During each heartbeat, the heart contracts and pumps blood through the arteries and blood vessels. When there is more stress, the body gets sympathetically activated, increasing heart rate and decreasing the variability in the heart rhythm.
Sympathetic arousal also leads to constriction of the blood vessels in the periphery, which lowers the relative blood flow through that tissue.
How is it measured ?
Blood Volume Pulse or heart rate can be measured by a plethysmograph like the BVP Sensor (Finger / Head)
