Transcript Slide 1

Breakdown of Topics in Respiratory
Physiology:
Ventilation, Gas Exchange, Control of
Respiration
Respiratory Physiology
1
Functions of the
Respiratory System
•
•
•
•
Respiration
Acid-base balance
Enabling vocalization
Defense against pathogens
and foreign particles
• Route for water and heat
losses
2
General Concepts of Respiration
• Ventilate: bring the oxygen to the
blood
• Gas exchange: diffusion of gasses
from alveoli into blood; then
gasses go to/from erythrocytes; to
/from Hemoglobin
• O2 utilization: Mitochondria need
the oxygen to make ATP (cellular
respiration)
3
Ventilation
• Ventilation is the process of bringing air into and out of the lungs.
• Lungs are the only organs that do not have smooth muscle in them.
They are just elastic tissue.
• The lungs cannot inflate on their own. They need to be tethered to
muscles in order to get volume changes, which causes pressure
changes, which regulate air flow.
• There are pressure gradients from the partial pressures of gasses. If
the partial pressure of a gas is increased, the concentration of that
gas increases, too.
• Your lungs also contain millions of macrophages, so they are a good
line of defense against pathogens. They also get rid of the dust and
other debris that accumulates in the lungs.
• They are also a route of heat and water loss. When you exhale, you
lose water vapor and heat. 90% of the heat lost from your body is
from exhaling.
4
Gas Exchange
• In the lungs, oxygen moves into the blood,
driven by pressure gradients, which are
similar to concentration gradients.
• Oxygen will diffuse down its concentration
gradient (from the lungs, into the plasma,
and into the cells) while CO2 moves down
its concentration gradient (from the cells,
into the plasma, and into the lungs).
• These two gas exchanges are called
external respiration.
5
Oxygen Utilization
• When oxygen enters the cells, some of it enters the mitochondria,
which uses oxygen as an electron acceptor (the mitochondria places
hydrogen ions on the oxygen and turns it into water). This excess
water leaves the cell and enters the tissues.
• The removal of oxygen from the plasma and the addition of water in
the tissues creates a driving force (known as the Starling principle)
to continuously draw oxygen into the tissues, since the water in the
tissues has diluted the number of particles there, and oxygen, as a
particle, will be sucked into the tissues.
• The gas exchange that occurs at the tissue capillary beds is called
internal respiration.
• The actual use of oxygen as a final electron acceptor(during a
process called oxidative phosphorylation) is called cellular
respiration.
6
General Concepts: Airway Anatomy
Surface area 70 sq
meters- each lung
(size of a large lecture
hall)!
Barrier/ thickness to
diffusion 0.2 microns
7
Carbon Monoxide
• This is an odorless, colorless gas from incomplete
burning of fuels.
• Carbon monoxide binds to hemoglobin 200x more
strongly than oxygen, so it drives the O2 from the
hemoglobin, and attaches in its place and stays there.
Carbon monoxide decreases the amount of oxygen that
can be transported by hemoglobin
• The person dies from suffocation; it makes the lips
cherry red.
• Cyanide poisoning kills in the same way, but the lips are
blue (cyanosis).
8
CO2 Transport
• When oxygen is on the hemoglobin molecule, it is called
oxyhemoglobin.
• Dissociation of oxyhemoglobin is when the oxygen is
released and enters the tissues.
• This dissociation increases as the pCO2 levels increase.
• In other words, when the carbon dioxide levels rise,
oxygen will jump off the hemoglobin and into the tissues.
Therefore, the most effective stimulus to the respiratory
center is an increase in pCO2.
• The waste product of cellular respiration is carbon
dioxide.
• CO2 will then attach onto the hemoglobin and be taken
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to the lungs to be expelled.
CO2 Transport
• CO2 is carried to the lungs on the hemoglobin, after the oxygen has
left to enter the tissues.
• The carbon dioxide reacts with water in the RBC to form carbonic
acid, which then breaks apart into a hydrogen ion (which lowers
blood pH) and a bicarbonate ion (which raises blood pH).
