functional anatomy of respiratory system and mechanics of breathing

7/30/2019 Functional Anatomy of Respiratory System and Mechanics of Breathing

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Functional anatomy of pulmonary

system, pulmonary circulation andmechanics of breathing

Presenter: Dr. Satyajit Majhi

Moderator: Dr. J.P. Sharma

www.anaesthesia.co.in Email: [email protected]

University College of Medical Sciences & GTB Hospital,Delhi


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5 Functions of the

Respiratory System

1. Provides extensive gas exchange surface areabetween air and circulating blood

2. Moves air to and from exchange surfaces of lungs3. Protects respiratory surfaces from outside

environment

4. Produces sounds

5. Participates in olfactory sense


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The Nose

Air enters the respiratory system:

through nostrils or external nares

into nasal vestibule

Nasal hairs: are in nasal vestibule

are the first particle filtration system


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The Nasal Cavity

The nasal septum:

divides nasal cavity into left and right

Superior portion of nasal cavity is the olfactory

region:

provides sense of smell

Mucous secretions from par nasal sinus and

goblet cells:

clean and moisten the nasal cavity

Lined by ciliated mucosal layer


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Epistaxis

Most common site Littles area

Situated anterior inferior part of nasal septum.

Anastomosis of 4 arteries, anterior ethmoidal, septal

branch of superior labial, septal branch ofsphenopalatine and greater palatine.

Woodruff area, anastomosis of sphenopalatine

artery and posterior pharyngeal artery causesposterior epistaxis


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Air Flow

Meatuses Constricted passageways that produce air

turbulence:

warm and humidify incoming air trap particles

During exhalation these structures:

Reclaim heat and moisture

Minimize heat and moisture loss


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The Palates

Hard palate:

forms floor of nasal cavity

separates nasal and oral cavities

Soft palate: extends posterior to hard palate

divides superior nasopharynx from lower pharynx


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Nasal Cavity


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The Pharynx and Divisions

A chamber shared by digestive and respiratory

systems

Extends from internal nares to entrances to larynx

and esophagus Nasopharynx

Oropharynx

Laryngopharynx


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The Nasopharynx

Superior portion of the pharynx

Contains pharyngeal tonsils and openings to left andright auditory tube

Pseudo-stratified columnar epithelium

The Oropharynx

Middle portion of the pharynx

Communicates with oral cavity

Stratified squamous epithelium

The Laryngopharynx

Inferior portion of the pharynx Extends from hyoid bone to entrance to larynx and

esophagus


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Cartilages of the Larynx 3 large, unpaired cartilages form the larynx:

the thyroid cartilage

the cricoid cartilage

the epiglottis

Air flow from the pharynx, enters the larynx:

a cartilaginous structure that surrounds theglottis


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ANATOMY OF LARYNX


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ANATOMY OF LARYNX


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The Thyroid Cartilage

Also called the Adams apple

Is a hyaline cartilage

Forms anterior and lateral walls of larynx

Ligaments attach to hyoid bone, epiglottis, and

laryngeal cartilages


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The Cricoid Cartilage Is a hyaline cartilage

Form posterior portion of larynx

Ligaments attach to first tracheal cartilage

Articulates with arytenoid cartilages

The Epiglottis Composed of elastic cartilage

Ligaments attach to thyroid cartilage and hyoid bone


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Cartilage Functions

Thyroid and cricoid cartilages support and protect:

the glottis

the entrance to trachea

During swallowing:

the larynx is elevated

the epiglottis folds back over glottis

Prevents entry of food and liquids into respiratorytract


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3pairs of Small Hyaline Cartilages of the

Larynx

arytenoid cartilages, corniculate (Santorini)

cartilages and Cuneiform (Wrisberg) cartilages

Corniculate and arytenoid cartilages function

in:

opening and closing of glottis

production of sound

Cartilage Functions


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The Glottis


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Ligaments of the Larynx

Vestibular ligaments and vocal ligaments: extend between thyroid cartilage and arytenoid cartilages

are covered by folds of laryngeal epithelium that project into

glottis

1) The Vestibular Ligaments

Lie within vestibular folds:

which protect delicate vocal folds


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Speech

Speech intermittent release of expired air while

opening and closing the glottis

Pitch determined by the length and tension of thevocal cords

Loudness depends upon the force at which the airrushes across the vocal cords

The pharynx resonates, amplifies, and enhancessound quality

Sound is shaped into language by action of thepharynx, tongue, soft palate, and lips


