Pulmonary ventilation is the mechanical process of air flowing in and out of the lungs due to pressure gradients and volume changes caused by contraction of respiratory muscles during inspiration and expiration. It serves to continually renew the air in the gas exchange areas of the lungs. In a healthy adult, pulmonary ventilation is approximately 6-7 liters per minute through tidal breathing of 500ml 12 times per minute, resulting in alveolar ventilation of around 4200ml per minute after accounting for the 150ml dead space. Pulmonary ventilation, alveolar ventilation, respiratory cycles, and the mechanics of respiration including respiratory muscles, pleural pressures, and pressure relationships are discussed in detail.

1. Lecture 5:Pulmonary Ventilation
Dr Shamshad

2. Guyton & Hall Textbook of Physiology - 13th ed. P. 465-467.

3. Pulmonary Ventilation
Defn: Mechanical process of air flow in or out of the lungs to the
atmp due to pr gradients & vol changes.
Cause: Contraction of skeletal muscles.
Two processes: Inspiration & Expiration.
Significance : pulmonary ventilation is to continually renew the
air in the gas exchange areas of the lungs.
Amount :6-7 litres /min

4. Pulmonary ventilation
● Flow of air b/w the atmp.
& the lung alveoli.
● Mechanical process
● Inspiration & Expiration
● Due to Pr gradient of air
b/w lungs & Atmp
Alveolar ventilation
● Exchange of air b/w Alveoli
& atmp.
● Chemical Process
● Internal & External respn.
● Based on partial pr of gases
b/w blood & atmp /tissues
● Amt air utilized for gaseous
exchange/min

5. Pulmonary ventilation
Alveolar ventilation
Respiratory cycle

6. In healthy adult
Pulmonary Ventilation
=Tidal Volume*Respiratory Rate
=500ml*12/minute
=6000ml/minute
AlveolarVentilation
=(Tidal Volume -Dead Space)*Resp Rate
=(500-150)ml*12/minute
=4200ml/minute

7. Respiratory Cycle & Respiratory Rate
Respiratory cycle : Sequence of inspiration & expiration
description of the changes in pressure, lung volumes
& airflow in one cycle.
Inspiration Rest Expiration Rest Inspiration
Respiratory Rate(RR): Number of breaths taken within a specific
amount of time (one minute).
In healthy adult:12-15 breaths/minutes

8. Respiratory cycle

9. ➢Eupnea: Normal quiet respiration
➢Bradypnea: Slow rate of respiration
➢Tachypnea: Increased rate of respiration
➢Apnea: Cessation of respiration
➢Hypoventilation: Decrease in Rate & Depth of ventilation.
➢Hyperventilation: Increase in Rate & Depth of ventilation
➢Hypoapnea: Shallow breathing
➢Dyspnea: Difficulty in breathing.

10. Mechanics of normal & forced respiration.
Lung mechanics: It is study of forces & factors responsible for
ventilation.
Mechanics of ventilation depends on
1. Muscles & bones of thoracic cage.
2. Pleura & pleural cavity.
3. Dead space & value & types.
4. Different pressure & derived pressures.
5. Elastic property of lungs and thorax
6. Surface tension of the alveoli.

12. Muscles of Respiration
Quiet Inspiration: Diaphragm,External intercostal muscles
Quiet Expiration: Passive relaxation of inspiratory muscles
Forced Inspiration:Ala nostrils, scalene of neck
Sternocleidomastoids, pectoris minor,lavator scapulae,
Forced Expiration: Internal intercostal, Rectus abdominis, External
oblique muscles.
Muscles of inspiration:Elevate the chest cage
Muscles of expiration: Depress the chest cage
Thoracic cage bones: Ribs, Sternum, Vertebral column.

13. Diaphragm(75%)
Dome shaped- Attached to lower ribs, sternum & vertebral column.
Nerve supply: Phrenic nerve- C3,4,5.
Action :>75% of quiet inspiration . vertical dimension of thorax.
Contraction dome/pulls the dome of muscle down.
Causes flow of air into lungs.
Relaxation: dome thus decrease vertical diameter.
Causes expulsion of gases.
Moves down 1.5 cm normal (7.5cms - forced ) inspiration
Abdominal contents forced downward & forward causing ↑ in vertically
Rib margins are lifted & moved outward causing ↑ transverse diameter

14. Applied :Reduced movement:Obesity(moderate to severe),Pregnancy,
Tight Clothing.
Paradoxical movement of diaphragm when paralyzed
Upward movement with inspiratory drop of intrathoracic pr.
Inspiration Expiration

15. External intercostals (25%)
Location: Obliquely b/w ribs in forward & downward direction.
Nerve supply: Intercostal nerves (T1-11).
Action and effects:T.S+ A.P ↑by 2 mechanisms:
1: 6–10 ribs rotates upwards and outwards by a “bucket-handle
movement” → ↑ T.S.
2: upper 4 ribs rotate the sternum in upward & outward (pump-
handle movement) → ↑ in vertically .
Applied: Paralysis does not seriously alter inspiration diaphragm is
so effective but sensation of inhalation is decreases.

