Many conditions/diseases have hypoxic or ischemic components.
Common abbreviations
A -
a -
v -
P or p -
C -
F -
I or i -
E or e -
Q -
A - alveolar
a - arterial
v - venous
P or p - partial pressure
C - content
F - fraction
I or i - inspired
E or e - expired
Q - Cardiac output
Meaning
FiO2
CaO2 pO2 pAO2
FiO2 - fraction of inspired air that is oxygen
CaO2 - arterial oxygen content
pO2 - partial pressure of oxygen
pAO2 - partial pressure of oxygen in the alveoli
A Drop in barometric pressure results in...
-Drop in PiO2
-The reduced pO2 is transferred all the way down the oxygen cascade.
What is the equation for the systemic oxygen delivery?
DO2 = Q x CaO2
Systemic Delivery of oxygen = cardiac output x oxygen content of arterial blood.
When PiO2 falls, CaO2 also falls, reducing systemic oxygen delivery.
Q = ?
CaO2 = ?
Q = HR x SV
CaO2 = ([Hb] x SaO2 xH) + (PaO2 x S)
CaO2 = ([Hb] x SaO2 xH) + (PaO2 x S)
What does
H = ?
S = ?
SaO2 = ?
H = Hufner's constant = 1.39 mL/g
S = Solubility coefficient
SaO2 = Solubility coefficient of O= 0.0225 mL/mm Hg
What is the first line of defence against on arrival at high altitudes?
Increase Cardiac Output (Q) via increasing Heart Rate and increasing Stroke Volume
(DO2 = Q x CaO2).
(Q = HR x SV)
What is the next phase after first line of defence?
Restoration of CaO2.
Restoration of CaO2
What are the two mechanisms?
Ventilatory Adjustments
Haematological adjustments
What are the two ventilatory compensation mechanisms?
The Hypoxic ventilatory response
The Hypercapnic ventilatory response
What is the alveolar ventilation equation?
PACO2 = k x (VCO2 / VA)
What is the relationship between alveolar PCO2 and ventilatory rate?
Alveolar PCO2 is inversely proportional to ventilatory rate. I.e. if ventilation doubles the PCO2 is halved.
What is the Alveolar Gas Equation?
PAO2 = PiO2 - (PACO2 / R)
R = indication of the substrates utilised i.e. fatty acids, CHO. Equals about .71 for fats and about 1.0 for CHO. R is a essentially a ratio of amount of CO2 produced to O2.
Why does Hyperventilation work?
The alveolar ventilation and gas equations explain why hyperventilation works as an adaptation to high altitude. If you double ventilation rate the change in PCO2 and PAO2 is halved.
If PiO2 drops from 150 mm Hg to 100 mm Hg. Using the alveolar gas equation what does PAO2 equal?
Eq. PAO2 = PiO2 - (PACO2 / R)
Sea Level PAO2 = 150 - (40/0.8) = 100 mm Hg
Pikes Peak PAO2 = 150 - (40/0.8) = 50 mm Hg
So PAO2 (and thus PaO2) has HALVED.
Why does Hyperventilation work? (continued)
If ventilation doubles PCO2 halves.
Redo the calculations to get PAO2