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respiratory physiology
Respiration: Physiology
Three forces involved in breathing
Torque: during inspiration, the ribs
have been elevated and twisted (at
chondral portion). Release of
muscular pull (end of inspiration)
causes ribs to unwind. The force
(torque) generated causes a
restoration force (return to neural
rib position).
Elasticity: lungs are highly elastic
and have been stretched during
inhalation due to expansion of the
thorax. When inspiratory muscles
stop contracting, then lungs want to
return to their resting shape and
Gravity: gravity acts on ribs to pull
them downward (during passive
exhalation) and works on abdominal
viscera with a downward force that
helps increase the area for the lungs
(during inhalation).
Animation of rib and diaphragm
• Inspiration: Active contraction of
diaphragm, external intercostals and
possibly scalene muscles expands
thoracic cavity. Lungs through linkage
to thorax, expand too*. Negative
press. is created in lungs, thus air
rushes in until intra-alveolar pressure =
to atmospheric pressure.
• Exhalation: Muscles of inhalation cease
to contract. The dilated thorax-lung
complex generates slightly positive
pressure and air is exhaled. Restoring
forces provided by abdominal contents
under pressure, lung elasticity, and ribs
which have been elevated and twisted
will "unwind" to provide torque. The
expiratory forces are passive or
nonmuscular during passive
Lung volumes:
Tidal volume: (TV) Vol. of air inhaled and exhaled
during a single expiratory cycle. Varies according
– Adult male: 600cc at rest
• 1670cc light work
• 2030cc heavy work
– Adult female: 450cc at rest.
Inspiratory Reserve Vol: (IRV) Quantity of air
which can be inhaled beyond that inhaled in a tidal
vol. @1500cc- 2500cc
Expiratory Reserve Vol: (ERV): amt. of air that can
be forcibly exhaled following quiet/passive
exhalation @1500cc
Residual Vol.: (RV): quantity of air that remains in
lungs and airways after max. exhalation--ranges
from 1000 to 1500cc in yg. adult males+
• Dead air spaces: No matter how deeply
we inhale, @150cc of residual vol. is
nonfunctional for respiratory purposes-called dead air--remains in dead air
spaces (nasal cavity, trachea, bronchi,
bronchioles)--it is last to be inhaled
and first to be exhaled.
• Yawn = What causes a yawn?
• Hiccup = spasm of diaphragm
– Persistent = last more than 48 hours
– Intractable = last longer than a month
• Causes
– CNS problems (stroke, injury)
– Metabolic problems
– Irritation of nerves
Lung capacities**:
Inspiratory capacity (IC): maximum vol. of air that can
be inhaled from resting expiratory level (REL) (REL =
state of equilibrium between lungs and thorax).
Vital capacity (VC): quantity of air that can be exhaled
after maximum inhalation
Young adult males= 3500 to 5000cc (aver = 4600cc
or 4.6 L)
Young adult females= 3100cc aver.
Measurement influenced by size, sex, & age
Maximum reached in 20’s; declines there after (see
next slide)
**Lung volumes refer to physical differences in lung volume,
while lung capacities represent different combinations of
lung volumes
3. Functional residual capacity
(FRC): quantity of air in
lungs and airways at resting
expiratory level = 38% of VC
4. Total lung capacity (TLC):
vol. of air within lungs and
airways at end of max.
Vital Capacity Based on Age
& Gender
VC (ml)
Age (Years)
Respiratory Volumes
Percent Vital Capacity
Inspiratory Volume
Vital Capacity
Total Capacity
Tidal Volume
2. What does pink bracket represent?
Influences on Volumes and Capacities
Body position: Interpretation
Role of residual volume
It provides air in alveoli for aerating the blood, EVEN
though air exchange may not be taking place. If this
residual air were not there, then O and CO2 would rise
and fall with each breath.
Factors affecting VC (besides body position when
measure taken): age, strength of respiratory muscles,
pulmonary compliance (distensibility of lung-thorax unit)
Restrictive pulmonary disorders: anything that
damages or destroys lung tissue, causes it to be
fibrotic or edematous, obstructs alveoli, or
restricts lung expansion and contraction.
Lung sounds
A. Pulmonary fibrosis: Lungs have lost elasticity
due to fibrous (scarring or thickening) tissue
building up in lungs.
