Abstract
Repetitive subconcussive head impacts across a season of contact sports participation are associated with a number of deficits in brain function. To date, no research has investigated the effect of such head impact exposure on dynamic cerebral autoregulation (dCA). To address this issue, 179 elite, junior-level (age 19.6 ± 1.5 years) contact sport (ice hockey, American football) athletes were recruited for pre-season testing. Fifty-two non-concussed athletes returned for post-season testing. Fifteen non-contact sport athletes (age 20.4 ± 2.2) also completed pre- and postseason testing. dCA was assessed via recordings of beat-by-beat mean arterial pressure (MAP) and middle cerebral artery blood velocity (MCAv) using finger photoplethysmography and transcranial Doppler ultrasound, respectively, during repetitive squat-stand maneuvers at 0.05 and 0.10 Hz. Transfer function analysis was used to determine Coherence (correlation), Gain (response amplitude), and Phase (response latency) of the MAP-MCAv relationship. Results showed that in contact sport athletes, Phase was reduced (p = 0.027) and Gain increased (p < 0.001) at post-season compared to pre-season during the 0.10 Hz squat-stand maneuvers, indicating cerebral autoregulatory impairment in both the latency and magnitude of the response. Changes in Phase were greater in athletes experiencing higher numbers and severity of head impacts. By contrast, no changes in dCA were observed in non-contact sport controls. Taken together, these results demonstrate that repetitive subconcussive head impacts occurring across a season of contact sports participation are associated with exposure-dependent impairments in the cerebrovascular pressure-buffering system capacity. It is unknown how long these deficits persist or if they accumulate year-over-year.
Highlights
Sport-related concussion is a global public health issue, with growing concern over the effects of repetitive subconcussive head impacts [1]
The remaining 18 contact sport athletes were diagnosed by team physicians and medical staff with a concussion during the season based on criteria outlined in the 4th Consensus Statement [24] and followed a different post-injury protocol that has been reported in a recent publication [21]
The data demonstrate greater deficits in dynamic cerebral autoregulation (dCA) in athletes exposed to a higher number of hits and higher Cumulative exposure to linear (cPLA) compared to those exposed to lower head impact levels based on data recorded from the xPatch system, the limitations of which are emphasized below
Summary
Sport-related concussion is a global public health issue, with growing concern over the effects of repetitive subconcussive head impacts [1]. A host of studies have revealed this type of exposure—experienced during participation in sports in which head impacts are common—is associated with various deficits to brain structure and function at a subclinical level: transient blood-brain barrier damage [3], alterations in white matter microstructure [4,5,6], altered cerebrovascular sensitivity to carbon dioxide [7], disrupted cerebral metabolism [8], altered resting functional connectivity [9], and altered taskbased cortical activation patterns [10] Many of these studies used head impact sensors whose accuracy has been questioned [11,12,13,14] and some did not include non-contact sport control athletes potentially limiting the interpretation of their results. To further elucidate this possibility, it is necessary to first identify which systems appear to be most susceptible to repetitive subconcussive head impacts
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