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: anaesthesia.co.in@gmail.com
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
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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
UNILATERAL BILATERAL
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
UNILATERAL BILATERAL
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
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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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www.anaesthesia.co.in
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