Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA060

Poster Communications

Cardiac autonomic modulation in adults with and without small abdominal aortic aneurysm

T. Bailey1,2, M. Perissiou2, M. Windsor2, M. Nam3, K. Greaves3,2, J. Golledge4,5, A. Leicht6, C. Askew2

1. School of Human Movement and Nutrition Science, The University of Queensland, Brisbane, Queensland, Australia. 2. VasoActive Research Group, University of the Sunshine Coast, Sippy Downs, Queensland, Australia. 3. Sunshine Coast Hospital and Health Service, Sunshine Coast University Hospital, Birtinya, Queensland, Australia. 4. Department of Vascular and Endovascular Surgery, The Townsville Hospital, Townsville, Queensland, Australia. 5. Queensland Centre for Peripheral Vascular Disease, James Cook University, Townsville, Queensland, Australia. 6. Sport and Exercise Science, James Cook University, Townsville, Queensland, Australia.

Patients diagnosed with small abdominal aortic aneurysm (AAA), defined as the abnormal dilatation of the abdominal aorta (30-55 mm), are at increased risk of cardiovascular events and mortality compared to older adults living without the condition1. Imbalances in autonomic modulation of cardiac activity (i.e. reduced parasympathetic and/or increased sympathetic activation) have been associated with increased cardiac risk in a range of chronic conditions, but not for patients with AAA. The aim of this study was to examine the influence of AAA on cardiac autonomic modulation, as assessed by heart rate variability (HRV), in older adults with and without small AAA. This study was approved by the Human Research Ethics Committee at the Metro North Hospital and Health Service in Brisbane. Patients with AAA (n=16; age, 72±4 y) and non-AAA older adults (n=19; age, 72±5 y) volunteered for the study, and rested quietly in the supine position for 25 min with the final 5-min period assessed for HRV. Recordings were analysed via specialised HRV software to compute linear parameters within the time-domain (SDNN, the standard deviation of RR intervals; RMSSD, root mean square of successive RR intervals; pNN50, % of adjacent RR intervals that differ in duration by >50 ms), the frequency-domain using the absolute power of the low frequency (LF, 0.04-0.15 Hz) and high frequency (HF, 0.15-0.40 Hz) bands, as well as non-linear geometric indices (SD1 and SD2 obtained by Poincaré plot). Groups were compared using an independent t-test and data are presented as mean±SE. Resting heart rate was similar between patients with AAA and older adults (60±3 vs 57±4 bpm; p=0.352). Patients with AAA exhibited significantly less time-domain and non-linear measures of HRV compared with older adults, including lower SDNN (16.3±2.7 vs 29.6±4.6 ms; p=0.018), RMSSD (17.7.5±3.8 vs 32.0±5.8 ms; p=0.046), pNN50 (1.2±5.1 vs 9.5±2.9 %; p=0.021), SD1 (12.5±2.7 vs 22.7±4.1 ms; p=0.046), and SD2 (18.9±2.8 vs 34.5±5.2 ms; p=0.014). There was also a tendency for lower frequency domain measures of HRV (LF, 146±63 vs 609±225 ms2; p=0.061; HF, 150±73 vs 473±165 ms2; p=0.087) in patients with AAA compared with older adults. Patients with AAA exhibited lower HRV compared with age-matched older adults, indicative of less parasympathetic and/or greater sympathetic modulations of heart rate. Reduced cardiac autonomic modulation may contribute to the elevated cardiovascular risk in AAA patients. Interventions aimed at improving cardiac autonomic modulations may reduce cardiovascular risk and improve long-term cardiovascular outcomes in this high-risk group.

Where applicable, experiments conform with Society ethical requirements