Baroreflex sensitivity during positional changes in patients with traumatic brain injury

Abstract

Background and significance. Traumatic brain injury (TBI) affects 1.7 million Americans annually leading to significant morbidity and health care costs. An important cause of morbidity in TBI is secondary brain injury due to abnormal cerebrovascular autoregulation (CA). Standard measures of CA are not amenable to use outside of the intensive care unit (ICU) and patients continue to be at risk for secondary brain injury post- ICU. Baroreflex sensitivity (BRS) is a non-invasive assessment of autonomic tone that may be useful in evaluating CA. Evaluation of BRS and its relation to CA has not been examined in patients with TBI and predictors of CA are unknown. Purpose. The specific aims for this study were to (1) examine the association between BRS and CA in patients with TBI, (2) compare BRS and CA in TBI patients and age and gender matched healthy volunteers (HV) and (3) identify predictors of BRS and CA in TBI.

Methods. This study used a two group comparative design with 52 subjects (26 with moderate to severe TBI; 26 HV).

Measurement of variables. BRS was calculated as heart rate/mean arterial pressure; CA was calculated as cerebral blood flow velocity using transcranial Doppler; and cognition was assessed using the Galveston Orientation and Amnesia Test (GOAT). Results. There was no significant correlation between BRS and CA, however, BRS had high specificity (77%) for normal CA. BRS was not significantly different between TBI and HV subjects, those with normal or abnormal CA nor was BRS an independent predictor of CA. Forty six percent of TBI subjects had abnormal CA after their TBI (mean = 59.58 ± 36.54 days) and 34.6% of HV had abnormal CA. Predictors of abnormal CA were male gender, ACE-Inhibitors and GOAT. Implications . BRS can be used to identify normal CA. The GOAT has potential for routine assessment of CA status in non-ICU areas. Large proportions of TBI subjects long after a TBI event and HV had abnormal CA. Thus assessment of CA status is important in TBI subjects after ICU discharge and further research is needed on the impact of pre-existing CA abnormalities in HV.