Mechanical Factors in Breathing

1
Mechanical Factors in Breathing
2
Mechanical Factors in Breathing
Patmos

• Air flows from region of high pressure to region
  of low pressure
• Flow (P1 P2)/R
• 1/r k
• Flow K(P1 P2)

Patmos Palv No air flow
Palv
Patmos
Patmos gt Palv Inspiration
Palv
Patmos
Patmos lt Palv Expiration
Palv
3
Mechanical Factors in Breathing
Patmos

• Two ways of producing the necessary pressure
  differences
• Alveolar pressure can be lowered below
  atmospheric pressure
• Natural negative pressure breathing

Patmos Palv No air flow
Palv
Patmos
Patmos gt Palv Inspiration
Palv
Patmos
Patmos lt Palv Expiration
Palv
4
Mechanical Factors in Breathing
Patmos

• Atmospheric pressure can be increased above
  alveolar pressure
• Positive pressure breathing

Patmos Palv No air flow
Palv
Patmos
Patmos gt Palv Inspiration
Palv
Patmos
Patmos lt Palv Expiration
Palv
5
Natural Breathing

• Accomplished by
• Active contraction of inspiratory muscles
• Thoracic volume increases
• Intrathoracic pressure decreases
• Pulls on the lungs
• Enlarges the alveoli

Increase in thoracic volume decrease
intrathoracic pressure
6
Natural Breathing

• Expands alveolar gas
• Decreases its pressure below atmospheric pressure
• Air at atmospheric pressure
• Flows into lungs

Increase in thoracic volume decrease
intrathoracic pressure
7
Respiratory Muscles

• Inspiratory muscles
• Diaphragm,external intercostals
• Others
• Scaleni, sternocleidomastoid, pectoralis minor
• Expiratory muscles
• Internal intercostals
• Abdominal recti

8
Respiratory Muscles

• Have no inherent rhythm
• Do not contract if they do not receive motor
  impulses
• Motor impulses originate from
• Higher centers, respiratory centers, spinal cord

9
Muscles of Inspiration

• Diaphragm
• Most important muscle of inspiration
• In quite breathing
• May be the only active inspiratory muscle
• Its motor nerve leaves the spinal cord C3,4,5

Diaphragm
Abdominal content
10
Muscles of Inspiration

• When the diaphragm move down
• Abdominal contents are forced downward
• Increase the vertical dimension of the thorax

Diaphragm
Abdominal content
11
Muscles of Inspiration

• In quite breathing
• Diaphragm moves down by about 10mm (1 cm)
• In forceful inspiration
• It can move down by 10 cm

Diaphragm
Abdominal content
12
Muscles of Inspiration

• The area of the diaphragm
• About 250 cm2
• During normal tidal breathing
• It increases the thoracic volume by
• 250 x 1 250 cm3

Diaphragm
Abdominal content
13
Muscles of Inspiration

• During forceful inspiration
• It increases the thoracic volume by
• 250 x 10 2500 cm3

Diaphragm
Abdominal content
14
Muscles of Inspiration
External intercostals Lift sternum upwards and
forwards AP diameter

• External intercostals
• Connect adjacent ribs
• Slope downwards forwards
• When they contract
• Ribs are lifted upwards
• Causing an increase in AP diameter
• Pump handle

Diaphragm
Abdominal content
15
Muscles of Inspiration

• When the external intercostals contract
• Ribs are lifted upwards
• In addition they are also moved outwards
• Bucket handle effect
• This increases the transverse diameter

Bucket handle effect
16
Overall Effects

• Of inspiratory muscles
• Increase the thoracic volume
• Increase lung volumes
• Decrease in intrapulmonary pressure
• Influx of air
• From region of high pressure
• To region of low pressure

17
Expiration

• During quite breathing
• Passive
• After inspiratory muscles relax
• Elastic recoil of lungs and chest wall
• Cause movement of air from lungs to atmosphere

18
Expiration

• During exercise
• Expiration is by active process
• Contraction of expiratory muscles
• Internal intercostals muscles
• Assist active expiration by
• Pulling ribs downwards and inwards

