Due to differences in modalities , time course , study design and outcomes , it is not possible to define a single ‘ physiological time window ’ for SRC recovery .
Multiple studies suggest physiological dysfunction may outlast current clinical measures of recovery , supporting a buffer zone of gradually increasing activity before full contact risk .
Aim or objective The aim of this study is to consoli date studies of physiological measures following sport-related concussion ( SRC ) to determine if a time course of postinjury altered neurobiology can be outlined .
This biological time course was considered with respect to clinical ly relevant outcomes such as vulnerability to repeat injury and safe timing of return to physical contact risk .
Autonomic Nervous System Responses to Concussion: Arterial Pulse Contour Analysis
The arterial pulse wave ( APW ) has a distinct morphology whose contours reflect dynamics in cardiac function and peripheral vascular tone as a result of sympathetic nervous system ( SNS ) control . With a transition from rest to increased metabolic dem and , the expected augmentation of SNS outflow will not only affect arterial blood pressure and heart rate but it will also induce changes to the contours of the APW . Following a sports concussion , a transient state cardiovascular autonomic dysfunction is present . How this state affects the APW has yet to be described . A prospect i ve , parallel-group study on cardiovascular autonomic control ( i.e. , digital electrocardiogram and continuous beat-to-beat blood pressure ) was performed in the seated upright position in 10 athletes with concussion and 7 non-injured control athletes .  Changes in APW were compared at rest and during the first 60 s ( F60 ) of an isometric h and grip test ( IHGT ) in concussed athletes and non-injured controls within 48 h and 1 week of injury . The concussion group was further separated by the length of time until they were permitted to return to play ( RTP > 1week ; RTP ≤ 1week ) . SysSlope , an indirect measurement of stroke volume , was significantly lower in the concussion group at rest and during F60 at 48 h and 1week ; a paradoxical decline in SysSlope occurred at each visit during the transition from rest to IHGT F60 . The RTP > 1week group had lower SysSlope ( 405 ± 200 ; 420 ± 88 ; 454 ± 236 mmHg/s , respectively ) at rest 48 h compared to the RTP ≤ 1week and controls . Similarly at 48 h rest , several measurements of arterial stiffness were abnormal in RTP > 1week compared to RTP ≤ 1week and controls : peak-to-notch latency ( 0.12 ± 0.04 ; 0.16 ± 0.02 ; 0.17 ± 0.05 , respectively ) , notch relative amplitude ( 0.70 ± 0.03 ; 0.71 ± 0.04 ; 0.66 ± 0.14 , respectively ) , and stiffness index ( 6.4 ± 0.2 ; 5.7 ± 0.4 ; 5.8 ± 0.5 , respectively ) . Use of APW revealed that concussed athletes have a transient increase in peripheral artery stiffness , which may be a compensatory adaptation to a paradoxical decline of stroke volume during the transition from rest to a state of increased metabolic dem and within 48 h of concussion . This dysfunction of the SNS appeared to be more pronounced among concussed athletes who were removed from participation for > 1 week compared to those who resumed play within 7 days
Due to differences in modalities , time course , study design and outcomes , it is not possible to define a single ‘ physiological time window ’ for SRC recovery .
Multiple studies suggest physiological dysfunction may outlast current clinical measures of recovery , supporting a buffer zone of gradually increasing activity before full contact risk .
Aim or objective The aim of this study is to consoli date studies of physiological measures following sport-related concussion ( SRC ) to determine if a time course of postinjury altered neurobiology can be outlined .
This biological time course was considered with respect to clinical ly relevant outcomes such as vulnerability to repeat injury and safe timing of return to physical contact risk .