Pulmonary Ventilation 2011-2012

8/12/2019 Pulmonary Ventilation 2011-2012

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Pulmonary VentilationFUNDAMENTAL OF

BIOMEDICAL SCIENCE VIIFRESHMEN YEAR PROGRAM


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Meaning of Respiration

There are two quiet different meaning of

respiration

1. Utilization of oxygen in the metabolism of

organic molecules by cells

2. The exchange of oxygen and carbon

dioxide between an organism and the

external environment Ventilation


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General Function of Respiratory

System

1. Provide oxygen

2. Eliminates carbon dioxide

3. Regulates the blood concentration of hydrogen ions (pH)

4. Form speech sounds (phonation)

5. Defends against microbes

6. Influences arterial concentration of chemical messenger

by removing some from pulmonary capillary blood andproducing and adding others to this blood

7. Traps and dissolves blood clots


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6

Review of the Structure of

Respiratory System


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Upper R.S

Lower R.S

NosePharynx

Associated structure

Larynx

Trachea

Bronchus

Lungs

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Structure of

Respiratory

System


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Alveolus

Artery & Vein

Bronchiole

Terminal bronchiole

Respiratory bronchiole

Capillary vessel

Alveolar duct

8


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1

2 3

4

5

6

789

1. Trachea

2. Primary bronchus3. Secondary bronchus

4. Tertiary bronchus

5. Bronchiole6. Terminal bronchiole

7. Respiratory

bronchiole

8. Alveolar duct

9. Alveolus


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1

2

3

4

5

6

7

8

9

10

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1. Type II alveolar cell

2. Alveolar capillary

membrane

3. Type I alveolar cell

4. Alveolar macrophage

5. Red blood cell

TRANSVERSE SECTION OF AN ALVEOLUS


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6

7

8

9

10

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TRANSVERSE SECTION OF AN ALVEOLUS

Red blood cell

Capillary endothelium

Capillary basement membrane

Epithelial basement membrane

Type I alveolar cell

Surfactant layer

DETAILS OF ALVEOLAR

CAPILLARY MEMBRANE


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Muscular

Control ofBreathing

Inspiration

muscles:

Diaphragm

External Intercostals

Sternocleido-mastodeus

Scalenus

Abdominal muscles


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Expiration muscles:

InternalIntercostals

AbdominalMuscles

Extrinsic elastic

recoil

Intrinsic elasticrecoil

Abdominal muscles


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STERNUM AND

DIAPHRAGM DURING

INSPIRATION ANDEXPIRATION

S.E = Sternum duringExpiration

S.I = Sternum during

Inspiration

D.E = Diaphragm during

Expiration

D.I = Diaphragm during

Inspiration


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Ventilation

Ventilation is defined as the exchange of air betweenthe atmosphere and alveoli

Like blood, air moves by bulk flow, from a region ofhigh pressure to one of low pressure by the equation:

F = P/R. For air flow into and out the lungs, the relevant

pressure are the gas pressure in the alveoli (PALV) andthe gas pressure in the atmosphere (PATM). The

pressure difference

P = |PATMPALV| All pressure in the respiratory system are given relativeto atmospheric pressure, which is 760 mmHg at sealevel


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Ventilation (cont)

During ventilation air moves into and out of the lungsbecause the alveolar pressure is alternately made lessthan and greater than atmospheric pressure (rememberthe Boyles law)

During inspiration and expiration the volume of the containerthe lungsis made to change, and these changes then cause, byBoyles law, the alveolar pressure changes that drive air flow intoor out of the lungs

There are no muscles attached to the lungs surface topull the lungs open and push them shutthe volumeof the lungs depend on the transpulmonary pressureand how stretchable the lung are.


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Boyles Law

The movement of air into and out of the lungsdepends on pressure change


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Transpulmonarypressure: the difference in pressure

between the inside and the outside of the lungs (PALVPIP)

ELASTIC

RECOIL

PALVPIP=

4 mm Hg

PALV= 0 mm Hg

Chest Wall

Intrapleural fluid

PIP = - 4 mmHg

PALV= ALVEOLAR

PRESSURE

PIP= INTRAPLEURALPRESSURE

ALVEOLI


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THE

PRESSURECHANGES


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Inspiration

During inspiration, the contractions of thediaphragm and inspiratory intercostal musclesincrease the volume of the thoracic cage

a. This make intrapleural pressure moresubatmospheric, increase transpulmonarypressure, and causes the lungs to expand to agreater degree than between breath

b. This expansion initially makes alveolar pressuresubatmospheric, which create the pressuredifference between atmosphere and alveoli todrive air flow into the lungs


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SEQUENCE OF EVENTS DURING INSPIRATION

NEURAL IMPULSE

DIAPHRAGM AND INSPIRATORY INTERCOSTAL MUSCLE CONTRACT

THORAX EXPANDS

PIPBECOMES MORE SUBATMOSPHERIC

TRANS PULMONARY PRESSURE

LUNGS EXPAND

PALVBECOMES SUBATMOSPHERIC

AIR FLOWS INTO ALVEOLI


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Expiration

During expiration, the inspiratory musclesceases contracting, allowing the elastic recoil ofthe chest wall and lungs to return them to their

original between-breatha. This initially compresses the alveolar air, raising

alveolar pressure above atmospheric pressureand driving air out of the lungs

b. In forced expiration, the contraction ofexpiratory intercostal muscles and abdominalmuscles actively decreases chest dimensions.


