6533b872fe1ef96bd12d3adc

RESEARCH PRODUCT

Retinal vessel analysis and heart rate variability

subject

description

Heart rate variability (HRV) is used to index the vegetative nervous system and is linked with cardiovascular and nervous diseases [1]. Funduscopic assessment of the retinal vasculature can be utilized to evaluate the health status of microcirculation and to assess the predisposition of major vascular diseases [2]. The purpose of this study was, for the first time, to examine the influence of HRV on microcirculation as an early marker of cardiovascular alteration. The study population was comprised of apparently healthy employees of a high-tech company in Germany. The participants spanned the entire age of the work force (18–65 years) and all levels of socioeconomic status. A total of 292 subjects were included in this study and took part in a health screening examination including fundus photography and a full day recording of heart rate. The institutional review board and the ethical committee of the University of Heidelberg approved the study in accordance with the Declaration of Helsinki. All participants gave written informed consent and were Caucasians. All participants were examined during daylight time. Blood pressure via sphygmomanometry was recorded from the dominant arm in the seated position after a standardized 5 min rest period. 24-hour heart rate was recorded as beat-to-beat intervals using t6 Suunto Memory Belt (SuuntoVantaa, Finland) at a 1 kHz sample rate. HRV parameters were calculated as reported previously in accordance with the Task Force Guidelines of The European Society of Cardiology and The North American Society of Pacing and Electrophysiology published in 1996 using the “ANS-Explorer” Software [3]. Details are described elsewhere [4]. Root mean square of successive differences (RMSSD) primarily reflects vagally mediated HRV, the standard deviation of all N–N (normal-to-normal) intervals (SDNN) reflects sympathetically and parasympatheticallymediatedHRVs. Frequencydomainpowerwas determined as low (LF) (0.04–0.15 Hz) and high frequency (HF) (0.15–0.4 Hz). HF primarily indicates parasympathetically mediated respiratory sinus arrhythmia, in contrast to LF, that reflects sympathetic and parasympathetic inputs to the sinus node and is described to be related to the baroreceptor function. In addition, a comprehensive ophthalmological examination including 45° non-mydriatic digital fundus photography (Topcon 3D OCT2000, Topcon Corp., Tokyo, Japan) was carried out. Retinal vessel analysis was performed using a semi-automated software for non-mydriatic fundus photos [5]. Within this software, the central retinal arterial equivalent (CRAE) and the central retinal venous equivalent (CRVE) were automatically calculated, representing a parameter of the central retinal artery/vein as the actual vessels lay behind the optic disc and cannot be directly examined. CRAE is inversely correlated to arterial hypertension while CRVE is positively correlated to the risk of stroke. These equivalents are determined based on the analysis of retinal vessels around the optic disc and an iterative calculation. The arterialvenous ratio (AVR) was computed as the quotient of CRAE and CRVE. Right eyes were evaluated, as correlations of retinal vessel equivalents between the right and left eyes are high [6]. The distribution of all continuous variables was determined and transformations were used when it was necessary to meet the assumptions of modeling [7]. In these analyses, potential explanatory and confounding variableswere entered separately beforemeasures of HRV and retinal vessel parameters. These parameters weremeasured individually and rater-blinded to all other variables. Two-sided Pearson correlation coefficients and partial correlation coefficients (PCCs) were used to reflect the associations between two variables independent of other variables in the model. As confounding variables, age, gender and mean arterial blood pressure (MAP) were evaluated as these parameters influence both HRV and retinal vasculature. A p-value of 0.05 was regarded as statistically significant. We used SPSS (Version 21, SPSS Inc., Chicago, IL) for data management and analysis. In the examined sample 40% of the participants (overall 292 subjects) were female and 17% were smokers. The mean age of the International Journal of Cardiology 176 (2014) 1268–1269