Resp 3 Flashcards
Gases, just like ions and water, move
according to the principles of —
diffusion
After gas exchange in the pulmonary capillaries,PO2 is actually --- mmHg due to bronchial circulation
95
To calculate a partial pressure, you must
determine the — concentration of the gas
to other molecules
relative
Partial Pressure (Pgas) refers to the
pressure of one gas in
a mix.
Pgas =
PATM x Fractional Concentration of Gas
Atmospheric Pressure (PATM) at sea level is --- mmHg and air is composed of --% nitrogen and --% oxygen (FiO2)
760
79
21
PN2 =
760 x 0.79 = 600 mmHg
PO2 =
760 x 0.21 = 160 mmHg
As air passes through the conducting zone of the lung, it is
humidified, creating a
partial (vapor) pressure for water (PH2O =
47 mmHg). This addition of water decrease) the partial pressure
of all other gases.
At normal alveolar ventilation and O2 absorption rates (250
ml/min), PAO2 is
100 mmHg. Increasing alveolar
ventilation will increase PAO2.
A gas within a liquid also exerts a —, designated in the same manner,
but calculated differently
partial
pressure
To calculate a partial pressure in a liquid solution, the
(2) are required
relative concentration and the solubility coefficient of the
gas
Solubility Coefficient.
Attractability of molecules to
water. If this number is high, the gas diffuses quickly.
Henry’s Law
Partial Pressure = Concentration of Dissolved Gas/(Solubility Coefficient)
is CO2 or O2 more soluble?
CO2 is more
soluble than
O2.
At a constant temperature, the amount of a gas that dissolves in liquid is directly proportional to the (2)
partial pressure and the solubility.
Conc. of Dissolved Gas=
Solubility Coefficient x Partial
Pressure
Gas Exchange at the Respiratory
Membrane Depends on (2)
- Transport rate through
the respiratory membrane. - The rate of alveolar
ventilation
An increase in alveolar ventilation will --- PAO2 and gas exchange with an upper limit of 150 mmHg (the PAO2 of humidified air.
increase
The rate of gas diffusion across the respiratory membrane depends on (5)
- Difference in Partial Pressures Across the Membrane (ΔP)
- Solubility of Gas in Fluid (S)
- Cross-Sectional Area of Membrane (A)
- Distance of Diffusion (d)
- Molecular Weight of Gas (MW)
Difference in Partial Pressures Across the Membrane (ΔP)
A tissue with high metabolic activity will have a
lower PO2, creating a larger partial pressure
gradient.
Solubility of Gas in Fluid (S)
CO2 is more soluble (S) than O2 so CO2 diffusion
more rapidly. This explains why there is rarely
ever a problem with CO2 exchange but often a
problem with adequately oxygenating blood.
Cross-Sectional Area of Membrane (A)
If more pulmonary capillaries are recruited, as in
exercise, the surface area (A) available for
diffusion increases (ex. converting Zone 2 into
Zone 3).
Distance of Diffusion (d)
If the thickness of the diffusion barrier increases
(d), such as with Pulmonary Fibrosis or Edema,
this decreases diffusion
V =
(ΔP x A x S)/(d x √MW)
V = Volume of gas
diffusing through the
tissue barrier per unit
time (ml/min)
Components of Respiratory Membrane: (6)
- Surfactant
- Alveolar Epithelium
- Alveolar Basement Membrane
- Interstitial Space
- Endothelial Basement Membrane
- Capillary Endothelium
Average width of respiratory membrane is
0.6 μm, 0.2 μm at slimmest
Under normal conditions, O2 transport into pulmonary
capillaries is —LIMITED, but under other
conditions (fibrosis, emphysema, strenuous exercise), it
can become —LIMITED.
PERFUSION
DIFFUSION
Diffusing Capacity of the Lung (DL)
Measures
respiratory membrane’s functional integrity
Measures respiratory membrane’s functional integrity
It is often useful to determine the diffusion characteristics of a patient’s lungs during their
assessment in the pulmonary function laboratory. It may be particularly important to
determine whether an apparent impairment in diffusion is a result of perfusion limitation or
diffusion limitation.
Diffusing Capacity of the Lung (DL)
Amount of a
gas entering pulmonary blood per unit time
(ml/min/mmHg)
– Need to know the gas’s alveolar pressure, pulmonary capillary
pressure, and rate of uptake by the blood.
Diffusing Capacity of the Lung (DL)
— cannot be calculated because of its rapid diffusion
and — is also difficult to calculate since most of O2 binds
to hemoglobin.
DLCO2
DLO2
— is ideal for DL since it is diffusion-limited.
