Parasympathetic Responses to Face Cooling in Adolescents with Sport-Related Concussion and After Clinical Recovery.

Face cooling (FC) initiates the mammalian dive reflex, which elicits a parasympathetic autonomic response. In our pilot study, collegiate athletes had a blunted parasympathetic response to FC within 10 days of sport-related concussion (SRC). The objective of the current study was to assess the FC response in adolescent athletes with acute SRC and after clinical recovery. Symptomatic adolescents with SRC (n = 23, 15.48 ± 1.2 years, 52% male) had heart rate (HR) and blood pressure (BP) measured during the FC test (7.83 ± 2.5 days since injury) and again after clinical recovery (46.44 ± 36.4 days later). Controls (n = 24, 15.83 ± 1.6 years, 58% male) performed the same assessments twice (48.00 ± 18.9 days apart). The main outcome measures were the rate of change in HR and HR variability (HRV) during the first 2 min of FC. Throughout FC, we found no significant differences between groups at the initial visit in the rate of change for HR (mean difference = 2.58 [-0.33, 5.50] bpm/min, p = 0.082), mean arterial BP (-0.02 [-3.49, 3.45] mmHg/min, p = 0.990), root mean square of successive differences (-13.46 [-34.02, 7.10] ms/min, p = 0.197) or low to high-frequency ratio (0.24 [-0.77, 1.25], p = 0.637). We also found no differences in our main outcome measures among concussed adolescents with delayed recovery (n = 10) compared with those with normal recovery (n = 13). A history of prior concussion had a significant effect on the HR and HRV responses to FC, suggesting that SRC may have prolonged effects on the autonomic nervous system (ANS). We conclude that acutely concussed adolescents do not differ from controls in parasympathetic response to FC acutely or upon recovery but that a history of concussion affects this response. We recommend that future studies control for concussion history when investigating the ANS in concussed adolescents.