Causes include: sand, asbestos, coal dust,
Some cases are idiopathic or cryptogenic (or
perhaps autoimmune)
EX: cryptogenic fibrosing alveolitis: The
thickening and scarring reduces the amount of
oxygen that can pass into the blood vessels from
affected alveoli. Therefore, as the disease
progresses, less oxygen than normal is passed
into the body when you breathe
EX: idiopathic pulmonary fibrosis
– B. Asthma is a respiratory disease
of the bronchi and bronchioles. The
symptoms include wheezing,
shortness of breath, and sometimes
a cough that will expel mucus. The
airways are very sensitive to
irritants which can include pollen,
dust, animal dander, and tobacco.
Even being out in cold air can be an
irritant. When exposed to an
irritant, the smooth muscle in the
bronchioles undergoes spasms.
– Most asthma patients have at least
some degree of bronchial
inflammation that reduces the
diameter of the airways and
contributes to the seriousness of
the attack.
– Asthma is not curable, but IS
– C. Emphysema: slowly progressive
– Bronchioles become filled with
mucus and are cut off from alveoli.
– Alveoli lose elasticity and may
• Would this affect inhalation or
• Exhaling becomes hard…etc. etc.
– Capillaries that surround alveoli
break apart.
– Lungs less able to exchange oxygen
for carbon dioxide.
– Normal lung tissue replaced with
thickened/scarred (fibrosis) tissue.
• Relaxation Pressure Curve (BLACK LINE):
• Pressure you can create without any muscular
involvement--also could be called recoil
pressure curve.
• In order to generate the right hand side of the
curve, ask person to take in 100% of vital
capacity, relax completely and let elasticity,
etc. take over (measure air flow at mouth).
• Diagram is linear until reach outer limits at
extremes of vol. which suggests that limits of
distensibility and compressibility are being
Chest cavity/thorax; Lungs; Relax pressure curve
• p
During breathing
(quiet, speech, etc.)
• At lung vol. above 38%VC,
inspiratory process is active
• At lung vol. below 38%VC,
expiratory process is active.
• Lung volume at 38% termed
resting expiratory level (REL)
• *Any time a system
moves away from
equilibrium, the
action is ACTIVE.
• A. Recoil pressure from lungs is equal to
thorax (chest cage)
• B. At B, chest cage is at equilibrium point
(resting volume), thus rib cage doesn’t
generate recoil pressure at 55% of VC. Only
recoil force from lungs is available from this
point (C)..
• D. As more air is inspired, both the chest cage
and the lungs produce increasing recoil forces,
as both want to decrease in size (they are
being stretched further and further).
• When air is passively exhaled, the system goes
back to A, or resting level.
• E. As air is exhaled below resting level,
negative recoil pressure is generated, as
thorax wants to expand due to increased
compression . At same time, lung is producing
less recoil pressure, as it approaches
Inspiration: Types
Quiet inspiration:
– Air flows from regions of higher pressure to
regions of lower press.
– When airways open and respiratory pump is in
neutral position at resting expiratory level (rem.
lungs & thorax operate as unit), resp. apparatus
assumes a natural resting position (lungs
somewhat expanded, thorax somewhat
– Outside air = press. of inside air.
– Expansion of the lung/thorax decreases alveolar
air press. Air rushes in until at end of
inspiration cycle, alveolar press= atmospheric
press. Thus, alveolar press. = to outside air
press. at two times—end of exhalation and end
of inspiration.
– Accomplished mainly by diaphragm, with help
from the external intercostals
The forces of inspiration must overcome (a)
resistance to air flow thru respiratory airways, (b)
resistance to deformation of respiratory tissue, (c)
elastic recoil of lungs/thorax unit
Forced inspiration: more vigorous in nature than
quiet inspiration. Accessory m. are used to help
diaphragm & external intercostals increase thoracic
volume (e.g., scalenus, sternocleidomastoid).
• Expiration
• Quiet or passive expiration: use of
recoil forces (passive forces; nonmuscular). Energy created in
stretched elastic tissue is released and
lung/thorax unit recoils back to neutral
– The farther away you go from the neutral
position during inhalation, the greater are
the restoring forces for the lungs as
compared to the thorax.
Only lungs
force at
this lung
• Active expiration
• Muscular force is used
– Abdominal
– Thoracic muscles
Must use
forces when
below REL
• What happens when speech
• Changes occur in the
breathing cycle when we
breath for speech.
– Quiet breathing = 40%
inhalation; 60% exhalation
– Breathing for speech = 10%
inhalation; 90% exhalation
What Volume of air is
inhaled per cycle?
• For life breathing, it is about
one-tenth of our vital
capacity or approximately
500 ml.
