Chapter22respiratorysystem2mechanicsofventilation 150223173350-conversion-gate02

CHAPTER 22: RESPIRATORY SYSTEM (2): MECHANICS OF VENTILATIONHuman Anatomy and Physiology II – BIOL153

Processes of Respiration

Pulmonary ventilation

External respiration

Transport

Internal respiration

Respiratorysystem

Circulatorysystem

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/InhalationExpiration/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 Cavity

Atmospheric pressure (Patm)0 mm Hg (760 mm Hg)

Thoracic wall

Parietal pleura

Visceral pleura

Pleural cavity

Transpulmonarypressure4 mm Hg(the differencebetween 0 mm Hgand −4 mm Hg)

Intrapleuralpressure (Pip)−4 mm Hg(756 mm Hg)

Intrapulmonarypressure (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

transpulmonary pressure 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

Insp

irati

on

Sequence of events Changes in anterior-posterior andsuperior-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.

Insp

irati

on



1

2




Inspiration



Insp

irati

on



1

2

3




Lungs are stretched;intrapulmonary volumeincreases.

Inspiration




Insp

irati

on



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).

Insp

irati

on



1

2

3

4

5Diaphragmmoves inferiorlyduringcontraction.



Inspiration

Forced Inspiration

1

Expir

ati

on



Diaphragmmovessuperiorlyas it relaxes.

Ribs andsternum aredepressedas externalintercostalsrelax.

Externalintercostalsrelax.

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

Expiration

1

Expir

ati

on



2





Thoracic cavity volumedecreases.

Expiration

1

Expir

ati

on



2

3






Elastic lungs recoilpassively; intrapulmonaryVolume decreases.

Expiration

1

Expir

ati

on



2

3

4







Intrapulmonary pressurerises (to +1 mm Hg).

Expiration

1

Expir

ati

on



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 duringinspiration; 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

ssure

rela

tive t

oatm

osp

heri

c pre

ssu

re (

mm

Hg)

Volu

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 pressureb) intrapulmonary pressurec) transpulmonary pressured) 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

Conductingzone

Respiratoryzone

Medium-sizedbronchi

Resi

stan

ceTerminalbronchioles

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 Decreased flexibility of thoracic cage

Respiratory Volumes and Capacities

Used to assess respiratory status Tidal 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)

MeasurementAdult maleaverage value

Adult femaleaverage value Description

Resp

irato

ryvolu

mes

Resp

irato

ryca

paci

ties

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)


5000

4000

3000

2000

1000

0

Mill

ilite

rs (

ml)

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


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 capacityb) Functional residual capacityc) Vital capacityd) 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

Chapter22respiratorysystem2mechanicsofventilation 150223173350-conversion-gate02

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