Transcript Respiratory Physiology

Respiratory Physiology
Pulmonary ventilation
Diffusion of gases
Transport of gases
Control of respiration
Respiration
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Ventilation: Movement of air into and out of
lungs
External respiration: Gas exchange between
air in lungs and blood
Transport of oxygen and carbon dioxide in
the blood
Internal respiration: Gas exchange between
the blood and tissues
Respiratory System Functions
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Gas exchange: Oxygen enters blood and carbon
dioxide leaves
Regulation of blood pH: Altered by changing blood
carbon dioxide levels
Voice production: Movement of air past vocal folds
makes sound and speech
Olfaction: Smell occurs when airborne molecules
drawn into nasal cavity
Protection: Against microorganisms by preventing
entry and removing them
Respiratory System Divisions
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Upper tract
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Nose, pharynx and
associated structures
Lower tract
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Larynx, trachea,
bronchi, lungs
Nasal Cavity and Pharynx
Nose and Pharynx
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Nose
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External nose
Nasal cavity
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Functions
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Passageway for air
Cleans the air
Humidifies, warms air
Smell
Along with paranasal
sinuses are resonating
chambers for speech
Pharynx
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Common opening for
digestive and respiratory
systems
Three regions
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Nasopharynx
Oropharynx
Laryngopharynx
Larynx
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Functions
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Maintain an open passageway for air movement
Epiglottis and vestibular folds prevent swallowed material from
moving into larynx
Vocal folds are primary source of sound production
Vocal Folds
Trachea
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Windpipe
Divides to
form
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Primary
bronchi
Carina:
Cough
reflex
Tracheobronchial Tree
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Conducting zone
Trachea to terminal bronchioles which is ciliated
for removal of debris
 Passageway for air movement
 Cartilage holds tube system open and smooth
muscle controls tube diameter
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Respiratory zone
Respiratory bronchioles to alveoli
 Site for gas exchange
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Tracheobronchial Tree
Bronchioles and Alveoli
Alveolus and Respiratory
Membrane
The normal adult human lung weighs
about 1000g and consists of about 50%
blood and 50% tissue by weight. About
10% of the total lung volume is composed
of various types of conducting airways
and some connective tissue. The
remaining 90% is the respiratory or gas
exchange portion of the lung, composed
of alveoli and supporting capillaries.
Thoracic Walls
Muscles of Respiration
Thoracic Volume
Pleura
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Pleural fluid produced by pleural membranes
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Acts as lubricant
Helps hold parietal and visceral pleural membranes
together
Ventilation
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Movement of air into and out of lungs
Air moves from area of higher pressure to area
of lower pressure
Pressure is inversely related to volume
Alveolar Pressure Changes
Changing Alveolar Volume
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Lung recoil
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Causes alveoli to collapse resulting from
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Elastic recoil and surface tension
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Surfactant: Reduces tendency of lungs to collapse
Pleural pressure
Negative pressure can cause alveoli to expand
 Pneumothorax is an opening between pleural
cavity and air that causes a loss of pleural
pressure
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Normal Breathing Cycle
Transpulmonary
pressure [pressure
difference between
the alveolar pressure
and the pleural
pressure]. It is the
measure of the elastic
forces that leads to
collapse of the lung
and it is called the
recoil pressure.
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The Opposing Force of Pulmonary
Elastance or Compliance
The lung is an elastic structure with an anatomical
organization that promotes its collapse to essentially
zero volume, much like an inflated balloon.
The term elastic means a material deformed by a force
tends to return to its initial shape or configuration when
the force is removed. It oppose lung inflation.
Elastance.
Compliance (distensibility) is the reciprocal of
elastance, is a measure of the ease of deformation
(inflation).
Compliance
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Measure of the ease with which lungs and
thorax expand
The greater the compliance, the easier it is for a
change in pressure to cause expansion
 A lower-than-normal compliance means the
lungs and thorax are harder to expand
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Conditions that decrease compliance
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Pulmonary fibrosis
Pulmonary edema
Respiratory distress syndrome
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Lung compliance: Which equals to change in volume
divided by change in pressure (1 cm = 200 ml). That is,
every time the transpulmonary pressure increases 1
centimeter of water, the lung volume, after 10 to 20
seconds, will expand 200 milliliters.
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1/3 to overcome pleural pressure
2/3 to overcome surface tension
Effect of thoracic cage: Compliance of both lung +
cage = 110 ml (instead of 200ml/cm)
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Surfactant: The surface active agent in water and
it consists of lipids, protein and ions.
Fetal lung surfactant also is not fully functional
until about the seventh month of gestation.
