The Oxygen Cascade I Flashcards

(36 cards)

1
Q

3 important things happen to the air

we breathe in:

A

O2% decrease
CO2% increase
H2O% increase

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2
Q

O2 Cascade: a succession of stages

A
Inspired air:
PiO2 » 150 mm Hg
PiCO2 » 0.3 mm Hg
Alveolar air:
PAO2 » 105 mm Hg 
PACO2 » 40 mm Hg 
Arterial blood:
PaO2 » 100 mm Hg
PaCO2 » 40 mm Hg 
Mixed venous:
PvO2 » 40 mm Hg 
PvCO2 » 45 mm Hg
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3
Q

Dalton’s Law of Partial Pressures

A

The TOTAL pressure of a gas is simply the
sum of the individual partial pressures (Pi) of
each constituent gas:

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4
Q

• ______air contains virtually no CO2. Therefore, all

______CO2 must come from metabolism.

A

Inspired

alveolar

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5
Q

• However, ____depends not only on how fast O2 is

utilized, but also on the kind of fuel metabolised.

A

VCO2

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6
Q

• For ________(i.e. at very high work rates):
1 molecule of CO2 is produced for every
molecule of O2 consumed.

A

carbohydrate

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7
Q

• Respiratory exchange ratio (R) =

A

VCO2/VO2
In steady state R = Respiratory Quotient
(RQ, measured at the tissue/blood compartment.)

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8
Q

VE is equal to VI only if

A

R is equal to 1 (i.e. carbohydrate)

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9
Q

Oxygen uptake can be expressed as

A

oxygen

consumption per kilogram of body weight.

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10
Q

Oxygen “uptake” Is the most relevant measure of the

A

cardiorespiratory system.

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11
Q

• Maximal oxygen uptake (VO2 max), or maximal

aerobic capacity, is the maximum rate of

A

oxygen consumption possible by an individual.

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12
Q

Fick Principle

A

Oxygen uptake into pulmonary circulation is dependent on the

aterio-venous O2 difference and cardiac output (Q).

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13
Q

The coupling between pulmonary convective
mechanisms and metabolic demand can be expressed
by

A

the alveolar gas equations.

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14
Q

Alveolar Gas Equation
• Clinically it is useful to know both the ___ gradient and
the amount of__________

A

“A-a”

“right-to-left shunt”.

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15
Q

• PAO2 therefore needs to be known, but this is difficult to ______.
• Instead, the ________________ are commonly
used.

A

measure

Alveolar Gas Equation

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16
Q

The Perfect Lung PO2

A

PO2 atm steps down alveoli, contant for artery. Steps down to mitochondria

17
Q

The realistic Lung oxygen cascade

A

PO2 atm steps down upper airway to alveoli, step down to cap. step down to artery. Steps down to tissue and mitochondria

18
Q

If PACO2 is known, then___________

can be used to calculate PAO2.

A

the alveolar gas equation

19
Q

For a well ventilated lung, PACO2 approx =

20
Q

Alveolar Ventilation

eqn

A

VA (dot)= fR x (VT – VD)

21
Q

At rest, changes in ____gases are small, since

VT/FRC small.

22
Q

How do these alter PACO2?
Hyperventilation:
Hypoventilation:

A

decr. PACO2 , and therefore
¯PaCO2
incr ­PACO2 , and therefore
­PaCO2

23
Q

Drops in the realistic Lung oxygen cascade (alveoli, cap, artery) due to

A

Ventilation & Perfusion inequalities or shunt

24
Q

Ventilation in alveoli is matched to Perfusion through pulmonary capillaries

25
Hypoxemia | definition
Abnormally low levels of oxygen (partial pressure, | content or % saturation) in arterial blood.
26
Hypoxemia | Common causes:
``` Hypoventilation (voluntary or pathological) Diffusion limitation Reduced PIO2 V/Q mismatch Right to left shunt ```
27
A Shunt refers to
``` blood which enters the arterial system without going through the ventilated areas of the lung. ```
28
Very Large Shunt Normally only a _____ % of total cardiac output (Qs/QT)
very small
29
Very Large Shunt Most commonly arises from
congenital heart | abnormalities.
30
Venous-to-arterial (rightto-left) circulatory shunts | may result in severe?
hypoxaemia
31
Blood Flow (perfusion): When standing, gravitational effects mean that blood flow
decreases from the base (bottom) to the apex | (top) of lungs.
32
Ventilation-Perfusion Ratio V(dot)/Q ratio takes into account _______variations in V(dot)A and capillary perfusion.
regional | eg. effects of gravity
33
Ventilation: Similarly, when standing, gravitational effects mean that ventilation
decreases from the base to the apex of the lung, but to a much lesser extent than the affect on blood flow. ie V/Q is lower at the base of the lung.
34
Pulmonary Hypoxic Vasoconstriction
Decreased tissue PO2 around underventilated alveoli constricts their arterioles, diverting blood to better ventilated alveoli
35
At the apex, low arterial pressure in the pulmonary circulation tends to collapse the small vessels, ____ blood flow.
incr­___Resistance | decr
36
At base of lungs, higher pressure distends vessels, | ____­blood flow.
decr___Resistance | incr