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RESPIRATORY SYSTEM
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The cells of the body need energy for all their metabolic activities.
Most of this energy is derived from chemical reactions, which can only take place
in the presence of oxygen (02), The main waste product of these reactions is
carbon dioxide (C02).
The respiratory system provides the route by which the supply of oxygen present
in the atmospheric air enters the body, and it provides the route of excretion for
carbon dioxide.
The condition of the atmospheric air entering the body varies considerably
according to the external environment, e.g. it may be dry, cold and contain dust
particles or it may be moist and hot. As the air breathed in moves through the air
passages to reach the lungs, it is warmed or cooled to body temperature,
moistened to become saturated with water vapour and' cleaned' as particles of
dust stick to the mucus which coats the lining membrane.
Blood provides the transport system for these gases between the lungs and the
cells of the body. Exchange of gases between the blood and the lungs is called
external respiration and that between the blood and the cells internal
respiration..
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ORGANS
• The organs of the respiratory
system are:
• nose
• pharynx
• larynx
• trachea
• two bronchi (one bronchus to
each lung)
• bronchioles and smaller air
passages
• two lungs and their coverings, the
pleura
• muscles of breathing - the
intercostal muscles and the
diaphragm.
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RESPIRATION
• The term respiration means the exchange of gases
between body cells and the environment.
This involves two main processes:
• Breathing (pulmonary ventilation).
This is movement of air into and out of the lungs.
Breathing supplies oxygen to the alveoli, and eliminates
carbon dioxide.
• Exchange of gases.
This takes place:
• in the lungs: external respiration
• in the tissues: internal respiration.
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MUSCLES OF BREATHING
• Expansion of the chest during inspiration
occurs as a result of muscular activity, partly
voluntary and partly involuntary.
• The main muscles used in normal quiet
breathing are the intercostal muscles and the
diaphragm
• During difficult or deep breathing they are
assisted by muscles of the neck, shoulders and
abdomen.
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INTERCOSTAL MUSCLES
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There are 11 pairs of intercostal muscles that occupy
the spaces between the 12 pairs of ribs. They are
arranged in twO layers, the external and internal
intercostal muscles.
The external intercostal muscle fibres. These extend
downwards and forwards from the lower border of the
rib above to the upper border of the rib below.
The internal intercostal muscle fibres. These extend
downwards and backwards from the lower border of
the rib above to the upper border of the rib below,
crossing the external intercostal muscle fibres at right
angles.
The first rib is fixed. Therefore, when the intercostal
muscles contract they pull all the other ribs towards
the first rib. Because of the shape and sizes of the ribs
they move outwards when pulled upwards, enlarging
the thoracic cavity. The intercostal muscles are
stimulated to contract by the intercostal nerves.
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DIAPHRAGM
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The diaphragm is a dome-shaped muscular
structure separating the thoracic and
abdominal cavities
It forms the floor of the thoracic cavity and
the roof of the abdominal cavity and consists
of a central tendon from which muscle fibres
radiate to be attached to the lower ribs and
sternum and to the vertebral column by two
crura.
When the muscle of the diaphragm is
relaxed, the central tendon is at the level of
the 8th thoracic vertebra .
When it contracts, its muscle fibres shorten
and the central tendon is pulled downwards
to the level of the 9th thoracic vertebra,
enlarging the thoracic cavity in length. This
decreases pressure in the thoracic cavity and
increases it in the abdominal and pelvic
cavities. The diaphragm is supplied by the
phrenic nerves.
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THORASIC CAVITY ENLARGED
• The intercostal muscles and the diaphragm contract
simultaneously, enlarging the thoracic cavity in all directions,
that is from back to front, side to side and top to bottom
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PLEURA AND PLEURAL CAVITY
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ALVEOLI
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PLEURA AND PLEURAL CAVITY
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The pleura consists of a closed sac of serous membrane (one for each lung) which
contains a small amount of serous fluid. The lung is invaginated (pushed into) into
this sac so that it forms two layers: one adheres to the lung and the other to the wall
of the thoracic cavity
The visceral pleura. This is adherent to the lung, covering each lobe and passing into
the fissures that separate them.