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The Laryngeal Musculature

Laryngeal muscle can be

Extrinsic muscles that

Elevates or depresses the hyoid bone

Intrinsic muscles that:

control vocal folds

open and close glottis

Coughing reflex: food or liquids went down the

wrong pipe


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Nerve supply of Larynx

Mucous membrane above vocal fold internal

laryngeal branch of superior laryngeal branch of

vagus nerve

Below that its supplied by recurrent laryngealnerve (RLN)

All intrinsic muscle, except cricothyroid RLN,

cricothyroid by external laryngeal branch of SLN

l l


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Laryngeal paralysisRLN

SLN

COMBINED

UNILATERAL BILATERAL

Cords remain in median or para-medianposition Cords remain in median or para-medianposition

Asymptomatic Dyspnoea and stridor, voice good


Ipsilateral cricothyroid muscle and anaesthesia

of larynx above the vocal cord

Both cricothyroid muscle paralysis and

anaesthesia of upper larynx

Asymptomatic Aspiration of food and weak voice


Cord remains in cadaveric position, 3.5 mm

from midline and unilateral paralysis of all

muscle except interarytenoid

All laryngeal muscle paralysed, both vocal cord

lie in cadaveric position and total anaesthesia

of larynx

Hoarsness of voice, aspiration and ineffective

cough

Aphonia, aspiration, inability to cough,

bronchopneumonia


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Sphincter Functions of the Larynx

The larynx is closed during coughing, sneezing, andValsalvas maneuver

Valsalvas maneuver

Air is temporarily held in the lower respiratory tract byclosing the glottis

Causes intra-abdominal pressure to rise when abdominalmuscles contract

Helps to empty the rectum

Acts as a splint to stabilize the trunk when lifting heavyloads


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Organization of the

Respiratory System

The respiratory system is divided into the upper

respiratory system, above the larynx, and the lower

respiratory system, from the larynx down


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The Respiratory Tract

Consists of a conducting portion:

from nasal cavity to terminal bronchioles

Transitional portion

the respiratory bronchioles and alveolar ducts Respiratory portion:

the alveoli and alveolar sac

Alveoli Are air-filled pockets within the lungs

where all gas exchange takes place


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The Trachea

Extends from the cricoid cartilage into mediastinum Formed of rings of cartilages, incomplete posteriorly

Lined by ciliated columnar epithelium

It bifurcates into right and left main bronchi at the level of

T5


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The Tracheal Cartilages

1520 tracheal cartilages:

strengthen and protect airway

discontinuous where trachea contacts esophagus

Ends of each tracheal cartilage are connected by:

an elastic ligament and trachealis muscle


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The Primary Bronchi

Right and left primary bronchi:

separated by an internal ridge (the carina)

The Right Primary Bronchus

Is larger in diameter and shorter (2.5 cm) than theleft

Descends at a steeper angle (25)

The Left Primary Bronchus

Is narrower and longer (5cm)

Descends at broader angle (55)


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Bronchi subdivide into secondary bronchi, eachsupplying a lobe of the lungs

Air passages undergo 23 orders of branching in thelungs

Tissue walls of bronchi mimic that of the trachea

As conducting tubes become smaller, structuralchanges occur

Cartilage support structures change

Epithelium types change Amount of smooth muscle increases


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Secondary Bronchi

Branch to form tertiary bronchi, also called the

segmental bronchi

Each segmental bronchus:

Supplies air to a single bronchopulmonary segment

The right lung has 10

The left lung has 8 or 9

Division of primary bronchus


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Right primary bronchus: Left primary bronchus

a) Upper lobe: Apical bronchus

Posterior

bronchus

Anterior bronchus

b) Middle lobe:

Lateral bronchus Medial bronchus

c) Lower lobe :

Apical bronchus

Medial basal

bronchus

Anterior basalbronchus

Posterior basal

bronchus

Lateral basal

bronchus

a) Upper lobe: Apical bronchus

Posterior

bronchus

Anterior bronchus

b) Lingula:

Superior bronchus Inferior bronchus

c) Lower lobe:

Apical bronchus

Anterior basal

bronchus

Posterior basalbronchus

Lateral basal

bronchus

Division of primary bronchus


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Bronchial Structure

The walls of primary, secondary, and tertiary bronchi:

contain progressively less cartilage and more smooth

muscle

increasing muscular effects on airway constriction andresistance


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The Bronchioles

Each tertiary bronchus branches into multiple

bronchioles

1 tertiary bronchus forms about 6500

terminal bronchioles

Bronchioles branch into terminal bronchioles


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Bronchiole Structure

Bronchioles:

have no cartilage

are dominated by smooth muscle

Autonomic Control

Regulates smooth muscle:

controls diameter of bronchioles

controls airflow and resistance in lungs


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Bronchodilation

Dilatation of bronchial airways Caused by sympathetic ANS activation

Reduces resistance

Bronchoconstriction Constricts bronchi

Caused by: parasympathetic ANS activation

histamine release (allergic reactions)