19
Pressure Changes in the Lungs and Thorax

• Lungs are separated from the rib cage by
• Parietal visceral pleura
• Between these there is
• Pleural fluid
• Lubricant film 20 ?m thick

Trachea
Pleural space
Bronchi
Alveoli
Diaphragm
20
Pressure Changes in the Lungs and Thorax

• The thoracic cage
• Has a tendency to expand
• The lungs
• Have a tendency to collapse
• Held together by the of pleural fluid

Trachea
Pleural space
Bronchi
Alveoli
Diaphragm
21
Pressure Changes in the Lungs and Thorax

• Intrathoracic (intra pleural) pressure
• Normally -5 mm Hg
• At the end of expiration during quiet breathing
• During inspiration it is -8 to 10 mm Hg
• It is a measure of elastic recoil of the
  stretched lungs and the compressed thoracic cage

Trachea
Pleural space
Bronchi
Alveoli
Diaphragm
22
Pressure Changes in the Lungs and Thorax
P atmos

• Alveolar pressure
• Pressure of the air inside the lung alveoli
• When glottis is open no air flowing into or out
  of the lung
• This pressure is equal to atmospheric pressure

P alv
Alveolus
23
Pressure Changes in the Lungs and Thorax
P atmos

• To cause inward flow of air into alveli during
  inspiration
• Pressure falls to values below atmospheric (-1 cm
  of water)
• This is enough to cause 0.5 liters of air move
  into lungs

P alv
Alveolus
24
Pressure Changes in the Lungs and Thorax
P atmos

• During expiration
• Alveolar pressure increases (1 cm of water)
• Enough to cause movement of 0.5 liters of air out
  of the lung

P alv
Alveolus
25
Pressure Changes in the Lungs and Thorax
Inspiration
Expiration

• Trans-pulmonary pressure
• Pressure difference between alveolar pressure and
  pleural pressure
• It is a measure of elastic forces in the lungs
  that tend to collapse the lungs
• Recoil pressure

Alveolar pressure
2
0
Trans-pulmonary pressure
-2
-4
-6
Pleural pressure
-8
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Elastic Resistance

• Lung tissue is elastic
• Natural un-stretched volume is 1 liter
• Elastic element neither stretched nor compressed
• Human lung at the end of expiration
• Volume 2.5 liters

Vol of lung
1 lt
2.5 lt
Thoracic cavity lung
5 lt
Thorax
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Elastic Resistance
Vol of lung

• Thus the elastic tissue is always under tension
• Tends to oppose expansion of the lungs

1 lt
2.5 lt
Thoracic cavity lung
5 lt
Thorax
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Elastic Resistance
Vol of lung

• The natural un-stretched thoracic volume is 5
  liters
• At end of expiration
• Volume of thorax is 2.5 liters
• The elastic tissues of thorax are compressed

1 lt
2.5 lt
Thoracic cavity lung
5 lt
Thorax
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Elastic Resistance
Vol of lung

• Thus
• Lungs tend to contract
• Thorax tends to expand
• The lungs and thorax
• Held together by the integrity of the pleural
  cavity

1 lt
2.5 lt
Thoracic cavity lung
5 lt
Thorax
30
Elastic Resistance
Vol of lung

• If a gas is introduced in the pleural space
• Chest volume tends to expand
• Lung volume tend to decrease (collapse of the
  lungs)

1 lt
2.5 lt
Thoracic cavity lung
5 lt
Thorax
31
Compliance

• Compliance
• Measure of the ability of the lung or chest
  cavity to be expanded
• The degree to which
• The lung volume can be changed
• By imposed intrapulmonary pressure

Increased compliance
?V
Volume in ml
?P
decreased compliance
Pressure cm H2O
32
Compliance

• Compliance
• Change in volume (liters)/change in pressure (cm
  H2O)
• Compliance of
• Adult male 0.09 to 0.26 L/ cm H2O
• Newborn 0.005 l/cm H2O
• At 10 yrs 0.06 L/ cm H2O
• Old age ? compliance

