Q.Percentage of oxygen present in inhaling air is:

Cardiopulmonary Resuscitation (CPR) and First Aid

When a person's heartbeat and breathing suddenly stop — for example after a cardiac arrest, drowning or electric shock — the brain begins to be starved of oxygen within minutes. Cardiopulmonary resuscitation (CPR) is the emergency technique that buys time by artificially keeping oxygenated blood moving until proper medical help arrives.

Why CPR works — the underlying idea

Normally the heart pumps blood and the lungs oxygenate it. If both stop, oxygen delivery to vital organs — especially the brain — halts, and permanent damage can begin quickly. CPR manually takes over both jobs:

• Chest compressions substitute for the heart's pumping. Pressing firmly and rhythmically on the centre of the chest squeezes the heart between the breastbone and spine, pushing blood out to the body and brain.
• Artificial (rescue) breathing — mouth-to-mouth ventilation — substitutes for breathing, forcing air into the victim's lungs so the circulated blood can pick up oxygen.

Together these maintain a trickle of oxygenated blood to the brain, preserving life until the heart can be restarted.

First aid — the broader principle …