"Experiments in the 1960s showed that experts in yoga in fact were indeed capable of slowing normal body processes, such as the rate of oxygen consumption, heart rate, and breathing. Indian television cameras captured 46-year-old Ramanand Yogi sitting in a sealed box, in which he used little more than half the calculated minimum amount of oxygen required to maintain life. For one hour, he survived on a bare quarter of what his body should have needed.
In other tests, yogis produced sweat on the forehead only, while others slowed the heart rate while sitting still"
My technique is to consciously slow breathing and relax all muscles, which will for very simple phsyiological reasons mean you need less oxygen, therefore need less blood flow, therefore your body slows your heart. The opposite, is to think of your heart going fast... voila... it goes faster!
Other connections that exist include a direct cause and affect between willpower and immune system, willpower and disease & symptoms, etc. It is known that depression and mental weakness causes the immune system to work less well; and merely pretending to be happy or healthy actually increases your health!
[EDIT: Further comment removed due to: I can't think of a careful or sensible way of phrasing them without inviting cared-for friends to think me foolish...]