MECHANICS OF BREATHING

1. DR.NILESH KATE.
M.D.
ASSOCIATE PROFESSOR,
DEPARTMENT OF PHYSIOLOGY,
ESIC MEDICAL COLLEGE& HOSPITAL,
SEDAM ROAD, GULBARGA.

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

3. INTRODUCTION – PASSSAGE OF AIR.

4. EXTERNAL AND INTERNAL RESPIRATION

5. 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

6. INTERNAL RESPIRATION
 Cellular metabolism
 Anaerobic glycolysis
 Aerobic oxidative metabolism in the
mitochondria

7. EXTERNAL AND INTERNAL
RESPIRATION
HEART
TISSUE
CELL
O2 + FOOD
CO2 + H2O
+ ATP
LUNGS
ATMOSPHERE
PULMONARY
CIRULATION
SYSTEMIC
CIRCULATION

8. AIR IS A COMPRESSABLE GAS WHICH
OBEYS BOYLE’S LAW
 P1V1 = P2V2
 If Volume increases, Pressure must decrease
 As lungs expand, pressure inside falls

9. BAROMETRIC PRESSURE
Mercury Hg
VACUUM
WEIGHT OF COLUMN
OF AIR = FORCE
FORCE/AREA = PRESSURE
Sea Level
760 mm

10. 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.

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

12. MECHANICS OF BREATHING.
 Eupnoea.-
 Inspiration.- active
process.
 Expiration.- passive
process.

13. THE TRANSMURAL PRESSURE GRADIENT
INFLATES THE LUNGS
 Thoracic cavity larger than lungs
 Transmural (Across Lung Wall) pressure
gradient holds thoracic wall and lungs in
close apposition
 This pressure gradient is balanced by the
elastic forces in the alveoli producing
equilibrium

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

15. MECHANISM OF INSPIRATION.
Active process,
Thorax – enlarged by
1) Rib movement,
2) Diaphragmatic
movement.
According to property
of gases
P= nRT/ V

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

17. RIB MOVEMENT.

18. 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

19. CLINICAL SIGNIFICANCE.
 Transection of spinal cord.
above 3rd
cervical spinal segment-
fatal – needs artificial respiration.
below 5th
cervical spinal segment –
not,
Phrenic nerve that innervate
diaphragm ( C 3,4,5)

20. ACCESSORY MUSCLES OF INSPIRATION.
 Scalene &
sternocleidomastoid
 Intrinsic muscles of
larynx
Abductors of vocal
cords – post
cricoarytenoids –
supplied by recurrent
laryngeal nerve,
branch of vagus.
Paralysis – Inspiratory
Stridor.

21. 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

22. EXPIRATION
760 mm Hg
758 mmHg
Lungs
Intrapleural pressure
Airways
Atmosphere
Pleural Sac
Thoracic
Wall
761 mm Hg

23. MECHANISM OF EXPIRATION.
 Anterior abdominal
wall muscles.
 Internal intercostal
muscles.
 Accessory muscles of
respiration.
○ Adductors of vocal
cords.
DIAGRAM

24. PRESSURE AND VOLUME CHANGES DURING
VENTILATION

25. 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.
 Factors affecting intrapulmonary pressure.
Valsalva manoeuvre (+100 mm Hg)
Muller’s manoeuvre (-80 mm Hg)

26. 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.

27. INTRAPLEURAL PRESSURE,(INTRA-
THORACIC PRESSURE)
 Factors affecting intra pleural
pressure.
 Physiological
Deep inspiration (-30 mm Hg.)
Valsalva manoeuvre (+60-70 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.

28. 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.

29. MEASUREMENT OF INTRA PLEURAL PRESSURE.
1 NEEDLE IN
INTRAPLEURAL
SPACE.
2 INTRA-ESOPHAGEAL
PRESSURE

30. APPLIED PHYSIOLOGY.
AIRWAY RESISTANCE
 Flow of air depends on the pressure gradient
(atmospheric, Pa, and intra-alveolar, Pi) and
the airway resistance, R
 F = (Pa - Pi)/R
 Resistance depends primarily on the radius
of the conducting airways
 Parasympathetic stimulation constricts,
while sympathetic dilates

31. APPLIED PHYSIOLOGY.
 What happens when you try to
exhale below the FRC?
Dynamic airway collapse”.
 What is the closing volume?

32. Whats the use of
knowing mechanics
of breathing.

33. MECHANICAL VENTILATION
 TYPES OF VENTILATORS
Hand control-
○ Bag valve mask
○ Continuous flow or anesthesia bag (T-piece)
Mechanical ventilators
○ Transport ventilators
○ ICU ventilators
○ PAP ventilators – for home use in sleep apnoea

34. Modes of ventilation
 Breath termination
Volume ventilation
Pressure ventilation
 Breath initiation.
Assist Control(ac)
Synchronized Intermittent Mandatory
Ventilation (SIMV)
Controlled Mechanical Ventilation (CMV)
Pressure Support Ventilation.(PSV)
Continuous Positive Airway Pressure (CPAP)
Positive End Expiratory Pressure. (PEEP)

35. 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.

36. SUMMARY
 Mechanics of respiration-Inspiration,
expiration.
 Muscles involved in pulmonary
pressure.
 Pressure changes during ventilation.
 Intrapleural & intrapulmonary
pressure.
 Measurements.
 Normal values.
 Applied aspects.

37. THANK YOU.