@article{Graff:2013,
  author  = "G. Graff and B. Graff and A. Kaczkowska and D. Makowiec and J. Amigó and J. Piskorski and K. Narkiewicz and P. Guzik",
  title   = "Ordinal pattern statistics for the assessment of heart rate variability",
  journal = "European Physical Journal-Special Topics",
  volume  = "Vol. 222",
  number  = "no. 2",
  pages   = "525--534",
  year    = "2013",
}