At higher elevations, oxygen levels in the atmosphere and air pressure decline, causing difficulty in breathing and even anoxia. This can lead to extreme fatigue, headaches, dizziness, nausea, and a loss of judgement, and someone at 5,000-7,500 metres above sea-level may faint and go into a coma. To combat this, oxygen bottles and special clothing are needed to survive at such heights, as well as systems that regulate air pressure on airplanes at 9,000-10,000 metres. Oxygen deficiency can occur at heights of 3,000-4,500 metres, and people may even lose consciousness at such elevations, but can be saved with immediate oxygen treatment.

In the comparison made in the verse below, this physical truth, the changes that take place in the chest with increasing height, is indicated in these terms:

When Allah desires to guide someone, He expands his breast to Islam. When He desires to misguide someone, He makes his breast narrow and constricted as if he were climbing up into the sky. That is how Allah defiles those who have no faith. (Quran chapter 6:125)