L1 - Respiration - Airflow Flashcards

1
Q

Which 4 factors have a role in determining air flow?

A

Type of air flow
Resistance of the pathway
Pressure gradients
Links between lung volume, resistance and airflow

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2
Q

What is laminar flow?

A

Steady flow down a tube in a uniform direction and speed

Flow rate is maximal in the centre but reduces towards the edge

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3
Q

During laminar flow movement of air into and out of the lungs is?

A

Proportional to the pressure gradient

Inversely proportional to the resistance

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4
Q

What is turbulent flow?

A

If flow rate moves beyond a critical value, irregular currents – vortices develop
Greater pressure gradient needed to obtain the same flow seen under laminar conditions – more effort

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5
Q

During turbulent flow the rate of gas movement is?

A

Proportional to square root of the pressure difference

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6
Q

What is transitional flow?

A

High numbers of bifurcations in the airways disrupt flow - creating eddies

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7
Q

What is determination of flow type governed by?

A
Reynolds number 
o	r - radius
o	v - velocity
o	ρ - density of the gas
o	η - viscosity
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8
Q

Reynolds number equation

A

Re = 2rvp/n

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9
Q

If Re < 1000 what flow is seen?

A

Laminar flow

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10
Q

If Re is between 1000 and 1500 what flow is seen?

A

Flow switching between laminar and turbulent

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11
Q

If Re is > 1500 what flow is seen?

A

Turbulent flow

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12
Q

What is Poiseuilles law?

A

Airway resistance is proportional to gas viscosity
Length of the tube but is inversely proportional to the fourth power of the radius
Small changes in airway diameter have a big impact on the resistance and therefore flow rate

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13
Q

In a normal individual what is the airway resistance throughout the lung?

A

Total airway resistance is 1.5cm H2O .s.litres-1

  • Pharynx-Larynx - 40%
  • Airways >2mm diameter – 40%
  • Airways <2mm diameter – 20%
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14
Q

In a COPD patient what is the airway resistance throughout the lung?

A

Total airway resistance is 5.0 H2O .s.litres-1

  • Pharynx-Larynx - 12%
  • Airways >2mm diameter – 18%
  • Airways <2mm diameter – 70% (huge difference from normal patients)
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15
Q

What are the 2 factors impacting airway resistance?

A

Airway diameter

Lung volume

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16
Q

How does airway diameter impact airway resistance?

A

Increased mucus secretion reduces airway diameter – increased resistance
Oedema – increased fluid retention in lung tissue – increased resistance

17
Q

How does lung volume impact airway resistance?

A

At a given lung volume, airway resistance is higher in COPD

At smaller volumes you have higher resistance

18
Q

What is the effect of dynamic pressures on airflow during inspiration?

A

During inspiration - forced expansion of higher airways

Dilation of airways – decrease in resistance

19
Q

What is the effect of dynamic pressures on airflow during expiration?

A

During expiration – forced collapse of higher airways

Constriction of airways – increase in resistance

20
Q

What impact does emphysema have on airway compression?

A

Airway compression is exaggerated

  • Loss of elastic tissue and break down of alveolar walls
  • Tethering between the walls of airspaces reduced
  • Airways less able to resist the collapse
21
Q

How are the issues of emphysema overcome?

A

Slow exhalation
Breathing takes place at a higher lung volume
Exhale through pursed lips

22
Q

When resistance is increased what is impaired about the lungs?

A

Inflation
In normal patient, after 1s of inspiration, lungs have reached tidal volume (500ml)
In COPD patients, after 1s of inspiration, lungs have only reached 60% of tidal volume

23
Q

How do you calculate interpleural pressure?

A

Alveolar pressure - transpulmonary pressure

24
Q

How do you calculate transmural pressure?

A

Airway pressure - intrapleural pressure