To explore the impact of co-occurring traumatic brain injury (TBI) on cardiovascular autonomic nervous system (CVANS) function in the subacute period among individuals with spinal cord injury (SCI).

CVANS impairment is an important post-injury consequence of SCI and TBI with myriad clinical implications. It is unclear how the presence of TBI contributes to CVANS outcomes after SCI.

A prospective study was performed in 58 persons with SCI. The first study encounter occurred within 51 (±39) days of SCI. Thirty-two participants were diagnosed clinically with co-occurring TBI (SCI+TBI: Age: 41±17 yr; Ht: 1.75±0.09 m; Wt: 80±17 kg), while 26 had no evidence of TBI (SCI: 49±15 yr; Ht: 1.66±0.06 m; Wt: 73±18 kg).  An historical group of age-matched control participants were included for analyses (CTRL: 46±14 yr; Ht: 1.73±0.09 m; Wt: 85±20 kg).  Participants had CVANS evaluation that included a digital electrocardiogram and beat-to-beat finger arterial blood pressure monitoring while in the supine position.  Fast-Fourier transform was performed on the signals and power was calculated for the total, low and high frequency power (TP, LF and HF, respectively) spectra and Mayer Wave (MW) activity. MW activity represents baroreceptor-mediated adjustments to the heart and peripheral vasculature at a frequency of ~0.1Hz as a purported means to modulate situational efferent CVANS outflow. All variables were log10 transformed and a MW proportion was calculated (MWProp= MWHR/MWSBP).

The omnibus models for all CVANS analyses had a significant group main effect and post-hoc analyses revealed that the SCI+TBI and SCI groups were significantly different than CTRL.  However, MWProp was the only outcome that significantly differentiated the SCI+TBI group from SCI and CTRL in post-hoc tests with the SCI+TBI group having the most discordant pattern.

MWProp demonstrates that co-occurring TBI further disrupts CVANS function in persons with SCI during the subacute period by altering baroreceptor-mediated discharge patterns.