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LIU Chuan Yong

刘传勇

Department of Physiology

Medical School of SDU

Tel 88381175 (lab)

88382098 (office)

Email: liucy@sdu.edu.cn

Website: www.physiology.sdu.edu.cn

Chapter 3

Elastic Properties of the Respiratory System

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Reference - Textbook

P 29 – 40 P 210 - 218 P 471 – 475

Reference – Course Website

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An Overview of Key Steps in Respiration

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Key Steps in Respiration

• Ventilation: Movement of air into and out of lungs

• Gas exchange between air in lungs and blood

• Transport of oxygen and carbon dioxide in the blood

• Internal respiration: Gas exchange between the blood and tissues

Newborn RDS : Signs and Syndrome

• Baby Aldridge– Premature infant (28 weeks gestation)– Breathing very fast– Dyspnea

• Chest was indrawing with each breath• Making a grunting sound

– Question • The mechanism?• Treatment and prevention

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Outline

• Part I Intrapleural Pressure and Mechanism of the Ventilation

• Part II Lung Compliance• Part III The Effect of Disease

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Part I Intrapleural Pressure and Mechanism of the Ventilation

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• Occurs because the thoracic cavity changes volume

• Insipiration uses external intercostals and diaphragm

• Expiration

• passive at rest

• uses internal intercostals and abdominals during severe respiratory load

• Breathing rate is 10-20 breaths / minute at rest, 40 - 45 at maximum exercise in adults

Ventilation

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Mechanisms of Breathing: Mechanisms of Breathing: How do we change the volume of the rib cage ?How do we change the volume of the rib cage ?

To Inhale is an ACTIVE processTo Inhale is an ACTIVE process• DiaphragmDiaphragm

Rib CageRib Cage

ContractContract

DiaphragmDiaphragmVolumeVolume

•External Intercostal Muscles External Intercostal Muscles

IntercostalsIntercostalsContractContract

to Liftto LiftRibRib

SpineSpine

RibsRibs VolumeVolume

Both actions occur simultaneously – otherwise not effectiveBoth actions occur simultaneously – otherwise not effective

Flail Chest （连枷胸）

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Pleura

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•Pleural fluid produced by pleural membranes

–Acts as lubricant

–Helps hold parietal and visceral pleural membranes together

Intrapleural Pressure

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Penumothorax

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Penumothorax

胸腔闭式引流术

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Alveolar Pressure Changes

During Respiration

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Chest WallChest Wall(muscle, ribs)(muscle, ribs)

Principles of BreathingPrinciples of BreathingFunctional Unit: Chest Wall and Lung Functional Unit: Chest Wall and Lung

ConductingConductingAirwaysAirways

DiaphragmDiaphragm(muscle)(muscle)

LungsLungsGas ExchangeGas Exchange

Follows Boyle’s Law:Follows Boyle’s Law:Pressure (P) x Volume (V) = ConstantPressure (P) x Volume (V) = Constant

Pleural CavityPleural CavityImaginary Space betweenImaginary Space betweenLungs and chest wallLungs and chest wall

Pleural CavityPleural CavityVery small space Very small space Maintained at negative pressureMaintained at negative pressureTransmits pressure changes Transmits pressure changes Allows lung and ribs to slideAllows lung and ribs to slide

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CWCW

Follows Boyle’s Law: PV= CFollows Boyle’s Law: PV= C

At Rest with mouth open PAt Rest with mouth open Pbb = P = Pi i = 0= 0

DD

PPii

AA

PSPS

PPbb

Airway OpenAirway Open

Principle of BreathingPrinciple of Breathing

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CWCW

Follows Boyle’s Law: PV= CFollows Boyle’s Law: PV= C

At Rest with mouth open PAt Rest with mouth open Pbb = P = Pi i = 0= 0Inhalation: Inhalation: - Increase Volume of Rib cageIncrease Volume of Rib cage- Decrease the pleural cavity pressureDecrease the pleural cavity pressure- Decrease in Pressure inside (P- Decrease in Pressure inside (Pii) ) lungslungs

DD

PPii

AA

PSPS

PPbb

Airway OpenAirway Open

Principle of BreathingPrinciple of Breathing

2

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CWCW

Follows Boyle’s Law: PV= CFollows Boyle’s Law: PV= C

At Rest with mouth open PAt Rest with mouth open Pbb = P = Pii = 0 = 0Inhalation: Inhalation:

- PPbb outside is now greater than P outside is now greater than Pii

- Air flows down pressure gradient- Air flows down pressure gradient- Until Pi = PbUntil Pi = Pb

DD

PPii

AA

PSPS

PPbb

Airway OpenAirway Open

Principle of BreathingPrinciple of Breathing

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CWCW

Follows Boyle’s Law: PV= CFollows Boyle’s Law: PV= C

DD

PPii

AA

PSPS

PPbb

Airway OpenAirway OpenAt Rest with mouth open PAt Rest with mouth open Pbb = P = Pii = 0 = 0

Exhalation: Opposite ProcessExhalation: Opposite Process- Decrease Rib Cage VolumeDecrease Rib Cage Volume

Principle of BreathingPrinciple of Breathing

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CWCW

Follows Boyle’s Law: PV= CFollows Boyle’s Law: PV= C

At Rest with mouth open PAt Rest with mouth open Pbb = P = Pii = 0 = 0

Exhalation: Opposite ProcessExhalation: Opposite Process- Decrease Rib Cage VolumeDecrease Rib Cage Volume- Increase in pleuralIncrease in pleural

cavity pressure cavity pressure - Increase P - Increase Pii

DD

PPii

AA

PSPS

PPbb

Airway OpenAirway Open

Principle of BreathingPrinciple of Breathing

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CWCW

Follows Boyle’s Law: PV= CFollows Boyle’s Law: PV= C

At Rest with mouth open PAt Rest with mouth open Pbb = P = Pii = 0 = 0

Exhalation: Opposite ProcessExhalation: Opposite Process- Decrease Rib Cage VolumeDecrease Rib Cage Volume- Increase PIncrease Pii

