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Y2S1 RESP. > Ventilation: Physics of Breathing > Flashcards

Ventilation: Physics of Breathing Flashcards

1
Q

Pulmonary ventilation

A

movement of air from atmosphere to alveoli

  • Regulation of ventilation
  • Matching of pulmonary blood flow to alveolar ventilation
  • Movement of O2 and CO2 between alveoli and blood
  • Transport of O2 and CO2 in blood and body fluids
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2
Q

Non-respiratory functions of ventilation

A
  • Expulsion of foreign bodies

- Defence against infection/disease

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3
Q

Alveolar Ventilation

A

the rate at which new air reaches these area

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4
Q

Dead space air

A

(about 150ml)
Some air that is breathed in never reaches gas exchange areas but fills respiratory passages (e.g. nose, pharynx, trachea

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5
Q

Alveolar Ventilation Rate (VA ) =

A

Freq x (VT – VD)

4200ml/min = 12breath/min x (500ml – 150ml)

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6
Q

abbreviations

A

VA, volume of alveolar ventilation per min

Freq, frequency of respiration per min

VT, tidal volume

VD, dead space volume

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7
Q

Lungs can be expanded and contracted in 2 ways:

A

Downward and upward movement of diaphragm to lengthen or shorten chest cavity
Elevation and depression of the ribs to increase or decrease anterioposterior diameter of chest cavity

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8
Q

how is normal breathing accomplished

A

entirely by method 1

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9
Q

During heavy breathing

A

During heavy breathing, normal elastic recoil not quick enough so need contraction of abdominal muscles too

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10
Q

Most important muscles that raise rib cage are:

A
  • External intercostals
  • Sternocleidomastoid (lift upward on sternum)
  • Anterior serrati (lift many ribs)
  • Scaleni (lift first two ribs)
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11
Q

Most important muscles that lower rib cage are:

A
  • Abdominal recti

- Internal intercostals

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12
Q

Intrapleural (Pleural) pressure

A

pressure is pressure of fluid in thin space between lung pleura and chest wall pleura – usually slight negative pressure

IP pressure varies over length of lungs

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13
Q

intrapleural pressure values

A

At start of respiration pleural pressure about -5 cm H2O
During inspiration expansion of chest cage pulls lungs outward so negative pressure increases to about -7.5 cm H2O
Air sucked into lungs
Expiration process reversed

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14
Q

Alveolar pressure

A

is the pressure of air inside the lung alveoli

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15
Q

alveolar pressure mechanism

A

When glottis open and no air flowing, pressure in all parts of respiratory tree is equal to atmospheric pressure (0 cm H2O)
During inspiration and chest wall expansion, alveolar pressure decreases to about -1 cm H2O
Pulls 0.5 L air into lungs
During expiration opposite occurs

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16
Q

Transpulmonary pressure

A

is the pressure difference between that in the alveoli and that on the outer surfaces of the lungs
It is a measure of the elastic forces that tend to collapse the lungs (recoil pressure)

17
Q

Overview of Inspiration

A
  • Change in volume leads to change in pressure
  • Main muscle of respiration - diaphragm. - Contraction flattens domes. Abdominal wall relaxes to allow abdominal contents to move downwards
  • Role of the intercostals – externals – with first rib fixed, two movements, forward movement of lower end of sternum, and upward and outward movement of ribs
  • Increases volume of thorax by about 500 ml – normal tidal volume
    Intrapleural pressure drops to approximately -7 mmHg
  • Decreases intrapulmonary pressure by approximately 1 mmHg
  • Accessory muscles in forced inspiration – respiratory distress – trapezius
18
Q

Quiet expiration

A

Passive – no direct muscle action normally
Cessation (relaxation) of muscle contraction
Elastic recoil – drives air out of lungs
Thoracic volume decreases by 500 ml
Intrapulmonary pressure increases
Air moves down pressure gradient

19
Q

Forced expiration:

A

Contraction of abdominal walls, forces abdominal contents up against diaphragm, and internal intercostals – pull ribs downwards

