and increases resistance

Decreases as lung volume rises because the airways are then pulled open

23
Q

Why is their resistance in straws being blown?

A

Hard work—> large resistance due to small cross sectional area

Very hard work—> larger resistance due to smaller cross sectional area

Puts lots of straws together- even if individually smaller

  • as a group have large cross sectional area
  • air flowing through in parallel fashion

Therefore- less resistance

24
Q

How does lung volume and airway resistance affect each other?

A

At high lung volumes, there is increased traction on small airways pulling them open

Traction on airway by elastic recoil of alveolar septa= radial traction”

  • decline lung volume
  • decrease in distending pressure (radial traction) on airways provided by lung inflation
  • Airway radius decreases—> resistance to airflow increases

Liken it to trying to blow through a rigid straw vs. a floppy straw

High lung vols

  • inflated lung more rigid
  • floppy airways are held open by this rigidity
25
Q

What has the greatest effect on resistance to airflow?

A

Radius changes have greatest effect

26
Q

How does Poiseuille’s law effect airflow?

A

R= 8nl/ pi x r^4

Length increase x2= resistance increases also by 2

Radius most critical

Reducing the radius by half increases resistance by 16

27
Q

Summarize airway resistance.

A

Flow= pressure gradient/ resistance V=🔼P/R

In COPD/asthma-large increase in airway resistance

For given difference (🔼P) between alveoli and atmosphere increasing resistance by 3, reduces flow (V) by 3

Therefore- to maintain normal flow the patient must increase the 🔼P by 3 to compensate and restore equivalent flow

How?-breathing harder- increasing thoracic volume even more - I.e. huge increase in workload for the patient

28
Q

What are the airflow patterns?

A

Terminal bronchioles airflow truly laminar

Trachea-airflow is turbulent

Transitional flow in the rest of the airways i.e. flow is intermediate between laminar and turbulent

In laminar conditions airflow is proportionate to the pressure gradient (🔼P)

If flow is turbulent-the airflow is proportionate to the square root of 🔼P

Turbulence= greater pressure gradient (🔼P) required to sustain same flow

= an effective increase in resistance

CPR 2 (32 decks)

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