Lungs At Altitude

Question 1

Pigas =

So PiO2 =

Answer 1

Pigas = pressure of inspired gas
= Patm x Figas

So PiO2 = 100KPa x 0.21 = 21KPa at sea level

Question 2

What is the alveolar gas equation?

What is the equation that links PACO2 to alveolar ventilation?

What is the equation that links PaO2 with PAO2?

Answer 2

PAO2 = PiO2 - PaCO2/R

PaCO2 = KVCO2/VA

PaO2 = PAO2 - (A-aDO2)
Usually PaO2 = 1 kpa less than PAO2

Question 3

What is the barometric pressure at 0, 4800, 6300, 8848m?

Answer 3

0
57
46
33.5 - so a third PiO2 at the top of Everest

Question 4

What is R?

Answer 4

It is the respiratory quotient usually around 0.8 but can vary slightly with diet

Question 5

What are the normal blood gases?

Answer 5

PaO2 = 10.5 — 13.5 KPa
PaCO2 = 4.5 - 6 KPa 
PH = 7.35-7.45

Question 6

Does FiO2 change with altitude?

Answer 6

No it will also remain constant only the PiO2 will change!

PaO2 = PiO2 - PaCO2/R

As PiO2 decreases so does PaO2

Hyperventilation can decrease PaCO2 and so increase PaO2

Question 7

What is the oxygen dissociation curve?
Why is it that shape?
What moves the curve right?
What moves the cure left?

Answer 7

A curve showing the relationship. Between oxygen partial pressure and oxygen saturation of the blood.

It is sigmoid shape due to the positive cooperactivity of oxygen

An increase in CO2, H+ and temp shifts the curve to the right

The opposite will shift it to the left

Question 8

What is the normal response of the lungs to altitude?

Answer 8

Usually at around 10,000 feet and due to the decreased PiO2:

Hypoxia — hyperventilation

However you can also have adaptive changes
Any alkalosis can be compensated by renal bicarbonate excretion

Question 9

What is PaO2 at the top Mount Everest?

PaCO2 is 1.5 Kpa

Answer 9

PiO2 = 0.21 x 33.5 (atm pressure) = 7KPa

PaO2 = 7 - 1.5/0.8

= 5.125 should be 10.5–13.5 Kpa

Question 10

What is acute mountain sickness?

Answer 10

Usually just travelled to an area over 2500m
Categorised by a headache and 1 other symptom
Tends to be younger people
Treated by decent!

Question 11

What is high altitude pulmonary oedema?

Answer 11

Unacclimatised individuals

AMS and cough

Due to a rapid ascent a over 2500m

At 4000m your risk is 2%

Treat with oxygen and decent

Question 12

Planes fly with a height of about 10,000 m why is this okay?

Answer 12

Effective cabin pressure brings it down to 8000ft equivalent

However PiO2 is still lower and therefore those with lung disease may be at risk when flying - may need to be tested before.

Question 13

What is a pneumothorax and why should you not fly with one?

Answer 13

pneumothorax occurs when air leaks into the space between your lung and chest wall. This air pushes on the outside of your lung and makes it collapse. Pneumothorax can be a complete lung collapse or a collapse of only a portion of the lung.

If your fly with air trapped in the lung it will expand and may cause large scale problems!