@article{Guzik:2018,
  author  = "P. Guzik and C. Piekos and O. Pierog and N. Fenech and T. Krauze and J. Piskorski and A. Wykrętowicz",
  title   = "Classic electrocardiogram-based and mobile technology derived approaches to heart rate variability are not equivalent",
  journal = "International Journal of Cardiology",
  volume  = "Vol. 258",
  pages   = "154--156",
  year    = "2018",
}