– Use diffusion coefficients to predict DL of other gases
Carbon monoxide
Decreased Surface Area (A) or Increased
Distance of the diffusion barrier (d), will —
gas diffusion.
decrease
What could an abnormally low DLCO test
indicate? (3)
Thickening of the Barrier
Decreased Surface Area
Decreased Uptake
Thickening of the Barrier (increase d)
– Interstitial edema or fibrosis
Decreased Surface Area (decrease A) (4)
– Emphysema
– Low Cardiac Output
– Tumors
– Ventilation-Perfusion Mismatch
Decreased Uptake (2)
– Anemia
– Decreased blood volume in
pulmonary capillaries
Someone with a thickened alveolar
membrane (pulmonary fibrosis) will
have (2)
diffusion limited oxygen transfer at
rest and it will be an even more
pronounced limitation with exercise.
Calculation of PAO2 is important because you can compare
the value to —.
PaO2
Calculation of PAO2 is important because you can compare
the value to PaO2.
A large difference indicates
a problem with diffusion.
Normal A-a gradient is — mmHg in a young, non-smoker.
The A-a gradient increases by — mmHg for each decade so a normal value for a 40 year-old would be — mmHg.
5-10
1
<14
You cannot easily measure —
PAO2
PAO2 is predicted based on: (3)
- The partial pressure of O2 inspired
- The PaCO2
- The ratio of CO2 produced/O2
consumed—the respiratory quotient
FiO2 is
the percentage of inspired oxygen (21%).
Patm is
the ambient atmospheric pressure (760 mmHg at sea level).
PH2O is
vapor pressure of water at 37°C and is equal to 47 mmHg.
PaCO2 is
arterial CO2 levels (normal is 40 mmHg)
Respiratory quotient (RQ) is
the ratio of CO2 produced (200 ml/min)
divided by the O2 consumed (250 ml/min), and its value is typically
0.8.
The partial pressures of the gases
ONLY include the gases that are
dissolved in the plasma.
If cells utilize more oxygen than
normal, the gradient —
which — flow of oxygen
from the blood to the tissues
increases
increases
Tissue PO2 is a function of: (2)
(1) The rate of O2 transport to the tissues in blood (blood flow) (2) The rate at which the tissues use O2.
Increased blood flow and/or
increased metabolism will
result in
more O2 delivery to
the tissues
Without Hemoglobin, CO would need to be --- L/min to transport sufficient oxygen to meet the needs of the tissues at rest.
83.3
–% of total oxygen content is
dissolved in plasma (PaO2 =
100 mmHg)
2
–% of O2 reversibly binds to
hemoglobin inside of the RBC
-does not contribute to partial
pressure
98
Hemoglobin A (α2b2):
4 subunits
each of which each binds 1 O2
molecule.
Iron must be in — state
to bind O2
ferrous (Fe2+)
The amount of oxygen
bound to Hb
depends on: (2)
- Plasma PO2
- Number of binding
sites in RBCs –
depends on the Hb
amount per RBC.
(normally each
RBC contains ~1
million Hb
molecules)
CaO2 =
ml of O2 carried by oxyhemoglobin plus ml of O2
carried dissolved in plasma
SaO2 is
the % saturation of hemoglobin
– Average 97%
Hb represents
g of hemoglobin/100 ml blood
– Average is 15 g Hb/100 ml blood
PaO2 is
the partial pressure of oxygen in arterial blood
– Average is 95 mmHg
Average CaO2 is ~ — ml O2/ 100 ml blood
19.782
Reduction in the amount of hemoglobin in the blood significantly --- the blood oxygen content.
reduces
2,3-BPG binds to Beta
subunits of deoxy HB
and
decreases its O2
affinity. It causes more
oxygen unloading.
At a high PO2,
hemoglobin’s
affinity for O2 is
—.
highest
The lower the
PO2, the more
likely O2 will
dissociate from
hemoglobin
Oxyhemoglobin Dissociation Curve
Shifts to the RIGHT (2)
• Indicates DECREASED affinity between hemoglobin and oxygen • In this instance, oxygen is MORE likely to dissociate from Hemoglobin.
BOHR EFFECT
Helps match
O2 delivery to
O2 demand, advantageous
since O2 can be released at
selective tissues.
RBCs contain 2,3-bisphosphoglycerate
– a metabolic intermediate. Levels of
2,3-BPG increase with exercise,
hypoxia from high altitude, pregnancy
and chronic lung disease.
Oxyhemoglobin Dissociation Curve Shifts to the LEFT (2)
• Indicates an INCREASED affinity between oxygen and
hemoglobin
• In this instance, oxygen is LESS likely to dissociate
from hemoglobin.
Oxyhemoglobin Dissociation Curve Shifts to
the LEFT
causes (4)
– Decreased PCO2
– Increased pH (ex. 7.6)
– Decreased temperature
– Decreased 2,3-BPG
