{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,12]],"date-time":"2025-10-12T04:27:25Z","timestamp":1760243245427,"version":"build-2065373602"},"reference-count":23,"publisher":"MDPI AG","issue":"12","license":[{"start":{"date-parts":[[2014,12,3]],"date-time":"2014-12-03T00:00:00Z","timestamp":1417564800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Entropy"],"abstract":"<jats:p>Autonomic activity affects beat-to-beat variability of heart rate and QT interval. The aim of this study was to explore whether entropy measures are suitable to detect changes in neural outflow to the heart elicited by two different stress paradigms. We recorded short-term ECG in 11 normal subjects during an experimental protocol that involved head-up tilt and mental arithmetic stress and computed sample entropy, cross-sample entropy and causal interactions based on conditional entropy from RR and QT interval time series. Head-up tilt resulted in a significant reduction in sample entropy of RR intervals and cross-sample entropy, while mental arithmetic stress resulted in a significant reduction in coupling directed from RR to QT. In conclusion, measures of entropy are suitable to detect changes in neural outflow to the heart and decoupling of repolarisation variability from heart rate variability elicited by orthostatic or mental arithmetic stress.<\/jats:p>","DOI":"10.3390\/e16126384","type":"journal-article","created":{"date-parts":[[2014,12,3]],"date-time":"2014-12-03T10:27:09Z","timestamp":1417602429000},"page":"6384-6393","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":19,"title":["Entropy Analysis of RR and QT Interval Variability during Orthostatic and Mental Stress in Healthy Subjects"],"prefix":"10.3390","volume":"16","author":[{"given":"Mathias","family":"Baumert","sequence":"first","affiliation":[{"name":"School of Electrical and Electronic Engineering, University of Adelaide, Adelaide SA 5005, Australia"}]},{"given":"Barbora","family":"Czippelova","sequence":"additional","affiliation":[{"name":"Department of Physiology, Jessenius Faculty of Medicine, Comenius University, Mala Hora 4, Martin 036 01, Slovakia"}]},{"given":"Anand","family":"Ganesan","sequence":"additional","affiliation":[{"name":"School of Medicine, University of Adelaide, Adelaide SA 5005, Australia"}]},{"given":"Martin","family":"Schmidt","sequence":"additional","affiliation":[{"name":"Institute of Biomedical Engineering, Technical University Dresden, Dresden 01069, Germany"}]},{"given":"Sebastian","family":"Zaunseder","sequence":"additional","affiliation":[{"name":"Institute of Biomedical Engineering, Technical University Dresden, Dresden 01069, Germany"}]},{"given":"Michal","family":"Javorka","sequence":"additional","affiliation":[{"name":"Department of Physiology, Jessenius Faculty of Medicine, Comenius University, Mala Hora 4, Martin 036 01, Slovakia"}]}],"member":"1968","published-online":{"date-parts":[[2014,12,3]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1557","DOI":"10.1161\/01.CIR.96.5.1557","article-title":"Beat-to-beat QT interval variability novel evidence for repolarization lability in ischemic and nonischemic dilated cardiomyopathy","volume":"96","author":"Berger","year":"1997","journal-title":"Circulation"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"113","DOI":"10.1159\/000026642","article-title":"Effect of posture and isoproterenol on beat-to-beat heart rate and QT variability","volume":"41","author":"Yeragani","year":"2000","journal-title":"Neuropsychobiology"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"H962","DOI":"10.1152\/ajpheart.00301.2008","article-title":"QT interval variability and cardiac norepinephrine spillover in patients with depression and panic disorder","volume":"295","author":"Baumert","year":"2008","journal-title":"Am. 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