Respiratory System
by
Prof. Dr. Uzma Zargham
Physiology Department
LM&DC
Respiratory System
by
Prof. Dr. Uzma Zargham
Physiology Department
LM&DC
OBJECTIVES
• To understand and explain
1. Physiologic anatomy of respiratory tract
2. Ventilation process
3. Compliance
The four major components of
respiration are
–
PULMONARY VENTILATION, which means the
inflow and outflow of air between the atmosphere and the
lung alveoli;
–
DIFFUSION OF oxygen and carbon dioxide between the
alveoli and the blood;
–
TRANSPORT OF oxygen and carbon dioxide in the
blood and body fluids to and from the body's tissue cells;
and
–
REGULATION of ventilation
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The respiratory system is divided into upper and
lower respiratory tracts
Conducting portion, which consists of the nasal
cavities, nasopharynx, larynx, trachea, bronchi
bronchioles, and terminal bronchioles;
Respiratory portion (where gas exchange takes
place), consisting of respiratory bronchioles,
alveolar ducts, and alveoli.
Alveoli are saclike structures. They are the main
sites for the principal function of the lungs—the
exchange of O2 and CO2 between inspired air and
blood.
MECHANICS OF VENTILATION
Ventilatory apparatus consists of
•Lungs
•Pump that ventilates them
Pump mechanism is provided by chest wall and
respiratory muscles
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Ventilation – movement of air into and out of
lungs
Done through change in size & volume of
thoracic cavity & lungs follow those
During inspiration thoracic cavity expand –
sub-atmospheric pressure produced in lungs,
Intra-pleural pressure more negative
During expiration thoracic cavity shortens –
Alveolar pressure increases, intra-pleural
pressure less negative
Muscles of inspiration
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Diaphragm
External intercostal
Others
Scalenae
Sternocleidomastoid
Serratus anterior
Muscles of Expiration
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Quiet expiration – a passive process
Inspiratory muscles relax
Thoracic cavity ↓, Alveolar pressure ↑
Pleural pressure less negative
During forceful expiration, internal intercostal
muscle and abdominal muscles
Diaphragm relax – into thoracic cavity pushing
lungs upward
A healthy, 45-year-old man is reading the newspaper. Which of
the following muscles are used for quiet breathing?
•A) Diaphragm and external intercostals
•B) Diaphragm and internal intercostals
•C) Diaphragm only
•D) Internal intercostals and abdominal recti
•E) Scaleni
•F) Sternocleidomastoid muscles
A healthy, 25-year-old medical student participates in a 10-km
charity run for the American Heart Association. Which of the
following muscles does the student use (contract) during
expiration?
•A) Diaphragm and external intercostals
•B) Diaphragm and internal intercostals
•C) Diaphragm only
•D) Internal intercostals and abdominal recti
•E) Scaleni
•F) Sternocleidomastoid muscles
AIRWAY PRESSURES
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Alveolar-pressure
Intra-pleural pressure
Trans-pulmonary pressure
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Tidal volume
Compliance of the Lungs
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The extent to which the lungs will expand for each
unit change in trans-pulmonary pressure is called
the lung compliance.
Change in lung volume for a unit change in
intrapleural pressure.
The total compliance of both lungs together in the
normal adult human being averages about 200
milliliters of air per centimeter of water.
That is, every time the intra-pleural pressure
changes1 centimeter of water, the lung volume,
will expand 200 milliliters.
Compliance diagram of lungs
Hysteresis
Determinants of compliance
•
1) Elastic forces of lungs and chest wall
Greater is elasticity lesser is compliance
• 2) Surface tension forces in alveoli
Greater is surface tension lesser is compliance
Compliance is reverse of elastic
recoil
Elastic forces of lungs
are determined by collagen and elastic content of the lungs
Responsible for 1/3of total elastic forces
Elastic forces of surface tension
Air fluid interface at alveolar surface
Responsible for 2/3 of elastic forces
• Loss of elastic recoil is seen in patients with
emphysema and is associated with an increase
in lung compliance (Plastic bag)
• Diseases associated with pulmonary fibrosis,
lung compliance is decreased(Stiff lungs)
Surfactant
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Nature—dipalmitoyl phosphatidylcholine +
Calcium
Source--- type ii pneumocytes
Function
Reduces surface tension(pure water; 72
dynes/cm, fluid in alveoli without surfactant;
50 dynes/cm, with surfactant; 5-30 dynes/cm)
immune response through SP-A and SP-D
Keeps alveoli dry
Respiratory distress syndrome of newborn
A deficiency of surfactant develops in newborns
Risk factors
•Premature birth
• Maternal diabetes
Respiratory distress syndrome of newborn
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Lack of surfactant
Small sized alveoli
Law of Laplace
P = 2X Surface tension/Radius
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The lecithin–sphingomyelin ratio is a marker of fetal
lung maturity.