The parietal pleura.. This is adherent to the inside of the chest wall and the thoracic
surface of the diaphragm. It remains detached from the adjacent structures in the
mediastinum and is continuous with the visceral pleura round the edges of the hilum
The pleural cavity. This is only a potential space. In health, the two layers of pleura
are separated by a thin film of serous fluid which allows them to glide over each
other, preventing friction between them during breathing. The serous fluid is
secreted by the epithelial cells of the membrane.
The two layers of pleura, with serous fluid between them, behave in the same way as
two pieces of glass separated by a thin film of water. They glide over each other
easily but can be pulled apart only with difficulty, because of the surface tension
between the membranes and the fluid. If either layer of pleura is punctured, the
underlying lung collapses owing to its inherent property of elastic recoil.
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CYCLE OF BREATHING
• The average respiratory rate is 12 to 15
breaths per minute.
Each breath consists of three phases:
• inspiration
• expiration
• pause.
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INSPIRATION
• When the capacity of the thoracic cavity is increased by
simultaneous contraction of the intercostal muscles and the
diaphragm, the parietal pleura moves with the walls of the thorax
and the diaphragm.
• This reduces the pressure in the pleural cavity to a level
considerably lower than atmospheric pressure. The visceral pleura
follows the parietal pleura, pulling the lung with it. This expands the
lungs and the pressure within the alveoli and in the air passages
falls, drawing air into the lungs in an attempt to equalise the
atmospheric and alveolar air pressures.
• The process of inspiration is active, as it needs energy for muscle
contraction. The negative pressure created in the thoracic cavity
aids venous return to the heart and is known as the respiratory
pump.
• At rest, inspiration lasts about 2 seconds.
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EXPIRATION
• Relaxation of the intercostal muscles and the
diaphragm results in downward and inward movement
of the rib cage and elastic recoil of the lungs.
• As this occurs, pressure inside the lungs exceeds that
in the atmosphere and so air is expelled from the
respiratory tract.
• The lungs still contain some air, and are prevented
from complete collapse by the intact pleura. This
process is passive as it does not require the
expenditure of energy.
• At rest, expiration lasts about 3 seconds, and after
expiration there is a pause before the next cycle begins
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PRESSURE-VOLUME-FLOW
DIAGRAMS
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PHYSIOLOGICAL VARIABLES AFFECTING
BREATHING
• Elasticity. Elasticity is the term used to describe the ability of the
lung to return to its normal shape after each breath. Loss of
elasticity of the connective tissue in the lungs necessitates forced
expiration and increased effort on inspiration.
• Compliance. This is a measure of the distensibility of the lungs, i.e.
the effort required to inflate the alveoli. The healthy lung is very
compliant, and inflates with very little effort. When compliance is
low the effort needed to inflate the lungs is greater than normal,
e.g. in some diseases where elasticity is reduced or when
insufficient surfactant is present. It should be noted that
compliance and elasticity are opposing forces.
• Airway resistance. When this is increased, e.g. in
bronchoconstriction, more respiratory effort is required to inflate
the lungs.
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LUNG VOLUME AND CAPACITIES
• In normal quiet breathing there are about 15
complete respiratory cycles per minute.
• The lungs and the air passages are never
empty and, as the exchange of gases takes
place only across the walls of the alveolar
ducts and alveoli, the remaining capacity of
the respiratory passages is called the
anatomical dead space (about 150 ml).
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LUNG VOLUME AND CAPACITIES
• Tidal volume (TV). This is the
amount of air passing into and out
of the lungs during each cycle of
breathing (about 500 ml at rest).
• Inspiratory reserve volume (lRV).
This is the extra volume of air that
can be inhaled into the lungs during
maximal inspiration, i.e. over and
above normal TV.
