chapter 22: respiratory system (#2)

CHAPTER 22:

RESPIRATORY SYSTEM

(2): MECHANICS OF

VENTILATION

Human Anatomy and Physiology II –

BIOL153

Processes of Respiration

Pulmonary

ventilation

External

respiration

Transport

Internal

respiration

Respiratory

system

Circulatory

system

Goals/Objectives

Explain the functional importance of the partial vacuum that exists in the intrapleural space

Relate Boyle’s law to the events of inspiration and expiration

Explain the relative roles of the respiratory muscles and lung elasticity in producing the volume changes that cause air to flow into and out of the lungs

List several physical factors that influence pulmonary ventilation

Explain and compare the various lung volumes and capacities

Define dead space

Indicate types of information that can be gained from pulmonary function tests

Mechanics of Breathing

Inspiration/Inhalation Expiration/Exhalation

Pressure Relationships in the

Thoracic Cavity Atmospheric pressure (Patm)

Pressure exerted by air surrounding body

760 mm Hg at sea level = 1 atmosphere

Respiratory pressures described relative to Patm

Intrapulmonary (intra-alveolar) pressure (Ppul)

Pressure in alveoli

Fluctuates with breathing

Always eventually equalizes with Patm

Intrapleural pressure (Pip)

Pressure in pleural cavity

Fluctuates with breathing

Always a negative pressure (<Patm and <Ppul)

Pressure Relationships in the

Thoracic CavityAtmospheric pressure (P

atm)

0 mm Hg (760 mm Hg)

Thoracic wall

Parietal pleura

Visceral pleura

Pleural cavity

Transpulmonary

pressure

4 mm Hg(the differencebetween 0 mm Hgand −4 mm Hg)

Intrapleural

pressure (Pip)

−4 mm Hg(756 mm Hg)

Intrapulmonary

pressure (Ppul

)

0 mm Hg(760 mm Hg)

Diaphragm

Lung

0

– 4

If Pip = Ppul or Patm lungs collapse

(Ppul – Pip) = transpulmonary pressure Keeps airways

open

Greater transpulmonarypressure larger lungs

Negative Intrapleural Pressure

Atelectasis (lung collapse)

Plugged bronchioles collapse of alveoli

Pneumothorax-air in pleural cavity From either wound in parietal or

rupture of visceral pleura

Treated by removing air with chest tubes; pleurae heal lung reinflates

Pulmonary Ventilation and Boyle's

Law

Volume changes pressure changes

Pressure changes gases flow to equalize

pressure

Boyles Law: Pressure (P) varies inversely with

volume (V):

P1V1 = P2V2 OR

P = 1/V

Relationship between pressure and volume of

a gas

Gases fill container; if container size reduced

increased pressure

In

sp

iratio

n

Sequence of eventsChanges in anterior-posterior and

superior-inferior dimensions

Changes in lateral dimensions

(superior view)

1

Diaphragmmoves inferiorlyduringcontraction.

Ribs areelevated and sternumflares asexternalintercostalscontract.

Externalintercostalscontract.

Inspiratory musclescontract (diaphragmdescends; rib cage rises).

Inspiration

Inspiration


Thoracic cavity volumeincreases.

In

sp

iratio

n




(superior view)

1

2




Inspiration



In

sp

iratio

n




(superior view)

1

2

3




Lungs are stretched;intrapulmonary volumeincreases.

Inspiration




In

sp

iratio

n




(superior view)

1

2

3

4



Externalintercostalscontract.Intrapulmonary pressure

drops (to –1 mm Hg).

Inspiration




Intrapulmonary pressuredrops (to –1 mm Hg).

Air (gases) flows intolungs down its pressuregradient until intrapulmonarypressure is 0 (equal toatmospheric pressure).

In

sp

iratio

n




(superior view)

1

2

3

4

5




Inspiration

Forced Inspiration

1

Ex

piratio

n




(superior view)

Diaphragmmovessuperiorlyas it relaxes.

Ribs andsternum aredepressedas externalintercostalsrelax.

Externalintercostalsrelax.

Inspiratory muscles relax(diaphragm rises; rib cagedescends due to recoil ofcostal cartilages).

Expiration

1

Ex

piratio

n




(superior view)

2





Thoracic cavity volumedecreases.

Expiration

1

Ex

piratio

n




(superior view)

2

3






Elastic lungs recoilpassively; intrapulmonaryVolume decreases.

Expiration

1

Ex

piratio

n




(superior view)

2

3

4







Intrapulmonary pressurerises (to +1 mm Hg).

Expiration

1

Ex

piratio

n




(superior view)

2

3

4

5 Diaphragmmovessuperiorlyas it relaxes.






Intrapulmonary pressurerises (to +1 mm Hg).

Air (gases) flows out oflungs down its pressuregradient until intrapulmonarypressure is 0.

Expiration

Forced Expiration

Intrapulmonary pressure.

Pressure inside lungdecreases as lung volume increases during

inspiration; pressureincreases during expiration.

Intrapleural pressure.

Pleural cavity pressure becomes more negative as chest wall expands during

inspiration. Returns to initial value as chest wall recoils.

Volume of breath. During

each breath, the pressure gradients move 0.5 liter ofair into and out of the lungs.

