This document summarizes the mechanics of breathing. It describes normal breathing rates and types of abnormal breathing. It discusses the boundaries of the thoracic cage and the two pleura layers. Breathing involves both positive pressure from inspiration and negative pressure from expiration. Inspiration is an active process using the diaphragm and intercostal muscles while expiration is usually passive. Gas exchange occurs through pressure gradients in the lungs. The document outlines the muscles, pressures, and mechanics involved in inspiration and expiration.

1. Mechanics of
Breathing
Dr. Sai Sailesh Kumar G
Assistant Professor
Department of Physiology
RDGMC

2. Eupnea
 Normal breathing - Eupnea
 Rate 12-16 breaths/min
 Increase in the rate - Tachypnea e.g: Exercise,
anxiety…
 Arrest of respiration- Apnea, e.g: deglutition apnea,
adrenaline apnea, Sleep apnea, voluntary apnea…
 Difficulty of breathing with marked awareness of effort
of breathing – Dyspnea e.g: Bronchial asthma

3. Boundaries of thoracic cage
Behind and laterally- Vertebral column and
ribs
In front and laterally – Sternum and ribs
In the lower part - Diaphragm
Upper part – upper ribs and tissues of neck
Heart, lungs and great vessels occupy the
thoracic cavity

4. Visceral and parietal pleura
Two pleura
Visceral and parietal
The gap between the two- pleural cavity
Filled with pleural fluid
Pressure- intra pleural pressure (negative)

5. Mechanism of ventilation of
lungs
Positive pressure method
Negative pressure method

6. Mechanism of ventilation
Ventilation
Movements of thorax
Inflation and deflation of lungs
Flow of air in and out of the lungs

7. Transport of gases
Gases travel from area of high pressure
to area of low pressure

8. Pressures
Atmospheric pressure (Barometric Pressure) –
760 mmHg
Pressure inside the lungs – Intra pulmonary
pressure/ Intra alveolar Pressure- 760 mmHg
Intra pleural pressure – 756 mmHg (-4 mmHg)
If the atmospheric air need to enter into the
lung, the intra pulmonary pressure should
drop.

9. Muscles of respiration
Muscles of inspiration
Normal inspiration – Diaphragm and External
intercostal muscles
Forced inspiration- as in exercise accessory
muscles of inspiration act, which are
sternocleidomastoid, pectoralis, elevators of
scapula etc.

10. Boyle's law
The absolute pressure exerted by a given
mass of an ideal gas is inversely
proportional to the volume.

11. Inspiration
Contraction of diaphragm and intercostal
muscles
Increase in thoracic volume
Increase in the intra pulmonary volume
Decrease in the intra pulmonary pressure
(759 mmHg)
Air enters into the lung down the pressure
gradient.

12. Mechanism of inspiration
Inside alveoli sub-atmospheric pressure
Air enters alveoli (Inspiration)
Draws along with it visceral pleura
Due to this dragging force + Elastic property
Contraction of inspiratory muscles
Thoracic cage and parietal pleura moves out

13. Expiration
The contracted muscles will relax
Decrease in thoracic volume
Decrease in the intra pulmonary volume
Increase in the intra pulmonary pressure
(761 mmHg)
Air moves out of the lung down the pressure
gradient.

14. Mechanism of expiration
Expiration
High pressure inside alveoli
Air is driven out of alveoli
Contracted muscles relaxes
Elastic recoil of lungs

15. Muscles of respiration
Muscles of Expiration
 Normal expiration – No muscles are actively involved in
normal quiet expiration. Expiration during quiet breathing is
passive. The inspiratory muscles that have contracted
relax during expiration.
 Forced expiration- Muscles of anterior abdominal wall
(rectus abdominus (six-pack muscles), external and
internal oblique), internal intercostal and latissimus dorsi
contract.

16. Forced expiration

17. Mechanism of ventilation
Normal quiet breathing
Inspiration is an active process
Expiration is a passive process

18. Movements of thoracic cage
During inspiration, dimensions of thoracic
cage increases
Increase in vertical dimension
Increase in the anteroposterior diameter
Increase in the transverse diameter

19. Increase in vertical dimension
 This is mainly brought about by contraction of diaphragm.
(dome shaped muscle at rest)
 In normal quiet respiration, diaphragm contracts
(becomes flat when contracts) and moves downwards for
about 1.5-3 cm.
 In forceful inspiration, vertical dimension is increased by
7-10 cm.
 75% of air entry during inspiration is by diaphragm
contraction.

20. Nerve supply to diaphragm
Phrenic nerve
The phrenic nerve is a nerve that originates
in the neck (C3, C4, C5) and passes down
between the lung and heart to reach the
diaphragm
Spinal cord injury above C3?