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Pulmonary Lobules

Are the smallest compartments of the lung

Are divided by the smallest trabecular partitions

(interlobular septa)

Each terminal bronchiole delivers air to a single

pulmonary lobule

Each pulmonary lobule is supplied by pulmonary

arteries and veins


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Exchange Surfaces

Within the lobule:

each terminal bronchiole branches to form several

respiratory bronchioles, where gas exchange takes place


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Alveolar Organization

Respiratory bronchioles are connected to

alveoli along alveolar ducts

Alveolar ducts end at alveolar sacs:

common chamber connected to many

individual alveoli


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An Alveolus

Has an extensive network of capillaries Is surrounded by elastic fibers

Alveolar Epithelium

Consists of simple squamous epithelium Consists of thin, delicate Type I cells

Patrolled by alveolar macrophages, also called dustcells

Contains septal cells (Type II cells) that produceSurfactant- an oily secretion which Contains phospholipids and proteins

Coats alveolar surfaces and reduces surface tension


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Respiratory Membrane - The thin membrane of

alveoli where gas exchange takes place

3 Parts of the Respiratory Membrane

Squamous epithelial lining of alveolus

Endothelial cells lining an adjacent capillary

Fused basal laminae between alveolar andendothelial cells

Diffusion- Across respiratory membrane is very rapid:

because distance is small

gases (O2 and CO2) are lipid soluble

Bl d S l t


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Blood Supply to

Respiratory Surfaces

Each lobule receives an arteriole and a venule

1. respiratory exchange surfaces receive blood:

from arteries of pulmonary circuit

2. a capillary network surrounds each alveolus:

as part of the respiratory membrane

3. blood from alveolar capillaries:

passes through pulmonary venules and veins

returns to left atrium


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Gross Anatomy of the Lungs

Left and right lungs:

are in left and right pleural cavities

The base:

inferior portion of each lung rests on superior

surface of diaphragm


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The Root of the Lung

Site of attachment of bronchus, nerves, and vessels

in hilus:

anchored to the mediastinum


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Lung Shape

Right lung:

is wider

is displaced upward by liver

Left lung:

is longer

is displaced leftward by the heart forming the cardiac

notch

Pleural Cavities and


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Pleural Cavities and

Pleural Membranes

2 pleural cavities: are separated by the mediastinum

Each pleural cavity:

holds a lung

is lined with a serous membrane (the pleura)

Pleura consist of 2 layers:

parietal pleura

visceral pleura

Pleural fluid:

lubricates space between 2 layers


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Blood supply to lungs

Lungs are perfused by two circulations: pulmonary

and bronchial

Pulmonary arteries supply systemic venous blood

to be oxygenated Branch profusely, along with bronchi

Ultimately feed into the pulmonary capillary network

surrounding the alveoli

Pulmonary veins carry oxygenated blood fromrespiratory zones to the heart


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Blood supply to lungs

Bronchial arteries provide systemic blood to the

lung tissue

Arise from aorta and enter the lungs at the hilus

Supply all lung tissue except the alveoli

Bronchial veins anastomose with pulmonary veins

Pulmonary veins carry most venous blood back to

the heart


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Pulmonary Circulation

Thin walled vessels at all levels.

Pulmonary arteries have far less smooth muscle inthe wall than systemic arteries.

Consequences of this anatomy- the vessels are:

Distensible.

Compressible. Low intravascular pressure.

Influences on Pulmonary Vascular


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Influences on Pulmonary Vascular

Resistance

Vessel diameter influenced by extra vascular forces:

Gravity

Body position

Lung volume Alveolar pressures/intrapleural pressures

Intravascular pressures

Control of pulmonary vascular resistance


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Control of pulmonary vascular resistance

Passive influence on PVR

Influence Effect on PVR mechanisim

Lung Volume(above FRC) Increase Lengthening andCompression

Lung Volume(below FRC) Increase Compression of Extraalveolar Vessels

Flow, Pressure Decrease Recruitment and DistensionGravity Decrease in Dependent

Regions

Recruitment and Distension

Interstitial Pressure Increase CompressionPositive Pressure

Ventilation

Increase Compression and

Derecruitment


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Gravity, Alveolar Pressure and Blood Flow

Pressure in the pulmonary arterioles depends on both mean

pulmonary artery pressure and the vertical position of the

vessel in the chest, relative to the heart.

