Respiratory Physiology
Prof. Omer Abdel Aziz Musa
Faculty of medicine
The National Ribat University
Respiratory Physiology
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Functions of respiratory system:
1. Gas exchange: O2 uptake, CO2 removal.
2. Regulation of acid-base balance.
3. Regulation of temperature.
4. Regulation of Body fluids.
5. Protection.
6. Endocrine & metabolic function.
7. Excretion e.g. Alcohol.
• 8. Speech.
ANATOMY
• Right lung three lobes and left two.
• Each lobe divided into segments.
• Trachea divides into main two
bronchi then bronchioles, terminal b.
and respiratory b. reaching the
alveolar ducts to the alveoli.
• Between the trachea and the alveoli
airways divide 23 times, 16
conducting & 7 from resp. b.
involved in gas exchange.
• area from 2.5 cm2 (trachea) to 11800
cm2 in alveoli ? Air velocity.
• 300 million alveoli, 70 m2.
• Alveoli lined by type 1 cells ( flat
lining ) and type 11 cells ( granular
pneumocytes secrete surfuctant ).
• Pleura.
• Respiratory muscles.
Mechanics of respiration
• Respiratory rate in adults 12-15/min.
• 500 ml in each breath, 6-8l/min.
• 250 ml of O2 taken, 200 ml CO2 expired/min.
Inspiration:
Inspiratory muscles:
1. Diaphragm: vertical axis, increase
thoracic cavity by 75% in quiet respiration.
2. External intercostal muscles:
anteroposterior diameter, 10% only .
3. Accessory inspiratory muscles: act in
forcible respiration: scalene and
sternocleidomastoid muscles.
Mecahnics
Contraction of insp. muscles decreases
intrapleural pressure from – 2.5mm Hg
to – 6mmHg : by increasing the thoracic
cavity the lungs will move with the
thoracic cage as the parietal and
visceral pleurae are in contact, the
pressure in airways decreases, leading
to entry of air from outside.
• In forcible insp. intrapleural pressure
reaches – 30mm Hg
Expiration:
• Passive process due to elastic recoil
of insp. muscle and lungs leading to
increased press. in airways and
outflow of air.
• Accessory expiratory muscles work
in forced expiration: abdominal
muscles and internal intercostal.
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• Respiratory muscles do not fatigue due to
alternation of contraction between:
1. inspiratory and expiratory muscles?
• 2. Diaphragm and internal intercostals?
• 3. the fibers of inspiratory muscles?
• 4. internal and external intercostals?
• 5. Diaphragm and external intercostals?
Q
• Inspiration during quiet breathing is
mainly produced by contraction of:
• 1.Internal intercostal muscles?
• 2.External intercostal m.?
• 3.Sternocleidomastoid m.?
• 4.Diaphragm?
• 5.Abdominal m.?
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Work of breathing
• 1. Elastic work: work performed by
the respiratory muscles in stretching
the elastic tissues of the chest wall
and lungs. During quiet inspiration
represents 65% of the work.
• 2. Non-elastic work: work performed
by respiratory muscles in:
• I. Moving non-elastic tissues
(viscous resistance, 7%).
• II. Moving air through air passages
(airway resistance, 28%)
Compliance of the lung and
chest wall
• It is the change in lung volume per
unit change in airway press.
V/ P
• Decreased: in pulmonary
congestion and fibrosis.
• Increased in emphysema.
Pulmonary circulation
• Lungs receive the whole cardiac
output (5L).
• Pulm. arterial press. 24/9 (av.15).
• Lt atrial press = 8 , oncotic press.
25
in drive to keep alveoli dry.
• Base of lungs more perfused and
more ventilated.?
Ventilation-perfusion
ratio V/Q
• Pulm. alveolar ventilation /
perfusion = 4.2/5.5 = 0.8.
