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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
7
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
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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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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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