Respiratory Distress Syndrome (RDS) is related
to non-functional alveolar surfactant.
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Work of breathing:
Compliance work: against elastic forces of lung
+ cage
Tissue resistance work: against viscosity of both
lung and cage
Airway resistance work
During quite breathing, 3-5% of total energy of
the body are spent for respiration, while in
heavy exercise, it increases up to 50 folds
Pulmonary Volumes
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Tidal volume
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Inspiratory reserve volume
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Amount of air inspired forcefully after inspiration of normal tidal
volume
Expiratory reserve volume
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Volume of air inspired or expired during a normal inspiration or
expiration
Amount of air forcefully expired after expiration of normal tidal
volume
Residual volume
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Volume of air remaining in respiratory passages and lungs after the
most forceful expiration
Pulmonary Capacities
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Inspiratory capacity
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Functional residual capacity
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Expiratory reserve volume plus the residual volume
Vital capacity
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Tidal volume plus inspiratory reserve volume
Sum of inspiratory reserve volume, tidal volume, and expiratory
reserve volume
Total lung capacity
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Sum of inspiratory and expiratory reserve volumes plus the tidal
volume and residual volume
Volumes
1- Tidal vol. (500ml)
Capacities
1- Inspiratory cap.
(3500ml)
2- Inspiratory reserve vol. 2- Functional residual
(3000ml)
cap. (2300ml)
3- Expiratory reserve vol. 3- Vital cap. (4600ml)
(1100ml)
4- Residual vol. (1200ml) 4- Total lung cap.
(5800ml)
Spirometer and Lung
Volumes/Capacities
Minute and Alveolar Ventilation
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Minute ventilation: Total amount of air moved
into and out of respiratory system per minute
Respiratory rate or frequency: Number of breaths
taken per minute
Anatomic dead space: Part of respiratory system
where gas exchange does not take place
Alveolar ventilation: How much air per minute
enters the parts of the respiratory system in
which gas exchange takes place
Respiratory dead space
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Is the space where no gas exchange occurs. It is either
anatomically (150 ml) (anatomical dead space (nose,
pharynx, larynx, trachea, bronchi, bronchioles); or
physiological dead space whereby some alveoli are not
functional because of absent or partial blood supply
(normally it should be zero).
So the total dead space is the sum of anatomical and
physiological dead spaces and so equals to 150 ml. So
the alveolar ventilation per minute equals to pulmonary
ventilation per minute minus dead space and equals to
500-150 = 350 ml/min X 12 = 4200 ml/min.
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Nerve stimulation (sympathetic, i.e., adrenalin
dilatation; parasympathetic, i.e., Ach.
constriction).
Cough reflex: afferent vagus nerve medulla
autonomic
inspiration of 2.5 liters closure of
epiglottis and vocal cords contraction of abdominal
muscles
sudden opening
expel air at a velocity
of 400 miles per hour + narrowing of trachea and
bronchi.
Sneeze reflex: Similar except to nasal passages instead
of lower airways. Afferent is fifth cranial
medulla
similar but depression of uvula so that large amounts of
air pass through the nose.
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Pulmonary circulation:
Blood supply to the lungs goes to bronchi (nutrition)
and respiratory units (gaseous exchange).
When O2 concentration drops to 70% (73mmHg), pulmonary
blood vessels constricts (opposite to other capillaries) and this is
important to shift the blood to more aerated areas.
Right atrial pressure is 25 mmHg systolic and 0 mmHg
diastolic.
Pulmonary artery pressure is 25mmHg systolic and
8mmHg diastolic (mean arterial pressure equals 15
mmHg)
Lung Zones
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In the normal, upright adult,
the lowest point in the lungs
is about 30 centimeters below
the highest point. This
represents a 23 mm Hg
pressure difference, about 15
mm Hg of which is above the
heart and 8 below.
For the whole lung, an ideal
ventilation to perfusion ratio
is between 0.8 to 1.0.
Perfusion across capillaries
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Capillary pressure equals
7mmHg (while it is 17 in
general circulation).
Plasma colloid equals 28
mmHg.
Interstitial colloid 14 mmHg
(7 in general circulation)
-ve interstitial pressure
equals 8 mmHg
Total = 29, so 29-28 =
1mmHg which removed by
lymphatics and evaporation
Physical Principles of Gas
Exchange
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Partial pressure
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The pressure exerted by each type of gas in a mixture
Dalton’s law: Ptotal = P1 + P2 + P3 + ... + Pn
Water vapor pressure
Diffusion of gases through liquids
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Concentration of a gas in a liquid is determined by its
partial pressure and its solubility coefficient
Henry’s law: concentration of dissolved gas =
pressure × SC
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Gases Comprising the Earth's Atmosphere
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The earth's atmosphere is a mixture of gases consisting
of about 78% molecular nitrogen (N2), 20.9 %
molecular oxygen (O2) and 1.0 % argon (Ar). Other
gases, like carbon dioxide (0.03%), are also detectable,
but only in trace amounts.
