Phys: Test 3: Lecture 3. Airflow Through The Airways

Front 1

o What are the 2 main forces that oppose air movement?

Back 1

 Compliance
• Ease of inflation
 Frictional resistance
• Tissue (lung and chest wall)
• Air movement

Front 2

• List the sources of tissue (viscous) resistance.

Back 2

o Lung and chest wall

Front 3

• What is the predominant resistance to air flow?

Back 3

o Airway resistance (80%, as opposed to 20% due to tissue resistance)

Front 4

o Resistance in the airway =

Back 4

change in pressure / V
 V being the flow of air
o Raw=P/V

Front 5

• Describe the patterns of airflow present in the lung and the predominant areas where they are found.

Back 5

o Laminar: terminal bronchioles
 Middle fastest, by the wall slowest
o Turbulent: trachea
 Gas flow is random, willy nilly movement
 You will see increased resistance
o Transitional : most of the lung

Front 6

• Describe the dependence of airway resistance on airway radius and length for laminar flow. Predict the effect of airway radius or length changes on resistance and air flow.

Back 6

o Resistance is inversely proportional to radius^4
o Resistance is proportional to length
o R=8nL/pie(r^4)
o n=viscosity
o so flow of gas= P(pie)r^4/8nL

Front 7

Flow of gas=?

Back 7

deltaP (pie) r^4 / 8nL

Front 8

• Describe the effect of turbulent flow on resistance to air movement. Describe the factors that promote turbulence, including the importance of the Reynold’s number.

Back 8

o Reynolds #= vDp/n
o v=velocity; D=diameter; p=density; n=viscosity
o Reynolds # greater than 2000 makes glow turbulent

Front 9

does turbulent or laminar flow create more air resistance?

Back 9

o Turbulence creates more air resistance than laminar flow

Front 10

• What is the main site of airway resistance?

Back 10

medium sized bronchi (which is NOT the narrowest vessel, which kinda goes against the equation, but they tend to have larger total CSA)

Front 11

• What has higher total CSA, lower airways or upper?

Back 11

Lower

Front 12

• Describe the dependence of airway resistance on lung volume. Explain how ‘radial traction’ accounts for this relationship.

Back 12

o Radial traction
 As lungs inflate, the connective tissues (parenchyma) stretch the airways open

Front 13

When do patients with obstructive disease tend to ventilate? why?

Back 13

large lung volumes;
because they have increased airway resistance they try minimize this resistance with large lung volumes to open up their airways

Front 14

o 3 things that can affect the bronchial smooth muscle tone?

Back 14

 Irritants
• Histamine/smoking (increase bronchiole smooth muscle tone)
 Parasympathetic tone
 Sympathetic B2 stimulation

Front 15

• List the three ways in which airway resistance can be increased in obstructive disease.

Back 15

 Chronic bronchitis
• Hypersecretion of mucus in airways
• Decreases the airway radius
 Asthma
• Increased bronchiole smooth muscle tone due to inflammation
• Radius is narrower, higher resistance
 Emphysema
• Loss of elastic tissue
• Fewer fibers attached to airways, less radial traction
o Airway is narrower b/c it is not getting pulled open by the elastic fibers

Front 16

o Transairway pressure (PTA)=?

Back 16

Airway Pressure-Plueral Pressure
- PTA=PAW-PPL

Front 17

o Transpulmonary pressure=?

Back 17

 =Alveolar pressure-Pleuaral pressure
 PTP=PA-PPL

Front 18

• What determines airway patency?

Back 18

o Transairway pressure

Front 19

o If PAW>PPL

Back 19

then PTA is positive and airway is open

Front 20

o If PAW<PPL

Back 20

then PTA is NEGATIVE and airway is compressed

Front 21

• During air flow, what is the relationship of airway pressure, alveolar pressure and mouth pressure?

Back 21

o Airway pressure > alveolar pressure
o Airway pressure < Mouth pressure

Front 22

Is the transairway pressure positive or negative during pre-inspiration? inspiration? expiration?

Back 22

ALL NEGATIVE!

Front 23

what is alveolar pressure the sum of? (PA)

Back 23

o Intrapleural pressure and elastic recoil pressure
PA= Pel + PPL

Front 24

• Explain why airflow is limited by airway compression during a forced expiration.

Back 24

o Muscles are compressing on intrapleural space
 This makes the intrapleural pressure positive
• The alveolar pressure also becomes positive
• Pressure at the mouth is 0
o End up with PAW<PPL
 Thus PTA is NEGATIVE
• Airway is compressed

Front 25

• Explain why airway collapse occurs more readily in obstructive lung disease.

Back 25

o RAW is increased
 Thus PAW falls faster (because of increased airway resistance)

Front 26

In emphysema what happens to elastic recoil? What does this do to PA and PAW? What does the effect on PAW do to Transairway Pressure (PTA)?

Back 26

Decreased elastic recoil leads to decreased PA and PAW.
Means that it is easier for PPL to be more positive than PAW, thus causing closure of airway

Front 27

In obstructive disease is resistance of the airway increased or decreased or unaffected?

Back 27

increased