Functional anatomy of pulmonary system, pulmonary circulation and mechanics of breathing

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Functional anatomy of pulmonary system, pulmonary
circulation and mechanics of breathing

• Presenter Dr. Satyajit Majhi
• Moderator Dr. J.P. Sharma

University College of Medical Sciences GTB
Hospital, Delhi
Email anaesthesia.co.in_at_gmail.com
www.anaesthesia.co.in
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5 Functions of the Respiratory System

1. Provides extensive gas exchange surface area
   between air and circulating blood
2. Moves air to and from exchange surfaces of lungs
3. 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
  of sphenopalatine and greater palatine.
• Woodruff area, anastomosis of sphenopalatine
  artery and posterior pharyngeal artery causes
  posterior 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
  and right 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
Air flow from the pharynx, enters the larynx a
cartilaginous structure that surrounds the glottis

• 3 large, unpaired cartilages form the larynx
• the thyroid cartilage
• the cricoid cartilage
• the epiglottis

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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
  respiratory tract

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Cartilage Functions
3 pairs 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

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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
  the vocal cords
• Loudness depends upon the force at which the
  air rushes across the vocal cords
• The pharynx resonates, amplifies, and enhances
  sound quality
• Sound is shaped into language by action of the
  pharynx, 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 laryngeal
  nerve (RLN)
• All intrinsic muscle, except cricothyroid RLN,
  cricothyroid by external laryngeal branch of SLN

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Laryngeal paralysis

• RLN
• SLN
• COMBINED

UNILATERAL BILATERAL
Cords remain in median or para-median position Cords remain in median or para-median position
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,
  and Valsalvas maneuver
• Valsalvas maneuver
• Air is temporarily held in the lower respiratory
  tract by closing the glottis
• Causes intra-abdominal pressure to rise when
  abdominal muscles contract
• Helps to empty the rectum
• Acts as a splint to stabilize the trunk when
  lifting heavy loads

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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
  the left
• 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, each
  supplying a lobe of the lungs
• Air passages undergo 23 orders of branching in
  the lungs
• Tissue walls of bronchi mimic that of the trachea
• As conducting tubes become smaller, structural
  changes 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

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Division of primary bronchus
Right primary bronchus Left primary bronchus
Upper lobe Apical bronchus Posterior bronchus Anterior bronchus Middle lobe Lateral bronchus Medial bronchus Lower lobe Apical bronchus Medial basal bronchus Anterior basal bronchus Posterior basal bronchus Lateral basal bronchus Upper lobe Apical bronchus Posterior bronchus Anterior bronchus Lingula Superior bronchus Inferior bronchus Lower lobe Apical bronchus Anterior basal bronchus Posterior basal bronchus Lateral basal 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 and resistance

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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
  dust cells
• Contains septal cells (Type II cells) that
  produce Surfactant- 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 and
  endothelial cells
• Diffusion- Across respiratory membrane is very
  rapid
• because distance is small
• gases (O2 and CO2) are lipid soluble

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Blood Supply to Respiratory Surfaces

• Each lobule receives an arteriole and a venule
• respiratory exchange surfaces receive blood
• from arteries of pulmonary circuit
• a capillary network surrounds each alveolus
• as part of the respiratory membrane
• 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

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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 from
  respiratory 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 in
  the wall than systemic arteries.
• Consequences of this anatomy- the vessels are
• Distensible.
• Compressible.
• Low intravascular pressure.

