Hypoxia Flashcards
What is the difference between Hypoxia and Hypoxaemia?
What factors can put your body under hypoxic stress?
What is the difference between Hypoxia and Hypoxaemia?
These terms can sometimes be used interchangeably but on some occasions they have very different meanings
Hypoxaemia - describes the blood environment
Anything below 8 kPa can be considered to be hypoxaemia
What factors can put your body under hypoxic stress?
Disease - if you impede the ability of outside air to get to the cells
Altitude - if the air you’re breathing in has a low oxygen content, then that reduces the starting point of the oxygen cascade
Review of Oxygen Transport
You begin with ambient air with a partial pressure of 21.3 kPa (this is 20.9% of total atmospheric pressure)
As altitude increases - barometric pressure decreases and this partial pressure decreases due to ………………. LAW (partial pressure of the environment is the sum of the partial pressures of the gases involved)
As the air moves into to the airway, it becomes ………………
As it goes down the different generations of airways - from conducting to respiratory airways - it mixes with the gases that are already in there (remember there is a bit of air that always remains in the lungs - this is why we can hold our breath)
If we take a deep breath in and hold it - the oxygen will keep moving into the blood until the gradient is lost
IMPORTANT POINT: blood arrives at the gas exchange surface …..% SATURATED with a partial pressure of …… kPa
It is then fully oxygenated (100% = 13.5 kPa)
The lungs have their own blood supply to keep them alive - they don’t get this via the pulmonary circulation, this is a separate thing
This bronchial drainage returns to the ……………… veins and dilutes the blood so the saturation decreases slightly (to 97% at 13.3 kPa)
As the blood circulates through the lungs, it is going to become equilibriated to match the tissues (wherever there’s a gradient) - oxygen will move in and carbon dioxide will move out
Mean PO2 in the alveolar space and in the arterial blood decreases with ………………
Review of Oxygen Transport
You begin with ambient air with a partial pressure of 21.3 kPa (this is 20.9% of total atmospheric pressure)
As altitude increases - barometric pressure decreases and this partial pressure decreases due to DALTON’s LAW (partial pressure of the environment is the sum of the partial pressures of the gases involved)
As the air moves into to the airway, it becomes HUMIDIFIED
As it goes down the different generations of airways - from conducting to respiratory airways - it mixes with the gases that are already in there (remember there is a bit of air that always remains in the lungs - this is why we can hold our breath)
If we take a deep breath in and hold it - the oxygen will keep moving into the blood until the gradient is lost
IMPORTANT POINT: blood arrives at the gas exchange surface 75% SATURATED with a partial pressure of 5.3 kPa
It is then fully oxygenated (100% = 13.5 kPa)
The lungs have their own blood supply to keep them alive - they don’t get this via the pulmonary circulation, this is a separate thing
This bronchial drainage returns to the pulmonary veins and dilutes the blood so the saturation decreases slightly (to 97% at 13.3 kPa)
As the blood circulates through the lungs, it is going to become equilibriated to match the tissues (wherever there’s a gradient) - oxygen will move in and carbon dioxide will move out
Mean PO2 in the alveolar space and in the arterial blood decreases with age
Oxygen Dissociation Curve
There is a range of partial pressures in the lungs but the shape of the ODC is such that we can fully oxygenate the blood even if the partial pressure in the lungs is lower when you’re older
The …………. line is the standard curve
The ……………. line is how it gets shifted in environments that are associated with increased metabolism (e.g. exercise) - this is associated with:
Increase in ……………..
Hyper………….
Increased …………………… concentration
With the ………………. line, the opposite changes take place
………………. - gives the overall impression of the position of the curve at any point - this can be used to determine whether it is a loading or an unloading environment
Essentially, the position of the ODC varies depending on how much metabolism is happening
The curve can also move up and down in which case the P50 does NOT change
…………………………….. = an abnormally increased concentration of haemoglobin in the blood
Polycythaemia could be due to reduction of plasma volume or an increase in red cell numbers (it causes an increased haematocrit)
If you have more haemoglobin then your ODC will go up
Anaemia will cause the ODC to move down
IMPORTANT NOTE: the haemoglobin is still 100% saturated but the total O2 in the blood changes (look carefully at the two scales on the y axis)
Oxygen Dissociation Curve
There is a range of partial pressures in the lungs but the shape of the ODC is such that we can fully oxygenate the blood even if the partial pressure in the lungs is lower when you’re older
The BLACK line is the standard curve
The BLUE line is how it gets shifted in environments that are associated with increased metabolism (e.g. exercise) - this is associated with:
Increase in acidity
Hypercapnia
Increased 2,3-DPG concentration
With the RED line, the opposite changes take place
P50 - gives the overall impression of the position of the curve at any point - this can be used to determine whether it is a loading or an unloading environment
Essentially, the position of the ODC varies depending on how much metabolism is happening
The curve can also move up and down in which case the P50 does NOT change
Polycythaemia = an abnormally increased concentration of haemoglobin in the blood
Polycythaemia could be due to reduction of plasma volume or an increase in red cell numbers (it causes an increased haematocrit)
If you have more haemoglobin then your ODC will go up
Anaemia will cause the ODC to move down
IMPORTANT NOTE: the haemoglobin is still 100% saturated but the total O2 in the blood changes (look carefully at the two scales on the y axis)
The Oxygen Cascade
The Oxygen Cascade
The Oxygen Cascade describes the decreasing oxygen tension from inspired air to respiring cells
The amount of gas that’ll diffuse across a membrane is proportional to: List 3 things
This is a representation of the oxygen cascade
You start with …….. kPa of oxygen at atmospheric pressure (this can be shifted up if you have oxygen therapy or shifted down in humid air)
Humidification - we lose a little bit of oxygen when we humidify the air in our airways
As you go further down the airways you mix with the air that is already in the airways
This bar can be moved …… (hyperventilation) or …………. (hypoventilation)
There should be ………. …………….. between the alveolar air and the post-alveolar capillaries (provided you can get the air to your alveoli you should be able to get it to your arteries)
There is a slight decrease between post-alveolar capillaries and arteries because of the ……………………… ………………………..
