mechanics of pulmonary ventlation by dr.jawairia

7/27/2019 Mechanics of Pulmonary Ventlation by Dr.jawairia

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Mechanics ofPulmonary Ventilation


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Respirationprimary function - O2supply & Co2 expulsion

Thoracic Cavity

Bony cage bounded by

sternumfront

vertebraebehind

12 pairs of ribs laterally

Intercostal MuscleDiaphragmBelow


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Lungspongy tissue

Irregularly cone shaped

Connected with trachea by bronchi Trachea connected to atmosphere.


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Upper Respiratory Tract

Includes

Nasal passages.

Pharynx (throat) Larynx (voice box)

Vocal folds


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Lower Respiratory Treat

Trachea

Two bronchi

Bronchioles Lungs


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Division of Trachea

23 Times

16 divisiononly conducting syst. Till

terminal bronchioles

7 divisionexchange of gases

IncludesResp bronchioles

Alveolar ducts + alveoli


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Pulmonary Ventilationinflow and outflow ofair in between atmosphere and lung alveoli

Done through change in size & volume of

thoracic cavity & lungs follow those changes During inspiration thoracic cavity expand

sub atmospheric pressure in lung alveoli,

Intrapleural pressure more negative During expiration thoracic cavity shortens

Alveolar pressure increases


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1 atm = 760 mmHg = 0 cm of water


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Muscle of Quiet Inspiration

Main muscles involved

1. Diaphragm (lengthening & shortening of

chest cavity)

2. External Intercostals (elevation and

depression of rib cage)


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Diaphragm

Nerve supply phrenic nerve , C 3,4,5

Contractionpulls the lower surface of lung

downward Descend by 1.5 cm in quiet

breathing, +7-10cm in forceful inspiration

In expiration diaphragm simply relaxes

60-75% of inspirationSection of spinal cord below or above C 3,4,5

Leads to complete cessation of breathing


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External Intercostal Muscles

2540% inspiration

Two type of movements

1. Pump handle

Sternum moves forward, ribsmoving up and away from spine,

Antero posterior diameter increases

2. Bucket handle

ribs moving outward,transverse diameter increase


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Accessory Inspiratory Muscle

During forceful inspiration, exercise & asthma

Sternocleidomastoid, serratus anterior & sclani


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Muscles of Expiration

Quiet expirationa passive process

Inspiratory muscles relax

Thoracic cavity in size, Alveolar pressure Pleural pressure less negative

During forceful expiration- internal

intercostals and abdominal muscles


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Alveolar Surface Tension

At the interface of air and water, water

molecules have great attraction to each other,

so tend to contract the surface

Water lining the interior of alveoli tend to

expel the air out

So alveoli tend to collapse

The net effect is to cause the elastic contractile

force of entire lungs, surface tension elastic

forces


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Surfactant Surface active agent, reduces the surface tension so

preventing the full collapse of alveoli Secreted by type II alveolar cells

Lipoprotein mixture in thin fluid layer on the interior

of alveoli

Composed of surfactant apoproteins, phospholipids,

dipalmityol-phasphatidylcholine, calcium ions

Dipalmitoyl component reduces the surface tension

Surface tension inversely proportional toconcentration of surfactant


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During inspiration water molecules moveapart & expiration close to each other

without surfactant, alveolar surfacetension is 50 dynes/cm2

With surfactant, alveolar surface tensionis 5- 30 dynes/cm2


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Law of LaPlace

In water bubblesurface tension directedinward to the center

The positive pressure in alveoli to push the airout is expressed by law of Laplace

Two factors,

Surface tension

Radius of viscous

P = 2 T/R T = Surface tension,

R = Radius of viscous


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Role of surfactant

Dec. ST

Dec. collapse pressure

Dec. work of breathing Inc. compliance

Prevents development of pulmonary edema


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D fi i R i di d


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Deficiency Respiratory distress syndrome

(RDS) of newborn

Surfactant secretion at 6th-7th of intrauterine

life into amniotic fluid

Surfactant secretion stimulated by gluco-

corticoid, thyroxin, epinephrine and by contact

of air with alveoli

Deficiency in premature babies, babies of

thyroid deficient, diabetic & smoker mothers

Smoker Deficient in surfactant

Premature babies also have smaller alveoli so

their collapse tendency is more.

mechanics of pulmonary ventlation by dr.jawairia

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