Cardiovascular and cardiorespiratory phase synchronization in normovolemic and hypovolemic humans

• Published in: European journal of applied physiology Vol. 115; no. 2; pp. 417 - 427
• Main Authors: Zhang, Qingguang, Patwardhan, Abhijit R., Knapp, Charles F., Evans, Joyce M.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.02.2015; Springer Nature B.V
• Subjects: Adult; Biomedical and Life Sciences; Biomedicine; Blood Pressure; Cardiovascular system; Dehydration - physiopathology; Fainting; Female; Human Physiology; Humans; Hypotension, Orthostatic - physiopathology; Hypovolemia - physiopathology; Male; Occupational Medicine/Industrial Medicine; Original Article; Physiology; Respiration; Sports Medicine; Supine Position; Weightlessness; Orthostatic stress; Cardiovascular coupling; Hypovolemia; Cardiorespiratory coupling; Phase synchronization
• ISSN: 1439-6319; 1439-6327
• DOI: 10.1007/s00421-014-3017-4

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.