Download partial pressure

1.
2.
3.
4.
5.
6.
Points to know and remember!
Air moves from regions of high pressure to low
pressure
Ventilation is a mechanical process which is
dependent on volume changes in the thoracic cavity
If thoracic volume changes thoracic pressure changes
If thoracic volume increases, gas pressure in the
thorax decreases and…
If thoracic volume decreases pressure increases
All atmospheric pressures refer to pressures at the
nose!
Objective 5
Ventilation
Ventilation (breathing) consists of:
1. Inspiration (inhalation):
air moves from the atmosphere into
the alveoli
2. Expiration (exhalation)
air moves from the alveoli into
the atmosphere
Air Movement Between the Atmosphere and Terminal
Bronchioles:
1. Air moves from areas of high pressure to areas of low
pressure
2. As air flows, it encounters resistance
Therefore, the flow of air through the passageways of the
respiratory system can be described by the following equation:
Air Flow =
Pressure 1 - Pressure 2
____________________________
Resistance
Where pressure 1 is atmospheric pressure pressure 2 is alveolar
pressure
Inhalation
Air moves from higher
pressure atmosphere into
lower pressure lungs
Exhalation
Air moves from higher
pressure lungs into lower
pressure atmosphere
Atmospheric pressure > Alveolar pressure
Atmospheric pressure < Alveolar pressure
760 mmHg – 759mmHg = a positive
pressure, therefore air enters
760 mmHg – 761mmHg = a negative
pressure, therefore air moves out
Air movement between terminal bronchi and alveoli:
powered by diffusion …..
Mechanism:
three relevant pressures
intra-alveolar pressure
(intrapulmonary pressure)
the pressure within the alveoli of the
lungs; this pressure fluctuates between
759 and 761 mmHg
Intrapleural pressure
the pressure within the pleural
cavity; this pressure is always less than
the pressure in the lungs by about 4 mmHg
atmospheric pressure
the pressure exerted by gases in the
atmosphere; at sea level, averages 760 mmHg
Intrapulmonary (Intra-alveolar) pressure falls below atmospheric pressure
during inhalation and rises above atmospheric pressure during exhalation:
During Inspiration
During Expiration
Atmospheric pressure = 760 mmHg
Intra-alveolar pressure = 759 mmHg
Atmospheric pressure = 760 mmHg
Intra-alveolar pressure = 761 mmHg
P = 759 mmHg
P = 761 mmHg
How Does Intra-alveolar Pressure Rise and Fall?
Boyle’s Law:
gas pressure is inversely related to the space (volume)
that it occupies
2.
Expansion of alveoli causes decreased alveolar gas pressure and promotes
inspiration
Compression of alveoli causes increased alveolar gas pressure and
promotes expiration
Compliance refers to the ability of the lungs to expand which is important
for inspiration (high compliance =easy expansion)
Elasticity refers to the ability of the lungs to recoil, which is important
for expiration
Factors That Promote Expansion
Factors That Promote Compression
1. Pleural fluid surface tension
1. Alveolar fluid surface tension
2. Negative intrapleural pressure
2. Elastic recoil of the lungs
3. Structural elements of the lungs
(alveolar septal walls)
Forced expiration can be accomplished when intrapulmonary pressure is reduced
beyond that of quiet breathing; this is accomplished by actively recruiting additional
muscles
abdominal muscles:
external oblique, internal oblique, transverse abdominus
thoracic muscles:
internal intercostals, latissimus dorsi, quadratus lumborum
Recall, the flow of air through the passageways of the respiratory system is
described by the following equation:
Air Flow =
Pressure 1
-
Pressure 2
Resistance
C.
Air Flow resistance

the pressure gradient between the alveoli and the atmosphere
is the force that drives lung ventilation