CO2 + H2O  H2CO3  H+ + HCO3This reaction is reversible, and would go mainly to the right in the
tissues and to the left in the lungs.
CO2 is transported in the blood predominately in the form of
bicarbonate.
The number of H+ ions in the blood depends partly on the amount of
CO2 in the blood. The more CO2 in the blood, the more H+ in the
blood, which makes the blood acidic. If the blood is too acidic,
bicarbonate ions are absorbed to raise the pH. If the blood is to
alkaline, bicarbonate ions are excreted by the kidneys.
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Respiratory System Contribution to
pH Balance in the Blood
• If a person has excess H+ ions in the blood (acidosis),
they will breathe more rapidly.
• If the person has an airway obstruction (such as
asthma), they cannot exhale the excess CO2.
• Because the H+ are building up, the carbonic acid will
also build up, causing a drop in pH (acidosis) in the
blood.
• Enzymes in the body cannot work outside of their
optimal pH range, so chemical reactions come to a halt.
• Hyperventilation results in too little CO2 in the blood, so
the person has a high pH (alkalosis), which also
denatures enzymes.
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Control of Respiration
• Changes in lung volume, and thus
ventilation, are dependent upon the
change in thoracic cavity volume.
• Alterations in the space inside the thoracic
cavity are the result mainly of the
contraction of the diaphragm, intercostal
muscles.
• These muscles are innervated by neurons
in the respiratory centers of the brain stem
(medulla and pons).
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Respiratory Centers:
Medulla oblongata and Pons
• Pons (Pneumotaxic Center)
– decreases respiratory rate
• Medulla
– Dorsal respiratory group
• Increases inspiration rate
– Ventral Respiratory Group
• Inactive during quiet
respiration
• Active during forced
respiration
Figure 41-1; Guyton & Hall
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Chemoreceptors
• Carbon Dioxide, Hydrogen Ions
– Central chemosensitive area of
medulla; senses levels of CO2
and H+ in CSF (both are acids)
• Oxygen
– Peripheral chemoreceptors; sense
oxygen levels in blood
• Aortic chemoreceptors (CN X)
• Carotid chemoreceptors (CN IX)
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Respiratory Chemoreceptors
• In the cardiovascular lecture, we learned about
baroreceptors detecting blood pressure in the aortic arch
and carotid sinus.
• The respiratory system has chemoreceptors in those
areas, too. They function to detect the O2, CO2, and pH
levels of the blood.
• The medulla oblongata also has chemoreceptors that
monitor pH. This information is sent to the other parts of
the respiratory centers (pons and other areas in the
medulla oblongata) to allow them to alter breathing rate
to maintain proper blood pH.
15
Control of Respiration
• Relaxed breathing only requires the
diaphragm to contract for inspiration, and
for the diaphragm to relax for expiration.
• Forced breathing requires the diaphragm
plus muscles that raise and lower the ribs
(external intercostals for inspiration,
internal intercostals for expiration).
• The respiratory centers are most sensitive
to the level of CO2 in the blood, rather than
the levels of oxygen.
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Control of Gas at Cellular Level
• The flow of blood through capillaries is
controlled by sphincters on the arterioles and
capillary beds to adjust the amount of blood
flowing to particular tissues.
• Cells and tissues that are undergoing increased
aerobic activity have less oxygen and more
CO2, lower pH, and increased temperature.
• When CO2 levels in the tissues are too high, the
smooth muscle sphincters relax to allow more
blood flow to increase gas exchange.
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Ventilation
Inspiration (inhalation)
Expiration (exhalation)
Normal inhalation, normal exhalation
Forced inhalation, forced exhalation
Concepts:
1. Pressure gradient created by
volume changes (Boyle’s Law)
2. Anatomy of lung and chest wall
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Inhalation and Exhalation vs. Force
• Ventilation requires ATP during inhalation, but
normal exhalation does not require ATP.
• Some people with respiratory problems need to
work at exhalation as well by using skeletal
muscle, and this means that they need to use
more ATP. Lungs are not muscular structures.