• For speech breathing, it
depends on the projected
length of the utterance and
may vary from 25 to 65
percent of our vital capacity.
What about muscular activity when breathing for
During breathing for speech, muscles of inspiration
and expiration are at least minimally active.
– Example: External intercostals are active during
inhalation to raise ribs, and are active during
initial portion of exhalation to brake the descent
of lung-thorax unit. At the same time, internal
intercostals are active .
• The internal intercostals are important for
the production of stressed syllables.
• How does the relaxation
pressure curve relate to
inhalation and exhalation
for speech?
– Air pressure is needed for
vibration of the vocal [email protected]
6-7cm H2O for normal
– This pressure must be
maintained despite a lung
volume that decreases as we
exhale during speech.
– By looking at the passive
pressures available, we can
determine muscular activity.
Respiratory Mechanisms for Speech
To speak, we need a certain amount of subglottic
pressure (Ps) (pressure below the vocal folds
necessary to maintain vibration). Ps varies between
6-10 cm H20. Further, we constantly change pitch,
loudness, and duration of syllables when speaking,
requiring adjustments between muscular forces and
relaxation forces for constant Ps.
Ps for comfortable speech @ 6 cm
Ps for loud speech @10 cm
Ps for singing @20-25
Ps for soft speech = @3
As a person speaks, lung volume decreases, but air
flow (required for voicing) and pressure remain
• 55% VC
Ps pressure
needed for
Passive expiratory
pressure, but it’s
excessive for speech.
Use inspiratory muscles
to check.
Relaxation pressure
enough to generate Ps,
but continued
phonation requires
abdominal muscles
Glass must be at least 12cm in height.
The pressure of the water is directly
proportional to the depth of the straw.
Thus, 6cm H2O of water pressure = straw
6cm deep in water.
5cm pressure for 5 sec = sufficient air
pressure for speech
• How do we maintain constant positive
subglottal pressure needed for speech?
• For any given speech act (and Ps pressure
needs), a different balance of active and
passive muscular forces are required to
maintain adequate pressure at the differing
lung volumes.
• Speech also requires us to designate stress in
words, sentences.
• How do we signify stress?
– Pitch
– Loudness
– Duration
• Stress is accomplished at the respiratory level
by little pulses of increased Ps pressure
through the brief contraction of expiratory
muscles (ESP internal intercostals). 1 – 3 cm
H2O change
• To achieve subglottic pressure necessary for
speech, we can:
– Adjust expiratory force OR
– Adjust airway resistance
• Muscles involved in sustaining expiratory force:
– Abdominal muscles active during onset of
phonation for speech (and singing), and during
lung volumes below @55 % vital capacity.
• When inhaling for speech, the greater the
volume of air we inhale, the greater the need is
to check the excessive relaxation pressure
that is generated
• “Respiratory Center“ is located in the pons and
medulla oblongata of the brain stem. It is part
of the autonomic system and as such is not
controlled voluntarily (we can control some
aspects of breathing [e.g., during speech, or
singing]; voluntary control over this automatic
activity (breathing) is managed by or is the
domain of the cerebral cortex.
• While resting, the respiratory center sends
out action potentials that travel along the
phrenic nerves into the diaphragm and the
external intercostal muscles of the rib cage,
causing inhalation. Relaxed exhalation occurs
between impulses when the muscles relax.
Respiratory Centers
• Pontine respiratory center reduces duration of
inspiration (thus can cause respiration to
increase or decrease); receives input from
higher centers (e.g., cortex) and thus adjusts
inspiration for speech, exercising, etc.
• VGR = sends motor (contraction) signals for 2
seconds to diaphragm and external intercostals
for tidal inhalation. They also fire expiratory
neurons for 3 seconds to allow passive OR
active expiration. These set rhythmicity of
tidal or resting respiratory cycle.
• DGR = are involved in altering the pattern for
ventilation in response to the physiological
needs of the body for O2 and CO2 exchange
and for blood acid-base balance related to
metabolic demands.
Cortical level : voluntary control over respiration
for activities such as speech, singing, coughing,
Medullary rhythmicity center: sets basic
respiratory rate, and adjusts for levels of
activity and metabolic demands.
Pontine center: limits inhalation duration.
Proprioceptive stretch receptors in the lungs,
pleura, and thoracic wall convey information about
the degree of the filling of the lungs
• Greater muscular pressure
must be used to counteract
the relaxation pressure at
high lung volumes for SOFT
speech, as compared to
normal or loud speech.