In physiology, perfusion is the process of a body delivering blood to a capillary bed in its biological tissue. The word is derived from the French verb "perfuser" meaning to "pour over or through." Blood perfusion can be measured as the percentage change in blood volume in local tissue resulting from a heart beat.
In general, blood perfusion depends upon cardiovascular, hormonal and circulatory health in humans.
Skin blood perfusion may be lower if skin temperature is low, or altitude is high. Also, the act of putting on a measurement device may temporarily lower local skin blood perfusion.
It is essentially a quality measure since good measurements from the Everion Device require a sufficiently high blood perfusion. For example Heart rate measurement requires blood perfusion values of above 0.25, and blood oxygenation measurements ideally require values above 0.5.