Passive head-up tilt and exercise significantly increased the short-term fractal correlation properties of heart rate dynamics (alpha(1)) from baseline (P < 0.001).
Observational (n=30)
Do exercise and passive head-up tilt alter the fractal and complexity properties of heart rate dynamics in healthy subjects?
Exercise and passive tilt increase short-term fractal correlation properties of heart rate dynamics, but overall complexity increases only during exercise.
p-value: p=<0.001
tk;1Passive head-up tilt and exercise result in specific changes in the spectral characteristics of heart rate (HR) variability as a result of reduced vagal and enhanced sympathetic outflow. Recently analytic methods based on nonlinear system theory have been developed to characterize the nonlinear features in HR dynamics. This study was designed to assess the changes in the fractal and complexity measures of HR behavior during the passive head-up tilt and during exercise. Fractal exponent (alpha(1)) and approximate entropy (ApEn), measures of short-term correlation properties and overall complexity of HR, respectively, along with spectral components of HR variability were analyzed during a passive head-up tilt test (n = 10) and a low-intensity steady-state exercise (n = 20) in healthy subjects. We observed that alpha(1) increased during the tilt test (from 0.85 +/- 0.22 to 1.48 +/- 0.20; P < 0.001) and during the exercise (from 1.00 +/- 0.22 to 1.37 +/- 0. 14; P < 0.001). ApEn also increased during the exercise (from 1.04 +/- 0.11 to 1. 11 +/- 0.08; P < 0.05), but it did not change during the tilt test. The normalized high-frequency spectral component decreased and the low-frequency component increased similarly during both the exercise and the tilt test (P < 0.001 for all). Exercise and passive tilt result in an increase of short-term fractal correlation properties of HR dynamics, which is related to changes in the balance between the low- and high-frequency oscillations in controlled situations. Overall complexity of HR dynamics increases during exercise but not during passive tilt.
Tulppo et al. (2001) conducted an observational in Healthy (n=30). Passive head-up tilt and exercise vs. Baseline/rest was evaluated on Fractal exponent (alpha(1)) and approximate entropy (ApEn) (p=<0.001). Passive head-up tilt and exercise significantly increased the short-term fractal correlation properties of heart rate dynamics (alpha(1)) from baseline (P < 0.001).