The document provides information on ventilation and the anatomy of the respiratory system. It defines ventilation as the mass movement of gas in and out of the lungs. It then describes the anatomy of the airways from the nostrils down to the alveoli. This includes details on structures like the nasal cavity, pharynx, larynx, trachea, bronchi, and terminal bronchioles. It also discusses factors that affect ventilation like pulmonary pressures, the mechanics of breathing, and control of breathing.

1. VENTILATION
Dr. Amith Sreedharan

2. DEFINITION
ANATOMY OF THE AIRWAYS
DISTRIBUTION OF VENTILATION
PULMONARY PRESSURES
MECHANICS OF BREATHING
FACTORS AFFECTING VENTILATION
SPIROMETRY VOLUMES
CONTROL OF BREATHING
ABNORMAL VENTILATION
REFERENCES

3. DEFINITION
• Mass movement of gas in and out of the lungs

4. ANATOMY
Nostrils (Nares)
• Transfer air back and forth between the
outside environment and the Nasal Cavity.
• These structures serve as the primary air
intake site.

6. Nasal Cavity
• A chamber that transfers air and gases back and
forth between the nostrils and the pharynx.
• Air is warmed and humidified – temp rises to
within 1⁰ F of body temperature and to within 2-3
% of full saturation with water vapour before it
reaches trachea.
• Partially filtered- turbulent filtration(>6 micron)
• Clinical significance

7. Pharynx
• The throat passage way that allows air and gases
to pass back and forth between the nasal cavity
and the glottis.
• During inspiration,pressure in pharynx fall below
atm.pressure
• Opposed by pharyngeal dilator
muscles(genioglossus and tensor palati)
• Patency in supine position maintained by tensor
palati,palatoglossus and palatopharyngeus

8. Epiglottis
• A flap-like structure in the lower pharynx that
is located above the glottis.
• The epiglottis operates like a valve that allows
air to pass through the glottis and into the
trachea during breathing, but, closes over the
glottis during the swallowing of food and drink
to prevent choking.

9. Glottis
• An opening that allows air to pass back and
forth between the pharynx and the larynx
during breathing
Larynx
• A set of cartilaginous structures and
membranes that allow air to pass back and
forth between the glottis and the trachea.
• The larynx (voicebox) also contains cord-like
membranes that produce sounds.

10. WIEBEL MODEL

11. Trachea
• Generation 0
• Length 11 cm
• Mean diameter 1.8 cm
• A tube reinforced by a series of u-shaped
cartilaginous rings that passes air back and
forth between the larynx and the primary
bronchi.
• Lined by ciliated columnar epithelium

12. Main Bronchus
• Generation 1
• A tubular structure that passes air back and
forth between the trachea and lobar bronchi
• 2 in nos
• Mean diameter – 12 mm
• Irregular shaped cartilage present in the walls
• The epithelial lining- ciliated columnar

13. LOBAR BRONCHI
• Generation 2 – 3
• 5-8 in nos
• Mean diameter 5 mm – 8mm
• Supply lobes
• Irregular shaped cartilages

14. Segmental Bronchi
• Generation 4
• 16-20 in nos
• Supplies segments
• A tubular passageway that passes air back and
forth between a lobar bronchus and the
remainder of a bronchial tree (
third, fourth, fifth degree branches, etc. ).
• Mean diameter 4 mm

15. Terminal Bronchiole
• Generations 5 - 16
• One of the smallest tubular passageways in
the lung that passes air back and forth
between the smallest bronchial tube and the
respiratory bronchiole.
• Mean diameter 0.7mm
• Cuboidal epithelium
• Strong helical muscle bands in the wall

16. Respiratory Bronchiole
• Generations 17- 19
• Transitional and respiratory zone
• The smallest air tubes in the lungs that passes
air back and forth between a terminal
bronchiole and an alveolar sac.
• Mean diameter 0.4mm
• Cuboidal to flat epithelium

17. ALVEOLAR DUCTS
• Generation 20,21,22
• Along with alveoli forms the lung parenchyma
• Mean diameter 0.3 mm
• Lined by alveolar epithelium
• Thin bands of muscle in alveolar septa