17. Inspiration Expiration
Muscles ➢ Contraction:Diaphragm
& External internal
intercostal muscles
➢ Daiphragm dome flattens
➢ Relaxation:Diaphragm &
External internal
intercostal muscles
➢ Daiphragm dome flattens
Ribs
Move
➢ up & out wards ➢ down & in wards
Thorax
Vol &Pr
➢ Vol increases &
➢ Air pr decreases
➢ Vol decreases &
➢ Air pr increases
Air flows ➔ Into lungs from atmp ➔ From lungs to atmp
Normal quiet respiration

21. Pleura & pleural cavity
Two layers :
1. Visceral :Attached to the lung parenchyma ,get
the same nerve supply not painful
(no pain receptors).
2. Parietal :Attached to inner aspect of thoracic
cavity, get the nerve supply from the
same,painful(contain pain receptors)
1. Intrapleural space:Space is closed space with
negative pressure , filled with pleural
fluid.
Intrapleural
space

22. Intrapleural Space: Has thin layer of mucoid transudate
(interstitial fluid + protein)
10-20 ml Secreted by Parietal layer.
Drained by lymphatics constant suction on pleura (-5cmH2O) of
(Mediastinum, superior - diaphragm, lateral)of parietal pleura
★ Helps create Negative pressure.
Functions:
➢ Lubricant for lungs to slide against chest wall facilitates change
in size & shape of lungs. Protects lungs from external damage.
➢ Prevents frictional irritation so membranes slide against each
other & are difficult to separate apart .

23. Pleural pressure
Defn:The pr of the fluid in the thin space b/w Visceral &Parital pleurae
Negative pr as compared to the atmp pr. < 760mmHg.
Beginning of the respiration is -5 cms of H2O
Function: This amount hold the lungs open to their resting position.
Negativity leads to sucking of air in lungs from the atmosphere.
During Normal quiet :the lungs and chest wall are stretched in
equal & opposite direction.
Intrapleural space increases but it being closed cavity ,negativity in it
increases more (-5 to 7.5cms of H2o)

24. Significance: If positive /equal to atmp pr
Leads to lungs collapse(recoil inwards)
Pneumothorax, Hemothorax, Chylothorax .

25. Pressures changes :During breathing
Atmospheric pressure :760mmHg/ Same=Zero
Alveolar pressure(Palv): More/same/less compared to atmp pr
Pleural pressure:(Ppl) always Negative/less than atmp pr .
Transpulmonary pr (Ptp) - Diff b/w alveolar pr & pleural pr.
(Ptp) = (Palv) - (Ppl)
Transthoracic pr (Ptt) - Diff b/w alveolar pr & body surface pr.
(Ptt) = (Palv) - (Patml)
Transchest pr (Pta)- Diff b/w alveoli pr & atmp pr.
(Pcw).= Ppl- Patm

26. 26
Pressure relationship

28. Alveolar pressure
● Defn: The pr of air inside the lung alveoli
● When glottis is open:
● No air moves into the & out of the lungs
● Pr in alveoli = atmp pr =760mmHg /Zero cms of H2O
● Quiet inspiration: Alveoli opens pr = -ve /-1cm of H2o
This pulls air into alveoli in 2 seconds
● Quiet expiration: Alveolar pr =+ve/ + 1cm of H2o
This forces the inspired air out of lungs during 2-3 seconds.

30. TRANSMURAL PRESSURE
Thoracic cavity larger than lungs
Transmural pr:Pr across Lung Wall
Pr gradient holds thoracic wall & lungs
in close apposition
Pr gradient is balanced by the elastic forces
in the alveoli producing equilibrium
Under static conditions,
Transmural pr = the elastic recoil pr
of the compartment.

31. Transpulmonary pressure
● Defn:Alveolar pr- Pr on
outer space of lungs
● Measure of the elastic
forces in the lungs
● Tends to collapse the lungs
at each instant of
respiration

32. 32
Physiological factors that affect:
Valsalva manoeuvre
Pathological factors:
Emphysema
Injury to thoracic wall will produce collapse of lungs

33. Dead spaces
Defn: A fraction of tidal volume of air that does not take part in
exchange of gases.
Types:
Anatomical :Vol. of air that does not reach the alveoli
Physiological: 1) Inspired air in alveoli that has no/less
blood supply.
2) Inspired air in alveoli that has normal blood flow
but less air reaches.
Normal Value:150 ml
Significance: regulation of temperature and humidification of air.
Increasing the depth of breathing is more effective in increasing
alveolar ventilation.
VT