ORIGINAL RESEARCH Heart rate variability indices for very short-term (30 beat) analysis. Part 1: survey and toolbox Anne-Louise Smith • Harry Owen • Karen J. Reynolds Received: 14 September 2012 / Accepted: 22 April 2013 / Published online: 15 May 2013 Ó Springer Science+Business Media New York 2013 Abstract Heart rate variability (HRV) analysis over very short ( \ 60 s) periods may be useful for monitoring dynamic changes in autonomic nervous system activity where steady-state conditions are not maintained (e.g. during drug administration, or the start or end of exercise). From the 1980s there has been a wealth of HRV indices produced in the quest for better measures of the change in parasympathetic and sympathetic activity. Many of the indices have been sparingly used and have not been investigated for application to short-term use. This study surveyed published methods of HRV analysis searching for indices that could be applied to very short time HRV analysis. The survey included measures of time domain, frequency domain, respiratory sinus arrhythmia, Poincare ´ plot, and heart rate characteristics. Indices were tested with short segments of archived data to remove those that pro- duced invalid results, or were mathematically equivalent to, but less well known than other indices. The survey identified a comprehensive list of 115 indices that were subsequently coded and screened. Of these, 70 were unique and produced a finite number with 60 s data, so are included in the Toolbox. These indices require validation against physiological data before they can be applied to short-term HRV analysis of cardiac autonomic nervous system activity. Keywords Autonomic nervous system (ANS) modulation Á Biomedical signal processing Á Heart rate variability (HRV) Á Software algorithms 1 Introduction Heart rate variability (HRV) analysis is turning its focus to measuring dynamic changes in cardiac autonomic activity. This requires analysis over shorter intervals than the normally used 5–20 min. There are many indices that have proven useful in longer 5–20 min HRV analysis, but which have not been applied systematically to short-term investigations. If these indices can be applied to short-term HRV analysis ( \ 1 min) they may provide detail on the changing effects of the autonomic nervous system on the heart and enable tracking of dynamic changes in real-time, e.g. recovery from exercise [1], drugs with fast response times (e.g. fentanyl) [2] or biphasic effects (e.g. midazolam or atropine) [3, 4]. The use of traditional time domain indices to charac- terize overall cardiac neural control by a single value and relate that to chronic disease and mortality is well docu- mented for time periods from 5 min to 24 h [5]. Short-term analysis looks at relatively stable subsets of data typically over 5–20 min [6–9]. Most interventions can be applied with an impulse or step function and assumptions of sta- tionarity are made even though the physiological response may still be changing throughout the measurement period. Electronic supplementary material The online version of this article (doi:10.1007/s10877-013-9471-4) contains supplementary material, which is available to authorized users. A.-L. Smith (&) Á K. J. Reynolds The Medical Device Research Institute, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia e-mail: anne-louise.smith@health.sa.gov.au A.-L. Smith Biomedical Engineering Dept, Flinders Medical Centre, Adelaide, Australia H. Owen School of Medicine, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia 123 J Clin Monit Comput (2013) 27:569–576 DOI 10.1007/s10877-013-9471-4