Attenuation of Spontaneous Baroreceptor Sensitivity after Concussion

Abstract

Introduction Cardiovascular autonomic nervous system (CV-ANS) function is negatively impacted after concussion. The arterial baroreflex buffers pressor and depressor challenges through efferent modulation of cardiac chronotropism and inotropism, and peripheral vascular tone. Baroreceptor sensitivity (BRS) reflects the capacity of the CV-ANS to accommodate dynamic metabolic demands in the periphery. The impact of concussion on BRS has yet to be defined. Methods Cardiovascular autonomic nervous system assessment (e.g., electrocardiogram and beat-to-beat systolic blood pressure [SBP]) was performed the seated upright position at rest within 48 h (V1) of concussion and 1 wk later (V2) in 10 intercollegiate male athletes with concussion and 10 noninjured male athletes. Changes in HR, SBP, high- and low-frequency HR variabilities (HF-HRV and LF-HRV, respectively), LF-SBP variability and BRS for increasing (BRSn-Up) and decreasing (BRSn-Dn) SBP excursions, and overall BRS (BRSn-Avg) were assessed for differences at V1 and V2. Results The concussion (age, 20 ± 1 yr; height, 1.79 ± 0.14 m; weight, 83 ± 10 kg) and control (age, 20 ± 1 yr; height, 1.78 ± 0.10 m; weight, 79 ± 13 kg) groups were matched for demographics. Concussed athletes had a significantly reduced BRSn-Up, BRSn-Dn, and BRSn-Avg compared with controls at V1 or V2; these changes occurred without differences in conventional markers of CV-ANS function (e.g., HF-HRV, LF-HRV, LF-SBP), HR, or SBP at either visit. Conclusions Reduced BRS is a postconcussive consequence of CV-ANS dysfunction during the first postinjury week. Because SBP was similar between groups, it may be speculated that reduced BRS was not afferent in origin, but represents a postinjury consequence of the central nervous system after injury.

An Evidence-Based Objective Study Protocol for Evaluating Cardiovascular and Cerebrovascular Indices Following Concussion: The Neary Protocol

“…With sports being such a popular activity for health, social, and psychological reasons, sport-related concussion and its potential long-term effects remain a major health problem [1]. Sport-related concussion and mild traumatic brain injury (mTBI) have been used synonymously and previous research has documented physiological changes post-injury [2,3,4,5]. Concussion has been defined as a “complex pathophysiological process affecting the brain, induced by traumatic biomechanical forces …” [6].…”

“…These affects can in turn distort neuronal membrane permeability [7]. The exact pathophysiology of mTBI is not fully understood, but it has been suggested that autonomic dysfunction [2,5] and changes in total blood volume and cerebral blood flow do occur [3,8]. Although mTBI is generally associated with autonomic-like symptoms [9], no single objective diagnostic test can determine concussion severity.…”

“…Considering the physiological changes that have been shown to occur following mTBI [2,3,19], it follows that measuring these changes can provide an indication as to how the injury is recovering from insult. It seems as though physiological measures, including heart rate variability (HRV) [2,4,20], blood pressure [2,5,16], cerebral metabolism [3,8,21], cerebral blood volume [3,8], cerebral blood flow velocity [3,22], and blood biomarkers [23], all tend to change as a result of mTBI, and thus all these parameters have to be analyzed, or at least a majority of them, to get the most information in order to understand what changes have occurred. To the author’s knowledge, no study has found or reported a single determining variable which can predict the status of severity of, or recovery from, sport-related concussion.…”

“…Simple objective measures can be utilized to assess many of the mentioned physiological changes. General cerebral metabolism can be monitored using non-invasive equipment, such as near-infrared spectroscopy (NIRS) [21], to measure cerebral oxygenation, while beat-to-beat blood pressure can be measured using photoplethysmography [2,5,30], cerebral blood flow velocity can be determined with a transcranial Doppler [22,31], and heart rate can be measured with an electrocardiogram (ECG) to record electrical and temporal cardiac dynamics. HRV analysis is best done using software programs that can deconstruct and measure each component of the raw ECG waveform [32].…”

Neuroprotection Following Concussion: The Potential Role for Cannabidiol

“…62 Concussion can initiate a neurometabolic cascade, 63 which can lead to an energy crisis, thereby impairing cerebral blood flow, 64 increasing intracellular calcium (Ca 2+ ) levels, 63,65 and disrupting autonomic functioning, 66,67 among other physiological consequences ( Figure 1). 63,66,[68][69][70][71][72][73][74][75][76] mTBIs generally occur due to rotational or twisting forces (accelerations or decelerations) 77,78 of the brain within the skull, thereby resulting in a disruption in homeostasis. In comparison, the endocannabinoid system is thought to have neuroprotective properties, 79,80 which could therefore ameliorate these disturbances in physiological homeostasis.…”