18. Alveolar Sac
• Generation 23
• Last generation of air passage
• A sac-like (blind) extension of a respiratory
bronchiole that is divided into many small
alveolar compartments.
• The alveolar sac will contain many small septa
that act as partitions between the alveoli.
• The septa and alveolar surfaces provide surface
area for gas exchange.
• 17 alveoli arise from each alveolar sac

19. Alveolus
• The smallest site in the lung for gas exchange.
• Made up of a thin membrane that is ideal for
diffusion of gases back and forth between the
air of the alveolar sac and the blood of
pulmonary capillaries.
• 270 – 790 million
• Mean diameter at FRC = 0.2 mm

20. Pulmonary acinus
• Aka primary lobule/terminal respiratory unit
• Zone supplied by first order respiratory
bronchioles,alveolar ducts and alveolar sacs
distal to a single terminal bronchiole.
• 30000 acinus present in human lung
• Diameter = 3.5mm
• Contain > 10000 alveolus

22. DISTRIBUTION OF VENTILATION
• Influenced by POSTURE and MANNER OF
VENTILATION.
• Right lung > Left lung (larger size)
• Lateral position : lower lung more ventilated
• Horizontal slices: uppermost portion one third
ventilated as base.
• Preferential ventilation only present at inspiratory
flow rates below 1.5 L/S.(N=0.5 L/S)
• At high rate,uniform distribution.

23. Minute Ventilation
Total volume of air entering and leaving
respiratory system each minute
Minute ventilation = VT x RR
Normal respiration rate = 12 breaths/min
Normal VT = 500 mL
Normal minute ventilation =
500 mL x 12 breaths/min = 6000 mL/min

24. Alveolar Ventilation
• Volume of air reaching gas exchange areas per
minute
Alveolar Ventilation = (VT x RR) – (DSV x RR)
Normal Alveolar Ventilation =
(500 mL/br x 12 br/min) – (150 mL/br X 12 br/min) =
4200 mL/min

25. DEAD SPACE
• An appreciable part of each inspiration do not
penetrate to those regions of gas exchange and
therefore exhaled unchanged.
• This fraction of Tidal volume(Tᵥ) = DEAD SPACE
• Alveolar ventilation(VA) : Effective part of minute
volume of respiration.
• Alveolar ventilation= respiratory rate × (Tᵥ - dead
space)
• RATIOS
• VD/VT = Wasted portion of breath
• VA/MV = utilised portion of MV

26. COMPONENTS OF DEAD SPACE
• APPARATUS DEAD SPACE: First part to be
exhaled if subject is employing any form of
external breathing apparatus.
• ANATOMICAL DEAD SPACE: Volume of the
conducting air passages
• ALVEOLAR DEAD SPACE: Part of inspired gas
that passes through anatomical dead space to
mix with gas at alveolar level , but does not
take part in gas exchange.

27. ANATOMICAL DEAD SPACE
FACTORS INFLUENCING:
• Size of subject – increases with size
• Age – from adulthood increases 1 ml/year.
• Posture- 150 ml sitting,100 ml supine
• Position of neck and jaw
 Neck extended,jaw protruded-143 ml
 Normal position – 119 ml
 Neck flexed,chin depressed – 73 ml
• Lung volume at end of inspiration- 20 ml additional
An.DS/each litre increase in LV
• Tracheal intubation,tracheostomy,LMA- decreased An.DS
• Drugs
• With Decreased Tidal volume, An.DS decreases

28. ALVEOLAR DEAD SPACE
FACTORS INFLUENCING:
• CARDIAC OUTPUT
• PULMONARY EMBOLISM
• POSTURE

29. PHYSIOLOGICAL DEAD SPACE
• Sum of all parts of Tidal volume that do not
participate in gaseous exchange
• Sum of anatomical dead space and alveolar
deadspace.
• 30 % of tidal volume
• Factors influencing:
• Age and sex
• Body size (17ml / every 10 cm ↑)
• Posture (↓es in supine)
• Pathology (PE,SMOKING)

30. PULMONARY PRESSURES
Atmospheric pressure = Patm
Intra-alveolar pressure = Palv
Pressure of air in alveoli
Intrapleural pressure = Pip
Pressure inside pleural sac
Transpulmonary pressure = Palv – Pip
Distending pressure across the lung
wall