They need the skeletal muscles in the thoracic
cage to change the thoracic volume, which
changes the pressure gradients.
• Air flows from high pressure to low pressure.
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Boyle's Law
P1V1=P2V2
• Pressure and volume are inversely related
(if other variables are kept constant.)
Boyle’s Law
assumes normal
circumstances,
not a person
who is in high
altitude or who
has variation in
body
temperature.
20
Air Pressure in Lungs
• Every time a molecule strikes the wall of a
container, it causes pressure. In a larger
container with fewer molecules, it takes a while
to strike the wall randomly, so there is less
pressure.
• The number of impacts on a container wall is the
pressure.
• The lungs must have a volume change to create
a pressure change, which is required to have air
move into and out of the lungs.
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Air Pressure in Lungs
• The diaphragm is the muscle that mostly
contributes to the volume change. When it
contracts, it pulls downward, and the
volume of the thoracic cavity increases.
• The external intercostals elevates the
ribcage, giving the lungs more room, so
they also increase the lung volume.
• Those two muscles cause increased
volume.
22
Air Pressure in Lungs
• Because the lungs are tethered to the thoracic cavity,
when your chest wall expands, your lungs expand with it.
The lungs are stuck to the chest wall because the serous
fluid in the pleural cavity makes the lungs stick to the
chest wall like two pieces of wet glass stuck together.
• When the lungs expand, their volume expands. That
means there is less pressure in the lungs than there is in
the outside air. Since air moves from high to low
pressure, air flows into the lungs.
• As air flows in, the alveoli expand, so the volume in each
air sac expands, so the pressure in the alveoli lowers. Air
in the conducting passages (bronchi) is at higher
pressure, so it will move from high to low pressure areas.
Therefore, air will move into the alveoli.
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Air Pressure in Lungs
• Air has weight; atmospheric pressure is 760 mmHg at sea level
(much less weight and pressure at high altitudes).
• Since air will flow from higher pressure to lower pressure areas, to
get the air to flow into our lungs, we need to have a lower pressure
in our lungs.
• We can decrease the pressure in our lungs by expanding the
volume. As we expand the volume of our thoracic cavity (taking a
breath), the pressure in the lungs drops, and air flows into the lungs.
• It is a small pressure difference, but it is enough to get 500 ml of air
to come into your lungs.
• At higher altitudes, even though the amount of oxygen is the same
(21%) there is less air pressure. At 8,000 feet in elevation, there is ¼
less pressure. This makes it harder to breathe.
• When you exhale, you simply relax the muscles, and if the lungs are
not being pulled open any more, the elastic tissue there will recoil,
making the lung volume smaller, so the pressure there increases.
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Lung Compliance
• Lung Compliance is how much the lung volume changes when the
pressure changes.
• Compliance can be considered the opposite of stiffness.
• A low lung compliance (increase in stiffness) would mean that the
lungs would need a greater than average change in pressure to
change the volume of the lungs. Instead of needing only 10 mmHg
pressure difference between the outside air and the lungs, would
now need a 20 mm difference.
• A high lung compliance would indicate that little pressure difference
is needed to change the volume of the lungs.
• More energy is required to breathe in a person with low lung
compliance. Persons with low lung compliance due to disease
therefore tend to take shallow breaths and breathe more frequently.
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Gases move down pressure gradients
Flow Rule:
P atm = 760 torr
How are the
pressure gradients
changed?
Patm – Palv
Resistance
p alveolar = 758 torr
Air moves from high
to low pressure
According to Boyle’s
law we will need to
create volume
changes!
PROBLEM! THE
LUNGS ARE NOT
MUSCULAR
STRUCTURES!
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Air Pressure in Lungs
• We are looking at two types of air
pressures: atmospheric pressure, and the
pressure of air deep in the lungs, called
the alveolar (pulmonary) pressure.
• As long as there is a difference in pressure
between these two, there will be a
pressure gradient, and air will flow.
• If they equal each other (such as during a
punctured lung, called a pneumothorax),
air will not flow.
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Air Pressure in Lungs
• Take a breath in and stop. Enough air has
come in now so that the air pressure in the
alveoli equals the atmosphere, so you no
longer get more air flowing in.