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SEQUENCE OF EVENTS DURING EXPIRATION

DIAPHRAGM AND INSPIRATORY INTERCOSTALS STOP CONTRACTING

CHEST WALL MOVES INWARD

PIPBACK TOWARD PREINSPIRATION VALUE

TRANSPULOMONARY PRESSURE BACK TOWARD PREINSPIRATION VALUE

LUNGS RECOIL TOWARD PREINSPIRATION SIZE

AIR IN ALVEOLI BECOMES COMPRESSED

PALVBECOMES GREATER THAN PATM

AIR FLOWS OUT OF LUNGS


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Relationship Between Flow and Pressure

R

PF

Flow (F

) is proportional to the pressure difference (P

) between twopoints and inversely proportional to the resistance (R) determined by

their radius

R

PPF

alvatm

Air moves into and out of the lungs because the alveolar pressure

is made alternately less than and greater than atmospheric pressure


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Airways Resistance

Factors determine airways resistance:

Directly proportional to the magnitude of the

frictional interaction between the flowing gas

moleculesthe viscosity of the airwhich much less

than that of bloodDirectly proportional to the length of the airways

Large diameter airways have decreased resistance

Autonomic nerve especially sympathetic decreasedresistance

RPPF alvatm


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Major Factor Influencing the Airway

Resistance

Physical factorsAirways are held open by transpulmonary pressure and by lateral

tractionopen wider during inspiration and may collapse duringforced expiration

Airways may partially or totally occluded by mucous accumulation Neuroendocrine agents

Parasympathetic nerves (neurotransmitter = acetylcholine) constrict

Circulating epinephrine dilates (action is on beta adrenergic)

Paracrine agents Histamine constricts Several eicosanoids, notably the leukotrienes, constrict

Several eicosanoids dilate


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Compliance

The compliance is expressed as the volume increase ofthe lungs for each unit increase in intra-alveolarpressure (cm3/mm Hg)

The greater the increase in volume for a given increasein pressure, the greater the compliance.

Lung compliance is determined by the elasticconnective tissues of the lungs, the surface tension ofthe fluid lining the alveoli, and the muscle tones.

The surface tension of the fluid is decreased bysurfactant that is produced by the type II cells of thealveoli


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)(atmalv

L

L

PP

VC

The greater the increase in volume for a given

increase in pressure, the greater the compliance.


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Alveolar Surface Tension

The alveolar surface tension tends to collapse the alveolithe greater the surface tension the lesser the

compliance


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Law of La Place

P = 2T

r

P = inward-directed collapsing pressureT = Surface tension

R = Radius of Bubble of Alveolus


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PULMONARY VENTILATION


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BREATHING PATTERNS

Eupnea = Normal quiet breathing

Apnea = A temporary cessation of breathing

Dyspnea = A painful or labored breathing + tachypnea

Costal breathing = Shallow (chest) breathing

Diaphragmatic breathing = Deep (abdominal) breathing


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Breathing Pattern

Eupnoea is normal quiet breathing

Apnea is a temporary cessation of breathing

Dyspnea is a painful or labored breathing +tachypnea

Costal breathing is shallow (chest) breathing

Diaphragmatic breathing is deep (abdominal)breathing


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Modified Respiratory Movement (cont)

Yawning: A deep inspiration through the widelyopened mouth producing an exaggerated depression ofthe mandible. It may be stimulated by drowsiness,fatigue, or someone elses yawning, but precise cause is

unknown Sobbing:A series of convulsive inspiration followedby a single prolong expiration. The rima glottidis closesearlier than normal after each inspiration so only a littleair enters the lungs with each inspiration

Crying:An inspiration followed by many shortconvulsive expirations, during which the rima glottidisremains open and the vocal folds vibrate; accompaniedby characteristic facial expressions and tears


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Modified Respiratory Movement

Coughing: along drown and deep inspiration followingby a complete closure of the rima glottidis, which results ina strong expiration that suddenly pushes the rima glottidisopen and sends a blast of air through the upper respiratory

passage. Stimulus for this reflex act may be a foreign bodylodged in the larynx, trachea, or epiglottis

Sneezing: Spasmodic contraction of muscles of expirationthat forcefully expels air through the nose and mouth.

Stimulus may be an irritation of the nasal mucosa. Sighing: A long drown and deep inspiration immediately

followed by a shorter but forceful expiration


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Pulmonary Ventilation 2011-2012

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