Lecture 8 - Control Of Ventilation At High Altitude Flashcards
What is the biggest factor that affects high altitude?
Barometric pressure
What happens to the barometric pressure as altitude increases?
Barometric pressure decreases
What would happen if the barometric pressure was at the equator?
You would not be able to climb as the barometric pressure would be too low and you would need supplementary oxygen
What does inspired air =
Pressure - water vapour x oxygen fraction
What is the alveolar gas equation?
PA02 - (inspired PO2) - (PO2/respiratory exchange ratio)
What is the barometric pressure at Everest?
It is around 250
What is the barometric pressure at the top of Everest?
250
What is the barometric pressure at the top of Everest?
Around 250
What is changes in arterial PO2 sensed by?
Peripheral chemoreceptors - below 10% is when the are activated
How could you change the partial pressure of CO2?
Increasing the ventilation rate
What happens at the top of Everest?
Lower inspired PO2, increases ventilation, decreases PCO2 and increases pH
What is the mmHg for water vapour?
47mmHg - it is the same everywhere
What is the fraction of O2?
21%
What is the level of barometric pressure at sea level?
760mmHg
What is PCO2 at rest?
40mmHg
What happens when there is an increase in altitude?
Acute increases in rate and depth of ventilation, peripheral chemoreceptors are stimulated by low PO2 and PO2 drives respiration due to hypoxia
What does an increase in heat rate due to hypoxaemia increase?
Increases O2 delivery to the pheriphery
What level of arterial pressure of O2 does ventilation start to increase? normal O2 is 160mmHg
70-60mmHg
Why do you get an increase in pH when CO2 decreases?
Because CO2 is important as a buffer for blood and in cerebral spinal fluid
What does an increase in pH cause?
Causes changes in Cheyenne stroke ventilation
What does a low PCO2 inactivate?
Central chemoreceptors which decrease ventilation, which is not ideal at high altitude. PCO2 rises and initiatives slow deep breaths by O2 demand is not met
What does an increase in pH to the cerebral spinal fluid do when CO2 changes in the blood due to a decrease in PCO2? - hypoxia
Causes the central chemoreceptors to stop firing ventilation and causes a reduction in ventilation which is not ideal at high altitude.
What are your breaths like at a high altitude?
Big deep breaths width pauses and another deep big breath. As you are constantly trying to fight the increase in pH but also the demand for CO2 at the same time
What happens to the blood brain barrier at high altitude?
Charged particles cannot cross,
Changes in spinal fluid pH,
Need to reduce pH in both CSF and blood,
Can take several days to acclimatise
What is acclimatisation?
The process to try and Normalise your pH, specifically cerebral spinal fluid pH - because it is the break on ventilation.
If you can get the pH more neutral or an acidic pH what can happen?
The central chemoreceptors can start work in again which is done by the choroid plexus
What is the choroid plexus?
It sits on the blood brain barrier and actively transports bicarbonate from the spinal fluid into the blood. Bicarbonate neutralises.
What organ can help with reducing the pH?
The kidney - but it takes a couple of days to process
What mode of transport does not allow your body to acclimatise?
Planes - if you fly to somewhere with a high altitude like Machu Picchu then you are at risk of acute mountain sickness as your body did not acclimatise
What is your arterial PO2 if you have COPD?
55mmHg - you would need supplementary oxygen if uou decides to walk up a mountain
What is considered to be high altitude?
Anything above 2000 metres
What do athletes do in regards to High altitude?
They train at high for a period of time so when they go back down it is easier. Although they need to train at a low altitude the majority of the time as they need to train at the best of their ability which is with a decent barometric pressure and good oxygen supply
What are some short physiological adaptions to an increase in altitude?
Increase in Diphosphoglycerate (2,3-DPG)
What does 2,3-DPG help with?
Helps release oxygen at lower tensions, makes it slightly harder for haemoglobin to take up oxygen from the lungs but this is compensated for an increase in ventilation
Increase in 2,3-DPG =
Stops the tissues become hypoxic
What is an increase in 2,3-DPG an important mechanism for?
To match o2 demand to o2 supply
What is a longer physiological adaption to altitude?
Increase in haematocrit which increases haemopoiesis
What is the initial response for an increase in haematocrit?
25% decrease in plasma volume, increase in urination, increase in respiratory loss of H20 as increase in ventilation and dry air,
increase in number of capillaries
What does an increase in the number of capillaries =
Improves diffusion of oxygen
What would be a longer term response to an increase in haematocrit?
Increase in haemopoiesis, get more red blood cells, decrease in O2 tension in the kidney and the kidney can release erythropoietin
What are the normal haematocrit levels at seal level?
50% at sea lebel
What are the haematocrit levels of people who live in the Andes at 6000 metres?
Up to 80%, increase the concentration in a solution then it becomes much more viscous so their blood will be like porridge
What does increases the number of capillaries allow?
Allows oxygenated blood to become closer to the tissues where it is needed
What are formed due to an increase number of capillaries?
More mitochondria and cellular respiratory enzymes are formed
What are the symptoms for acute mountain sickness?
Headache, anorexia, nausea, malaise, lack of energy, disturbed sleep and occasional vomiting
What physiologist looked into acute mountain sickness?
John west
What is the best treatment for acute mountain sickness?
Descent of the mountain - going down to a lower altitude
What is the best treatment for acute mountain sickness?
Descent is the best treatment - going to a lower altitude
What is the best treatment for acute mountain sickness?
Descent is the best treatment - going to a lower altitude
What are some other treatments for acute mountain sickness?
Oxygen, acetazolamide, dexamethasone
Describe acetazolamide
It’s a carbonic anhydrase inhibitor so causes slight acidosis. Stops the equation shifting back the other way so keeps it slightly acidic
Describe dexamethasone
Effective in that it increases ventilation rate - but if you stop taking it then ventilation rate will decrease straight away
What equipment is useful to have if you are climbing a mountain and have symptoms of acute mountain sickness?
Gamow bag - inflate and climb inside
What are the symptoms for high altitude pulmonary edema?
Breathless, more noticeable at night lying down, crackles during auscultation and frothy pink sputum
What causes high altitude pulmonary edema?
Uneven vasoconstriction
What happens during uneven vasoconstriction?
Blood pressure increases and heart rate increases - starts to cause ultra structural changes
What does an increase in pressure in the small capillaries do?
Starts to cause leakage of red blood cells and other components of the blood
What ultra structural changes occur? - due to uneven vasoconstriction
Happens around the blood gas barrier, diffusion across this barrier is very important and increases a large level of fluid - affects how oxygen and other gases diffuse
What is the pink/red frothy sputum due to?
Proteins in the blood escaping into the airways
What is another ultra structural change due to high altitude pulmonary edema?
Breaks in epithelial layers - where proteins and components can escape
What are the symptoms of high altitude cerebral edema?
Develop with acute mountain sickness, confusion, ataxia (muscle coordination)
What is the treatment for high altitude cerebral edema?
Descent, increasing barometric pressure - Gamow bag
What do the kidneys produce that is useful in adaptions for altitude?
Hypoxic inducible factor 1 - only stable under hypoxic conditions, stimulates bone marrow to produce or stop apoptosis and allows red blood cells to mature
How can you increase red blood cells without increasing altitude?
Blood doping, increasing erythropoietin
How long does it take to see changes in red blood cells?
3 weeks
Who is famous for increasing their erythropoietin?
Lance Armstrong - used it illegally for the Tour de France
What are the symptoms of chronic mountain sickness?
Headache, somnolence (strong desire to fall asleep), depression
