Vagus reflex

The vagus nerve plays a role in (amongst other things) controlling the pulse. The vagus reflex is a reaction which can reduce the pulse rate during tachycardia (racing pulse). The following stimuli may produce the vagus reflex:
 * tensing the lower abdomen (similar to straining at stool)
 * gentle pressure on the closed eyes
 * a gulp of ice-cold water
 * splashing ice-cold water on the face
 * immersing the arms in ice-cold water
 * finger stuck down the throat
 * the insertion of an IV needle
 * cough or sneeze (involuntary or autonomic works best)
 * holding breath (after exhaling) - see Valsalva manoeuvre