this driving force is opposed by resistance: the greatest
resistance is encountered in medium sized bronchioles (at
terminal bronchioles, diffusion takes over)
although resistance in the bronchial tree is usually
pretty low, it exists and can be related to this equation:
length of tube X viscosity
Resistance
radius4
Factors Increasing Resistance
Factors Decreasing Resistance
bronchoconstriction
bronchodilation
-PNS
-SNS
-acetylcholine
-epinephrine
-histamine
-increased pO2
-decreased pCO2
Other factors
•solid obstructing tumors
•mucus accumulation
•inflammation
Objective 8
External/Internal Respiration
A. Basic Principles
Dalton’s Law of Partial Pressures: the total pressure exerted by a
mixture of gases is the sum of the pressures exerted individually by
each of the gases in the mixture
Note: the individual pressure of a single gas in a mixture is
called partial pressure (p); and it is directly proportional to
the percentage of that gas in the total mixture
Thus:
760 mmHg = pN2 + pO2 + pCO2 + other gases.....
Dalton’s Law
And:
pO2 = 20.9% X 760 mmHg
0.209 X 760 mmHg
159 mmHg
pCO2 = 0.04% X 760 mmHg
.0004 X 760 mmHg
0.3 mmHg
Percentages of Atmospheric Gases
What is the partial pressure of O2 in a space cabin filled with
60% O2 at total pressure of 380 mmHg? Assume little or no
humidity.
a.152 mmHg
b.190 mmHg
c. 228 mmHg
d. 633 mmHg
e. 684 mmHg
Henry’s Law: when a mixture of gas comes into contact with a
liquid, a gas will dissolve into the liquid in proportion to its
partial pressure (p)
and will diffuse until equilibrium is achieved (gases diffuse into and
out of liquids from high to low partial pressure)
As the partial pressure gradient rate of transfer
Note: other factors that effect gas movement into and out of
the blood are:
•properties of the diffusion barrier
(as thickness , rate of transfer
•gas solubility (as solubility , rate of transfer
•temperature of the liquid (as the temperature of the liquid , gas
solubility
B. External and
Internal Respiration
External Respiration:
the diffusion of gases
between the alveolar air
and the blood in the
pulmonary capillaries
across the respiratory
membrane
O2 diffuses into the
blood and CO2 diffuses
out of the blood
Internal Respiration
the diffusion of gases
between the blood of
tissue capillaries and
interstitial fluid
CO2 diffuses into the
blood and O2 diffuses out
of the blood
Gases diffuse into and
out of the blood from
high to low partial
pressure
Arterial Blood:
pO2 = 100 mmHg
pCO2 = 40 mmHg
Venous Blood:
pO2
= 40 mmHg
pCO2 = 45 mmHg
Remember - gases diffuse according to partial pressure gradients!
Which way do they diffuse?
External respiration
Internal respiration
Alveoli
Arterial blood
Partial pressures of alveolar air
pO2
pCO2
104 mmHg
40mmHg
Partial pressures arterial blood leaving
alveolar capillaries
pO2
pCO2
104mmHg
40mmHg
Gas exchange
pO2
pCO2
40mmHg
45mmHg
Partial pressures venous blood
entering alveolar capillaries
Pulmonary capillaries
Partial pressures arterial blood entering
tissue
pO2
pCO2
104mmHg
40mmHg
Gas exchange
Partial pressures venous blood
leaving tissue
pO2
pCO2
40mmHg
45mmHg
Venous blood
pO2
pCO2
< 40mmHg
45mmHg
Partial pressures in tissue interstitial
fluid
Tissues
Ventilation-Perfusion Coupling:
When alveolar pO2 is low, local arterioles constrict
When alveolar pO2 is high, local arteriole dilate
When alveolar pCO2 is low, bronchioles constrict
When alveolar pCO2 is high, bronchioles dilate
Objective 9
Blood Gas Transport:O2
A.
Oxygen Transport

oxygen is transported through the blood in two ways

about 1.5% of the O2 transported is dissolved in the
plasma; this is the O2 that exerts partial pressure

about 98.5% is carried by hemoglobin in RBC’s:
Hb
+
reduced hemoglobin
4O2
Hb(O2)4
oxyhemoglobin
Most important factor in determining how much O2 combines with
Hb is ????
The Hb-O2 Dissociation Curve – describes the
relationship between partial pressure and the % of O2
binding sites on Hb that are full
% saturation (%
HbO2) in arterial
blood, at pO2 =
104 mmHg
% saturation (%
HbO2) in venous
blood, at pO2 =
40mmhg
Under normal
circumstances, tissue
only receive 25% of
the O2 delivered to
them by HbO2
The Hb-O2 Dissociation Curve
S shaped curve with plateau
At pO2 less than 40mm Hg the
affinity of O2 for Hb is low. Think,
where is pO2 40mm Hg? What
does this mean for the unloading
of O2 in the tissues?
At pO2 = 60mm Hg Hb is
90% saturated, additional
in pO2 has little effect

the extent to which hemoglobin binds to oxygen depends on
several factors, including pO2, pCO2, temperature and blood
BPG levels

the oxygen-hemoglobin dissociation curve demonstrates the
effect of pO2 and the principle of cooperative binding
pO2, veins
pO2, arteries
Factors that Favor a “Right Shift” (Reduce HbO2 Affinity):

