The Heart Rate Variability Multifractality Spectrum and not the Power Spectrum Is Altered in Paraplegic Individuals With Low-Level Lesion

Paolo Castiglioni1, Giampiero Merati1, Andrea Faini2
1IRCCS Fondazione Don C. Gnocchi, 2IRCCS Istituto Auxologico Italiano


Abstract

Background. The integrative control of the autonomic nervous system (ANS) may contribute substantially to the multifractal-multiscale dynamics of heart rate variability (HRV) and we recently proposed a method for HRV multifractal analysis at different scales separately (goo.gl/CvCnmN). Aim. To evaluate the HRV multifractal-multiscale structure with our multifractal spectrum in an ANS model of altered integrative regulation with intact cardiac innervation. Methods. We recorded R-R intervals (RRI) for 10 minutes in 14 spinal cord injured (SCI) individuals with lesion below the 12th thoracic vertebra and in 34 matched able-bodied (AB) controls. The SCI group has intact autonomic cardiac and splanchnic control, but altered ANS integrative control. LF and HF powers and LF/HF powers ratio were calculated by FFT. The generalized Hurst coefficients, h(q,tau), with temporal scale tau between 6 and 120 seconds, and q in the range –Q≤q≤Q with Q=4, were calculated by our complexity method. At each scale tau we calculated SD(tau), standard deviation over q of h(q,tau), and the multifractality index MFi(tau) as SD(tau)/(2Q). MFi(tau) represents a temporal spectrum of multifractality, being ≥0 and increasing at scales tau where multifractality increases. Groups were compared by Mann–Whitney test. Results. Spectral powers were similar in SCI and AB groups (LF power: 2.8+0.1 vs 2.8+0.1; HF power: 2.3+0.1 vs 2.2+0.1; LF/HF: 0.56+0.05 vs 0.56+0.06; values in AB vs SCI as mean +SE, with power in ms^2 after Log10 transformation). By contrast, MFi(tau) was lower in SCI individuals at tau <7 s (AB: 0.47+0.12; SCI: 0.29+0.05; median+SE; p<0.05) and around 24 s (AB: 0.22+0.02; SCI: 0.12+0.02; p<0.05). Conclusion. In low-level SCI individuals, the HRV spectrum of multifractality reveals alterations in the ANS integrative control undetected by traditional power spectral analysis and associated with loss of multifractality at specific scales.