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Only a portion of each tidal volume is delivered to the
alveoli. The total air volume of all lung alveoli before
inspiration (end-expiration) is by definition the
Functional Residual Capacity. For a normal adult, the
FRC is about 2500 ml. So, if the volume of fresh
ambient air reaching the alveoli is 300 ml, it is added to
an FRC of 2500 ml. As a result, the partial pressures of
alveolar gases do not fluctuate markedly with each
breath since only a portion of the FRC is exchanged.
Factors affecting the diffusion of gasses in
air:
Pressure X Area X Temperature
D = ----------------------------------------------,
distance X SQR(Molecular Weight)
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diff. coef. = T/SQR(MW)
(constant)
 Solubility of O2 = 0.024
 Solubility of CO2 = 0.57 (20 times of O2)
Diffusion of Gases through the Respiratory Membrane
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The respiratory unit: respiratory
bronchioles, alveolar ducts, atria,
and alveoli.
Blood flows as a sheet.
Respiratory membrane is 0.2
micrometer thickness and
composed of: 1) fluid (surfactant),
2) epithelium, 3) epithelial basement
membrane, 4) interstitial fluid, 5)
capillary basement membrane, 6)
endothelial cells
Physical Principles of Gas
Exchange
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Diffusion of gases through the respiratory
membrane
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Depends on membrane’s thickness, the diffusion coefficient of
gas, surface areas of membrane, partial pressure of gases in
alveoli and blood
Relationship between ventilation and
pulmonary capillary flow
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Increased ventilation or increased pulmonary capillary blood
flow increases gas exchange
Physiologic shunt is deoxygenated blood returning from lungs
Effect of ventilation perfusion ratio on
alveolar gas concentration
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VA/Q = 0 O2 = 40, CO2 = 45mmHg
VA/Q = infinity O2 = 149, CO2 = 0mmHg
VA/Q = normal O2 = 104, CO2 = 40mmHg
If less than normal then called physiological
shunt
If more than normal then called physiological
dead space
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Normally at the tip of the
lung, VA/Q is (2.5) times
normal (phys. dead space),
while at the base, it is (0.6)
times normal (phys. shunt).
Normally, there are
abnormal VA/Q ratios in
the upper and lower
portions of the lung. In the
upper both ventilation and
perfusion are low but VA is
more than Q, so there is
physiological dead space, but
in the lower VA is less than
Q, so there is physiological
shunt.
Changes in Partial Pressures
Hemoglobin and Oxygen
Transport
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Oxygen is transported by hemoglobin (97%) and is
dissolved in plasma (3%)
Oxygen-hemoglobin dissociation curve shows that
hemoglobin is almost completely saturated when
P02 is 80 mm Hg or above. At lower partial
pressures, the hemoglobin releases oxygen.
A shift of the curve to the left because of an
increase in pH, a decrease in carbon dioxide, or a
decrease in temperature results in an increase in the
ability of hemoglobin to hold oxygen
Hemoglobin and Oxygen
Transport
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A shift of the curve to the right because of a decrease in
pH, an increase in carbon dioxide, or an increase in
temperature results in a decrease in the ability of
hemoglobin to hold oxygen
The substance 2.3-bisphosphoglycerate increases the
ability of hemoglobin to release oxygen
Fetal hemoglobin has a higher affinity for oxygen than
does maternal
Oxygen-Hemoglobin
Dissociation Curve at Rest
Bohr effect:
Temperature effects:
Shifting the Curve
Transport of Carbon Dioxide
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Carbon dioxide is transported as bicarbonate ions
(70%) in combination with blood proteins (23%)
and in solution with plasma (7%)
Hemoglobin that has released oxygen binds more
readily to carbon dioxide than hemoglobin that has
oxygen bound to it (Haldane effect)
In tissue capillaries, carbon dioxide combines with
water inside RBCs to form carbonic acid which
dissociates to form bicarbonate ions and hydrogen
ions
Transport of Carbon Dioxide
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In lung capillaries, bicarbonate ions and hydrogen
ions move into RBCs and chloride ions move out.
Bicarbonate ions combine with hydrogen ions to
form carbonic acid. The carbonic acid is converted
to carbon dioxide and water. The carbon dioxide
diffuses out of the RBCs.
Increased plasma carbon dioxide lowers blood pH.
