Resp 3 Flashcards by sophie rosen

Gases, just like ions and water, move

according to the principles of —

diffusion

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After gas 
exchange in the 
pulmonary 
capillaries,PO2 
is actually --- 
mmHg due to 
bronchial 
circulation

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To calculate a partial pressure, you must
determine the — concentration of the gas
to other molecules

relative

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Partial Pressure (Pgas) refers to the

pressure of one gas in

a mix.

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Pgas =

PATM x Fractional Concentration of Gas

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Atmospheric Pressure (PATM) at sea level is --- mmHg and air is 
composed of --% nitrogen and --% oxygen (FiO2)

760
79
21

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PN2 =

760 x 0.79 = 600 mmHg

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PO2 =

760 x 0.21 = 160 mmHg

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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.

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At normal alveolar ventilation and O2 absorption rates (250

ml/min), PAO2 is

100 mmHg. Increasing alveolar

ventilation will increase PAO2.

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A gas within a liquid also exerts a —, designated in the same manner,
but calculated differently

partial

pressure

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To calculate a partial pressure in a liquid solution, the

(2) are required

relative concentration and the solubility coefficient of the
gas

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Solubility Coefficient.

Attractability of molecules to

water. If this number is high, the gas diffuses quickly.

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Henry’s Law

Partial Pressure = Concentration of Dissolved Gas/(Solubility Coefficient)

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is CO2 or O2 more soluble?

CO2 is more
soluble than
O2.

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At a constant temperature, the amount of a gas that dissolves in liquid is directly proportional to the (2)

partial pressure and the solubility.

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Conc. of Dissolved Gas=

Solubility Coefficient x Partial

Pressure

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Gas Exchange at the Respiratory

Membrane Depends on (2)

Transport rate through
the respiratory membrane.
The rate of alveolar
ventilation

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An increase in alveolar 
ventilation will --- PAO2 and 
gas exchange with an upper 
limit of 150 mmHg (the PAO2 
of humidified air.

increase

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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)

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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.

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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.

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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).

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Distance of Diffusion (d)

If the thickness of the diffusion barrier increases
(d), such as with Pulmonary Fibrosis or Edema,
this decreases diffusion

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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)

1. Surfactant 2. Alveolar Epithelium 3. Alveolar Basement Membrane 4. Interstitial Space 5. Endothelial Basement Membrane 6. 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)

1. The partial pressure of O2 inspired 2. The PaCO2 3. 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)

--% of O2 reversibly binds to hemoglobin inside of the RBC -does not contribute to partial pressure

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)

1. Plasma PO2 2. 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