Respiration 1.ppt

7/28/2019 Respiration 1.ppt

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Respiration

Dr Sabeen Haq


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Respiration

Introduction

Internal respiration, cellular respiration

External respiration

Breathing

Mechanical act of moving gases in and out


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Steps of external respiration

Breathing

Exchange of gases between alveoli and

pulmonary blood

Transport of gases to tissues

Exchange of gases between tissues and systemic

circulation First 2 steps by respiratory system

Last two steps by circulatory system


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Anatomy of airway


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Conducting zone

Respiratory airway starting from nose till

terminal bronchiole is conducting zone.


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Respiratory unit

It is gas exchange area

Respiratory

bronchioles,

alveolar ducts, atria

and alveoli


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Functions of respiratory system

Respiratory function

Evaporation and heat loss

Increases venous return

Acid base balance

Enables vocalization

Defense against inhaled foreign materials

Lungs activate angiotensin II

Nose - smell


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Mechanics of respiration

Pleural pressure:

Pressure of fluid inside pleural cavity Slightly negative pressure

Varies from -5 to -7.5cm of H2O during

inspiration and expiration


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Alveolar pressure:

Pressure of air

inside lung

alveoli


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Mechanics of respiration Cont.

Transpulmonary pressure:

Difference between alveolar pressure andpleural pressure

Measure of elastic forces in the lungs that

tend to collapse the lungs during respirationAlso known as recoil pressure


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Compliance:

Distensibility (stretchability):

Ease with which the lungs can expand.

100 x more distensible than a balloon.

Elasticity:

Tendency to return to initial size after distension.

High content of elastin proteins.

Very elastic and resist distension.

Recoil ability.

Physical Properties of the Lungs


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Compliance

The extent to which lungs can expand for each

unit increase in transpulmonary pressure

Total compliance of both lungs = 200ml / cm

of H2O transpulmonary pressure


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Compliance diagram

Compliance is determined by elastic forces of

lungs which are:

Elastic forces of lung tissues itself

Elastic forces caused by surface tension of the

fluid that lines the inside walls of alveoli


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Compliance diagram

Tissue elastic forces tending to collapse the

lungs represent only 1/3rd of the total lung

elasticity and fluid-air surface tension forces

represent about 2/3rd.


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Compliance of thorax and lungs

together

To inflate lungs in thoracic cavity, twice as much

pressure is requires than that to inflate lungs

alone

Compliance of total system is half i.e around 110

ml


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Lungs can be expanded or contracted by:

Upward or downward movement ofdiaphragm

Elevation or depression of ribs


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Muscles of inspiration

They contract the diaphragm and elevate the rib

cage

Quiet inspiration:

Diaphragm = vertical diameter

External intercostals = anteroposterior and

lateral diameter

Forceful inspiration

Sternocleidomastoid

Anterior serrati

scleni


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Muscles of expiration

Quiet expiration:

Relaxation of diaphragm and elastic recoil of

lungs, chest wall and abdominal structures

Forceful expiration:

Abdominal recti

Internal intercostals


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Work of breathing

Quiet breathing

Inspiration = active process

Expiration = passive process

Work of inspiration

Compliance work

Tissue resistance work

Airway resistance work


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Work of breathing Cont.

Energy required:Quiet respiration = 3-5 % of total energy

Energy requirement increases up to 50 folds in

case of

Increase airway resistance (COPD)

Decrease pulmonary compliance (Fibrosis)

Decreased lung elastic recoil (Emphysema)

When increased ventilation needed ( Exercise)


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Surfactant

Surfactant decreases surface tension to 1/2 -1/12. Secreted by type II alveolar epithelial cells

Dipalmitoyl phosphatidylcholine + surfactant

apoproteins + calcium ions

Surface tension of

pure water = 72 dynes/cm

Alveolar fluid without surfactant = 50 dynes/cm

Alveolar fluid with surfactant = 5-30 dynes/cm


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Surfactant


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Pressure in occluded alveoli

Surface tension tends to collapse the alveoli

Pr = 2 surface tension / radius of alveoli

Pressure in average size alveoluswith normal surfactant = 4 cm of H2O

with no surfactant = 18 cm of H2O

Inverse relationship of radius with pressure


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Respiratory distress syndrome of

newborn

Radius of alveoli in premature babies is quarter

as compared to that in adults.

Surfactant begin to secrete around 6 to 7th

month of gestation.

So tendency of alveoli to collapse is 6-8 times

higher

Treatment = continuous positive pressure

ventilation


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Respiration 1.ppt

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