An L–S ratio of 2 or more indicates fetal lung
maturity and a relatively low risk of infant respiratory
distress syndrome, and L/S ratio of less than 1.5 is
associated with a high risk of infant respiratory
distress syndrome. (after 32 weeks)
• Compliance of lungs= 200 ml/cm of water
• Compliance of lung and chest wall = 110
ml/cm of water
A man inspires 1000 ml from a spirometer. The intra-pleural
pressure was −4 cm H2O before inspiration and −12 cm H2O the
end of inspiration. What is the compliance of the lungs?
•A) 50 ml/cm H2O
•B) 100 ml/cm H2O
•C) 125 ml/cm H2O
•D) 150 ml/cm H2O
•E) 250 ml/cm H2O
Work of breathing
It is the energy expended during inhalation and
exhalation
In quiet breathing energy is required during
inspiration only.
•Compliance work –65%
•Tissue viscosity/resistance work
•Air way resistance work (Increase in COPD)
Inspiratory work in quiet breathing (3 to 5% of total O2
consumption)
energy expenditure can rise by 50 fold in strenuous exercise
Lung volumes and capacities
Lung volumes
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The tidal volume is the volume of air inspired or expired with
each normal breath; 500 ml
The inspiratory reserve volume is the extra volume of air
that can be inspired over and above the normal tidal volume
when the person inspires with full force; 3000 ml.
The expiratory reserve volume is the maximum extra volume
of air that can be expired by forceful expiration after the end of
a normal tidal expiration; 1100 ml.
The residual volume is the volume of air remaining in the
lungs after the most forceful expiration; this volume averages
about 1200 milliliters
Lung capacities
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The inspiratory capacity equals the tidal volume plus the inspiratory
reserve volume. (about 3500 milliliters)
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The functional residual capacity equals the expiratory reserve volume
plus the residual volume. This is the amount of air that remains in the lungs
at the end of normal expiration (about 2300 milliliters)
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The vital capacity equals the inspiratory reserve volume plus the tidal
volume plus the expiratory reserve volume. This is the maximum amount
of air a person can expel from the lungs after first filling the lungs to their
maximum extent and then expiring to the maximum extent (about 4600
milliliters)
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The total lung capacity is the maximum volume to which the lungs can be
expanded with the greatest possible effort (about 5800 milliliters); it is
equal to the vital capacity plus the residual volume.
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VC = IRV + VT + ERV
VC = IC + ERV
TLC = VC + RV
TLC = IC + FRC
FRC = ERV + RV
Spirometry
• Pulmonary ventilation can be studied by
recording the volume of air moving into and
out of the lungs, a method called spirometry.
• Volume of air and speed of movement can be
studied.
Spirometer
How to measure Functional Residual Capacity
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To measure functional residual capacity, the
spirometer must be used in an indirect manner,
by means of a helium dilution method.
A spirometer of known volume is filled with
air mixed with helium at a known
concentration.
Before breathing from the spirometer, the
person expires normally
• At this point, the subject immediately begins to
breathe from the spirometer.
• Helium is diluted by functional residual
capacity
• By extent of helium dilution FRC can be
measured
How to measure Functional Residual Capacity
By--Helium
dilution
• FRC = Hei
1 X Spiro
initialmethod
vol.
Hef
• RV = FRC – ERV
• TLC = FRC + IRV
•
A patient has a dead space of 150 ml, functional residual
capacity of 3 L, tidal volume of 650 ml, expiratory reserve
volume of 1.5 L, total lung capacity of 8 L, and respiratory
rate of 15 breaths/min.
What is the residual volume?
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A) 500 ml
B) 1000 ml
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C) 1500 ml
D) 2500 ml
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E) 6500 ml
The minute respiratory volume
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The minute respiratory volume is the total amount of
new air moved into the respiratory passages each
minute; this is equal to the tidal volume times the
respiratory rate per minute.
•
The normal tidal volume is about 500 milliliters, and
the normal respiratory rate is about 12 breaths per
minute. Therefore, the minute respiratory volume
averages about 6 L/min.