• When you relax, the lungs recoil, air
comes out, and when the two pressures
equal each other, air stops flowing out.
• You will get zero pressure differences
upon maximum inhalation and exhalation.
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Oxygen-Hbg Dissociation Curve
• X-axis is partial pressure
of oxygen (pO2)
• Y-axis is saturation of
Hgb with O2
• The partial pressures of
respiratory gases found in
arterial blood correspond
most closely to those
partial pressures found in
the alveoli.
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Oxygen-Hbg Dissociation Curve
• Hgb in the blood leaving
the lungs is about 98%
saturated with O2.
• This graph demonstrates
that 98% of Hbg is still
saturated when pO2 is
only 70 mm (when it first
arrives in the tissues).
• By the time pO2 reaches
100mm (in the lungs),
Hbg is already 100%
saturated.
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Significance
• In the lungs, pO2 is 100 mm Hg.
Hemoglobin is still 100% saturated at this
pO2 level.
• In the body cells, pO2 is 40 mm Hg.
Hemoglobin is still about 75% saturated at
this low pO2 level.
• The difference of 25% saturation means
that hemoglobin gives up only about 25%
of its O2 to body cells as it passes by.
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Left shift
CAUSE:
pH increased
CO2 decreased
Temperature decreased
32
Right shift
CAUSE:
pH decreased
CO2 increased
Prostaglandin release (fever) 33
Shifts
• A left shift will increase oxygen's affinity for hemoglobin.
– In a left shift condition (alkalosis or hypothermia)
oxygen will have a higher affinity for hemoglobin (it
won’t leave!).
– This can result in tissue hypoxia even when there is
sufficient oxygen in the blood.
• A right shift decreases oxygen's affinity for hemoglobin.
– In a right shift (acidosis or fever) oxygen has a lower
affinity for hemoglobin. Blood will release oxygen
more readily.
– This means more O2 will be released to the cells, but
it also means less oxygen will be carried from the
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lungs in the first place.
Vacuum in Lungs
• There is another anatomical structure you need
to remember: the plural cavity. Each lung is
surrounded by a parietal and visceral serousal
membrane.
• The serousal cells make a lubricating fluid so the
lungs don’t rub against the thoracic cavity,
causing heat generation, which can denature
proteins.
• This fluid has cohesive properties. If you put two
pieces of wet glass together, you have to use
more force to pull them apart than if they were
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dry. You have to break the vacuum.
Vacuum in Lungs
• The surface of the lungs are tightly
stuck to the surface of the thoracic
wall.
• If they are disengaged, they will recoil
like deflated balloons.
• If the vacuum in the pleural cavity is
broken, the lung will collapse.
• They need to be reinflated by the
administration of oxygen.
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Mechanics of Ventilation
• Normal Inspiration
• Is an active process (It’s work! It
uses ATP)
– Contract Diaphragm and it moves
inferiorly to increase thoracic
volume -60-75% of volume change
– Contract external intercostals

Forced Inspiration
Accessory muscles
needed
Sternocleidomastoid
Scalenes
Serratus anterior
Others (erector spinae)

Diaphragm
When the chest wall moves, so do the lungs! Why are
the lungs right up against the chest wall?
Pleural Space or Cavity
1.
a vacuum (contains no
air)
2.
pleural fluid (water) has
surface tension
Result? Lung
moves with the
chest wall
Lungs are not muscular
organs, they cannot actively
move. They move with the
chest wall.
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What happens if the lung dissociates from the chest wall?
•
•
•
Pneumothorax: air in the pleural cavity
Hemothorax: blood in the pleural cavity
How?
– Injury (Gun shot, stabbing)
– Spontaneous (tissue erosion, disease lung)
– Bleeding wound
•
•
Chest wall recoils outward (barrel chest)
Lung recoils inward (atelectasis = alveolar, lung collapse)
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Mechanics of Ventilation
• Normal Expiration-
• A Passive process
• Simply relax the muscles of
inspiration
• Rely on the elastic properties
of lung (like a balloon
deflating on its own)
• Forced Expiration
• Relax muscles of inhalation
AND
• Contract internal intercostals
• Contract Abdominal muscles
• Internal and external obliques
• Transverse abdominis
• Rectus abdominis
40
Emphysema
• COPD (chronic obstructive pulmonary disease)
is emphysema plus chronic bronchitis.