• Inspiratory capacity (IC). This is the
amount of air that can be inspired
with maximum effort. It consists of
the tidal volume (500 ml) plus the
inspiratory reserve volume
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LUNG VOLUME AND CAPACITIES
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Functional residual capacity (FRC). This is the
amount of air remaining in the air passages
and alveoli at the end of quiet expiration.
Tidal air mixes with this air causing small
changes in the composition of alveolar air. As
blood flows continuously through the
pulmonary capillaries, this means that
exchange of gases is not interrupted between
breaths, preventing marked changes in the
concentration of blood gases. The functional
residual volume also prevents collapse of the
alveoli on expiration.
Expiratory reserve volume (ERV). This is the
largest volume of air which can be expelled
from the lungs during maximal expiration.
Residual volume (RV). This cannot be directly
measured but is the volume of air remaining
in the lungs after forced expiration.
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LUNG VOLUME AND CAPACITIES
• Vital capacity (VC). This is the
maximum volume of air which can be
moved into and out of the lungs:
VC = Tidal volume + IRV + ERV
• Alveolar ventilation. This is the
volume of air that moves into and out
of the alveoli per minute. It is equal to
the tidal volume minus the anatomical
dead space, multiplied by the
respiratory rate:
• Alveolar ventilation = (TV - anatomical
dead space) x respiratory rate
= (500 - 150) rnl x 15 per minute = 5.25
litres per minute
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EXCHANGE OF GASES
• Although breathing involves the alternating
processes of inspiration and expiration
• Gas exchange at the respiratory membrane
and in the tissues is a continuous and ongoing
process.
• Diffusion of oxygen and carbon dioxide
depends on pressure differences, e.g.
between atmospheric air and the blood, or
blood and the tissues.
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COMPOSITION OF AIR
• Air Pressure reduces as we go above sea level
and increases in the sea.
• Air is a mixture of gases: nitrogen, oxygen,
carbon dioxide, water vapour and small
quantities of inert gases.
• Each gas in the mixture exerts a part of the
total pressure proportional to its
concentration, i.e. the partial pressure.This is
denoted as, e.g. PO2, PCO2.
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ALVEOLAR AIR
• The composition of alveolar air remains fairly constant and is
different from atmospheric air.
• It is saturated with water vapour and contains more carbon
dioxide, and less oxygen. Saturation with water vapour
provides 6.3 kPa (47 mmHg) thus reducing the partial
pressure of all the other gases present.
• Gaseous exchange between the alveoli and the bloodstream
(external respiration) is a continuous process, as the alveoli
are never empty, so it is independent of the respiratory
cycle. During each inspiration only some of the alveolar
gases are exchanged.
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EXPIRED AIR
• This is a mixture of alveolar air and atmospheric air in
the dead space .
• Exchange of gases occurs when a difference in partial
pressure exists across a semipermeable membrane.
• Gases move by diffusion from the higher
concentration to the lower until equilibrium is
established .
• Atmospheric nitrogen is not used by the body so its
partial pressure remains unchanged and is the same in
inspired and expired air,alveolar air and in the blood
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EXTERNAL/INTERNAL RESPIRATION
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EXTERNAL RESPIRATION
• This is exchange of gases by diffusion between the alveoli of the
lungs and the pulmonary blood capillaries .
• It results in the conversion of deoxygenated blood coming from
heart to oxygenated blood returning to the heart.
• During inspiration, atmospheric air containing oxygen enters the
alveoli. Deoxygenated blood is pumped from the right ventricle
through the pulmonary artery into the pulmonary capillaries
surrounding the alveoli.
• The pO2 of alveolar air is 105mm Hg .At rest po2 of deoxygenated
blood entering your blood capillaries is only 40mm Hg.
• As a result of this difference in pO2 ,there is net diffusion of oxygen
from alveoli into deoxygenated blood until equilibrium is reached,
and the pO2 of now oxygenated blood is 105mm Hg.
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EXTERNAL RESPIRATION
• While O2 diffuses from the alveoli into deoxygenated blood ,
there is a net diffusion in CO2 in the opposite direction.