Dead Space" and Its Effect on Alveolar
Ventilation
• Some of the air a person breathes never reaches
the gas exchange areas but simply fills
respiratory passages where gas exchange does
not occur, such as the nose, pharynx, and
trachea.
• This air is called dead space air because it is
not useful for gas exchange.
• It is 150 ml
How to measure dead space
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Measurement of anatomical dead space by
nitrogen washout method
Breathing in pure oxygen and breathing out in
N2 meter
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VD = Gray area x VE (Expired Vol. of gas) /
Pink area + Gray area
Areas measured in cm-sq, so 30/30+70 x 500
= 150ml
Physiological Dead Space
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In addition to anatomical dead space.
Included those alveoli which are not functional.
Anat. D.S + Alv. D.S
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The air going to physiological dead space called
wasted ventilation
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Physiological dead space bigger than anat. Dead
space
Alveolar ventilation
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Alveolar ventilation per minute is the total volume of new air
entering the respiratory zone each minute.
It is equal to the respiratory rate times the amount of new air
that enters these areas with each breath.
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VT is the tidal volume, and VD is the physiologic dead space
volume.
Thus, with a normal tidal volume of 500 milliliters, a normal
dead space of 150 milliliters, and a respiratory rate of 12
breaths per minute,
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alveolar ventilation equals 12 × (500 - 150), or 4200 ml/min.
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A patient has a dead space of 150 ml, functional
residual capacity of 3 L, tidal volume of 650 ml,
expiratory reserve volume of 1.5 L, a total lung
capacity of 8 L, respiratory rate of 15 breaths/min.
What is the alveolar ventilation?
A) 5 L/min
B) 7.5 L/min
C) 6.0 L/min
D) 9.0 L/min
Non Respiratory movement of air
into Resp. Tract
Cough
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Protective reflex
Larynx, trachea and bronchi – very sensitive to foreign
matter
Irritant receptors – responsive to mechanical, chemical
irritants
Afferent impulses – vagus to cough center in medulla
2.5 L inspired & glottis closed vocal cords shut tightly
Abdominal muscle & other expiratory muscles contract
Alveolar pressure ↑ to + 100mmHg
Air exploded out and posterior nares closed
Velocity – 70 – 100 miles/hours
Sneezing
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Like cough reflex
Irritation in nose, mechanical or chemical
Afferent impulses through trigeminal nerve to
sneezing center in medulla
Uvula is depressed, so expelled air through
nose & Month
Hiccup
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Characterized by short inspiration because of
brief sudden contraction of diaphragm
Glottis closed – characteristic sensation and
sound
Because of stimulation of nerve ending in GIT
and abdominal cavity
Phrenic nerve irritation
Yawning
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Caused by the under-ventilation of alveoli →↓
PO2
Induces deep inspiration
Characterized by wide – opened month
Prevent collapse of alveoli by increasing
ventilation
Also ↑ venous return
Functions of respiratory passages
Functions of dead space
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Warm and humidify air---- air conditioning
Trap particles up to 6 micrometers in nose
1-5 micrometers till terminal bronchiole
Less than 1 micrometer in alveoli
Cilia in respiratory tract till terminal
bronchioles---cough out secretions
• Protective peptides
• IgA Ab
Effect of nervous system and other
mediators on airway resistance
• Airway resistance is offered by small bronchi
and large to medium sized bronchioles
• Effect of sympathetic N.S (broncho-dilation)
• Effect of parasympathetic system (bronchoconstriction)
• Effect of histamine & SRA
Function of Respiratory System
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Resp. Functions – ventilation & Exchange of
gases
Functions other than respiration
Functions other than respiration
1.Synthetic function – synthesis of surfactant, heparin,
histamine, serotonin, prostaglandins
2.Angiotensin I to angiotensin II by Angiotensin
converting enzyme (ACE)
3.Filters small blood clots
4.Regulation of body temperature
5.Regulation of acid-base balance
6. Reservoir of blood
7. Route of drug administration
8.
Producing of voice – phonation
Vocalization
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Speech has central and peripheral components
It involves
• CNS,
• Respiratory tract,
• Articulation and resonance apparatus in mouth and
nasal cavities
Speech has two mechanical components
Phonation
articulation
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Peripheral Speech components involve
(1) phonation, which is achieved by the larynx,
and
(2) articulation, which is achieved by the
structures of the mouth.
(3) resonance by nasal cavities, para-nasal
sinuses and chest cage