• Emphysema is generally caused by smoking.
• The alveoli have broken, leaving spaces where
gas exchange cannot take place.
• Compliance decreases, so It is difficult to expel
the air in the lungs.
• Each inhalation is a forced inspiration also.
• When the ribs are continually raised with each
breath, they eventually remain in the upright
position, causing a barrel chest.
41
Exhalation Problem: COPD
• Normal exhalation is
passive, requires no
ATP. But forced
expiration (such as
emphysema patient)
recruits abdominal
muscles. The muscles
enlarge with time,
creating a barrelshaped chest, typical
of emphysema
patients and COPD.
42
COPD
• In everyone, the midsized bronchioles do not have
cartilage rings to hold them open, and during exhalation,
the sides of the bronchioles collapse and touch each
other.
• If there is not enough surfactant, they stick to each other
with greater strength (like two wet pieces of glass), and
the person has to forcefully exhale with each breath to
overcome the cohesiveness of the fluid.
• Surfactant is like adding soap to the fluid so the surfaces
come apart easier.
43
Exhalation
• Giving oxygen in high concentration helps get air into
their lungs, but it reduces the drive for them to breathe.
CO2 is a powerful driving force for ventilation. When a
person has COPD, they have less CO2, and oxygen
becomes the driving force.
• If we give them oxygen, the drive for them to breathe
becomes diminished. They eventually wind up on a
positive pressure ventilator, but the disease progresses,
and they die from suffocation.
• A continuous positive airway pressure machine is called
a CPAP machine.
44
CPAP Machine
45
Both the Lung and Chest Wall are Elastic
• Both lung and chest wall have the
tendency to recoil
• What is recoil? Tendency to snap back
to resting position
(like a stretched rubber
band recoils when you
let go of one end)
The chest wall recoils outward (springs out)
The lung recoils inward (ie. it collapses!)
46
Palv (mmHg)
• Increase in lung volume decreases intra-alveolar pressure
(we now have a pressure gradient) = air goes in.
• Decrease in lung volume raises intra-alveolar pressure
above atmosphere = air goes out.
expiration
inspiration
Palv=0
Palv=+1
Palv=0
Palv=0
Breath vol. (L)
Palv= -1
0.5
When the pressure at the alveoli are at 0 (no difference between their pressure and
atmospheric pressure), no air flows in or out of the lungs.
Pressures
Patm and Palv
create the pressure
gradient that drives
ventilation
Atmospheric Pressures (Patm)- pressure of the outside air (760mmHg=760 torr
= 1 atm).
Intra-alveolar pressure (Palv) pressure within the alveoli of the lungs. Equal to
Patm (0mmHg) at rest, but varies during phases of ventilation.
Intra-pleural pressure – (Pip) pressure in the intra-pleural space.
• Pressure is negative because of the lack of air in the intrapleural space,
lymph drainage, and opposing forces of lung and chest wall.
48
Air Flow
• If atmospheric pressure is greater than
alveolar pressure, air flows into the lungs.
• If atmospheric pressure is less than
alveolar pressure, air flows out of the
lungs.
• Transpulmonary pressure is the difference
between the alveolar and intra-pleural
pressures.
49
Positive vs. Negative Pressure
Breathing
P atm = 760 torr
•
•
•
•
Normally, the pressure
gradient is produced by
changing palv
Positive
Air moves from high
Pressure
to low pressure
breathing
This is called negative
pressure breathing
If one changes patm, then this
is positive pressure breathing
Ex. bag, cpr, mouth to mouth
p alveolar = 758 torr
Is this positive or negative
pressure breathing?