• The pCO2 of deoxygenated blood is 45 mm Hg whereas of
alveolar air is 40 mm Hg due to this difference in pCO2 ,
carbon dioxide diffuses from the blood into the alveoli until
the pCO2 of blood decreases to 40 mm Hg. This is the pCO2 of
fully saturated blood.
• Thus the pO2 & pCO2 of oxygenated blood leaving the lungs
are same as in the alveolar air.
• The carbon dioxide that diffuses into the alveoli is eliminated
from the lungs during expiration.
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INTERNAL RESPIRATION
• The left ventricle pumps oxygenated blood into aorta and through
systemic arteries to capillaries to tissue cells.
• This is exchange of gases by diffusion between tissue blood capillaries and
tissue cells called internal respiration
• It results in conversion of oxygenated blood to deoxygenated blood.
• Oxygenated blood entering the tissue capillaries has a pO2 105mm Hg,
whereas tissue cells have an average pO2 40 mm Hg. Due to this difference
in pO2 , oxygen diffuses from the oxygenated blood through interstitial
fluid and into tissue cells until the pO2 of blood decreases to 40mm Hg.
This is the average pO2 of deoxygenated blood entering tissue venules at
rest.
• At rest, only about 25 % of the available oxygen in oxygenated blood
actually enters tissue cells.This amount is sufficient to support the needs
of resting cells.
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INTERNAL RESPIRATION
• Thus deoxygenated blood still retains considerable oxygen.
• During exercise, more oxygen diffuses from the blood into active cells.
• While oxygen diffuses from the tissue blood capillaries into tissue
cells, carbon dioxide diffuses in the opposite direction.
• The average pCO2 of tissue cells is 45mm Hg, whereas that of tissue
capillary oxygenated blood is 40mm Hg.
• As a result, carbon dioxide diffuses from tissue cells through interstitial
fluid into oxygenated blood until pCO2 in the blood increases to 45mm
Hg, the pCO2 of tissue capillary deoxygenated blood.
• The deoxygenated blood now returns to the heart.
• From here it is pumped to the lungs for another cycle of external
respiration.
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EXTERNAL/INTERNAL RESPIRATION
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TRANSPORT OF GASES IN THE
BLOOD STREAM
• Transport of blood oxygen and carbon dioxide is essential for internal
respiration to occur. When oxygen and carbon dioxide enter blood, certain
physical and chemical changes occur that aid in gas transport and exchange.
Oxygen
Oxygen is carried in the blood in:
• chemical combination with haemoglobin as oxyhaemoglobin (98.5 %)
• solution in plasma water (1.5%) because
• Oxyhaemoglobin is an unstable compound that under certain conditions
readily dissociates releasing oxygen. Factors that increase dissociation
include low O2 levels, low pH and raised temperature. In active tissues
there is increased production of carbon dioxide and heat, which leads to
increased release of oxygen. In this way oxygen is available to tissues in
greatest need. When oxygen leaves the erythrocyte, the deoxygenated
haemoglobin turns purplish in colour
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TRANSPORT OF GASES IN THE
BLOOD STREAM
Carbon dioxide
Under normal resting conditions, each 100 ml of deoxygenated
blood contains about 5 ml of carbon dioxide.
Carbon dioxide is one of the waste products of metabolism. It is
excreted by the lungs and is transported by three
mechanisms:
• as bicarbonate ions (HC03-) in the plasma (70%)
• some is carried in erythrocytes, loosely combined with
haemoglobin as carbaminohaemoglobin (23%).
• some is dissolved in the plasma (7%).
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SPIROMETER
• Ventilation deals with the measurement of the body as an air
pump, determining its ability to move volumes of air and the
speed with which it moves the air.
• The most widely performed measurement is ventilation.
• This is performed using devices called spirometers that
measure volume displacement and the amount of gas moved
in a specific time.
• Usually this requires the patient to take a deep breath and
then exhale as rapidly and completely as possible.
