Heart rate persons with coronary artery disease. The heart rate is rhythmically generated by the sinoatrial node. It is also influenced by central factors through sympathetic and parasympathetic nerves. Nervous influence over the heartrate is centralized within the two paired cardiovascular centres of the medulla oblongata. The cardioaccelerator regions stimulate activity via sympathetic stimulation of the cardioaccelerator nerves, and the cardioinhibitory centers decrease heart activity via parasympathetic stimulation as one component of the vagus nerve. During rest, both centers provide slight stimulation to the heart, contributing to autonomic tone. This is a similar concept to tone in skeletal muscles. Normally, vagal stimulation
Heart rate monitor watches, smart bands and cell phones often use PPG sensors. Garmin, Polar, Suunto and Fitbit are vendors selling consumer heart rate products. Most companies use their own proprietary Heart Rate algorithms. Garmin and other Smart Watch companies use technology from Firstbeat The newer, wrist based heart rate monitors have achieved almost identical levels of accuracy as their chest strap counterparts with independent tests showing up to 98% accuracy. Optical devices when used with rigorous activity can be less accurate or when used under water. Currently Heart rate variability is less available on optical devices. The Apple watch now includes HRV.