Altitude

Question 1

What is partial pressure determined by?

Answer 1

The concentration of gas within the mix (eg 21% O2) and the total pressure of the mix (eg atmospheric pressure)

Question 2

What happens to barometric pressure as altitude increases?

Answer 2

It falls (known as hypobaria)

Question 3

What happens to the partial pressure of O2 as altitude increases?

Answer 3

It falls

Question 4

State daltons law

Answer 4

The pressure exerted by a mixture of gases is equal to the sum of the partial pressures of each gas in the mixture

Question 5

What would the partial pressure of O2 be at Everest?
Barometric pressure - 230mmHg
% O2 conc - 21%

Answer 5

230 x 0.21 = 48 mmHg

Question 6

What is the oxygen transport cascade?

Answer 6

The progressive change in the environments oxygen pressure to all organs, tissues, cells and mitochondria in the body

Question 7

What are the requirements of the oxygen transport cascade?

Answer 7

Must be energy efficient,
Sensitive - to the demands,
Responsive,
Efficient in allowing O2 penetration to blood

Question 8

Whats the law of gaseous diffusion?

Answer 8

That gases travel down their pressure gradient

Question 9

Why do we see record breaking performances at altitude?

Answer 9

Two immediate reflex responses occur:
-Hyperventilation -> stimulation of peripheral chemoreceptors which increases the rate and depth of breathing,

-Tachycardia -> stimulation of peripheral chemoreceptors which increases CO2, this then increases O2 delivery to tissues

Question 10

What stimulates chemoreceptors?

Answer 10

Low PO2 and high PCO2

Question 11

What drives respiration?

Answer 11

The partial pressure of O2

Question 12

Outline the hyperventilation cycle

Answer 12

A low PO2 activates peripheral chemoreceptors, increasing ventilation.
This increases PO2 and decreases PCO2 and increases pH.
The low PCO2 inactivates central chemoreceptors, decreasing ventilation.
PCO2 then rises and initiates slower deeper breathing but O2 demand not met.
This causes hypoxia and the cycle begins again

Question 13

Why does PCO2 decreases in the hyperventilation cycle?

Answer 13

Its necessary to prevent sustained hyperventilation

Question 14

What initial adaptations occur in response to altitude?

Answer 14

• Increased renal HCO3 secretion

- increase in 2-3 DPG

Question 15

Why does increased renal HCO3 excretion occur in response to hyperventilation at altitude?

Answer 15

Hyperventilation decreases PCO2 which decreases H+ ions in the blood. This can cause alkalosis - which is bad so these responses occur to stop this.
So reduced HCO3 absorption at PCT,
Increase in H+ secretion, and
Increase in HCO3 secretion. This maintains balance.

Question 16

What is respiratory alkalosis?

Answer 16

Disturbance in acid and base balance due to alveolar hyperventilation

Question 17

If theres an increase in H+ what happens to ventilation?

Answer 17

Peripheral chemoreceptors increase ventilation

Question 18

What happens to ventilation if PCO2 decreases?

Answer 18

Central chemoreceptors decrease respiration

Question 19

What causes the physiological adaptions to occur at altitude?

Answer 19

Reduction in PO2 and accompanying arterial hypoxemia

Question 20

Why is an increase in 2-3 DPG beneficial response at altitude? O

Answer 20

The mechanism improves O2 delivery to tissues. It causes a shift in oxyhaemaglobin curve to the right, allowing Hb to release O2 at higher PO2 so more O2 is available to tissues during hypoxia.

Question 21

What long term adaptations occur as a result of altitude?

Answer 21

• increase in haematocrit

- angiogenesis

Question 22

How do we get an increase in haematocrit in response to altitude?

Answer 22

Initially, you lose plasma volume due to increased urination and respiratory loss of water - which increases haematocrit,
Over time, you get an increase in haemopoiesis (prod of RBC and platelets),
This decreases O2 tension in the kidney and they release erythropoietin, which increases the haematocrit.

Question 23

Why is angiogenesis beneficial adaptation to altitude?

Answer 23

Improves diffusion of O2,
Increases SA for gas exchange,
More mitochondria and cellular respiratory enzymes are formed

Question 24

What is acute mountain sickness?

Answer 24

The impact of hypoxia on the body

Question 25

What determined the severity of AMS?

Answer 25

Rate of ascent,
Altitude attained,
Length of time at altitude,
Degree of physical exertion,
Individuals physiological susceptibility

Question 26

What are the major symptoms of AMS?

Answer 26

Headache, fatigue, dizziness, anorexia, cyanosis

Question 27

What is HAPE and HACE?

Answer 27

High altitude pulmonary/cerebral oedema - serious complications with altitude that require immediate medical treatment and descent

Question 28

Outline the process of HAPE

Answer 28

Alveolar hypoxia -> hypoxic pulmonary vasoconstriction -> increased capillary pressure -> increased hydrostatic pressure and damage to capillary walls -> oedema
Now decreased O2 delivery

Question 29

What happens in HACE?

Answer 29

Cerebral hypoxia leads to either vasogenic or cytotoxic oedema which both increase intracranial pressure and lead to impaired brain function