The respiratory system regulates blood pH by
regulating plasma carbon dioxide levels
Haldane effect
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It was pointed out that an increase in carbon dioxide in the
blood causes oxygen to be displaced from the hemoglobin (the
Bohr effect), which is an important factor in increasing oxygen
transport.
The reverse is also true: binding of oxygen with hemoglobin
tends to displace carbon dioxide from the blood.
The Haldane effect results from the simple fact that the
combination of oxygen with hemoglobin in the lungs causes the
hemoglobin to become a stronger acid.
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This displaces carbon dioxide from the blood and into
the alveoli in two ways:
(1) The more highly acidic hemoglobin has less
tendency to combine with carbon dioxide to form
carbaminohemoglobin, thus displacing much of the
carbon dioxide that is present in the carbamino form
from the blood.
(2) The increased acidity of the hemoglobin also causes
it to release an excess of hydrogen ions, and these bind
with bicarbonate ions to form carbonic acid; this then
dissociates into water and carbon dioxide, and the
carbon dioxide is released from the blood into the
alveoli and, finally, into the air.
CO2 Transport and Cl- Movement
Ventilation-perfusion coupling:
Respiratory Areas in Brainstem
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Medullary respiratory center
Dorsal groups stimulate the diaphragm
 Ventral groups stimulate the intercostal and
abdominal muscles
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Pontine (pneumotaxic) respiratory group
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Involved with switching between inspiration and
expiration (respiratory ramp).
Pontine (apneuostic center) prevents the switch
off of the respiratory ramp.
Respiratory Structures in Brainstem
Rhythmic Ventilation
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Starting inspiration
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Increasing inspiration
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Medullary respiratory center neurons are continuously active
Center receives stimulation from receptors and simulation from parts of
brain concerned with voluntary respiratory movements and emotion
Combined input from all sources causes action potentials to stimulate
respiratory muscles
More and more neurons are activated
Stopping inspiration
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Neurons stimulating also responsible for stopping inspiration and receive
input from pontine group and stretch receptors in lungs. Inhibitory
neurons activated and relaxation of respiratory muscles results in
expiration.
Modification of Ventilation
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Cerebral and limbic
system
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Chemical control
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Respiration can be
voluntarily controlled
and modified by
emotions
Carbon dioxide is major
regulator
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Increase or decrease in pH
can stimulate chemosensitive area, causing a
greater rate and depth of
respiration
Oxygen levels in blood
affect respiration when a
50% or greater decrease
from normal levels exists
Modifying Respiration
Regulation of Blood pH and
Gases
Herring-Breuer Reflex
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Limits the degree of inspiration and prevents
overinflation of the lungs
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Infants
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Reflex plays a role in regulating basic rhythm of breathing
and preventing overinflation of lungs
Adults
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Reflex important only when tidal volume large as in
exercise
Ventilation in Exercise
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Ventilation increases abruptly
At onset of exercise
 Movement of limbs has strong influence
 Learned component
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Ventilation increases gradually
After immediate increase, gradual increase occurs
(4-6 minutes)
 Anaerobic threshold is highest level of exercise
without causing significant change in blood pH
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If exceeded, lactic acid produced by skeletal muscles
Effects of Aging
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Vital capacity and maximum minute
ventilation decrease
Residual volume and dead space increase
Ability to remove mucus from respiratory
passageways decreases
Gas exchange across respiratory membrane is
reduced
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Other types of respiratory control as:
Voluntary control
 Irritant receptors of airways.
 Lung “J” receptors
 Brain edema
 Anesthesia
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Periodic breathing (normally damped).
Slow blood flow to the brain (heart failure)
 Increased negative feedback gain (brain damage)
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Sleep apnea
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Loss of spontaneous breathing
May last for > 10 seconds
May recur 300-500 per night sleep
May be due to obstruction of pharynx
 May be due to impaired CNS respiratory drive
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Respiratory investigations
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Blood pH
Blood gas determination
Respiratory function tests
Maximum expiratory flow
 FCV
 FEV1
 FVC/FEV1 ratio
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Types of respiratory abnormalities
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Obstructive
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Restrictive
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Pulmonary emphysema
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Pneumonia
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Infection, filling of areas with fluid and
consolidation leading to hypoxia and hypercapnia.
Atelectasis
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Infection, obstruction, alveolar damage, decrease
diffusing capacity, and may lead to pulmonary
hypertension.
Lung collapse
Asthma: Spastic contraction to bronchioles leading to
hypoxia.
Hypoxia
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Circulatory hypoxia:
Histotoxic hypoxia
Anemic hypoxia
Hypoxic hypoxia