21. Spinal cord injury above C3?
Diaphragm does not gets motor signals
Diaphragm activity will be stopped
They will never be able to do inspiration
Artificial respiration is required

22. Hiccups
 Hiccups (also spelled hiccough) are sudden,
involuntary contractions (spasms) of the diaphragm
muscle.
 When the muscle spasms, the vocal cords snap shut,
producing the hiccup sound.
 Hiccups are often rhythmic. They are usually just a
temporary minor annoyance, but prolonged hiccups
may signal a major medical problem

23. Management of Hiccups
 HICCUPS may be managed with several methods
 stimulation of the pharynx
 compression of the eyeballs
 gastric lavage
 sedation
 inhalation of carbon dioxide
 Phrenic nerve block

24. Increase in antero-posterior and
transverse dimension
This is by contraction of external intercostal
muscles
Each rib is connected anteriorly to sternum and
posteriorly to vertebral column
External intercostal muscles run forwards and
downwards.
Contraction of external intercostal muscles pulls
lower ribs upwards.

25. Internal intercostal muscles
Contracts during forced expiration
Internal intercostal muscles run backward
and downwards.
Contraction of internal intercostal muscles
pulls upper ribs downwards.
These intercostal muscles are innervated by
intercostal nerves (T1-T10).

26. Increase in antero-posterior and
transverse dimension
 Contraction of external intercostal muscles cause
movement of ribs forward and upward, outward and
upwards.
 Forward and upward movement of ribs increases the
anterio-posterior diameter of thoracic cage. (pump
handle movement)
 Outward and upward movement of ribs increase the
transverse diameter of thoracic cage. (bucket handle
movement)

27. Pump handle movement
Increase in the antero-posterior
diameter of thoracic cage
Upper ribs becomes horizontal
Sternum moves away from vertebral column
During inspiration
External intercostal muscles contract

28. Pump handle and bucket handle
movements

29. Breath sounds
 Breath sounds are produced by turbulant flow of
air through trachea and larger bronchi.
 Depending on quality of sound- two types
1. Vesicular breath sounds- Inspiration is higher pitch than
expiration, No pause between inspiration and expiration
2. Bronchial breath sounds- Expiratory phase is longer
than inspiratory phase, There is distinct pause between
inspiration and expiration

30. Work of breathing
 Work is done only in inspiration and forced
expiration
 No work is done in normal quiet expiration
Work= Force x displacement = Pressure x volume

31. Work of breathing
 During inspiration all dimensions of thorax
increases and certain amount of work has to be
done by the respiratory muscles to overcome three
factors
1. Compliance work or elastic work
2. Tissue resistance work
3. Airway resistance work

32. Work of breathing
 Compliance work: This work is done to overcome
elastic resistance. (work done in stretching the
elastic tissue of chest wall and lungs)
 Tissue resistance work: work done to overcome
inelastic tissues
 Airway resistance work: Work done to overcome
the frictional force of air moving through the
respiratory passages

33. Work of breathing
 Total work done in quiet breathing- 0.3 – 0.8 kg-
m/min
 Work done is increased in
A. Exercise
B. Obstruction to air flow – bronchial asthma
C. Pulmonary fibrosis

34. First Cry

35. Pulmonary circulation
 Carries deoxygenated blood from right ventricle to
alveoli.
 Returns oxygenated blood from alveoli to left
atrium.
 Lung is the only organ that receives entire
cardiac output.
 Effect of gravity is less on pulmonary circulation as
the distance of pulmonary vessels from the heart is
less.

36. Pulmonary circulation
 Pulmonary veins are highly distensible and act as
blood reservoirs .
 As pulmonary blood vessels are highly distensible,
pulmonary circulation is called low pressure and
low resistance system.
 Pulmonary arteries are the only post natal
arteries that carry deoxygenated blood.
 Pulmonary veins are the only post natal veins
that carries oxygenated blood.

37. Pulmonary circulation
 Angiotensin converting enzyme produced by
endothelial cells of pulmonary vasculature helps in
the conversion of angiotensin I to angiotensin II,
which has a major role in maintaining blood
pressure.
 The pulmonary pressure in 24/9 mmHg (systemic
pressure is 120/80 mmHg)
 Pulmonary hydrostatic pressure is 10 mmHg and
oncotic pressure is 25 mmHg.

38. Dryness of alveoli
 The inward directed pressure gradient of 15 mmHg
in the pulmonary circulation.
 Surfactant lining the alveoli decreases the surface
tension and prevents fluid collection
 Rich lymphatic supply to lungs that rapidly drain
away the excess fluid.

39. Pulmonary edema
 When there is increase in the pulmonary interstitial
fluid pressure, that leads to sudden filling of
pulmonary interstitial spaces and alveoli with large
amounts of fluid.
 Common cause- left ventricular failure, gas
poisoning

40. Pulmonary hypertension
 Sustained elevation of pulmonary arterial pressure.
 If not treated, leads to increase in the right
ventricular after load and right heart failure and
death.

41. THANK YOU