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 > Palv
Inspiration
Palv
Patmos
Patmos < Palv
Expiration
Palv
25-Feb-19
Respiratory Movements

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 > Palv
Inspiration
Palv
Patmos
Patmos < Palv
Expiration
Palv
25-Feb-19
Respiratory Movements

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 > Palv
Inspiration
Palv
Patmos
Patmos < Palv
Expiration
Palv
25-Feb-19
Respiratory Movements

5. Respiratory Movements
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
25-Feb-19
Respiratory Movements

6. Respiratory Movements
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
25-Feb-19
Respiratory Movements

7. Respiratory Movements
Respiratory Muscles
Inspiratory muscles
Diaphragm,external intercostals
Others
Scaleni, sternocleidomastoid, pectoralis minor
Expiratory muscles
Internal intercostals
Abdominal recti
25-Feb-19
Respiratory Movements

8. Respiratory Movements
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
25-Feb-19
Respiratory Movements

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
25-Feb-19
Respiratory Movements

10. Muscles of Inspiration
When the diaphragm move down
Abdominal contents are forced downward
Increase the vertical dimension of the thorax
Diaphragm
Abdominal content
25-Feb-19
Respiratory Movements

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
25-Feb-19
Respiratory Movements

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
25-Feb-19
Respiratory Movements

13. Muscles of Inspiration
During forceful inspiration
It increases the thoracic volume by
250 x 10 = 2500 cm3
Diaphragm
Abdominal content
25-Feb-19
Respiratory Movements

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
25-Feb-19
Respiratory Movements

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
25-Feb-19
Respiratory Movements

16. Respiratory Movements
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
25-Feb-19
Respiratory Movements

17. Respiratory Movements
Expiration
During quite breathing
Passive
After inspiratory muscles relax
Elastic recoil of lungs and chest wall
Cause movement of air from lungs to atmosphere
25-Feb-19
Respiratory Movements

18. Respiratory Movements
Expiration
During exercise
Expiration is by active process
Contraction of expiratory muscles
Internal intercostals muscles
Assist active expiration by
Pulling ribs downwards and inwards
25-Feb-19
Respiratory Movements

19. Pressure Changes in the Lungs and Thorax
Trachea
Lungs are separated from the rib cage by
Parietal & visceral pleura
Between these there is
Pleural fluid
Lubricant film 20 m thick
Pleural space
Bronchi
Alveoli
Diaphragm
25-Feb-19
Respiratory Movements

20. Pressure Changes in the Lungs and Thorax
Trachea
The thoracic cage
Has a tendency to expand
The lungs
Have a tendency to collapse
Held together by the of pleural fluid
Pleural space
Bronchi
Alveoli
Diaphragm
25-Feb-19
Respiratory Movements

21. Pressure Changes in the Lungs and Thorax
Trachea
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
Pleural space
Bronchi
Alveoli
Diaphragm
25-Feb-19
Respiratory Movements

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
25-Feb-19
Respiratory Movements

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
25-Feb-19
Respiratory Movements

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-Feb-19
Respiratory Movements

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
Trans-pulmonary pressure -2 -4 -6
Pleural pressure -8
25-Feb-19
Respiratory Movements

26. Respiratory Movements
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
25-Feb-19
Respiratory Movements

27. Respiratory Movements
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
25-Feb-19
Respiratory Movements

28. Respiratory Movements
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
25-Feb-19
Respiratory Movements

29. Respiratory Movements
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
25-Feb-19
Respiratory Movements

30. Respiratory Movements
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
25-Feb-19
Respiratory Movements

31. Respiratory Movements
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
25-Feb-19
Respiratory Movements

32. Respiratory Movements
Compliance
Compliance
Change in volume (liters)/change in pressure (cm H2O)
Compliance of
Adult male = 0.09 to 0.26 L/ cm H2O
Newborn = 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
25-Feb-19
Respiratory Movements

33. Respiratory Movements
Airway Resistance
Trachea
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
Bronchi 2 3 4 17
Respiratory bronchiole 18 19
Respiratory zone 20
Alveolar duct 21 22 23
25-Feb-19
Respiratory Movements

34. Respiratory Movements
Airway Resistance
Trachea
Conducting zone
Airway resistance
Frictional resistance
Offered by the walls of tracheobronchial tree
This is note evenly distributed 1
Bronchi 2 3 4 17
Respiratory bronchiole 18 19
Respiratory zone 20
Alveolar duct 21 22 23
25-Feb-19
Respiratory Movements

35. Respiratory Movements
Airway Resistance
Trachea
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
Bronchi 2 3 4 17
Respiratory bronchiole 18 19
Respiratory zone 20
Alveolar duct 21 22 23
25-Feb-19
Respiratory Movements

36. Respiratory Movements
Airway Resistance
Airway resistance VS airway generations
Within the chest
Trachea, lobar & segmental bronchi 0ffer 80% of the remaining resistance
Small airways with diameter less than 2mm contribute 20%
0.08
0.06
Airway resist (cm H2O/L/S)
0.04
Segmental bronchi
Terminal bronchi
0.02 5 10 15 20
Airway generations
25-Feb-19
Respiratory Movements

37. Respiratory Movements
Airway Resistance
Airway resistance VS airway generations
Cross section of individual peripheral airways are small
Their large numbers
Generate large overall cross section area
Lowers the resistance
0.08
0.06
Airway resist (cm H2O/L/S)
0.04
Segmental bronchi
Terminal bronchi
0.02 5 10 15 20
Airway generations
25-Feb-19
Respiratory Movements

38. Determinants of Airway Resistance
Airway resistance VS lung volumes
Lung volumes
Greater tethering effect of lung parenchyma on airways
Produce an increase in cross section area of each airway
Results in reduced resistance 4 3
Airway resist (cm H2O/L/S) 2 1 2 4 6 8
Lung volumes (L)
25-Feb-19
Respiratory Movements

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
25-Feb-19
Respiratory Movements

40. Determinants of Airway Resistance
Under normal condition
Airways diameter “large”
Interaction between gas molecules negligible
Length of conducting tube relatively constant
25-Feb-19
Respiratory Movements

41. Determinants of Airway Resistance
Resistance is largely controlled by radius
Bronchial tree contain smooth muscle
Under the influence of autonomic nerves
Parasympathetic
Sympathetic
25-Feb-19
Respiratory Movements

42. 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
25-Feb-19
Respiratory Movements

43. Respiratory Movements
Airway Resistance
Certain disease condition
Increase airway resistance
Asthma
Contraction of bronchial smooth muscles
Narrowing of airways
Increased airway resistance
25-Feb-19
Respiratory Movements

44. Respiratory Movements
Airway Resistance
Chronic bronchitis
Oedema of bronchial mucosa
Excessive secretion by bronchial mucosa
Increase airway resistance
Intramural masses
Bronchogenic carcinoma
Occlude airways
25-Feb-19
Respiratory Movements

45. Respiratory Movements
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
25-Feb-19
Respiratory Movements

46. Respiratory Movements
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
25-Feb-19
Respiratory Movements