It’s not something which is known to help ES symptoms generally, but there have been a few discussions which you could have a read of:
RAPHAEL et al. (1994) - Effects of the cervical collar on cerebrospinal fluid pressure - General / Research Papers - Living with Eagle
Jugular Dysautonomia - General / Research Papers - Living with Eagle
Q-Collar jugular compression device to protect from brain injuries in sports 
- General - Living with Eagle
Consult with Dr. Costantino - General - Living with Eagle
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