Increased temperature

Elevated pCO2

Reduced pH

Elevated 2,3 bisphosphoglycerate
Factors that Favor a “Left Shift” (Increase HbO2 Affinity):

Decreased temperature

Reduced pCO2

Elevated pH

Reduced 2,3 bisphosphoglycerate
The 2,3-Bisphosphoglycerate Pathway in Erythrocytes
note: the Bohr Effect refers to the effect
of pH on hemoglobin/O2 affinity; low pH
weakens the hemoglobin-O2 bond
When tissues are active:
•Increased CO2 is released
•This increases H+ concentration (lowers pH)
•At higher p CO2 and lower pH, O2 has a lower
affinity for Hb
•Therefore more O2 is released

Globin binds to NO and protects it from being
destroyed by heme:

when HBO2 circulates to tissues, it releases
both O2 and NO

NO induces vasodilation and increases blood
flow
Whose hemoglobin has more O2 Affinity?
Objective 10

Carbon Dioxide Transport
carbon dioxide is carried in three ways

7-10% of the CO2 is dissolved in the plasma; this
is the pCO2 that exerts partial pressure

20-30% of the CO2 diffuses into red blood cells and
attaches to hemoglobin (not to heme, the globin
portion):
Hb
+
hemoglobin
CO2
HbCO2
carbaminoglobin
60-70% of the CO2 diffuses into the red blood cell and is
converted to HCO3- (bicarbonate) which is then carried in
the plasma

CO2
CO2
CO2
+ H 2O
+ H 2O
CO2 + Hb
CO2
Haldane Effect:
H+ + HCO3-
HCO3-
HCO3Cl-
H+
HHbCO2
reduced Hb has a greater
capacity to bind CO2 than HbO2
does
Objective 11
Neural Control of Ventilation
There are two clusters of neurons involved in the regulation of
ventilation rate:


Ventral Respiratory Group
Location
ventral medulla; extends from the pons to the
spinal cord
Function:
sets the basic ventilation rate
contains inspiratory neurons and
expiratory neurons
Dorsal Respiratory Group:
Location:
dorsal medulla, near the root of cranial
nerve IX
Function:
integrate impulses from peripheral stretch
receptors and chemoreceptors and relays them
to the ventral respiratory group
Ventral Respiratory Group
 Inspiratory Neurons Fire
Impulses are carried to the diaphragm by
the phrenic nerve and the external
intercostal muscles by the intercostal
nerves
The thorax enlarges and inspiration occurs
Inspiration lasts for 2 seconds
 Expiratory Neurons Fire
Inhibitory impulses are delivered to the
inspiratory neurons; the diaphragm and the
external intercostals relax
The thorax compresses and exhalation
occurs
Expiration lasts for 3 seconds
The Pons
Pontine Respiratory Center: modifies the basic rhythm in
concert with vocalization, sleep,
exercise and other activities
Apneustic Center
assists in the transition between
inspiration and expiration
Central receptors
Peripheral chemoreceptors
(aortic and carotid bodies)
Dorsal
respiratory
group
Pontine
respiratory
centers
Modifies respiratory
rhythm to match body
activities
Ventral
respiratory
group
Other inputs include:
Hypothalamus and cerebral cortex
(I’m gonna hold my breath until you
let me …)
Respiratory diaphragm
Peripheral stretch
receptors (Herring
Breuer Reflex)

Inflation Reflex (Hering Breuer Reflex)
 lung inflation activates stretch receptors in the visceral pleura
and in the conducting portions of the bronchial tree

vagal afferents inhibit VRG neurons

phrenic nerve is inhibited, inspiration stops

Hypothalamus
various stimuli (pain, fear, increased temperature)
alter breathing rate/pattern
The most important regulator of ventilation is arterial
pCO2 concentrations
pO2, pCO2, pH and Ventilation Rate …..