Increased compliance
?V
Volume in ml
?P
decreased compliance
Pressure cm H2O
33
Airway Resistance
Trachea
0

• Resistance offered to air as it flows through the
  respiratory airways
• Flow (P1-P2)/R
• Vol of air that flow in/out of alveolar
• Directly proportional to pressure gradient
• Indirectly proportional to resistance

Conducting zone
1
2
Bronchi
3
4
17
Respiratory bronchiole
18
19
Respiratory zone
20
Alveolar duct
21
22
23
34
Airway Resistance
Trachea
0

• Airway resistance
• Frictional resistance
• Offered by the walls of tracheobronchial tree
• This is note evenly distributed

Conducting zone
1
2
Bronchi
3
4
17
Respiratory bronchiole
18
19
Respiratory zone
20
Alveolar duct
21
22
23
35
Airway Resistance
Trachea
0

• During quiet breathing with mouth closed
• Nose offers 50 of total resistance
• During mouth breathing
• Pharynx offers 25 of overall resistance
• This figure can increase up to 50 during
  exercise

Conducting zone
1
2
Bronchi
3
4
17
Respiratory bronchiole
18
19
Respiratory zone
20
Alveolar duct
21
22
23
36
Airway Resistance

• Within the chest
• Trachea, lobar segmental bronchi 0ffer 80 of
  the remaining resistance
• Small airways with diameter less than 2mm
  contribute 20

Airway resistance VS airway generations
0.08
0.06
Airway resist (cm H2O/L/S)
0.04
Segmental bronchi
Terminal bronchi
0.02
5
10
15
20
Airway generations
37
Airway Resistance

• Cross section of individual peripheral airways
  are small
• Their large numbers
• Generate large overall cross section area
• Lowers the resistance

Airway resistance VS airway generations
0.08
0.06
Airway resist (cm H2O/L/S)
0.04
Segmental bronchi
Terminal bronchi
0.02
5
10
15
20
Airway generations
38
Determinants of Airway Resistance

• Lung volumes
• Greater tethering effect of lung parenchyma on
  airways
• Produce an increase in cross section area of each
  airway
• Results in reduced resistance

Airway resistance VS lung volumes
4
3
Airway resist (cm H2O/L/S)
2
1
2
4
6
8
Lung volumes (L)
39
Determinants of Airway Resistance

• Others
• Resistance is proportional to
• Length of airway
• Physical properties of the gas
• Density, viscosity
• Resistance is inversely proportional to
• 4th power of radius of the airway

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Determinants of Airway Resistance

• Under normal condition
• Airways diameter large
• Interaction between gas molecules negligible
• Length of conducting tube relatively constant

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Determinants of Airway Resistance

• Resistance is largely controlled by radius
• Bronchial tree contain smooth muscle
• Under the influence of autonomic nerves
• Parasympathetic
• Sympathetic

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Determinants of Airway Resistance

• Parasympathetic activity causes
• Constriction of smooth muscles
• Reduction in cross section of airways
• Increased resistance
• Increased secretion of mucous glands
• Sympathetic activity
• Bronchodilatation
• Inhibition of mucous glad secretion
• Reduction in resistance

43
Airway Resistance

• Certain disease condition
• Increase airway resistance
• Asthma
• Contraction of bronchial smooth muscles
• Narrowing of airways
• Increased airway resistance

44
Airway Resistance

• Chronic bronchitis
• Oedema of bronchial mucosa
• Excessive secretion by bronchial mucosa
• Increase airway resistance
• Intramural masses
• Bronchogenic carcinoma
• Occlude airways

45
The Work of Breathing

• Breathing involves
• Application of force over distance
• Work is performed by respiratory muscles
• Stretching elastic tissues of chest wall lungs
• Elastic work, compliance work
• Moving inelastic tissue (viscous resistance)
• Tissue resistance work

46
Work of Breathing

• Work involved in moving air through the
  respiratory passages
• To overcome airway resistance
• Normally negligible
• But can be marked
• With increase in ventilation (turbulence)
• In asthma