• Both ventilation and perfusion
decreases towards the apex,
but the perfusion decreases
more, so V/Q increases at the
apex (more PO2
T.B) at apex.
Physiological dead
space
• It is the area where no gas
exchange takes place. It
includes the anatomical dead
space and any area either not
ventilated or not perfused.
Anatomical dead space
• It is the airways which conduct
air without gas exchange. Its
volume is 150ml.
• Alveolar ventilation /min = (500 –
150) x 12 = 4200 cm3.
Bronchial tone
• Bronchioles have no cartilage and more
smooth muscles.
• Bonchio. dilate during inspiration by
sympathetic discharge. B2 receptors.
salbutamol.
• Broichio. constrict during expiration by
parasympathetic- muscaranic receptors.
ipratropium.
• Non cholinergic – nonadrenergic
innervation produces bronchodilation
VIP?
• Irritants, cool air, exercise lead to
bronchoconstriction.
• Circadian rhythm: Max. constriction at
about 6 a.m. and max. dilation at 6
p.m.
• Substance P ,adenosine ( A1 receptor ),
& leukotrienes cause bronchoconst.
Quiz
• Bronchoconstriction is
produced by
• 1.Sympathetic stimulation.
• 2.Substance P.
• 3.VIP.
• 4.Surfactant.
• 5.Normal saline.
•2
Surfactant
• Lipid surface tension lowering agent.
• Produced by type II alveolar epithelial
cell.
• Composed of phospholipids, neutral
lipids, proteins and CHO.
• Functions:1. Lower surface tension in
alveoli.
2. Helps to prevent pulmonary
edema.
• Maturation of surfactant is
accelerated by glucocorticoid
(cortisol).
• Surfactant decreases in smokers.
• Cardiac surgery with interruption of
pulm circulation, pulm, artery
occlusion, main bronchus occlusion
and long term 100% 02 can decrease
surfactant.
• Surfactant deficiency can cause
infant respiratory distress syndrome
(IRDS, hyaline membrane disease) in
premature babies.
• Surfactant (Synthetic and bovine)
can be given by inhalation.
Summary
• Inspiration is an active process due to
contraction of respiratory muscles:
diaphragm & external intercostal muscles.
• Intapleural pressure at end of quiet
expiration is -2.5 mmHg and goes down to 6 during inspiration.
• V/Q is normally 0.8
• Compliance of the lung is the change in
volume due to the change in pressure.
• Dead spaces are anatomical or
physiological: no gas exchange.
• Work of breathing is either elastic or
non-elastic.
• Bronchial tone can be affected by
many factors which are related to
asthma.
• Surfactant? def. can cause IRDS.
Gas Laws
Gas laws
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O2
20.98%
CO2
0.04%
N2
78.06%
Inert
0.092%
Gases expand to fill available
volume.
• The volume occupied by a specific
no. of gases molecules at a constant
temp. and press. is constant.
Laws
The pressure of a gas in a mixture
is directly proportional to the temp.
and no. of moles and inversely
proportional to the volume.
P. Pressure.
N. no. Moles.
P = nRT
R. gas constant.
V
T. temp.
V. volume.
Barometric press. at sea level is 760mm
Hg (pa).
Then PO2 = 20.94 x760 = 160mm Hg.
100
Gas diffuses from areas of high pressure
to areas of low pressure depending
on.
1. Concentration gradient and surface
area (directly).
2. Nature of barrier between the zones.
Thickness of membrane (inversely).
Gases dissolve in liquids depending on
their solubility and their partial
press. in the mix.
Partial press. of water vapor affect the
partial press. of gases.
Measurement
As gas volume vary with temp. and
press and amount of water vapor in
them varies it is imp. to correct its
measurement to a set of standards.
- Recording spirometors.
- N2 emits light in electric field in
vacuo.
- O2 + Co2 electrodes.
- infrared absorption spectroscopy.
- chromatography and mass
spectrometry.
