HRV under tilted postural provocation states for differentiating between prolonged disorders of consciousness and...

To evaluate heart rate variability (HRV) during 75° head-up tilt (HUT) test for differentiating prolonged disorders of consciousness (pDOC) and emergence from minimally conscious state (EMCS).

A total of 51 participants were enrolled: 18 pDOC patients (7 vegetative state, 11 minimally conscious state), 10 EMCS patients, and 23 healthy controls (HC). Linear HRV metrics were analyzed during supine/tilt positions. Linear Mixed-Effects Models (LMM) were applied to account for repeated measures and other mixed effects. Spearman's correlation was used to examine associations between HRV measures and Coma Recovery Scale-Revised (CRS-R) total scores.

LMM including pDOC, EMCS, and HC revealed a significant main effect of time for all HRV indices during the HUT test. Significant group effects were observed for standard deviation of normal-to-normal intervals (SDNN), low frequency (LF), high frequency (HF), and normalized LF (nLF), with HC showing significantly higher SDNN, LF, and HF than pDOC patients. Significant group-by-time interactions were found for proportion of the number of times successive heartbeat intervals exceeded 50 ms divided by the total number of NN intervals, nHF, and LF/HF. Age had a significant negative effect on SDNN, LF, HF, and nLF. In a secondary LMM restricted to pDOC and EMCS patients, significant group effects persisted for SDNN, LF, and HF, with EMCS showing higher values than pDOC; no significant group-by-time interactions were observed. Correlation analyses indicated that tilt-induced LF and SDNN were positively correlated with CRS-R total scores.

pDOC patients demonstrate weaker autonomic responses to postural stimuli than EMCS and HC.

HUT-based HRV assessment provides a promising and non-invasive tool for pDOC/EMCS differentiation, guiding rehabilitation planning.