Negative
Pressure
breathing
50
18
Iron Lung
• This chamber is an iron lung, invented for polio patients,
whose respiratory nerves were paralyzed. When we are
normally breathing, we are changing thoracic volume, so
we are using negative pressure breathing. But a
paralyzed person cannot move their respiratory muscles.
• It works like a reverse vacuum. There is less air pressure
in the tank, so there is less pressure on the chest, so the
chest recoils more, to help get air in. The vacuum then
reverses, increases pressure on the chest, air flows out.
51
Acute Mountain Sickness
(Altitude Sickness)
• When you visit someone in a high elevation (5,000 m)
you might get acute mountain sickness.
• Symptoms:
– Severe headache, fatigue, dizziness, palpitation and nausea.
• Cause:
– Pulmonary edema.
• Why do you get pulmonary edema?
– High elevations have lower pO2 levels.
– This causes hypoxia (lack of oxygen) in the pulmonary
capillaries
– This causes increased pulmonary arterial and capillary
pressures (pulmonary hypertension)
– That causes the pulmonary edema
52
Respiratory Cycle
53
Ventilation Volume
• When you breathe in, you inhale about 500 ml. You exhale about
500 ml. Therefore, 500 ml is your TIDAL VOLUME.
• Not all 500 ml gets down deep to your alveoli. About 150 ml of it
stays in the conductive zone (bronchi and trachea). About 350 ml
reaches the alveoli. That is considered your alveolar ventilation
volume.
• That is the amount of air that can undergo gas exchange. If you
want to calculate how much air moves in and out per minute, take
the tidal volume and multiply it by breathing rate (about 12 breaths
per minute for adult, 20 for children).
500 x 12 = total ventilation
Tidal volume – 150 x 12 = alveolar ventilation
54
Lung function
tests
•
•
• Spirometry
– Static lung tests
• Volumes and capacities
• No element of time
involved, ie. How long
does it take you to push
the air out? Normal
expiration takes 2-3 x
longer than inspiration
•
Lung volumes are assessed by
spirometry.
Subject breathes into a closed
system in which air is trapped
within a bell floating in H20.
The bell moves up when the
subject exhales and down when
the subject inhales.
– Dynamic lung tests
• Time element, rate of
exhale
• How much, how quickly?
55
Spirometry measures lung volumes
• The tidal volume, vital capacity, inspiratory capacity and
expiratory reserve volume can be measured directly with
a spirometer.
• Most air (80%) is exhaled during the first second of
exhalation. You take a maximum inhale, then a
maximum exhale (vital capacity). The pen moves down
the paper, showing time.
• You can calculate how much air you blew out (vital
capacity), and the amount of air you blew out in one
second (expiratory reserve volume in one second).
• Expiratory reserve volume divided by vital capacity
should be 80%. If you are less than 80%, it is suggestive
of an obstructive pulmonary disorder.
56
ERV
ERV/VC
=80%
VC
ERV
ERV/VC
=47%
VC
Dynamic
Lung Tests
Someone with
COPD takes
longer than
one second
to exhale
80%.
57
Obstructive Lung Diseases
• Obstructive lung diseases are
characterized by inflamed and easily
collapsible airways, obstruction to airflow,
and frequent hospitalizations.
• Examples
– Asthma
– Bronchitis
– Chronic obstructive pulmonary disease
(COPD)
58
Restrictive Lung Diseases
• These are extrapulmonary or pleural respiratory
diseases that restrict lung expansion, resulting in a
decreased lung volume (rapid, shallow
breathing), an increased work of
breathing, and inadequate ventilation
and/or oxygenation. Decreased vital
capacity.
–
–
–
–
Cystic Fibrosis
Infant Respiratory Distress Syndrome
Weak respiratory muscles
Pneumothorax
59
Capacities are two or more volumes added together
60
Capacities are two or more volumes added together
These are measured with a
spirometer
This is estimated, based on
height and age
These are calculated
FRC = ERV + RV
TLC = RV + ERV + TV + IRV
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Quiz yourself (color version)
1
3
8 9
10
4
5
7
2
6
62
Quiz yourself (what the test will look like)
1
3
8 9
10
4
5
7
2
6
63
You don’t need to memorize the normal numbers, just the definitions
•
•
Respiratory Cycle: A single cycle of inhalation and exhalation
Respiratory rate: number of breaths per minute (usually about 12-18; children
higher 18-20).