20
Q

when is energy required in the work of breathing

A
  • contract the muscles of inspiration – in quiet breathing contraction of the diaphragm comprises 75% of energy expenditure
  • stretch elastic elements
  • overcome airway resistance
  • overcome frictional forces arising from the viscosity of the lung and chest wall
  • overcome inertia of the air and tissues
21
Q

resistance in vessels

A

+ Turbulent flow – likely to occur with high velocities and large diameter airways
+ Greatest resistance to airflow is found in the segmental bronchi - cross sectional area is relatively low and airflow is high and turbulent
+ At the smallest airways, flow is laminar and the resistance is small (there is a large total cross-sectional area due to large number of small airways combined)

22
Q

Static Compliance

A

the extent to which the lungs will expand for each unit increase in transpulmonary pressure (given time to reach equilibrium)

23
Q

The elastance of the lungs (measure of elastic recoil) is

A

the reciprocal of compliance (E = 1/C). So high compliance means low elastic recoil

24
Q

Compliance diagram opposite is determined by 2 elastic forces:

A

Elastic forces of the lung tissue itself
determined mainly by elastin and collagen fibres among lung parenchyma
deflated lungs, fibres are contracted and kinked
expanded lungs, fibres become stretched and unkinked
Elastic forces caused by surface tension of fluid that lines alveoli

25
Q

Pulmonary Fibrosis, a restrictive lung disease

A
  • Disease process causes deposition of fibrous tissue, so lungs become stiff
  • Lung compliance is decreased, resulting in smaller than normal changes in lung volume for small changes in transpulmonary pressure
  • Patients breath more shallowly and rapidly
  • decreases in RV, FRC, TLC
26
Q

Emphysema, a chronic obstructive pulmonary disease (COPD)

A
  • Common consequence of cigarette smoking
  • Alveolar and capillary walls progressively destroyed, particularly elastic tissue
  • Lung compliance is increased, resulting in larger than normal changes in lung volume for small changes in transpulmonary pressure
  • However, as airways tend to collapse on expiration, airway resistance is also increased
  • Patients breath more slowly and deeply
  • increases in RV, FRC, TLC
27
Q

Chronic bronchitis, also a COPD

A
  • Mucus and airway inflammation produce an increase in airway resistance
  • increases in RV, FRC, TLC, however compliance is normal
28
Q

Elastic Forces due to Surface Tension

A
  • Surface tension is a measure of the force acting to pull a liquid’s surface molecules together at an air-liquid interface
  • In the lungs this results in the alveoli trying to force the air out of them so allowing the alveoli to collapse
29
Q

Law of LaPlace

A

states that the pressure (P) within a fluid-lined alveolus is dependent on the surface tension of the fluid (T) and the radius of the alveolus (r)

-So if 2 alveoli are connected together but have different diameters, air will flow from smaller alveoli to larger alveoli

30
Q

P

A

= (2 x T) / r

31
Q

Production of Surfactant

A
  • Lipid components enter Type II cell from bloodstream
  • Secreted by Type II alveolar epithelial cells
  • Surfactant is a complex mixture of phospholipids

Dipalmitoylphosphatidylcholine (DPPC)
proteins (surfactant apoproteins, SP-A, SP-B, SP-C & SP-D)
ions (calcium)

  • Part of DPPC molecule dissolves in fluid while rest spreads over surface of fluid
  • Alveolar macrophages help in degrading surfactant, Type II cells take up rest and recycle or destroy it
32
Q

Role of Surfactant

A
  • Surfactant greatly reduces the surface tension of H2O
  • Thus increases compliance, so easier to inflate lungs
  • Surfactant reduces pressure by 4.5 times
  • By reducing surface tension minimises fluid accumulation in alveolus
    Surfactant helps keep alveolus size relatively uniform during respiratory cycle
33
Q

Spirometry

A

method for studying pulmonary ventilation

34
Q

Tidal volume

A

volume of air inspired or expired with each normal breath (500ml)

35
Q

Inspiratory reserve volume

A

is extra volume of air that can be inspired over and above normal tidal volume (2500ml)

36
Q

Expiratory reserve volume

A

is max extra volume of air that can be expired by forceful expiration after end of normal tidal expiration (1100ml)

37
Q

Residual volume

A

volume of air remaining in lungs after most forceful expiration (1200ml)

Y2S1 RESP. (38 decks)

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