When Breathing Fails

Challenges to clear

• Work through all four cases correctly.
• Answer the carbon-monoxide case correctly.

The task

Each of these is a failure of oxygen supply, but for a different reason.

What this lesson covers

• A trekker arriving at 4000 metres feels breathless and dizzy, though the air is perfectly clean. Why? Best choice: The air pressure is lower, so less oxygen crosses into the blood with each breath — Diffusion depends on partial pressure. Lower pressure means a weaker gradient at the alveoli, so less oxygen is taken up.
• After two weeks at that altitude the trekker feels much better. What has the body done? Best choice: Made more red blood cells, so the blood carries more oxygen — Acclimatisation: more red cells and more haemoglobin compensate for the thinner air. This is why athletes train at altitude.
• Someone sleeping in a closed room with a burning coal sigri is found unconscious. Carbon monoxide poisoning is suspected. Why is CO so dangerous? Best choice: It binds to haemoglobin far more strongly than oxygen does, so the blood cannot carry oxygen — Carboxyhaemoglobin is stable and does not release its load. The blood is full but useless — and the victim feels no breathlessness.
• A person is pulled from water and is not breathing, but has a pulse. What is the immediate priority? Best choice: Give artificial respiration at once and call for medical help — The brain begins to suffer damage within minutes without oxygen. Restoring air movement is the immediate priority.

Hint

Trace where the failure happens: in the air (altitude), in the blood (carbon monoxide), or in the airway (drowning, choking).