The effects of subconcussive head impacts on cerebral vascular reactivity
Authors: Ryan Caleb , Pereira Felipe , Miller Spencer , Picking Haley , Kawata Keisuke , Johnson Blair 
Published: May 2023

Purpose: One bout of repetitive subconcussive head impacts (SHI) can increase biomarkers of neurological injury, decrease neurovascular coupling, and alter cerebral autoregulation. It is unclear whether a bout of repetitive SHI alters cerebral vascular reactivity to carbon dioxide (CVR). We tested the hypotheses that CVR to hypercapnia (CVRhyper) and hypocapnia (CVRhypo) will decrease after a bout of repetitive SHI in healthy participants. Methods: Eight healthy participants (age: 20±2 y; BMI: 23±3 kg/m2; 2 women) completed four CVR tests: one prior to a bout of SHI (PRE), and three follow-up tests at 2 h, 24 h, and 72 h after the SHI. SHI were induced by 20 soccer headers projected from a soccer JUGS machine (1 header/30 s at 40 km/h and from 12.2 m). Mean arterial pressure (MAP), heart rate (HR), end tidal carbon dioxide tension (PETCO2), middle cerebral artery blood velocity (MCAV) and posterior cerebral artery blood velocity (PCAV) were measured prior to and during each CVR test. MCA conductance (MCAcon) and PCA conductance (PCAcon) were calculated as the quotient of MCAv and PCAv to MAP, respectively. During the CVRhyper test, participants inhaled 6% CO2, 21% O2, 73% N2 gas for 2 min or until PETCO2 was 10 mmHg greater than baseline. 3 min after the CVRhyper test, participants hyperventilated until PETCO2 was 10 mmHg less than baseline for 2 min (CVRhypo). PETCO2 values were plotted against MCAV, PCAV, MCAcon, and PCAcon at baseline and the last 10 s of each CVR test. The slopes of these linear regression lines were calculated for each variable and for both CVR tests. Data are presented as mean±SD. Results: There were no differences from PRE to post SHI for resting HR, PETCO2, MCAV, PCAV, MCAcon, or PCAcon (all p>0.13). A time effect was found for resting MAP (PRE: 90±10; 2 h: 101±8; 24 h: 86±4; 72 h: 88±10 mmHg; p=0.02). There were no differences from PRE to post SHI for the CVRhyper test for MCAV (PRE: 0.10±0.20; 2 h: 0.27±0.17; 24 h: 0.24±0.31; 72 h: 0.24±0.31 cm/s/mmHg; p=0.13), MCAcon (PRE: -0.0009±0.0014; 2 h: -0.0001±0.0023; 24 h: -0.0002±0.0017; 72 h: -0.0011±0.0017 cm/s/mmHg/mmHg; p=0.36), PCAV (PRE: 0.02±0.13; 2 h: 0.07±0.07; 24 h: 0.12±0.18; 72 h: 0.14±0.13 cm/s/mmHg; p=0.26), or PCAcon (PRE: 0.0018±0.0011; 2 h: 0.0014±0.0007; 24 h: 0.0033±0.0033; 72 h: 0.0012±0.0007 cm/s/mmHg/mmHg; p=0.18). There were also no differences from PRE to post SHI for the CVRhypo test for MCAV (PRE: 0.10±0.20; 2 h: 0.27±0.17; 24 h: 0.24±0.31; 72 h: 0.24±0.31 cm/s/mmHg; p=0.13), MCAcon (PRE: 0.0006±0.0019; 2 h: 0.0019±0.0011; 24 h: 0.004±0.0049; 72 h: 0.0025±0.0016 cm/s/mmHg/mmHg; p=0.10), PCAV (PRE: 0.02±0.13; 2 h: 0.07±0.07; 24 h: 0.12±0.18; 72 h: 0.14±0.13 cm/s/mmHg; p=0.26), or PCAcon (PRE: 0.0018±0.0016; 2 h: 0.0019±0.0007; 24 h: 0.004±0.0033; 72 h: 0.0037±0.0014; p=0.09). Conclusion: These preliminary data indicate that a bout of soccer headings does not change CVR to carbon dioxide in the MCA or PCA in healthy adults. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.