•
•
•
•
Tidal Volume: normal breath in and out. Usually about 500 ml.
Inspiratory Reserve Volume: take in a normal breath, stop, now inhale as
much more as you can. In other words, this is the amount of air that can be
forcefully inhaled after a normal inhalation.
Expiratory Reserve Volume (Expiratory capacity): take a normal breath
in, a normal breath out, then breathe out the most you can. In other words,
this is the amount of air that can be forcefully exhaled after a normal
exhalation. This is the air needed to perform the Heimlich maneuver. The
maneuver decreases the thoracic cavity volume, causing increased
pressure in lungs. That causes forced air with high pressure to be expelled
from the lungs.
Residual volume: The amount of air left in your lungs after you exhale
maximally. This air helps to keep the alveoli open and prevent lung
collapse. This is estimated based on height and age.
64
Capacities are two or more volumes added together
65
You don’t need to memorize the normal numbers, just the definitions
•Vital capacity: The volume of air a patient can exhale maximally after a forced
inspiration. Maximum deep breath in, then exhale as much as possible. Vital
capacity divided by expiratory reserve volume should be 80%. If it is lower than
that, the person has either obstructive or restrictive lung disease. To tell which
one, look at VC. If it is normal, it is obstructive. If it is low, they have restrictive
lung disease.
•Total Lung Capacity (TLC): the sum of all lung volumes
•Inspiratory Capacity: amount of air for a deep breath in after normal
exhalation
•Functional residual capacity: amount of air left in your lungs after a normal
exhale. You have to calculate this:
•FRC = ERV + residual volume.
–
–
–
In COPD, their FRC increases.
They have a barrel chest
The lungs don’t have as much recoil, have decreased tidal volume, cannot exhale enough
66
Capacities are two or more volumes added together
67
You don’t need to memorize the normal numbers, just the definitions
•
•
•
Dead Space: Area where air fills the passageways and never contributes to
gas exchange. Amounts to about 150 ml.
Minute Respiratory Volume (MRV): tidal volume x respiratory rate. This
calculation does not take into account the volume of air wasted in the dead
space. A more accurate measurement of respiratory efficiency is alveolar
ventilation rate.
Alveolar Ventilation Rate (AVR)
AVR = (TV – Dead Space) x Respiratory Rate
Summary of lung calculations
FRC = ERV + RV
TLC = RV + ERV + TV + IRV
MRV = TV x RR
AVR = (TV – Dead Space) x RR
You DO need to
know these
formulas.
68
Lung Capacity and Disease—
Summary
• Obstructive Disease:
– Normal VC
– Increased TLC, RV,
FRC.
– VC/ERV is less than
80%
• Restrictive Disease:
– Decreased VC
– Decreased TLC, RV,
FRC
– VC/ERV less than
80%
FRC: ERV +RV. Why is this important?
It’s the volume of air in your lungs at the end of a normal
exhale.
It represents the normal equilibrium position of your chest
wall trying to spring out and lung to recoil, but forced
together due to pleural cavity.
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Sample Questions
Minute Respiratory Rate is the volume of air that enters the airways (passes the
lips) each min.
MRV = Tidal volume x rate of breathing
= (500 ml/breath) x 12 breaths/min
= 6,000 ml/min
Alveolar ventilation rate is the volume of air that fills all the lung’s respiratory
airways (alveoli) each min. In a normal, healthy lung, this might be:
AVR = (tidal volume – dead space volume) x rate of breathing
= (500 ml/breath – 150 ml) x 12 breaths/min
= (350 ml/breath) x 12 breath/ min
= 4, 200 ml/min
In a diseased, poorly perfused lung, this value may well be much lower.
Then, is panting an example of hyper, normal, or hypoventilation????
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Hyper and Hypo Ventilation
• The deeper regions of your lungs get more
blood flow and the upper regions have more air
flow.
