Hypoxia Flashcards
What parameter defines hypoxaemia?
PO2 < 8 kPa
Describe how the partial pressure of oxygen changes from inspired air to the tissues.
21.3 —> 20 (conducting airways) —> 13.5 (alveoli) —> 13.5 (PaO2 immediately past exchange surface) —> 13.3 (diluted by return of bronchial circulation) —> 5.3 (mixed venous blood)
How does PAO2 and PaO2 change with age?
DECREASES
How can the partial pressure of oxygen in the alveoli (after mixing) be changed?
It’ll continue to move down its concentration into the blood until it reaches equilibrium.
What percentage of cardiac output goes to perfuse the bronchial tree?
1%
State the normal arterial and venous PO2.
Arterial = 13.3
Venous = 5.3
NOTE: only 25% of haemoglobin desaturates when going from arteries to veins
How does dissolved oxygen affect the oxygen that is bound to haemoglobin?
The PO2 (dissolved oxygen) only counts for a small part of oxygen transport in the blood (the rest is bound to haemoglobin) but it is like the conductor of an orchestra. Uptake of dissolved oxygen into tissues is NOT keeping you alive directly, but it is accompanied by a LARGE unloading of oxygen from haemoglobin, which provides a sufficient supply of oxygen to the tissues.
State four factors affecting the oxygen cascade.
V/Q mismatch
Alveolar Ventilation
Diffusion Capacity
Cardiac Output
State the different energy sources for different durations of exercise.
(in order of increasing duration of exercise - longest at the bottom) Intramuscular ATP Phosphocreatine Lactic Acid Aerobic
Describe how ventilation changes with submaximal exercise.
If we initiate submaximal exercise we increase the oxygen demand. Ventilation takes a little bit of time to meet these demands.
So, once exercise is finished, ventilation will remain higher for a little while longer to repay the oxygen debt from the start.
Describe and explain the ventilatory response to exercise.
When exercise begins, respiratory rate rapidly increases from around 12-20 then it remains stable for a long time.
Tidal volume then increases considerably (more efficient at increasing ventilation than increasing respiratory rate).
Eventually you get to a point where increasing tidal volume any further is energy inefficient.
Then respiratory rate increases further.
State the five challenges of altitude.
Hypoxia Solar Radiation Thermal Hydration Dangerous
What’s the difference between accommodation and acclimatisation.
Accommodation = ACUTE response to this kind of change - rapid physiological change in response to a change in oxygen in the oxygen environment Acclimatisation = physiology becomes more efficient so that you can get more out of the environment
What have the benefits of increased ventilation and PaO2 been attributed to?
Renal compensation for the respiratory alkalaemia
Increased sensitivity to hypoxia
Where is erythropoietin produced?
Renal cortex
