Cardiovascular and cardiorespiratory phase synchronization in normovolemic and hypovolemic humans

Qingguang Zhang, Abhijit R. Patwardhan, Charles F. Knapp, Joyce M. Evans

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


We investigated whether and how cardiovascular and cardiorespiratory phase synchronization would respond to changes in hydration status and orthostatic stress. Four men and six women were tested during graded head-up tilt (HUT) in both euhydration and dehydration (DEH) conditions. Continuous R–R intervals (RRI), systolic blood pressure (SBP) and respiration were investigated in low (LF 0.04–0.15 Hz) and high (HF 0.15–0.4 Hz) frequency ranges using a phase synchronization index (λ) ranging from 0 (complete lack of interaction) to 1 (perfect interaction) and a directionality index (d), where a positive value of d reflects oscillator 1 driving oscillator 2, and a negative value reflects the opposite driving direction. Surrogate data analysis was used to exclude relationships that occurred by chance. In the LF range, respiration was not synchronized with RRI or SBP, whereas RRI and SBP were phase synchronized. In the HF range, phases among all variables were synchronized. DEH reduced λ among all variables in the HF and did not affect λ between RRI and SBP in the LF region. DEH reduced d between RRI and SBP in the LF and did not affect d among all variables in the HF region. Increasing λ and decreasing d between SBP and RRI were observed in the LF range during HUT. Decreasing λ between SBP and RRI, respiration and RRI, and decreasing d between respiration and SBP were observed in the HF range during HUT. These results show that orthostatic stress disassociated interactions among RRI, SBP and respiration, and that DEH exacerbated the disconnection.

Original languageEnglish
Pages (from-to)417-427
Number of pages11
JournalEuropean Journal of Applied Physiology
Issue number2
StatePublished - Feb 2015

Bibliographical note

Funding Information:
This study was supported by KY NASA EPSCoR Grant NNX07AT58A and the National Center for Research Resources and the National Center for Advancing Translational Sciences, National Institutes of Health, through Grant UL1TR000117. The authors thank all the subjects for volunteering. We are grateful to staff of the University of Kentucky Clinical Research Center, and of the Wyle Science, Technology and Engineering Group for the assistance in experiment performance and data collection. We also would like to acknowledge Dr. Michael Rosenblum of Department of Physics and Astronomy at Potsdam University, Germany for valuable discussion of the phase synchronization approach used in the present study.

Publisher Copyright:
© 2014, Springer-Verlag Berlin Heidelberg.


  • Cardiorespiratory coupling
  • Cardiovascular coupling
  • Hypovolemia
  • Orthostatic stress
  • Phase synchronization

ASJC Scopus subject areas

  • Orthopedics and Sports Medicine
  • Public Health, Environmental and Occupational Health
  • Physiology (medical)


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