The Effects Of Subconcussive Head Impacts On Spontaneous Dynamic Cerebral Autoregulation

PURPOSE: Dynamic cerebral autoregulation (dCA) assessed during squat-to-stand protocols is impaired after an acute bout of subconcussive head impacts (SHI). However, it is unknown if spontaneous dCA (dCAS) at rest is altered following a bout of SHI. We tested the hypothesis that dCAS is impaired following a bout of SHI. METHODS: Eight healthy participants (age: 20 ± 2 y; BMI: 23 ± 3 kg/m2; 2 women) participated. dCAS was derived from 5 min of quiet rest in the semi-recumbent position prior to a bout of SHI and at 2 h, 24 h, and 72 h post SHI. SHI were induced by 20 soccer headers (1 header/30 s) projected from a JUGS soccer machine at 40 km/h from 12.2 m. End-tidal carbon dioxide tension (PETCO2), mean arterial pressure (MAP), and middle cerebral artery blood velocity (MCAV) were measured continuously at each time point. dCAS was assessed in the MCA using transfer function analysis. Data are presented as mean ± SD. RESULTS: There were no differences from PRE to post SHI for PETCO2 (p = 0.65) or MCAV (p = 0.67). There was a treatment effect for MAP (PRE: 90 ± 10; 2 h: 101 ± 8; 24 h: 86 ± 4; 72 h: 88 ± 10 mmHg; p = 0.02). For dCAS, there were no differences in the VLF for gain (PRE: 0.45 ± 0.19; 2 h: 0.52 ± 0.14; 24 h: 0.58 ± 0.29; 72 h: 0.67 ± 0.02 cm/s/mmHg; p = 0.38), phase (PRE: 1.04 ± 0.43; 2 h: 1.09 ± 0.66; 24 h: 0.82 ± 0.36 rad; p = 0.60), or coherence (PRE: 0.42 ± 0.09; 2 h: 0.45 ± 0.18; 24 h: 0.46 ± 0.19; 72 h: 0.41 ± 0.21 au; p = 0.89) or in the LF for gain (PRE: 0.84 ± 0.30; 2 h: 0.89 ± 0.47; 24 h; 0.80 ± 0.25; 72 h: 0.84 ± 0.23 cm/s/mmHg; p = 0.79), phase (PRE: 0.69 ± 0.35; 2 h: 0.57 ± 0.19; 24 h: 0.82 ± 0.38; 72 h: 0.71 ± 0.12 rad; p = 0.35), or coherence (PRE: 0.68 ± 0.11; 2 h: 0.69 ± 0.10; 24 h: 0.69 ± 0.13; 72 h: 0.67 ± 0.19 au; p = 0.85). CONCLUSIONS: These preliminary data indicate that an acute bout of SHI does not change indices of dCAS in the MCA.