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
9. 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.
12. 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
17. 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. 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.
20. 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
21. EX PIRATION
760 mm Hg
758 mmHg
Lungs
Intrapleural pressure
Airways
Atmosphere
Pleural Sac
Thoracic
Wall
761 mm Hg
22. ME C HANISM OF EX PIRATION.
Anterior abdominal
wall muscles.
Internal intercostal
muscles.
Accessory muscles of
respiration.
○ Adductors of vocal
cords.
DIAGRAM
24. 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)
25. 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.
26. 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.
27. 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.
28. MEASUREMENT OF INTRA PLEURAL PRESSURE.
1 NEEDLE IN
INTRAPLEURAL
SPACE.
2 INTRA-ESOPHAGEAL
PRESSURE
29. 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
32. 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. 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.