31. Atmospheric Pressure
760 mm Hg at sea level
Decreases as altitude increases
Increases under water
Other lung pressures given relative
to atmospheric (set Patm = 0 mm Hg)

32. Intra-alveolar Pressure
Pressure of air in alveoli
Given relative to atmospheric pressure
Varies with phase of respiration
During inspiration = negative
(less than atmospheric)
During expiration = positive
(more than atmospheric)
Difference between Palv and Patm /(Pᵥᵥ)
drives ventilation

33. Factors determining intra-alveolar
pressure
Quantity of air in alveoli
Volume of alveoli
Lungs expand – alveolar volume increases
Palv decreases
Pressure gradient drives air into lungs
Lungs recoil – alveolar volume decreases
Palv increases
Pressure gradient drives air out of lungs

34. Intrapleural Pressure
Pressure inside pleural sac
Always negative under normal
conditions
Always less than Palv
Varies with phase of respiration
At rest, -5 mm Hg(MEAN)

35. Negative pressure due to elasticity in
lungs and chest wall
Lungs recoil inward
Chest wall recoils outward
Opposing pulls on intrapleural space
Surface tension of intrapleural fluid
hold wall and lungs together

36. Transpulmonary Pressure
Transpulmonary pressure = Palv – Pip
Distending pressure across the lung
wall
Increase in transpulmonary pressure:
Increase distending pressure across
lungs
Lungs (alveoli) expand, increasing
volume

40. Pressure-volume curves of the lung
during inspiration and expiration.
HYSTERESIS

42. PARABOLIC (LAMINAR) FLOW PROFILE

43. PATTERNS OF AIRFLOW
Laminar flow.
Turbulent flow.
Transition flow

44. Inspiration of air into trachea via mouth
and nose.
Accomplished by inspiratory chest wall
muscle contraction.

45. • TRUNK / CHEST WALL
RIBCAGE
ABDOMEN
Separated by DIAPHRAGM

46. DIAPHRAGM
• Membranous muscle separating abdominal
cavity and chest
• SA = 900 cm²
• Most important inspiratory muscle
• Motor innervation: Phrenic N(C3,4,5)
• Contraction Increase in lung volume

47. MECHANICS OF DIAPHRAGM
MOVEMENT
• ‘Piston in cylinder’ Analogy
• ‘Non piston’ behaviour
• Combination (piston + non piston)
• Combination of all the above mechanisms and
change in shape involving ‘tilting and
flattening’ of diaphragm in AP direction.

48. RIBCAGE MUSCLES
• RIBCAGE = CYLINDER/BUCKET
• Length
• governed by DIAPHRAGM
• And secondarily by flexion and extension of
Spine
• CROSS SECTION
• By movement of RIBS

49. MECHANICS OF RIBCAGE MUSCLES
• ‘BUCKET HANDLE’ ACTION
• ‘PUMP HANDLE’ MOVEMENT

50. Intercostal muscles
• External intercostals
 Deficient anteriorly
 Primarily inspiratory
• Internal intercostals
 Deficient posteriorly(less powerful)
 Primarily expiratory
 Parasternal portion is inspiratory.
• Intercostalis intima
 Posture plays important role in ICM action.
 Extreme postural changes reverts activity of intercostal
muscles

51. ACCESSORY MUSCLES
 Silent in normal breathing
 Increased ventilation(about 50 L/min) leads to recruitment of
ACCESSORY muscles.
• MUSCLES
 Generally inspiratory
 Sternocleidomastoid M
 Pectoralis minor M
 Serrati M
 Extensors of vertebral column
 ABDOMINAL M
 Generally expiratory
 Rectus abdominis
 Obliques – external and internal
 Transversalis
 Muscles of pelvic floor(supportive)

52. INSPIRATION
• Ribcage inspiratory muscles (ext &parasternal
int ICM) and Diaphragm act in parallel to
inflate the lungs.
• Scalene muscles (supportive role)
• POSTURE decides the dominant role
• Diaphragm contraction alone results in
widening of lower ribcage and indrawing of
upper ribcage countered by IC and neck
muscle

