{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,12]],"date-time":"2025-10-12T03:52:58Z","timestamp":1760241178731,"version":"build-2065373602"},"reference-count":39,"publisher":"MDPI AG","issue":"12","license":[{"start":{"date-parts":[[2019,12,15]],"date-time":"2019-12-15T00:00:00Z","timestamp":1576368000000},"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>Stays at high altitude induce alterations in cardiovascular control and are a model of specific pathological cardiovascular derangements at sea level. However, high-altitude alterations of the complex cardiovascular dynamics remain an almost unexplored issue. Therefore, our aim is to describe the altered cardiovascular complexity at high altitude with a multiscale entropy (MSE) approach. We recorded the beat-by-beat series of systolic and diastolic blood pressure and heart rate in 20 participants for 15 min twice, at sea level and after arrival at 4554 m a.s.l. We estimated Sample Entropy and MSE at scales of up to 64 beats, deriving average MSE values over the scales corresponding to the high-frequency (MSEHF) and low-frequency (MSELF) bands of heart-rate variability. We found a significant loss of complexity at heart-rate and blood-pressure scales complementary to each other, with the decrease with high altitude being concentrated at Sample Entropy and at MSEHF for heart rate and at MSELF for blood pressure. These changes can be ascribed to the acutely increased chemoreflex sensitivity in hypoxia that causes sympathetic activation and hyperventilation. Considering high altitude as a model of pathological states like heart failure, our results suggest new ways for monitoring treatments and rehabilitation protocols.<\/jats:p>","DOI":"10.3390\/e21121224","type":"journal-article","created":{"date-parts":[[2019,12,17]],"date-time":"2019-12-17T02:59:01Z","timestamp":1576551541000},"page":"1224","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":7,"title":["Alterations of Cardiovascular Complexity during Acute Exposure to High Altitude: A Multiscale Entropy Approach"],"prefix":"10.3390","volume":"21","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-8924-8234","authenticated-orcid":false,"given":"Andrea","family":"Faini","sequence":"first","affiliation":[{"name":"Istituto Auxologico Italiano, IRCCS, Department of Cardiovascular, Neural and Metabolic Sciences, S.Luca Hospital, 20149 Milan, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3003-6499","authenticated-orcid":false,"given":"Sergio","family":"Caravita","sequence":"additional","affiliation":[{"name":"Istituto Auxologico Italiano, IRCCS, Department of Cardiovascular, Neural and Metabolic Sciences, S.Luca Hospital, 20149 Milan, Italy"},{"name":"Department of Management, Information and Production Engineering, University of Bergamo, 24044 Dalmine, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9402-7439","authenticated-orcid":false,"given":"Gianfranco","family":"Parati","sequence":"additional","affiliation":[{"name":"Istituto Auxologico Italiano, IRCCS, Department of Cardiovascular, Neural and Metabolic Sciences, S.Luca Hospital, 20149 Milan, Italy"},{"name":"Department of Medicine and Surgery, University of Milano-Bicocca, 20126 Milan, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8775-2605","authenticated-orcid":false,"given":"Paolo","family":"Castiglioni","sequence":"additional","affiliation":[{"name":"IRCCS Fondazione Don Carlo Gnocchi, 20148 Milan, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2019,12,15]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"13","DOI":"10.1007\/s10286-006-0395-7","article-title":"The autonomic nervous system at high altitude","volume":"17","author":"Hainsworth","year":"2007","journal-title":"Clin. Auton. Res."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"322","DOI":"10.1111\/jsr.12012","article-title":"High-altitude hypoxia and periodic breathing during sleep: Gender-related differences","volume":"22","author":"Lombardi","year":"2013","journal-title":"J. Sleep Res."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"120","DOI":"10.1378\/chest.14-0317","article-title":"Sex and Acetazolamide Effects on Chemoreflex and Periodic Breathing During Sleep at Altitude","volume":"147","author":"Caravita","year":"2015","journal-title":"Chest"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"521","DOI":"10.3414\/ME09-02-0053","article-title":"The HIGHCARE investigators Linear and Fractal Heart Rate Dynamics during Sleep at High Altitude: Investigation with Textile Technology","volume":"49","author":"Castiglioni","year":"2010","journal-title":"Methods Inf. Med."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"390","DOI":"10.3389\/fphys.2018.00390","article-title":"High Altitude Affects Nocturnal Non-linear Heart Rate Variability: PATCH-HA Study","volume":"9","author":"Boos","year":"2018","journal-title":"Front. Physiol."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"565","DOI":"10.1042\/cs0950565","article-title":"Cardiovascular autonomic modulation and activity of carotid baroreceptors at altitude","volume":"95","author":"Bernardi","year":"1998","journal-title":"Clin. Sci."