• This is called forced vital capacity , this gives an indication of
how much air can be moved by the lungs and how freely this
air moves.
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WATER-SEALED SPIROMETER
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SPIROMETER
• The instrument used to measure lung capacity and volume is
called a spirometer. The record obtained from this device is
called spirogram.
• Most of the respiratory measurement can be adequately carried
out by the classic water-sealed spirometer.
• This consists of an upright, water filled cylinder containing an
inverted counter weighted bell.
• Breathing into the bell changes the volume of gases trapped
inside, and the change in volume is translated into vertical
motion, which is recorded on the moving drum of a kymograph.
• The excursion( movement) of the bell will be proportional to
tidal volume.
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PEAK FLOW METER
• A peak flow meter is a device that measures how well a person's
lungs are working.
• A peak flow meter is a portable, inexpensive, hand-held device
used to measure how air flows from your lungs in one "fast
blast." In other words, the meter measures your ability to push
air out of your lungs(i.e breathe out air).
• It measures the airflow through the bronchi and thus the degree
of obstruction in the airways.
• If someone with asthma can't blow out as much air as usual, this
may mean he or she is going to have an asthma flare-up.
• Many health care providers believe a peak flow meter may be of
most help for people with moderate and severe asthma as they
can adjust their daily medication.
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PEAK FLOW METER
• A peak flow meter measures
the patient's maximum speed of
expiration, or peak expiratory
flow rate (PEFR or PEF).
• Peak flow readings are higher
when patients are well, and
lower when the airways are
constricted.
• From changes in recorded
values, patients and doctors
may determine lung
functionality, severity of asthma
symptoms, and treatment
options.
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HOW TO USE A PEAK FLOW
METER?
Step 1: Before each use, make sure the sliding marker or arrow on the Peak
Flow Meter is at the bottom of the numbered scale (zero or the lowest
number on the scale).
Step 2: Stand up straight. Remove gum or any food from your mouth. Take
a deep breath (as deep as you can). Put the mouthpiece of the peak flow
meter into your mouth. Close your lips tightly around the mouthpiece. Be
sure to keep your tongue away from the mouthpiece. In one breath blow
out as hard and as quickly as possible. Blow a "fast hard blast" rather than
"slowly blowing" until you have emptied out nearly all of the air from your
lungs.
Step 3: The force of the air coming out of your lungs causes the marker to
move along the numbered scale. Note the number on a piece of paper.
Step 4: Repeat the entire routine three times. (You know you have done
the routine correctly when the numbers from all three tries are very close
together.)
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HOW TO USE A PEAK FLOW
METER?
Step 5: Record the highest of the three ratings. Do not calculate an
average. This is very important.
You can't breathe out too much when using your peak flow meter but
you can breathe out too little. Record your highest reading.
Step 6: Measure your peak flow rate close to the same time each day.
You and your health care provider can determine the best times. One
suggestion is to measure your peak flow rate twice daily between 7and
9 a.m. and between 6 and 8 p.m.
You may want to measure your peak flow rate before or after using
your medicine. Some people measure peak flow both before and after
taking medication. Try to do it the same way each time.
Step 7: Keep a chart of your peak flow rates. Discuss the readings with
your health care provider.
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SCALE OF A PEAK FLOW METER
• The best of three readings is used as the recorded value of the
Peak Expiratory Flow Rate.
• It may be plotted out on graph paper charts together with a
record of symptoms or using peak flow charting software. This
allows patients to self-monitor and pass information back to
their doctor or nurse.
• Peak flow readings are often classified into 3 zones of
measurement according to the American Lung Association;
green, yellow, and red. Doctors and health practitioners can
develop an asthma management plan based on the greenyellow-red zones.
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Zone
Reading
Description
Green Zone
80 to 100 percent of the
usual or normal peak flow
readings are clear
A peak flow reading in the
green zone indicates that
the asthma is under good
control.