- Pi is greater than PPi is greater than Pbb

- Air flows down pressure gradientAir flows down pressure gradient- Until PUntil Pii = P = Pbb again again

DD

PPii

AA

PSPS

PPbb

Airway OpenAirway Open

Principle of BreathingPrinciple of Breathing

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Resistance of the Ventilation

• Elastic Resistance

– Determined by the Compliance

– Lung and Thoracic Cage Compliance

• Inelastic Resistance

– Airway Resistance

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Part II Lung Compliance

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Change in lung volume for each unit change in transpulmonary pressure = stretchiness of lungs V/P

Transpulmonary pressure is the difference in pressure between alveolar pressure and pleural pressure.

There are 2 different curves according to different phases of respiration.

The curves are called : Inspiratory compliance

curveExpiratory compliance

curve Shows the capacity of lungs to

“adapt” to small changes of transpulmonary pressure.

Hysteresis （滞后现象）

Compliance of lungs occurs due to elastic forcesCompliance of lungs occurs due to elastic forces..A. Elastic forces of the lung tissue itself

B. Elastic forces of the fluid that lines the inside walls of alveoli and other lung air passages

Elastin + Collagen fibresSurface Tension

Experiment:

By adding saline solution there is no interface between air and alveolar fluid. (B forces were removed)

surface tension is not present, only elastic forces of tissue (A)

Transpleural pressures required to expand normal lung = 3x pressure to expand saline filled lung.

Conclusion of this experiment:

Tissue elastic forces (A) = represent 1/3 of total lung elasticity

Fluid air surface tension (B) = 2/3 of total lung elasticity.

water molecules are attracted to one another.

The force of surface tension acts in the plane of the air-liquid boundary to shrink or minimize the liquid-air interface

In lungs = water tends to attract forcing air out of alveoli to bronchi = alveoli tend to collapse (!!!)

Elastic contractile force of the entire lungs (forces B)

Surface active agent in water = reduces surface tension of water on the alveolar walls

Pure water (surface pressure)

72 dynes/cm

Normal fluid lining alveoli without surfactant (surface pressure)

50 dynes/cm

Normal fluid lining alveoli with surfactant

5-30 dynes/cm

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• Phospholipid produced by alveolar

type II cells.

• Develop at 24 weeks’ gestation

• Produces surfactant at 34 weeks

• Lowers surface tension.

– Reduces attractive forces of

hydrogen bonding

– by becoming interspersed

between H20 molecules.

“The pressure inside a balloon is calculated by twice the surface tension, divided by the radius.”

Pressure to collapse generated by alveoli is inversely affected by radius of alveoli

the smaller a bubble, the higher the pressure acting on the bubble

Smaller alveoli have greater tendency to collapse

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CollapseCollapse

ExpandExpand

Effect of Surface Tension on Alveoli sizeEffect of Surface Tension on Alveoli size

AirAir FlowFlow

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Surfactant prevents alveolar collapse

Physiology Importance of Surfactant

• Reduces surface tension and elastic recoil, – making breathing easier

• Reduces the tendency to pulmonary edema

• Equalize pressure in large and small alveoli

• Produces hysteresis, which “props” alveoli open

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The compliance of lungs + thorax = 1/2 of lungs alone.

Part III The Effect of Disease

• Lung fibrosis （肺纤维化）• Emphysema ( 肺气肿）• Respiratory Distress Syndrome (RDS) of the

Newborn （新生儿呼吸窘迫综合症）

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Lung fibrosis• The lungs are stiffened

– By the laying down of collagen and fibrin bundles

• Compliance is reduced

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Emphysema• Destroy of the parenchyma

– Less elastic recoil

• Compliance increase

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Newborn RDS : Signs and Syndrome

• Baby Aldridge– Premature infant (28 weeks gestation)– Breathing very fast– Dyspnea

• Chest was indrawing with each breath• Making a grunting sound

– Question • The mechanism?• Treatment and prevention

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Newborn RDS

• Most common respiratory illness in NICU• Occur in premature neonate• Surfactant deficiency• Risk factors

– Asphyxia （窒息）– Male– Acidosis– DM mother

0

20

40

60

80

100

27 28 29 30 31 32 33 34 35 36

(wks)胎龄 (

%)发

病率

Relationship between Gestational Age and RDS Morbidity

gestational age(wks)

morbidity (%)

28~30 >70

31~32 40~55

33~35 10~15

>36 1~5

窒息低体温剖宫产糖尿病母亲婴儿（ IDM ）

早产

肺泡 PS

肺泡不张

PaCO2 通气 V/Q PaO2

严重酸中毒

肺毛细血管通透性

气体弥散障碍透明膜形成

呼吸性酸中毒 代谢性酸中毒

collapsed alveoli filled with hyaline membranes

Chest X-ray

• Ground glass appearance• Reticulogranular • air bronchograms

diffuse and symmetrical ground glass infiltrates

• Reticulogranular with air bronchograms

Before PS treatment 　　　 After PS treatment

Treatment: Surfactant Replacement

Home Work ： Case Study– Mechanics of Breathing.pdf– Pulmonary Structure and Lung Capacities.pdf– Pneumothorax.pdf

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