Eyeball pressure stimulation induces subtle sympathetic activation in patients with a history of moderate or severe traumatic brain injury.

Objective: After traumatic brain injury (TBI), there may be persistent central-autonomic-network (CAN) dysfunction causing cardiovascular-autonomic dysregulation. Eyeball-pressure-stimulation (EPS) normally induces cardiovagal activation. In patients with a history of moderate or severe TBI (post-moderate-severe-TBI), we determined whether EPS unveils cardiovascular-autonomic dysregulation.

Methods: In 51 post-moderate-severe-TBI patients (32.7 ± 10.5 years old, 43.1 ± 33.4 months post-injury), and 30 controls (29.1 ± 9.8 years), we recorded respiration, RR-intervals (RRI), systolic and diastolic blood-pressure (BPsys, BPdia), before and during EPS (120 sec; 30 mmHg), using an ocular-pressure-device (Okulopressor®). We calculated spectral-powers of mainly sympathetic low (LF: 0.04-0.15 Hz) and parasympathetic high (HF: 0.15-0.5 Hz) frequency RRI-fluctuations, sympathetically mediated LF-powers of BPsys, and calculated normalized (nu) LF- and HF-powers of RRI. We compared parameters between groups before and during EPS by repeated-measurement-analysis-of-variance with post-hoc analysis (significance: p < 0.05).

Results: At rest, sympathetically mediated LF-BPsys-powers were significantly lower in the patients than the controls. During EPS, only controls significantly increased RRIs and parasympathetically mediated HFnu-RRI-powers, but decreased LF-RRI-powers, LFnu-RRI-powers, and LF-BPsys-powers; in contrast, the patients slightly though significantly increased BPsys upon EPS, without changing any other parameter.

Conclusions: In post-moderate-severe-TBI patients, autonomic BP-modulation was already compromised at rest. During EPS, our patients failed to activate cardiovagal modulation but slightly increased BPsys, indicating persistent CAN dysregulation.

Significance: Our findings unveil persistence of subtle cardiovascular-autonomic dysregulation even years after TBI.