53. EXPIRATION
• No musculature required in quiet breathing in
supine position
• Elastic recoil of lungs provide energy required
for expiration and is also aided by weight of
abdominal contents
• In upright position and stimulated ventilation
the INTERNAL ICM and Abdominal wall M are
active in returning the ribcage and Diaphragm
to resting position

55. EFFECT OF POSTURE ON MUSCLES
UPRIGHT: In Standing/Sitting position , Ribcage
muscles more used(67 % contribution)
• Scalene and parasternal internal ICM support
SUPINE:Diaphragm upward(4 cm up)
• Decreased FRC
• Fibre length decreased in supine position
• More effective contraction
LATERAL: Only lower dome of Diaphragm pushed
higher into chest,upper dome is flat.
• Lower dome contract effectively
• Increased ventilation of lower lung.

56. CHEMORECEPTOR ACTIVATION
• Respiratory muscle response to hypoxia /
hypercarbia for an equivalent minute volume.
• Hypoxia stimulates mostly inspiratory muscles
• Hypercapnea stimulates both inspiratory and
expiratory muscles.
NEXT

57. Factors Affecting Pulmonary Ventilation
 Lung Compliance
 Airway Resistance

58. Lung Compliance
• Ease with which lungs can be stretched
V
Lung Compliance =
(Palv – Pip)
Larger lung compliance
• Easier for inspiration
• Smaller change in transpulmonary pressure
needed to bring in a given volume of air
FACTORS AFFECTING COMPLIANCE
Elasticity
• More elastic less compliant
Surface tension of lungs
• Greater tension less compliant

59. Surface Tension in Lungs
Thin layer fluid lines alveoli
Surface tension due to attractions between water
molecules
Surface tension = force for alveoli to collapse
or resist expansion
• To Overcome Surface Tension
Surfactant secreted from type II cells
• Surfactant = detergent that decreases surface tension
Surfactant increases lung compliance
• Makes inspiration easier

60. Resistance to airflow
• < 1 cm H₂O pressure gradient (alveolar to
atmospheric pressure) sufficient to cause enough
airflow for quiet breathing
• Greatest amount of resistance to airflow is not in
minute air passages of terminal bronchioles but in
some larger bronchioles and bronchi near trachea.
• In disease,smaller bronchioles play a greater role in
determining airflow resistance because of small size
and they are easily occluded by
 Muscle contraction in their walls
 Edema occuring in walls
 Mucus collecting in lumen

61. Nervous and local control of bronchial
musculature
• Sympathetic dilation of bronchioles
• Direct control relatively weak because few fibers
penetrate central portions of lung
• Cause dilation of bronchioles
• Parasympathetic constriction
• Few parasympathetic fibers penetrate lung
parenchyma
• Also activated by local irritation(noxious
gases,infection)
• Local factors – histamine,SRS-A

62. FACTORS AFFECTING LUNG VOLUME

63. LUNG VOLUMES

64. • Tidal volume (TV):
• The tidal volume (TV) is the volume of air that is
drawn into the lungs during inspiration from the end-
expiratory position (and also leaves the lungs
passively during expiration in the course of quiet
breathing).

65. • Inspiratory reserve volume (IRV): Maximum volume of air
inspired from the end-tidal inspiratory level.
• Expiratory reserve volume (ERV): The expiratory reserve
volume (ERV) is the maximum volume of air that can be
forcibly exhaled after a quiet expiration has been completed
(i.e., from the end-expiratory position).
• Residual volume: The residual volume (RV) is the volume of
air that remains in the lungs after a maximal expiratory effort.
always left in lungs, even with forced expiration.
Not measured with spirometer

66. • The functional residual capacity (FRC) is the
volume of air that remains in the lungs at the
end of a normal expiration.
• The inspiratory capacity (IC) is the maximum
volume of air that can be inhaled from the
end-expiratory position. It consists of two
subdivisions:
• tidal volume and the inspiratory reserve
volume (IRV).

67. • The total lung capacity (TLC) is the total
volume of air contained in the lungs at the end
of a maximum inspiration.
• The vital capacity (VC) is the volume of air that
is exhaled by a maximum expiration after a
maximum inspiration.
• So in total there are 4 volumes and 4
capacities.

