MECHANICS OF BREATHING

2. OBECTIVES
Introduction-
Mechanics of respiration-Inspiration,
expiration.
Muscles involved in pulmonary
pressure.
Pressure changes during ventilation.
Intrapleural & intrapulmonary
pressure.
Normal values.
Applied aspects.

3. EX TERNAL AND INTERNAL RESPIRATION

4. EXTERNAL RESPIRATION
External respiration-Ventilation or
breathing: air moved in and out of lungs
Exchange of gases -Oxygen and Carbon
Dioxide exchange in the lungs
Transport of gases- Oxygen and Carbon
Dioxide transported by blood to and from
tissues
Internal respiration- Exchange of Oxygen
and Carbon Dioxide between tissue and
blood

5. RESPIRATORY PRESSURES
TWO TYPES
1) Intraalveolar
pressure or Intra
pulmonary pressure
(760 mm Hg)
2) Intrapleural
pressure or
Intrathoracic pressure
(758 mm Hg)
Atmospheric pressure.
760 mm Hg.

6. REST PRESSURES
760 MM Hg
758 mmHg
Lungs
Intrapleural pressure
Airways
Atmosphere
Pleural Sac
Thoracic
Wall

7. MECHANICS OF BREATHING.
Eupnoea.-
Inspiration.- active
process.
Expiration.- passive
process.

8. INSPIRATION
760 mm Hg
754 mmHg
Lungs
Intrapleural pressure
Airways
Atmosphere
Pleural Sac
Thoracic
Wall
759mm Hg

9. MECHANISM OF INSPIRATION.
Active process,
Thorax – enlarged by
1) Rib movement,
2)Diaphragmatic
movement.

10. MECHANISM OF INSPIRATION.
Rib movement.
1 Pump handle
movement.(2-6th)
2 Bucket handle
movement.(7-10th)
Contraction of external
intercostal muscles.

11. RIB MOVEMENT.

12. MECHANISM OF INSPIRATION.
( CONT..)
Diaphragmatic
movement.
downward movement
1.5 cm in eupnoea.
7 cm in deep inspiration.
1cm decent = 200-300 ml
air sucked in. (75% of
tidal volume)
DIAGRAM

13. ACCESSORY MUSCLES OF INSPIRATION.
Scalene &
sternocleidomastoid
Intrinsic muscles of
larynx

14. EXPIRATION
Return of ribs to rest position causes
diminishing of lung volume
Return of diaphragm to rest position also
causes diminishing of lung volume
Diminishing of lung volume causes pressure
in lung to raise to a higher value than
atmospheric pressure
Air flows out of the lungs

15. EX PIRATION
760 mm Hg
758 mmHg
Lungs
Intrapleural pressure
Airways
Atmosphere
Pleural Sac
Thoracic
Wall
761 mm Hg

16. ME C HANISM OF EX PIRATION.
Anterior abdominal
wall muscles.
Internal intercostal
muscles.
Accessory muscles of
respiration.
○ Adductors of vocal
cords.
DIAGRAM

17. PRESSURE CHANGES DURING
VENTILATION
INTRAPULMONARY PRESSURE,( INTRA-ALVEOLAR
PRESSURE)
● In quite breathing = 0 atmospheric pressure i.e.
760 mm Hg.
● During inspiration -- 759 mm Hg.
● During expiration -- 761 mm Hg.

18. PRESSURE CHANGES DURING VENTILATION
INTRAPLEURAL PRESSURE,(INTRA-
THORACIC PRESSURE)
● In quite breathing (-2 mm Hg.)
● Reason – balance between
○ Lung – Tendency to collapse due to Intraalveolar
negative pressure..
○ Thoracic cage – Tendency to expand due to ribs and
elastic tissue.

19. INTRAPLEURAL PRESSURE,(INTRA-
THORACIC PRESSURE)
Factors affecting intra pleural
pressure.
Physiological
● Deep inspiration (-30 mm Hg.)
● Effect of gravity. (-7 apex, -2 Base)
○ Clinical significance – during first part of
inspiration more of inspired gas goes to
apices than to bases.

20. INTRAPLEURAL PRESSURE,(INTRA-
THORACIC PRESSURE) cont…
Pathological
● Emphysema – loss or decrease in lung elasticity.
decrease in Intrapleural pressure.
leads to expansion of thoracic
cage, i.e. barrel shaped chest.
● Injury to thoracic wall. (Pneumothorax)
leads to collapse of lung.

21. Resistance and Disease
COLDS
ASTHMA: Constriction of small airways, excess mucus,
and histamine-induced edema
BRONCHITIS : Long term inflammatory response
causing thickened walls and overproduction of mucous
EMPHYSEMA: Collapse of smaller airways and
breakdown of alveolar walls
ALVEOLAR SURFACE TENSION – Deficiency leads to
increase in negative Intraalveolar pressure and collapse
of lung.

22. THANK YOU.