},{"key":"ref_7","first-page":"6679","article-title":"Heart rate and cardiovascular variability at high altitude","volume":"2007","author":"Bernardi","year":"2007","journal-title":"Conf. Proc. IEEE Eng. Med. Biol. Soc."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"759","DOI":"10.1093\/eurheartj\/ehs140","article-title":"Effects of acetazolamide on central blood pressure, peripheral blood pressure, and arterial distensibility at acute high altitude exposure","volume":"34","author":"Parati","year":"2013","journal-title":"Eur. Heart J."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"698","DOI":"10.1016\/S0008-6363(97)00003-5","article-title":"Models of brachial to finger pulse wave distortion and pressure decrement","volume":"33","author":"Gizdulich","year":"1997","journal-title":"Cardiovasc. Res."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"1810","DOI":"10.1001\/jama.2017.16192","article-title":"Does This Patient Have Acute Mountain Sickness? The Rational Clinical Examination Systematic Review","volume":"318","author":"Meier","year":"2017","journal-title":"JAMA"},{"key":"ref_11","unstructured":"Task Force of the European Society of Cardiology (1996). The North American Society of Pacing Electrophysiology. Heart Rate Variability: Standards of Measurement, Physiological Interpretation, and Clinical Use. Circulation, 93, 1043\u20131065."},{"key":"ref_12","doi-asserted-by":"crossref","unstructured":"Castiglioni, P., Parati, G., and Faini, A. (2019). Information-Domain Analysis of Cardiovascular Complexity: Night and Day Modulations of Entropy and the Effects of Hypertension. Entropy, 21.","DOI":"10.3390\/e21060550"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"068102","DOI":"10.1103\/PhysRevLett.89.068102","article-title":"Multiscale Entropy Analysis of Complex Physiologic Time Series","volume":"89","author":"Costa","year":"2002","journal-title":"Phys. Rev. Lett."},{"key":"ref_14","doi-asserted-by":"crossref","unstructured":"Castiglioni, P., Coruzzi, P., Bini, M., Parati, G., and Faini, A. (2017). Multiscale Sample Entropy of Cardiovascular Signals: Does the Choice between Fixed- or Varying-Tolerance among Scales Influence Its Evaluation and Interpretation?. Entropy, 19.","DOI":"10.3390\/e19110590"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"5865","DOI":"10.1016\/j.physa.2013.07.075","article-title":"Modified multiscale entropy for short-term time series analysis","volume":"392","author":"Wu","year":"2013","journal-title":"Phys. A Stat. Mech. Its Appl."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"2202","DOI":"10.1109\/TBME.2009.2021986","article-title":"Refined Multiscale Entropy: Application to 24-h Holter Recordings of Heart Period Variability in Healthy and Aortic Stenosis Subjects","volume":"56","author":"Valencia","year":"2009","journal-title":"IEEE Trans. Biomed. Eng."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"H2039","DOI":"10.1152\/ajpheart.2000.278.6.H2039","article-title":"Physiological time-series analysis using approximate entropy and sample entropy","volume":"278","author":"Richman","year":"2000","journal-title":"Am. J. Physiol. Heart Circ. Physiol."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"211","DOI":"10.1111\/j.2517-6161.1964.tb00553.x","article-title":"An Analysis of Transformations","volume":"26","author":"Box","year":"1964","journal-title":"J. R. Stat. Soc. Ser. B (Methodol.)"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"021906","DOI":"10.1103\/PhysRevE.71.021906","article-title":"Multiscale entropy analysis of biological signals","volume":"71","author":"Costa","year":"2005","journal-title":"Phys. Rev. E"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"989","DOI":"10.1152\/japplphysiol.01059.2009","article-title":"Contributions of central and peripheral chemoreceptors to the ventilatory response to CO2\/H+","volume":"108","author":"Forster","year":"2010","journal-title":"J. Appl. Physiol."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"1600","DOI":"10.1152\/jappl.2001.90.4.1600","article-title":"Invited Review: Physiological consequences of intermittent hypoxia: Systemic blood pressure","volume":"90","author":"Fletcher","year":"2001","journal-title":"J. Appl. Physiol."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"131","DOI":"10.1016\/B978-0-444-63274-6.00007-2","article-title":"Mechanism of Sympathetic Activation and Blood Pressure Elevation in Humans and Animals Following Acute Intermittent Hypoxia","volume":"Volume 209","author":"Xing","year":"2014","journal-title":"Progress in Brain Research"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"248","DOI":"10.1097\/MAJ.0b013e3181629a32","article-title":"Effect of rapid ascent to high altitude on autonomic cardiovascular modulation","volume":"336","author":"Chen","year":"2008","journal-title":"Am. J. Med. Sci."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"2537","DOI":"10.1152\/jappl.1994.77.6.2537","article-title":"Sympathetic and parasympathetic indicators of heart rate control at altitude studied by spectral analysis","volume":"77","author":"Hughson","year":"1994","journal-title":"J. Appl. Physiol."