Heart Rate Variability to Assess the Heart-Brain Axis in Disorders of Consciousness: a Responsiveness Analysis

Brain injuries may compromise the heart-brain axis resulting in altered heart rate variability (HRV). Thus, we aim to identify the HRV indices better reflecting the improvements in the heart-brain connections expected to occur in brain-injured patients undergoing rehabilitation. We enrolled 21 patients with Disorder of Consciousness (DoC) admitted to our rehabilitation center after a brain lesion. HRV was assessed at rest and during a reactivity test. The assessments were performed twice: 1) at admission and 2) at discharge from a rehabilitation program. Overall, the patients’ clinical conditions were improved at discharge. Spectral powers with frequency $\gt0.05 \mathrm{~Hz}$ increased with medium effect size after rehabilitation. The self-similarity coefficients at scales around 18 s decreased after rehabilitation, with an almost large effect size during the reactivity test. Thus, some HRV measures change at the end of a rehabilitation program in parallel with a general clinical improvement in DoC patients.