Effect of prolonged head-down bed rest on complex cardiovascular dynamics

• Published in: Autonomic Neuroscience Vol. 86; no. 3; pp. 192 - 201
• Main Authors: Fortrat, Jacques-Olivier, Sigaudo, Dominique, Hughson, Richard L, Maillet, Alain, Yamamoto, Yoshiharu, Gharib, Claude
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.01.2001; Elsevier BV; Elsevier
• Subjects: Adult; Baroreflex; Bed Rest; Bed Rest - adverse effects; Biological and medical sciences; Blood Pressure; Blood Pressure - physiology; Blood pressure regulation; Cardiovascular Physiological Phenomena; Chaos; Fourier Analysis; Fractals; Fundamental and applied biological sciences. Psychology; Head-Down Tilt; Head-Down Tilt - adverse effects; Head-Down Tilt - physiology; Heart Rate; Heart Rate - physiology; Heart rate variability; Hemodynamics. Rheology; Humans; Hypotension, Orthostatic; Hypotension, Orthostatic - etiology; Hypotension, Orthostatic - physiopathology; Male; Orthostatic hypotension; Time Factors; Vertebrates: cardiovascular system; Weightlessness Simulation; Weightlessness Simulation - adverse effects; Chaos; Blood pressure regulation; Heart rate variability; Baroreflex; Orthostatic hypotension; Human; Heart rate; Postural hypotension; Cardiovascular control; Blood pressure; Hemodynamics
• ISSN: 1566-0702; 1872-7484
• DOI: 10.1016/S1566-0702(00)00212-5

We postulated that a change in complex dynamics of the cardiovascular system could be involved in the orthostatic intolerance observed after simulated weightlessness. Supine recordings of 1024 consecutive pulse intervals and systolic blood pressures were obtained on 7 subjects adapted to a 42 day head-down bed rest (day 22 and 42) but also before and 6 days after head-down bed rest (−6°). Coarse graining spectral analysis was used to extract the non-harmonic (fractal) component from each time series. The power spectral densities of this fractal component are inversely proportional to their frequency (1/f β). We fitted an inverse power law estimate to the fractal component to determine the spectral exponent β. The complex dynamics of blood pressure and heart rate variability were also analyzed by correlation dimension and non-linear prediction. Bed rest induced orthostatic intolerance in 4 subjects. There was a significant increase in the spectral exponent β of RR-interval variability during and after head-down bed rest (before: 1.039±0.090; during: 1.552±0.080 and 1.547±0.100; after: 1.428±0.040). Analysis of the blood pressure dynamics indicated lower correlation dimensions during head-down bed rest and higher coefficients of predictability after head-down bed rest. Complexity alterations of RR-interval and blood pressure variability were not linked with one another during head-down bed rest. These alterations seemed to be correlated with the orthostatic intolerance observed after bed rest. These results suggest a change of the integration level of cardiovascular autonomic regulation.