• If you hyperventilate, the rate and depth of
ventilations increases, so more air gets to
alveoli. After voluntary hyperventilation, apnea
(no breathing) may occur b/c the arterial blood
contains less carbon dioxide
• Hypoventilation is dealing only with conductive
zone. When you pant, you are just shifting air in
the conducting zone. You are not increasing air
to the alveoli. Panting is hypoventilation.
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Respiratory vs. Metabolic
Acidosis and Alkalosis
•
•
•
•
•
•
RESPIRATORY ACIDOSIS AND ALKALOSIS is abnormal blood pH which is caused
by abnormal breathing rates. It is not necessarily a disease, since hyperventilating
from stress is not a disease.
Respiratory alkalosis is caused by hyperventilation. This increases the amount of
CO2 that you are exhaling. CO2 is an acid, so if you hyperventilate, you are exhaling a
lot of acid, so your blood plasma pH will increase (alkalosis)
Respiratory acidosis is caused by hypoventilation. This decreases the amount of
CO2 that you are exhaling. If you hypoventilate, you are not exhaling enough acid, so
your blood plasma pH will decrease (acidosis). Respiratory acidosis can also be
caused by interference with respiratory muscles by disease, drugs, toxins.
METABOLIC ACIDOSIS AND ALKALOSIS is abnormal blood pH which is not
caused by abnormal breathing rate.
Metabolic acidosis can be caused by
– Salicylate (aspirin) overdose
– Untreated diabetes mellitus (leading to ketoacidosis)
Metabolic alkalosis can be caused by
– excessive vomiting (loss of acid from stomach)
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Compensations for Respiratory vs.
Metabolic Acidosis and Alkalosis
• Respiratory alkalosis can be compensated by
– excreting an alkaline urine (kidneys excrete more bicarbonate)
– Cannot hypoventilate since hyperventilation is the problem in the first
place!
• Respiratory acidosis can be compensated by
– excreting an acidic urine (kidneys excrete more H+)
•
Cannot hyperentilate since hypoventilation is the problem in the first place!
• Metabolic acidosis can be compensated by
– excreting an acidic urine
– hyperventilation
• Metabolic alkalosis can be compensated by
– Excreting an alkaline urine
– Hypoventilation
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Acid-Base Conditions
• Excessive diarrhea
Causes the problem of low HCO3 (bicarbonate)
Leads to pH in blood (acidosis)
Lungs Compensate by:
pCO2 (hyperventilation, which decreases the CO2
content in the blood, thereby removing acid
from the blood)
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Acid-Base Conditions
• Ingesting excessive stomach antacids
Causes the problem of high HCO3 (bicarbonate)
Leads to pH in blood (alkalosis)
Lungs Compensate by:
pCO2 (hypoventilation, which increases the CO2
content in the blood, thereby adding acid
from the blood)
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Acid-Base Conditions
• Aspirin overdose
Causes the problem of high acid, low HCO3 (bicarbonate)
Leads to pH in blood (acidosis)
Lungs Compensate by:
pCO2 (hyperventilation, which decreases the CO2
content in the blood, thereby removing acid
from the blood)
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Acid-Base Conditions
• Anxiety or hysteria with panting
(hypoventilation)
The patient hypoventilates
Causes the problem of high pCO2
Leads to  pH in blood (acidosis)
Lungs Compensate by:
 HCO3 (by hyperventilation, which decreases the CO2
content in the blood, thereby removing acid
from the blood)
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Pulmonary Embolism
• Pulmonary Embolism: blockage of the pulmonary
artery (or one of its branches) by a blood clot, fat, air or
clumped tumor cells. The most common form of
pulmonary embolism is a thromboembolism, which
occurs when a blood clot, generally in a vein, becomes
dislodged from its site of formation, travels to the heart,
goes into a pulmonary artery, and becomes lodged in the
smaller artery in the lungs, blocking blood flow and
oxygen to that region of the lung.
• Symptoms may include difficulty breathing, pain during
breathing, and possibly death. Treatment is with
anticoagulant medication.
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