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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

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Control of pulmonary vascular resistance
Passive influence on PVR
Influence Effect on PVR mechanisim
? Lung Volume (above FRC) Increase Lengthening and Compression
? Lung Volume (below FRC) Increase Compression of Extra alveolar Vessels
? Flow, ?Pressure Decrease Recruitment and Distension
Gravity Decrease in Dependent Regions Recruitment and Distension
? Interstitial Pressure Increase Compression
Positive 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

• Active Influences on PVR

Increase
Sympathetic innervation
a- adernergic agonist
Thromboxane/PGE2
Endothelin
Angiotensin
Histamine
Alveolar hypoxemia
Decrease
Parasympathetic innervation
Acetylcholine
ß- 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
  20 mmHg.
• Functions to reduce the mismatching of
  ventilation and perfusion.
• Not a strong response due to limited muscle in
  pulmonary vasculature.
• General hypoxemia (high altitude or
  hypoventilation) can cause 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 O2, CO2 and H?
  levels
• Rapid respond
• Pulmonary stretch receptors prevent over
  inflation of lungs (promote expiration)

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Pulmonary ventilation

• Inhalation
• always active
• Exhalation
• active or passive

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3 Muscle Groups of Inhalation

• Diaphragm
• contraction draws air into lungs
• Increases transverse diameter of thorax
• 75 of normal air movement
• External intercostals muscles
• assist inhalation
• 25 of normal air movement
• Accessory muscles assist in elevating ribs
• sternocleidomastoid
• serratus anterior
• pectoralis minor
• scalene muscles

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Muscles of Active Exhalation

• Internal intercostal and transversus thoracis
  muscles
• depress the ribs and decreases thoracic volume
• Abdominal muscles
• compress the abdomen
• force diaphragm upward
• Forcefully contracts while coughing and sneezing

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Inspiration
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Expiration
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Ventilation

• Depends on
• Lung volume
• Alveolar ventilation
• Anatomic and physiological dead space
• 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

• Resting tidal volume
• in a normal respiratory cycle
• Expiratory reserve volume (ERV)
• after a normal exhalation
• Residual volume
• after maximal exhalation
• minimal volume (in a collapsed lung)
• Inspiratory reserve volume (IRV)
• after a normal inspiration

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4 Calculated Respiratory Capacities

• Inspiratory capacity
• tidal volume inspiratory reserve volume
• Functional residual capacity (FRC)
• expiratory reserve volume residual volume
• Vital capacity
• expiratory reserve volume tidal volume
  inspiratory reserve volume
• Total lung capacity vital capacity
  residual volume
• Closing capacity Minimum volume at which
  smaller airways begin to close and causes air
  trapping.

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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

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Dead space

• Anatomical
• Volume of conducting airway
• Its about 150ml
• Physiological
• Volume of gas that does not eliminate CO2
• Volume is same as above
• It is increased in many lung disease

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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 and
  base 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 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)
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Compliance

• An indicator of expandability
• ?V/?P (200 ml/ cm H2O)
• Low compliance requires greater force
• High compliance requires less force
• Factors Governing Compliance
• Connective-tissue structure of the lungs
• Level of surfactant production
• Mobility of the thoracic cage

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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

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Elastic properties of chest wall

• Lung has a tendency to collapse inward and chest
  wall 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

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Surface tension

• Surfactant reduces surface tension forces by
  forming a 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

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Stabilization of Alveolar size

• Role of surfactant
• Law of Laplace P2T/r
• Without surfactant smaller alveolar have
  increased collapse would tend to empty into
  larger alveoli
• Big would get bigger and small would get smaller
• Surfactant automatically offsets this physical
  tendency
• As the alveolar size ? surfactant is concentrated
  which ? surface tension forces, off-setting the ?
  in radius

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Resistance

• Airway resistance
• Or
• Tissue resistance

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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

?P
F
R
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• The amount of gas flowing into and out of the
  alveoli is 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 movements
  become 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 nervous
  system dilates bronchioles and reduces air
  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 wall
  resistance
• Air flow resistance is around 1 cm H2O/L/sec
• Increases up to 5 folds in obstructive lung
  disease
• ? by obesity, fibrosis, ascites

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Work of breathing

• Done by respiratory muscles to over come elastic
  and frictional 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
12 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 shallow
  breathing(?elastic work)

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References

• 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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