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"521","DOI":"10.1007\/BF00357674","article-title":"Effects of high altitude acclimatization on heart rate variability in resting humans","volume":"73","author":"Perini","year":"1996","journal-title":"Eur. J. Appl. Physiol."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"8","DOI":"10.1016\/j.ajem.2004.09.023","article-title":"Relationship between arterial oxygen saturation and heart rate variability at high altitudes","volume":"23","author":"Saito","year":"2005","journal-title":"Am. J. Emerg. Med."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"263","DOI":"10.1007\/s13246-015-0354-5","article-title":"Linear and nonlinear dynamics of heart rate variability in the process of exposure to 3600 m in 10 min","volume":"38","author":"Zhang","year":"2015","journal-title":"Australas. Phys. Eng. Sci. Med."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"73","DOI":"10.1186\/1475-925X-13-73","article-title":"Effects of acute hypoxia on heart rate variability, sample entropy and cardiorespiratory phase synchronization","volume":"13","author":"Zhang","year":"2014","journal-title":"Biomed. Eng. Online"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"17","DOI":"10.1088\/0967-3334\/34\/1\/17","article-title":"K-nearest-neighbor conditional entropy approach for the assessment of the short-term complexity of cardiovascular control","volume":"34","author":"Porta","year":"2013","journal-title":"Physiol. Meas."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"755","DOI":"10.1088\/0967-3334\/36\/4\/755","article-title":"Limits of permutation-based entropies in assessing complexity of short heart period variability","volume":"36","author":"Porta","year":"2015","journal-title":"Physiol. Meas."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"4","DOI":"10.1016\/j.wem.2009.12.022","article-title":"Heart Rate Nonlinear Dynamics During Sudden Hypoxia at 8230 m Simulated Altitude","volume":"21","author":"Vigo","year":"2010","journal-title":"Wilderness Environ. Med."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"262","DOI":"10.1161\/01.CIR.100.3.262","article-title":"Enhanced sympathetic and ventilatory responses to central chemoreflex activation in heart failure","volume":"100","author":"Narkiewicz","year":"1999","journal-title":"Circulation"},{"key":"ref_33","doi-asserted-by":"crossref","unstructured":"Chao, H.-H., Yeh, C.-W., Hsu, C.F., Hsu, L., and Chi, S. (2019). Multiscale Entropy Analysis with Low-Dimensional Exhaustive Search for Detecting Heart Failure. Appl. Sci., 9.","DOI":"10.3390\/app9173496"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"2562","DOI":"10.1249\/MSS.0000000000001384","article-title":"The Effect of Sex on Heart Rate Variability at High Altitude","volume":"49","author":"Boos","year":"2017","journal-title":"Med. Sci. Sports Exerc."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"343","DOI":"10.1089\/ham.2010.1039","article-title":"The Prevalence of and Risk Factors for Acute Mountain Sickness in the Eastern and Western Alps","volume":"11","author":"Mairer","year":"2010","journal-title":"High Alt. Med. Biol."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"51","DOI":"10.2170\/jjphysiol.52.51","article-title":"Reserved Higher Vagal Tone under Acute Hypoxia in Tibetan Adolescents with Long-Term Migration to Sea Level","volume":"52","author":"Zhuang","year":"2002","journal-title":"JJP"},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"1968","DOI":"10.1152\/jappl.1993.75.5.1968","article-title":"Autonomic regulation of heart rate response to exercise in Tibetan and Han residents of Lhasa (3658 m)","volume":"75","author":"Zhuang","year":"1993","journal-title":"J. Appl. Physiol."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"40","DOI":"10.1016\/j.resp.2018.04.002","article-title":"Differential responses of autonomic function in sea level residents, acclimatized lowlanders at >3500 m and Himalayan high altitude natives at >3500 m: A cross-sectional study","volume":"254","author":"Dhar","year":"2018","journal-title":"Respir. Physiol. Neurobiol."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"659","DOI":"10.2147\/COPD.S194426","article-title":"Blood pressure response to exposure to moderate altitude in patients with COPD","volume":"14","author":"Schwarz","year":"2019","journal-title":"COPD"}],"container-title":["Entropy"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1099-4300\/21\/12\/1224\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T13:42:32Z","timestamp":1760190152000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1099-4300\/21\/12\/1224"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2019,12,15]]},"references-count":39,"journal-issue":{"issue":"12","published-online":{"date-parts":[[2019,12]]}},"alternative-id":["e21121224"],"URL":"https:\/\/doi.org\/10.3390\/e21121224","relation":{},"ISSN":["1099-4300"],"issn-type":[{"type":"electronic","value":"1099-4300"}],"subject":[],"published":{"date-parts":[[2019,12,15]]}}}