68. Centres
1. Voluntary Control --- Motor Cortex
2. Involuntary (autonomic) Control --Brain Stem
 Pons
 Medulla Oblongata
• Medulla contains two centres of breathing
 Inspiratory Centre containing inspiratory neurones
 Expiratory Centre containing expiratory neurones
• For quiet breathing (eupnoea); I neurones responsible for
inspiration; expiration when I neurones cease firing.
• I neurones cease (probably) by a “slow loop negative feedback”
mechanism
• During exercise (hyperpnoea) I neurones inhibited by
Pneumotaxic centre in the Pons region

69. Medullary Respiratory Centre
• Two regions:
• 1) Dorsal respiratory group(DRG) – Inspiratory Centre
• 2) Ventral respiratory group(VRG) – Expiratory Centre
• • Probable that cells of the inspiratory centre have
the property of “intrinsic periodic firing” - responsible
for the basic rhythm of ventilation
• • With all stimuli abolished inspiratory cells generate
repetitive bursts of action potentials - nervous
impulses along efferent nerves to respiratory muscles

70. • Expiratory Centre
• Quiescent during normal quiet breathing
• In exercise hyperpnoea when breathing is more
forceful, expiration becomes active due to the
expiatory neurones.
• Pneumotaxic Centre(PRG) - Upper Pons
• Appears to switch off inspiration and so regulate
inspiratory volume and respiration rate.
• Apneustic Centre
• Neurones are suggested to have an excitatory effect
on the inspiratory neurones prolonging the ramp
action potentials

71. Respiratory Reflexes
pH of body fluids/plasma is the most potent stimulus to the
respiratory centre
↓ pH > ↑ pCO2 > ↓ pO2
Detected by
1. Peripheral Chemoreceptors
 aortic bodies
 carotid bodies
1) Small highly perfused shunts of the main arteries
2) Sensory (afferent) signals to medulla by, vagus (ao) and
glossopharyngeal (ca)
3) pH is the predominant trigger. pO2 less important except
at altitude or in disease

72. CHEMORECEPTORS

73. Central Chemoreceptors
Surface of the Medulla Oblongata
• Measure pH of cerebrospinal fluid (CSF) and brain tissue
fluid
• Main aim of respiratory control is brain pH homeostasis
Hydrogen ions [H+] do not freely pass blood/CSF barrier
• But CO2 does easily (no lactic acid effect on central
chemoreceptors)
• In CSF CO2 + H2O = H+ + [HCO3 ] - H+ liberated then influences
the central chemoreceptors

74. BRAIN STEM
MOTOR NEURONS
PHRENIC AND INTERCOSTAL NERVES
NEUROMUSCULAR JUNCTION
RESPIRATORY MUSCLES
LUNGS
VENTILATION

75. ABNORMALITIES
APNEUSTIC BREATHING
• occurs with lesions of the pons and is characterized
by prolonged inspiratory duration.
KUSSMAUL BREATHING
• Seen in ketoacidosis
• Virtually no pause between breaths(air hunger)
GASPING RESPIRATION(CEREBRAL HYPOXIA)
• Irregular,quick inspirations associated with
extensions of the neck and followed by a long
expiratory pause.

76. Cheyne-Stokes breathing is one form of periodic breathing
characterized by a cyclic rise and fall in ventilation with
recurrent periods of apnea or near apnea.
• Hyperapneic phase more than apneic phase
• Supramedullary lesions(tegmentum of pons)
Biot’s breathing
• tidal volumes of fixed amplitude are separated by
periods of apnea.
• Apneas may be separated by periods of gradually
increasing and decreasing breathing

79. REFERENCES
1. FISHMAN’S PULMONARY DISEASES AND
DSISORDERS
2. CROFTON AND DOUGLAS’S RESPIRATORY
DISEASES
3. NUNN’S APPLIED RESPIRATORY PHYSIOLOGY
4. GUYTON’S TEXTBOOK OF PHYSIOLOGY
5. GANONG REVIEW OF PHYSIOLOGY
6. PLEURAL DISEASES - LIGHT

80. THANK YOU