Yellow Zone
50 to 80 percent of the
usual or normal peak flow
readings
Indicates caution. It may
mean respiratory airways
are narrowing and
additional medication may
be required
Red Zone
Less than 50 percent of the Indicates a medical
usual or normal peak flow emergency. Severe airway
readings
narrowing may be
occurring and immediate
action needs to be taken.
This would usually involve
contacting a doctor or
hospital.
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ARTIFICIAL VENTILATION
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ARTIFICIAL VENTILLATION
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Mechanical devices or artificial respirators are used in hospitals for
reduced breathing or respiratory failure.
These devices provide artificial ventilation, supply enough oxygen and
eliminate the right amount of carbon dioxide, maintain the desired
arterial partial pressures of carbon dioxide and oxygen.
Mechanical aids for manual artificial ventilation consists of a mask,
breathing valve and self -filling bag.
The mask, which is of soft rubber or plastic, is held firmly over the
patient’s mouth and nose so that it fights tightly.
The breathing valve serves to guide the air so that fresh air or air enriched
with oxygen is supplied to the patient and expired air is conducted away.
The bag is squeezed with one hand and functions as a pump. It is selfexpanding and fills automatically with fresh air or oxygen when the patient
breathes out.
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VENTILATORS
• When artificial ventilation is to be maintained
for a long time or during anesthesia a
ventilator is used.
• They are designed to match human breathing
waveform/pattern.
• These are sophisticated equipment with a
large number of controls which assist in
maintaining proper and regulated breathing
activity.
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NEGATIVE PRESSURE VENTILATORS
• Natural inspiration is a result of negative pressure in the pleural cavity
generated by the movement of diaphragm, ventilators were initially
designed to create the same effect.
• These ventilators are called negative-pressure ventilators.
• In this design, the flow of air to lungs is facilitated by generating negative
pressure around the patient’s thorasic cage.
• The negative pressure moves the thorasic walls outward, expanding the
intra-thorasic volume and dropping pressure inside the lungs, resulting in a
pressure gradient between atmosphere and the lungs which causes the flow
of atmospheric air into the lungs.
• The inspiratory and expiratory phases of the respiration are controlled by
cycling the pressure inside the body chamber.
• Due to several engineering problems impeding the implementation of the
concept and difficulty of accessing the patient for care and monitoring,these
ventilators have not become popular.
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POSITIVE PRESSURE VENTILATORS
• Generate the inspiratory flow by
applying a positive pressure greater
than atmospheric pressure-to the
airways.
• During the inspiration, the inspiratory
flow delivery system creates a positive
pressure in the patient circuit and the
exhalation control system closes the
outlet to the atmosphere.
• During the expiratory phase, the
inspiratory flow delivery system stops
the positive pressure at the exhalation
system and opens the valves to allow
the exhaled air into the atmosphere.
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MODES OF OPERATION IN
POSITIVE PRESSURE VENTILATORS
Spontaneous mode.
• In Spontaneous breath delivery, the ventilator
responds to the patient’s effort to breath
independently.
• The patient can control the volume and rate of
respiration.
• Spontaneous breath delivery is used for those
patients who are on their way to full recovery but are
not completely ready to breathe from the
atmosphere without mechanical assistance.
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MODES OF OPERATION IN
POSITIVE PRESSURE VENTILATORS
Mandatory Mode
• When delivering mandatory breaths, the
ventilator controls all parameters of the
breath such as tidal volume, inspiratiry flow
waveform, respiration rate and oxygen
content of the breath.
• Mandatory breaths are normally delivered to
the patients who are incapable of breathing
on their own.
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TYPES OF VENTILATORS
• ANAETHESIA VENTILATORS
They are generally small and simple equipments used
to give regular assisted breathing during an
operation.
• INTENSIVE CARE VENTILATORS
They are more complicated, give accurate control over
a wide range of parameters and often incorporate
‘patient triggering facility’,
i .e. the ventilator delivers air to the patient when the
patient tries to inhale.
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THANK
YOU
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