pCO2 and peripheral chemoreceptors:
increased pCO2 leads to hyperventilation
decreased pCO2 leads to hypoventilation
Normal pCO2 in arteries is 40
mmHg
Note:
Hypercapnia is increased arterial
pCO2
Hypocapnia is decreased arterial
pCO2
The most important regulator of ventilation is arterial
pCO2 concentrations
Remember the value!
Arterial PCO2 is 40 mmHg
Central Chemoreceptors

CO2 diffuses into the CSF and reacts with H2O to
form H2CO3

the H+ that is generated activates
central chemoreceptors

decreased CSF pH leads to hyperventilation

increased CSF pH leads to hypoventilation
Normal arterial
pO2 is 100 mmHg

pO2 and peripheral chemoreceptors
if pO2 falls below 60 mmHg,
hyperventilation occurs
ventilation rate is less sensitive to pO2
than pCO2
Arterial pH:

Decreases in arterial pH lead to hyperventilation
and increases in arterial pH lead to
hypoventilation, even if the pO2 and pCO2 are
normal
Decreased arterial pH leads to hyperventilation
Increased arterial pH leads to hypoventilation
Terms used for ventilation

eupnea:
normal quiet breathing

apnea
cessation of breathing

hyperpnea
deep, vigorous breathing

dyspnea
difficult, labored breathing

tachypnea
rapid breathing
Objective 12
Disorders Associated With Respiration
Emphysema:

Cause(s):


decreased  antitrypsin activity
increased elastase activity
compounded by smoking, pollution, aging
and COPD
Characteristics:
permanent enlargement of respiratory
bronchioles, alveolar ducts and alveoli
destruction of alveolar walls
loss of elasticity

Leads to dyspnea, enlarged (barrel) chest, low diffusing
capacity
Emphysema Patient With “Barrel Chest”
http://www.pathguy.com/lectures/emphysema_blues.jpg
Asthma


Cause(s):
Intrinsic Asthma:
caused by Type I hypersensitivity
Extrinsic Asthma
nonimmune; caused by infection,
stress, inhaled irritants, drug
ingestion or exercise
Characteristics:
chronic airway inflammation and
hyperresponsive tracheobronchial
tree

leads to dyspnea, coughing
wheezing and copious mucus
secretion
http://www.aaaai.org/patients/topicofthemonth/1105/images/asthma.jpg
Tuberculosis

Cause:

Characteristics:
Infection with Mycobacterium tuberculosis

reactivation or reinfection produces
respiratory symptoms:
chest pain, bloody sputum, granulomas and
lung cavitation

can spread to other organs such as
the skeleton, digestive viscera,
adrenal glands, genitourinary
tract and the heart
http://www.hipusa.com/eTools/webmd/AZ_Encyclopedia/tuberculosis.jpg
Lung Cavitation
Lung Granuloma
http://www.inflammation-atinterfaces.de/content/images/897fccd1
0585a8b8ce4ccd011563e178.jpg
http://images.google.com/imgres?imgurl=http://w
ww.granuloma.homestead.com/files/tb_gross_lun
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Bronchogenic Carcinoma
genetic causes; smoking, air pollution,

Cause:

Characteristics:
radiation exposure, industrial chemicals

cough, weight loss, chest pain and dyspnea;
increased sputum production; tumor
obstruction of airways; frequent metastasis
http://www.som.tulane.edu/cl
assware/pathology/medical_
pathology/New_for_98/Lung
_Review/Lung_carcinoma/Br
onchogenicCA-gross.jpg
Cystic Fibrosis

Cause:

Characteristics:
defective gene encoding Cl- transporter
in respiratory epithelial cells

mucus accumulation leads to chronic cough,
persistent lung infections, obstructive
pulmonary disease

digestive tract and reproductive
tract also involved; malabsorption
of nutrients, fat soluble vitamin
deficiencies
http://www.pathguy.com/l
ectures/cystic_fibrosis.jp
g
Normal People
People With Cystic
Fibrosis
http://www.the-aps.org/education/lot/cell/diag2.JPG