ORIGINAL ARTICLE Peripheral photoplethysmography variability analysis of sepsis patients Paul M. Middleton • Collin H. H. Tang • Gregory S. H. Chan • Sarah Bishop • Andrey V. Savkin • Nigel H. Lovell Received: 21 July 2010 / Accepted: 27 October 2010 / Published online: 14 December 2010 Ó International Federation for Medical and Biological Engineering 2010 Abstract Sepsis is associated with impairment in auto- nomic regulatory function. This work investigates the application of heart rate and photoplethysmogram (PPG) waveform variability analysis in differentiating two cate- gories of sepsis, namely systemic inflammatory response syndrome (SIRS) and severe sepsis. Electrocardiogram- derived heart period (RRi) and PPG waveforms, measured from fingertips (Fin-PPG) and earlobes (Ear-PPG), of Emergency Department sepsis patients (n = 28) with dif- ferent disease severity, were analysed by spectral technique, and were compared to control subjects (n = 10) in supine and 80° head-up tilted positions. Analysis of covariance (ANCOVA) was applied to adjust for the confounding factor of age. Low-frequency (LF, 0.04–0.15 Hz), mid- frequency (MF, 0.09–0.15 Hz) and high-frequency (HF, 0.15–0.60 Hz) powers were computed. The normalised MF power in Ear-PPG (MFnu Ear ) was significantly reduced in severe sepsis patients with hyperlactataemia (lacta- te [ 2 mmol/l), compared to SIRS patients (P \ 0.05). Moreover, in a group of normal controls, MFnu Ear was not altered by head-up tilting (P [ 0.05), suggesting that there may be a link between 0.1 Hz ear blood flow oscillation and tissue metabolic changes in sepsis, in addition to autonomic factors. The study highlighted the value of PPG spectral analysis in the non-invasive assessment of peripheral vas- cular regulation in sepsis patients, with potential implica- tions in monitoring the progression of sepsis. Keywords Sepsis  Photoplethysmography  Power spectrum analysis  Cardiovascular variability analysis  Peripheral circulation 1 Introduction There has been increasing interest in the last decade both in non-invasive monitoring of the cardiovascular system through the analysis of heart rate, blood pressure and other signals representing cardiac or vascular function, and in this context, more subtle changes associated with cardio- vascular control. The spontaneous beat-to-beat fluctuations in heart rate and blood pressure, also known as heart rate variability (HRV) and blood pressure variability (BPV), P. M. Middleton (&)  S. Bishop Prince of Wales Clinical School, University of New South Wales, Kensington, NSW 2031, Australia e-mail: pmmiddleton@ambulance.nsw.gov.au P. M. Middleton  C. H. H. Tang  G. S. H. Chan  A. V. Savkin  N. H. Lovell Biomedical Systems Laboratory, School of Electrical Engineering and Telecommunications, University of New South Wales, Kensington, NSW 2052, Australia P. M. Middleton Emergency Department, Prince of Wales Hospital, Randwick, NSW 2031, Australia P. M. Middleton School of Public Health, University of Sydney, Sydney, NSW 2006, Australia P. M. Middleton Ambulance Research Institute, Ambulance Service of NSW, Sydney, Australia C. H. H. Tang Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, Johor 81310, Malaysia N. H. Lovell Graduate School of Biomedical Engineering, University of New South Wales, Kensington, NSW 2052, Australia 123 Med Biol Eng Comput (2011) 49:337–347 DOI 10.1007/s11517-010-0713-z