About 1% of the cardiac output on your arterial side ends up perfusing the bronchial tree and this 1% gets dumped back into the circulation and causes a slight decrease in saturation
The difference between arteries, veins and tissues depends on the demand at the time
In tissues, the PO2 …………………. with increased exercise
ARTERY PO2 = 13.3 kPa
VEIN PO2 = 5.3 kPa
25% of the haemoglobin desaturates when going from the arteries to the veins
Oxygen is transported as:
Dissolved - 2%
BOUND TO HAEMOGLOBIN - 98%
The dissolved oxygen doesn’t really contribute to the oxygen delivery itself but it acts like the ‘conductor of an orchestra’ - it controls everything else
The big drop in partial pressure of oxygen from the arteries to the tissues isn’t keeping you alive directly, but this drop in partial pressure is associated with a big unloading of haemoglobin which is associated with a whole load of oxygen
So we need this change in partial pressure (from arteries to tissues) to facilitate the unloading of haemoglobin
Factors affecting the oxygen cascade: list 4 things
The Oxygen Cascade
The Oxygen Cascade describes the decreasing oxygen tension from inspired air to respiring cells
The amount of gas that’ll diffuse across a membrane is proportional to:
Surface area for gas exchange
Diffusion constant (CO2 diffuses faster than O2)
Diffusion gradient
This is a representation of the oxygen cascade
You start with 21.3 kPa of oxygen at atmospheric pressure (this can be shifted up if you have oxygen therapy or shifted down in humid air)
Humidification - we lose a little bit of oxygen when we humidify the air in our airways
As you go further down the airways you mix with the air that is already in the airways
This bar can be moved UP (hyperventilation) or DOWN (hypoventilation)
There should be NO CHANGE between the alveolar air and the post-alveolar capillaries (provided you can get the air to your alveoli you should be able to get it to your arteries)
There is a slight decrease between post-alveolar capillaries and arteries because of the bronchial drainage
About 1% of the cardiac output on your arterial side ends up perfusing the bronchial tree and this 1% gets dumped back into the circulation and causes a slight decrease in saturation
The difference between arteries, veins and tissues depends on the demand at the time
In tissues, the PO2 decreases with increased exercise
ARTERY PO2 = 13.3 kPa
VEIN PO2 = 5.3 kPa
25% of the haemoglobin desaturates when going from the arteries to the veins
Oxygen is transported as:
Dissolved - 2%
BOUND TO HAEMOGLOBIN - 98%
The dissolved oxygen doesn’t really contribute to the oxygen delivery itself but it acts like the ‘conductor of an orchestra’ - it controls everything else
The big drop in partial pressure of oxygen from the arteries to the tissues isn’t keeping you alive directly, but this drop in partial pressure is associated with a big unloading of haemoglobin which is associated with a whole load of oxygen
So we need this change in partial pressure (from arteries to tissues) to facilitate the unloading of haemoglobin
Factors affecting the oxygen cascade:
Alveolar Ventilation
Ventilation/Perfusion Matching - if you are ventilating airways that are not perfused or hyper-perfused, you wont achieve efficient gas exchange. If you perfuse unventilated alveoli then you’re going to leave with the same saturation that you came with
Diffusion Capacity - some disease can affect the parenchyma (the functional subunits - the alveolar capillary membranes) can become thickened and less conducive to exchange
Cardiac Output - if you increase cardiac output then you increase the amount of blood flowing through and getting the opportunity to oxygenate hence increasing oxygen delivery
This is what the cascade looks like if you’re breathing really ………….. air
In such situations, your exercise capacity is greatly reduced
This is what the cascade looks like if you’re breathing really hypoxic air
In such situations, your exercise capacity is greatly reduced
Imagine that we built a teleportation device that could transport us to the summit of Everest. Assuming we had some lovely warm clothing, what would happen to us if we went directly there in less than a second?
What are the Five challenges of altitude
REMEMBER
q=force of contraction