Driving pressure (gradient) for perfusion is different in the 3

lung zones:

Flow in zone 1 may be absent because there is inadequate

pressure to overcome alveolar pressure.

Flow in zone 3 is continuous and driven by the pressure in

the pulmonary arteriole pulmonary venous pressure.

Flow in zone 2 may be pulsatile and driven by the pressure

in the pulmonary arteriole alveolar pressure (collapsing

the capillaries).


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Control of Pulmonary Vascular Resistance


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Control of Pulmonary Vascular Resistance

Active Influences on PVR:

Increase

Sympathetic innervation

- adernergic agonist

Thromboxane/PGE2

Endothelin

Angiotensin

Histamine

Alveolar hypoxemia

Decrease

Parasympathetic innervation

Acetylcholine

- adrenergic agents

PGE1

Prostacycline

Nitiric oxide

Bradykinin


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Hypoxic Pulmonary Vasoconstriction

Alveolar hypoxia causes active vasoconstriction at level of pre-capillary arteriole.

Mechanism is not completely understood:

Response occurs locally and does not require innervation.

Mediators have not been identified.

Graded response between pO2 levels of 100 down to 20mmHg.

Functions to reduce the mismatching of ventilation andperfusion.

Not a strong response due to limited muscle in pulmonaryvasculature.

General hypoxemia (high altitude or hypoventilation) cancause extensive pulmonary artery vasoconstriction.


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Regulation of breathing

Medullary rhythmicity center

Nerves extend to intercostals and diaphragm

Signals are sent automatically

Expiratory center is activated during forced breathing

Pneumotaxic area

Controls degree of lung inflation; inhibits inspiration

Apneustic area

Promotes inspiration


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Chemoreceptors

Breathing can be controlled voluntarily, up to a point

Too much CO2 and H+ will stimulate inspiratory area,

phrenic and intercostal nerves

Central chemoreceptors: medulla oblongata

monitors CSF


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Peripheral chemoreceptors

Aortic bodies (vagus nerve)

Carotid bodies (glossopharyngeal nerve)

Respond to fluctuations in blood O, CO2 and H

levels

Rapid respond

Pulmonary stretch receptors prevent over inflation oflungs (promote expiration)


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Pulmonary ventilation

Inhalation:

always active

Exhalation: active or passive


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3 Muscle Groups of Inhalation

1. Diaphragm: contraction draws air into lungs

Increases transverse diameter of thorax

75% of normal air movement

2. External intercostals muscles: assist inhalation 25% of normal air movement

3. Accessory muscles assist in elevating ribs: sternocleidomastoid

serratus anterior pectoralis minor

scalene muscles


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Muscles of Active Exhalation

1. Internal intercostal and transversus thoracis

muscles:

depress the ribs and decreases thoracic volume

2. Abdominal muscles:

compress the abdomen

force diaphragm upward

Forcefully contracts while coughing and sneezing

Inspiration


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Inspiration

Expiration


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Expiration


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Ventilation

Depends on

Lung volume

Alveolar ventilation

Anatomic and physiological deadspace

Regional difference in ventilation


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Lung volume

Total lung volume is divided into a series of volumes

and capacities useful in diagnosis in pulmonary

function tests

Measure rates and volumes of air movements


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4 Pulmonary Volumes

1. Resting tidal volume:

in a normal respiratory cycle

2. Expiratory reserve volume (ERV):

after a normal exhalation3. Residual volume:

after maximal exhalation

minimal volume (in a collapsed lung)

4. Inspiratory reserve volume (IRV):

after a normal inspiration

4 Calculated


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4 Calculated

Respiratory Capacities

1. Inspiratory capacity:

tidal volume + inspiratory reserve volume

2. Functional residual capacity (FRC):

expiratory reserve volume + residual volume

3. Vital capacity:

expiratory reserve volume + tidal volume +inspiratory reserve volume

4. Total lung capacity:vital capacity + residual volume

Closing capacity: Minimum volume at which smallerairways begin to close and causes air trapping.

Respiratory Volumes and capacities


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Alveolar Ventilation

Amount of air reaching alveoli each minute

Calculated as:

AV= RR X (TV DV) = 12 X (500-150) = 4200 ml/min

Alveoli contain less O2, more CO2 than atmospheric

air:

because air mixes with exhaled air


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Alveolar Ventilation Rate

Determined by respiratory rate and tidal volume:

for a given respiratory rate:

increasing tidal volume increases alveolar ventilation rate

for a given tidal volume:

increasing respiratory rate increases alveolar ventilation

d


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Dead space

Anatomical

Volume of conducting airway

Its about 150ml

Physiological

Volume of gas that does not eliminate CO

Volume is same as above

It is increased in many lung disease

h f b h


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Mechanics of breathing

Depends on

Pressure volume curve

Compliance

Elastic properties of chest wall

Surface tension

Resistance

l


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Pressure volume curve

The pressure volume curve varies between apex andbase of the lung. At the base the volume change is

greater for a given change in pressure.

