heart, as suggested by a decrease in heart rate. In addition, scopolamine and low dose atropine can markedly increase HRV. However, though the heart rate slowing in proportional to the (low) dose of atropine, the increase in HRV varies widely across and within individuals. This suggests that even for vagal activity to the heart, HRV may be a limited marker. Thrombolysis The effect of thrombolysis on HRV (assessed by pNN50) was reported in 95 patients with acute MI. HRV was higher 90 minutes after thrombolysis in the patients with patency of the infarct-related artery. However, this difference was no longer evident when the entire 24 hours were analyzed. Exercise training Exercise training may decrease cardiovascular mortality and sudden cardiac death. Regular exercise training is also thought to modify cardiac autonomic control. Individuals who exercise regularly have a 'training bradycardia' (i.e., low resting heart rate) and generally have higher HRV than sedentary individuals. Biofeedback The technique called resonant breathing biofeedback teaches how to recognize and control involuntary heart rate variability. A randomized study by Sutarto et al. assessed the effect of resonant breathing biofeedback among manufacturing operators; depression, anxiety and stress significantly decreased. A first overall meta-analysis by Goessl VC et al. (24 studies, 484 individuals, 2017) indicates ''HRV biofeedback training is associated with a large reduction in self-reported stress and anxiety'', while mentioning that more well-controlled studies are needed. Wind instruments One study that surveyed the physiological effects of playing Native American flutes found a significant HRV increase when playing both low-pitched and high-pitched flutes. Normal HRV values Even though there are no widely accepted standard values for HRV that can be used for clinical purposes, multiple studies have measured and reported normal values for various populations: See also Heart rate turbulence Sinus rhythm References External links Association for Applied Psychophysiology and Biofeedback Biofeedback Federation of Europe 1996 guidelines Review on the mechanisms of cardiovascular variability in the Journal of Physiology HRV Seminar – Physiology & Methods HRV Seminar – Clinical Use & Factors that Influence HRV Courses and educational materials Heart Rate Variability and Ayurveda Medical statistics Cardiology Statistical signal processing Medical signs