“…With TBI, HRV has been shown to predict brain death and cerebrovascular dysregulation (Ryan et al, 2011), and HRV is associated with autonomic dysfunction in multiple other pathological states including sepsis, shock, and adrenal insufficiency (Morris et al, 2007; Werdan et al, 2009), each of which can co-occur in TBI. Further work suggests that HRV can be an effective mortality predictor, among hemodynamically stable patients with TBI (Ryan et al, 2011). Importantly, there is evidence that BDNF levels (Pal et al, 2014), BDNF genetic variability (Yang et al, 2010), and cortisol levels (Pal et al, 2014) are associated with HRV, making autonomic instability a plausible mechanism by which cortisol regulation of BDNF affects mortality risk.…”