Hence alveolar ventilation declines with height from base

to apex.

This is because at the base the lungs are slightly

compressed by the diaphragm so upon inspiration have

greater scope to expand.

Thus a small change in intrapleural pressure brings about

a relatively large change in volume


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Elastance

Ph i l d i i l f d f i


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Physical tendency to return to original state after deformation

Lung volume at any given pressure is slightly more during deflation

than it is during inflation, it is called Hysteresis (due to surface

tension)

C li


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Compliance

An indicator of expandability

V/P (200 ml/ cm HO)

Low compliance requires greater force

High compliance requires less force

Factors Governing Compliance

1. Connective-tissue structure of the lungs

2. Level of surfactant production

3. Mobility of the thoracic cage

F t Th t Di i i h L C li


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Factors That Diminish Lung Compliance

Fibrosis or scar tissue in lung

Decrease surfactant

Restricted movement of chest wall

Deformity of thorax

Ossification of costal cartilages

Paralysis of intercostal muscles

Blockage of smaller air way

El ti ti f h t ll


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Elastic properties of chest wall

Lung has a tendency to collapse inward and chestwall springs out ward

FRC is the equilibrium volume where both force

balance each other

Chest wall tends to expand at volumes up to about

75% of total vital capacity

S f t i


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Surface tension

Surfactant reduces surface tension forces by forminga monomolecular layer between aqueous fluid lining

alveoli and air, preventing a water-air interface

Produced by type II alveolar epithelial cells

Complex mix-phospholipids, proteins, ions

dipalmitoyl lecithin, surfactant apoproteins, Ca++ ions

St bili ti f Al l i


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Stabilization of Alveolar size

Role of surfactant Law of Laplace P=2T/r

Without surfactant smaller alveolar haveincreased collapse & would tend to empty into

larger alveoli Big would get bigger and small would get smaller

Surfactant automatically offsets this physicaltendency

As the alveolar size surfactant is concentratedwhich surface tension forces, off-setting the inradius

R i t


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Resistance

Airway resistance

Or

Tissue resistance

Ai i t


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Airway resistance

Friction is the major nonelastic source of resistance

to airflow

The relationship between flow (F), pressure (P), and

resistance (R) is:

F =PR


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The amount of gas flowing into and out of the alveoliis directly proportional to P, the pressure gradient

between the atmosphere and the alveoli

Gas flow is inversely proportional to resistance with

the greatest resistance being in the medium-sized

bronchi


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As airway resistance rises, breathing movementsbecome more strenuous

Severely constricted or obstructed bronchioles:

Can prevent life-sustaining ventilation

Can occur during acute asthma attacks which stops

ventilation

Epinephrine release via the sympathetic nervoussystem dilates bronchioles and reduces air resistance

Tissue resistance


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Tissue resistance

Due to tissue displacement during ventilation (lungs,thorax, diaphragm)

It is the 20% of total resistance

Mainly from lung tissue resistance and chest wallresistance

Air flow resistance is around 1 cm HO/L/sec

Increases up to 5 folds in obstructive lung disease

by obesity, fibrosis, ascites

Work of breathing


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Work of breathing

Done by respiratory muscles to over come elastic andfrictional forces opposing inflation.

W= F X S ( force X distance)

= P X V= area under P-V curve

Normal breathing

active inhalation

passive exhalation (work of exhalation recovered from

potential energy stored in expanded lungs & thorax during

inspiration)


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Area 1 = work done against elastic forces ( compliance) = 2/3

Area 2 = work done against frictional forces ( resistance work) =1/3

Area 1+2 = total work done = 2/3 + 1/3 = 1


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TV elastic component of work

RR ( flow) frictional work

People with diseased lungs assume a ventilatory

pattern optimum for minimum work of breathing.

COPD/Obstructive disease-Slow breathing with

pursed lips( frictional work)

Fibrosis/Restrictive disease-Rapid shallowbreathing(elastic work)

References


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Millers Anesthesia- Ronald D. Miller 7th edition

Respiratory physiology- John B. West, 8th edition

A Practice of Anesthesia- Wylie and Chuchill

Davidson, 5th

edition


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functional anatomy of respiratory system and mechanics of breathing

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