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Egan's Chapter 11 - Gas Exchange
Egan's Chapter 11 - Gas Exchange & Transport
57
Physics
10/11/2011

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Term
Oxygen
Definition
normal atmospheric inspired partial pressure of oxygen (Pio2) of 159 mm Hg to a low point of 40 mm Hg or less in the capillaries. The intracellular Po2 (approximately 5 mm Hg) provides the final gradient for oxygen diffusion into the cell.
Term
Carbon Dioxide
Definition

partial pressure of carbon dioxide (Pco2) is highest in cells (approx. 60 mm Hg) and lowest in room air (1 mm Hg)

 

alveolar partial pressure of carbon dioxide, or PAco2, varies directly with body's production of carbon dioxide and inversely with alveolar ventilation

Term
RULE OF THUMB - Oxygen/CO2 Content
Definition

if patient breathing room air, sum of alveolar Po2 (PAo2) and alveolar Pco2 (PAco2) = about 140 mm Hg (100 mm Hg and 40 mm Hg).

Changes in ventilation that cause PAco2 to vary will vary the resulting PAo2 to keep total at 140 mm Hg.

Term
whenever a patient is breathing room air at sea level, the RT should not expect to see a PAo2 any higher than _______ during hyperventilation. Po2 values higher than _______ indicate that the patient is breathing supplemental oxygen.
Definition

120 mm Hg , 120 mm Hg

 

For carbon dioxide or oxygen to move between the alveoli and the pulmonary capillary blood, the following three barriers must be penetrated: (1) alveolar epithelium, (2) interstitial space, and (3) capillary endothelium

Term
barriers to CO2/O2
between alveoli & pulmonary capillary blood
Definition
  1. alveolar epithelium
  2. interstitial space
  3. capillary endothelium
Term
to pass into and out of RBCs, gases must traverse the __________________
Definition
erythrocyte membrane (red blood cells)
Term
Carbon dioxide diffuses approx. _______ across alveolar-capillary membrane than does oxygen, because of its _______________.
Definition
20 times faster
much higher solubility in plasma
Term
The diffusion time in the lung depends on _________
Definition
the rate of pulmonary blood flow
Term
blood normally takes approx. ________ to pass through pulmonary capillary
Definition
0.75 seconds
Term
If blood flow ______, i.e. during heavy exercise, capillary transit time can _____ to as ____ as ______
Definition
increases
decrease
low
0.25 seconds
Term
arterial blood reflects ___________
Definition
pulmonary gas exchange
Term
venous blood reflects _________
Definition
events occurring in the tissues
Term
Pao2 of healthy individuals breathing air at sea level ______ alveolar Po2 of 100 mm Hg, but is approx. _________ than the calculated Pao2.
Definition
does not equal
5 to 10 mm Hg less
Term
right-to-left anatomical shunts
Definition
  1. bronchial venous drainage
  2. thebesian venous drainage
Term
A high V/Q ratio indicates that ventilation is _________, perfusion is ________________.
Definition
greater than normal
less than normal, or both
Term
In areas with a high V/Q ratio, the Po2 is _____ and the Pco2 is _____ than normal.
Definition
higher
lower
Term
Conversely, a low V/Q indicates that
Definition
ventilation is less than normal
perfusion is greater than normal
or both
Term
In areas with low V/Q, the alveolar Po2 is _____ and the Pco2 is _____ than normal.
Definition
lower
higher
Term
Farther down the lung, perfusion increases _____________________ so the lung bases receive  _____________________ as do the apexes.
Definition

linearly in proportion to the hydrostatic pressure
nearly 20 times as much blood flow

(lungs have more blood at bottom than top due to gravity)

Term
Like perfusion, ventilation also is increased in the lung bases, with ca. four times as much ventilation going to the bases than to the apexes of the upright lung
Definition
Like perfusion, ventilation also is increased in the lung bases, with ca. four times as much ventilation going to the bases than to the apexes of the upright lung
Term
Majority of oxygen is carried in...
Definition
...a reversible chemical combination with hemoglobin (Hb) inside the RBC
Term
With complete oxygen binding, all electrons become ______, and _____ is converted to its ____ state (referred to as _______ and abbreviated ______).
Definition
paired
Hb
oxygenated
oxyhemoglobin
HbO2
Term
In whole blood, each gram of normal Hb can carry...
Definition
approx. 1.34 ml of oxygen
Term

SaO2 = [HbO2÷ Total Hb] × 100

SaO2 = Hb saturation (Sao2)

Definition
Term

with Po2 < 60 mmHg, curve steepens dramatically

CaO2 = (0.003 × PO2) + (Hbtot × 1.34 × SO2)

Definition
Term
Cao2 = Total oxygen content
Definition
Term
Po2=Partial pressure oxygen in blood = same here as PaO2
Definition
Term
Hbtot = Total hemoblobin content (in g/dl)
Definition
Term
So2 = Hb sat. with oxygen (as decimal) = same here as SaO2
Definition
Term
Note: (0.003xPaO2) = amount dissolved in plasma
(Hb x 1.34 x SaO2) = amount bound to hemoglobin
Definition
Term
The normal Cao2 concentration is
Definition
16-20 ml/dl
Term
As we breathe in the water vapor pressure _______
Definition

displaces some of the oxygen

This pressure gradient is called a cascade

Term
Alveolar CO2 & arterial CO2 are
Definition
nearly same in healthy adult
Term
if CO2 production increases
Definition
alveolar minute ventilation stays or decreases
Term
Normal partial pressure of CO2 in alveoli is
Definition
PACO2 (normal) = 40 mmHg
Term
PIO2 stands for
Definition
partial pressure of inspired oxygen
Term
PIO2 formula
Definition

PIO2 = FIO2 (PB - 47)

 

47 = Water Vapor Pressure

Term
Normal PIO2 at sealevel
Definition
149.73 mmHg
Term
Alveolar air equation
Definition

PAO2 = FIO2(PB - 47) - 1.25(PACO2)

 

If FIO2 greater than 60%, drop the multiply by 1.25 part

Term
PaO2 and PaCO2 relationship is
Definition

Inverse

if one increases, the other decreases and vice versa

Term
Carbon Dioxide & Oxygen diffusion speeds across alveolar capillary membrane
Definition
CO2 diffuses 20 times faster than oxygen, because it has hiher solubility in plasma
Term
venous blood =
Definition
deoxyginated blood
Term
normal speed of blood through capillary
Definition

0.75 sec

 

Can go as low as 0.25

Term
Effect of blood flow speed on diffusion
Definition
If flows too fast diffusion cannot occur
Term
Definition
Term
Definition
Term
venus blood reflects
Definition
tissue oxygenation
Term
Once PAO2 (100 mmHg) hits circulation, what happens to PaO2?
Definition
arterial O2 pressure can be 5 - 10 mmHg lower because of right to left shunts & regional differences
Term
Shunt
Definition
a right to left side shortcut of the heart
Term
Two shunts
Definition
  1. bronchial venous drainage
  2. thebesian venous drainage
Term
Perfusion =
Definition
blood flow
Term
Higher ventilation/perfusion ratio means
Definition

greater ventilation or lower bloodflow or both

 

(ideal is even between both)

Term
High V/Q ration =
Definition
higher ventilation and lower perfusion
Term
Low V/Q ration =
Definition
Lower ventilation and higher perfusion
Term
Oxyhemoglobin =
Definition
HbO2
Term
How much oxygen can a gram of Hemoglobin hold?
Definition
1.34 ml oxygen
Term
figure Saturation of arterial oxygen in percentages
Definition
%SaO2 = [HbO2 / Total Hb] x 100