Medical Engineering & Physics 28 (2006) 297–303 Complex character analysis of heart rate variability following brain asphyxia Yuanyuan Cai a , Yihong Qiu a , Lan Wei a , Wei Zhang a , Sijun Hu b , Peter R. Smith b , Vincent P. Crabtree b , Shanbao Tong c , Nitish V. Thakor c , Yisheng Zhu a,∗ a Department of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200030, China b Department of Electronic & Electrical Engineering, Loughborough University, UK c Department of Biomedical Engineering, Johns Hopkins School of Medicine, USA Received 4 December 2004; received in revised form 11 April 2005; accepted 25 May 2005 Abstract In the present study Renyi entropy and L–Z complexity were used to characterize heart rate variability (HRV) of rats that were suffered from brain asphyxia and ischemia. Two groups of rats were studied: (a) rats (n = 5) injected with NAALADase inhibitor, 2-PMPA, which has been proven neuroprotective in asphyxia injury and (b) control subjects (n = 5) without medication. Renyi entropy and L–Z complexity of the R–R intervals (RRI) at different experiment stages were investigated in the two groups. The results show that both measures indicate less injury and better recovery in the drug injection group. The dynamic change of 90min RRI signal after the asphyxia was investigated. The sudden reduction of the two parameters shows their sensitivity to the asphyxia insult. © 2005 IPEM. Published by Elsevier Ltd. All rights reserved. Keywords: Brain asphyxia; Heart rate variability; Renyi entropy; L–Z complexity 1. Introduction In the past years, brain injury following asphyxia and ischemia has attracted more and more attention. Asphyxia is the major cause of prenatal brain injury, which could lead to later psychomotor deficits [1]. In western countries, stroke is the third killer of people, about 700,000 people experience a new or recurrent stroke each year and 88% of all strokes are ischemic [2]. Brain ischemia is ready to lead to neuron death and stroke is the leading cause of long-term disability in the United States. Currently, experimental research has been done to inves- tigate ways to prevent severe injury in asphyxia conditions. One medicine, called 2-PMPA, a kind of NAALADase inhibitor, has been tested, and its certain neuroprotection ∗ Corresponding author. Tel.: +86 21 62933451. E-mail address: yszhu@sjtu.edu.cn (Y. Zhu). functionality has been proven by stained sections of the brain [3]. In addition, it is well known that cerebrovascular disease can alter cardiovascular and autonomic function. Researches over the past 20 years suggest that stroke may determine a major derangement of autonomic balance and cardiac dys- rhythmias [4]. It has been found that insular cortex, amygdale and lateral hypothalamus are the most important control sites of the autonomic function [5]. Although the patho- genesis of the complications such as cardiac dysrhythmias is still incompletely understood, those areas would obvi- ously be influenced during the attack of stroke, and result in central autonomic cardiovascular deregulation involving the sympathetic and the parasympathetic neural systems [6]. The analysis of heart rate variability (HRV) is known to provide useful information about disturbances in autonomic regulation. HRV refers to the beat-to-beat alteration of the heart, which is reported to be a promising marker to quantify 1350-4533/$ – see front matter © 2005 IPEM. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.medengphy.2005.05.002