• STDP O C, 760mm Hg, dry
(Standard temp. and press. dry).
• BTPS Body temp. and press.,
saturated with water vapor.
• ATPS Ambient temp., press.
Saturated with water vapor.
Partial pressure of a gas
• Partial pressure of a gas in a mix. of
gases is equal to the total press.
multiplied by the fraction or % the
gas in the mixture. (P).
• Diffusion of a gas is affected by:
1. Solubility
2. Molecular weight as it increase
when Mwt is low
Co2 diffusion >O2
Thanks
Lung Volumes &
Capacities
Lung volumes
• Tidal volume: is the amount of
air that moves into the lung
with each normal inspiration.
• Inspiratory reserve volume:
amount of air inspired by a max.
insp. after a normal insp.
• Residual volume: amount of air
left in the lungs after max. exp.
• Expiratory reserve volume:
amount of air expired by a max.
exp. After a normal exp.
• Respiratory minute volume:
(Pulmonary ventilation) amount
of air inspired per min.
Capacities
• Vital capacity: amount of air
expired by a max exp. after a
max. insp.
• Inspiratory capacity: amount of
air inspired by a max. insp. after a
normal exp.
• Expiratory capacity: max exp.
after normal insp.
• Total lung capacity: amount of air
present in lungs after max. insp.
Pulmonary function
tests
• Function:
1. Diagnosis.
2. Follow up.
3. Compensation.
4. Preoperative assessment.
PFT
1. Spirometry: pocket, microlab,
computerized.
- FEV1: forced expiratory volume in the
first second.
- FVC : forced vital capicity.
- Peak expiratory flow rate PEFR.
- Maximum expiratory flow loop.
1. Peak flow meter: PEFR.
2. Blood gases.
3. Transfer factor.
4. Static lung volumes.
Quiz
• A patient with nocturnal cough
showed the following findings in
PFT: FEV1 2L, FVC=4L, FEV1 after
salbutamol inhaler=2.5L, his
diagnosis is:
• 1. Chronic bronchitis.
• 2. Emphysema.
• 3. Obstructive lung disease.
• 4. Asthma.
• 5. Restrictive lung disease.
PFT in asthma diagnosis
• 1. FEV / FVC
<70%.
• Peak flow meter:
I. Spontaneous variability 20%.
II. Reversibility
15%
III.Provocation:
a. Exercise
20%
b. Histamine challenge.
Gas exchange
• Inspired air will be saturated with
water vapor in the lungs decreasing
PO2 in alveoli.
Insp. air
EXP. air
Po2
116
PCo2
32
PH2O
47
PN2
565
PO2
158
PCo2
0.3
PO2
100
PH2O
5.7
PCo2
40
PN2
596
PH2O
47
PN2
573
Oxygen transport
Oxygen transport:
• O2 delivery to the tissues
depend on:
• 1. O2 entering the lungs.(PO2)
• 2. Adequacy of gas exchange.
• 3. Blood flow to the tissues.
• 4. Capacity of the lungs to carry
O2.
Gas transport between
lungs and tissues:
• Oxygen diffuses out of alveolar gas into
the blood stream and CO2 diffuses from
the blood into the alveoli down their partial
press. gradients.
• Diffusion capacity of the lungs for a given
gas is directly proportional to the alveolocapillary membrane (pulm. epithelium,
capillary endothelium & their basement
membranes) and inversely proportional to
its thickness.
Carriage of O2:
• 1. Dissolved in plasma: 2%, amount
dissolved depend on O2 tension, at PO2
(100), 0.3 ml dissolved/100ml while at PO2
40 only 0.12 ml/100ml blood (venous).
• Dissolved O2 reaches the tissues, imp. For
cornea & cartilage. It can be increased by
increasing inhaled O2.
• 2. Combined with Hb: 98%, each Hb
molecule carries 4 O2 molecules? and
each combination enhances the next?
Oxygen dissociation
curve