Q34. David’s fitness challenge last year was to climb Mt Kilimanjaro - the summi
ID: 3519977 • Letter: Q
Question
Q34. David’s fitness challenge last year was to climb Mt Kilimanjaro - the summit of which is 5895m above sea level. At this altitude, atmospheric pressure is 480 mmHg.
a) Calculate the partial pressure of oxygen at this altitude. How does this compare to the partial pressure of oxygen at sea level? [1 mark]
b) At this altitude, David’s arterial pO2 would be approximately 45 mmHg. Assuming that he hadn’t been there long enough for any kind of adaptation to occur, what effect would this arterial pO2 have on the oxygen saturation of John’s haemoglobin? [0.5 marks]
c) What would happen to David's ventilation rate during the ascent? Describe the mechanisms by which this change occurs. Describe what happens to alveolar pO2 and pCO2 as a consequence of this change? [2.5 marks]
Could you please show your workings in part A of this question so I can understand better.
Thank you for your help.
Explanation / Answer
a.)
According to law: Partial pressure of a gas in air = Total pressure of that air x fraction of gas present in that air.
We know that 21% of environmental gas is Oxygen.
So Partial pressure of Oxygen at that altitude is = 480 mmHg x ( 21/100)
= 100.8 mmHg.
At sea level environmental pressure is 760mmHg, So at sea level, the partial pressure of oxygen is 760 x 0.21 = 159.6 mmHg. So partial pressure at this altitude is less than the partial pressure of sea level.
b)
Partial pressure of O2 in blood = ( FiO2 x Atmospheric pressure) - ( partial pressure of CO2 / Respiratory quotient)
Oxygen saturation of hemoglobin depends on avalable oxygen molecules in the blood. The higher the arterial pressure of oxygen--> means higher O2 molecule in blood---> Higher saturation of hemoglobine [ remember 1 gm of Hb can hold max of 1.34 ml of oxygen].
As there is low partial pressure of oxygen( 45mmHg) than normal arterial partial pressure of oxygen ( normal is arround 100 mmHg, remember atmospheric partial pressure of oxygen and partial pressure of xygen is blood is different) --> there will be less oxygen molecule ----> saturation of hemoglobin will be less than normal ( because David has not got the chance of adaptation).
c. During ascent, there is reduced partial pressure of oxygen, --> various receptor ( peripheral chemorecepetor, central chemoreceptor, strectch receptors in lung, ) sense the low oxygen concentration and high carbon dioxide concentration-->Send this information the respiratory center at medulla oblongata ---> Result increased respiratory rate via increased sympathetic nervous system.
As the ventilation rate will be increased---> More oxygen will eneter from environment to alveoli ( max O2 will depend on atmospheric partial pressure O2) and more carbondioxide will be exhaled out from lung---->there will be absolute decrease in carbon dioxide concentration as the actual exhale rate of carbon dioxide will increase due to increased ventilation rate and relative increased oxygen cocentration in the alveoli, there will be no absolute rise in oxygen concentration as the environmental partial pressure of oxygen is constant at that particular atmospheric pressure.
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