Pre

ssu

re

re

lative

to

atm

osp

he

ric

p

re

ssu

re

(m

m H

g)

Vo

lu

me

(L

)

Inspiration Expiration

Intrapulmonarypressure

Trans-pulmonarypressure

Intrapleuralpressure

Volume of breath

5 seconds elapsed

+2

0

–2

–4

–6

–8

0.5

0

Clicker Question

The pressure in the pleural cavity is known as

__________.

a) intrapleural pressure

b) intrapulmonary pressure

c) transpulmonary pressure

d) atmospheric pressure

Goals/Objectives

Explain the functional importance of the partial vacuum that exists in the intrapleural space

Relate Boyle’s law to the events of inspiration and expiration

Explain the relative roles of the respiratory muscles and lung elasticity in producing the volume changes that cause air to flow into and out of the lungs

List several physical factors that influence pulmonary ventilation

Explain and compare the various lung volumes and capacities

Define dead space

Indicate types of information that can be gained from pulmonary function tests

Physical Factors Influencing

Pulmonary Ventilation

Three physical factors influence the ease of air

passage and the amount of energy required

for ventilation.

Airway resistance

Alveolar surface tension

Lung compliance

Airway Resistance

Relationship between flow (F), pressure

(P), and resistance (R) is:

∆P - pressure gradient between atmosphere

and alveoli (2 mm Hg or less during normal

quiet breathing)

Gas flow changes inversely with resistance

Conducting

zone

Respiratory

zone

Medium-sized

bronchi

Re

sista

nc

eTerminal

bronchioles

1 5 10 15 20 23Airway generation

(stage of branching)

Airway Resistance

Resistance usually insignificant

Large airway diameters in first part of conducting zone

Progressive branching of airways as get smaller, increasing total cross-sectional area

Resistance greatest in medium-sized bronchi

Resistance disappears at terminal bronchioles where diffusion drives gas movement

Alveolar Surface Tension

Attracts liquid molecules to one another at gas-liquid interface

Resists any force that tends to increase surface area of liquid

Water–high surface tension; coats alveolar walls reduces them to smallest size

Lung Compliance

Measure of change in lung volume that occurs

with given change in transpulmonary pressure

Higher lung compliance easier to expand

lungs

Normally high due to

Distensibility of lung tissue

Surfactant, which decreases alveolar surface

tension

Diminished by

Nonelastic scar tissue replacing lung tissue

(fibrosis)

Reduced production of surfactant

Respiratory Volumes and

Capacities

Used to assess respiratory statusTidal volume (TV)

Inspiratory reserve volume (IRV)

Expiratory reserve volume (ERV)

Residual volume (RV)

Combinations of respiratory volumes

Inspiratory capacity (IC)

Functional residual capacity (FRC)

Vital capacity (VC)

Total lung capacity (TLC)

Measurement

Adult male

average value

Adult female

average value Description

Respira

tory

volum

es

Respira

tory

capacities

Summary of respiratory volumes and capacities for males and females

Tidal volume (TV)

Inspiratory reservevolume (IRV)

Expiratory reservevolume (ERV)

Residual volume (RV)

500 ml 500 ml

3100 ml

1200 ml

1200 ml

1900 ml

700 ml

1100 ml

Amount of air inhaled or exhaled with each breath under restingconditions

Amount of air that can be forcefully inhaled after a normal tidalvolume inspiration

Amount of air that can be forcefully exhaled after a normal tidalvolume expiration

Amount of air remaining in the lungs after a forced expiration

Maximum amount of air contained in lungs after a maximuminspiratory effort: TLC = TV + IRV + ERV + RV

Maximum amount of air that can be expired after a maximuminspiratory effort: VC = TV + IRV + ERV

Maximum amount of air that can be inspired after a normal tidalvolume expiration: IC = TV + IRV

Volume of air remaining in the lungs after a normal tidal volumeexpiration: FRC = ERV + RV

6000 ml

4800 ml

3600 ml

2400 ml

4200 ml

3100 ml

2400 ml

1800 ml

Total lung capacity (TLC)

Vital capacity (VC)

Inspiratory capacity (IC)

Functional residualcapacity (FRC)


Capacities

5000

4000

3000

2000

1000

0

Millilite

rs (m

l)

Spirographic record for a male

6000

Inspiratoryreserve volume

3100 ml

Expiratoryreserve volume

1200 ml

Residual volume1200 ml

Inspiratorycapacity3600 ml

Functionalresidualcapacity2400 ml

Vitalcapacity4800 ml

Total lungcapacity6000 ml

Tidal volume 500 ml


Capacities

Dead Space

Anatomical dead space

No contribution to gas exchange

Air remaining in passageways; ~150 ml

Alveolar dead space–non-functional alveoli due to collapse or obstruction

Total dead space-sum of anatomical and alveolar dead space

Pulmonary Function Tests

Spirometer-instrument for measuring

respiratory volumes and capacities

Clicker Question

During pulmonary tests, a patient is asked to breath in normally and then inhale additionally as much as possible into the spirometer. The capacity being measured is the:

a) Inspiratory capacity

b) Functional residual capacity

c) Vital capacity

d) Total lung capacity

Pulmonary Function Tests

To measure rate of gas movement

Forced vital capacity (FVC)—gas forcibly

expelled after taking deep breath

Forced expiratory volume (FEV)—amount of

gas expelled during specific time intervals of

FVC

chapter 22: respiratory system (#2)

Education

high pressure

negative pressure

pressure changes area

pulmonary ventilationexplain

respiratory muscles

air surrounding body

relative roles

lung elasticity