1. inability to attend scheduled clinic visits and/or comply with the study protocol 2. history of traumatic brain injury (tbi) or any other non covid brain pathology 3. active malignancy 4. substance use at baseline 5. severe or unstable physical disorders or major cognitive deficits at baseline 6. hbot for any reason prior to study enrolment 7. chest pathology incompatible with pressure changes (including moderate to severe asthma) 8. ear or sinus pathology incompatible with pressure changes 9. an inability to perform an awake brain mri 10. active smoking

1. inability to attend scheduled clinic visits and/or comply with the study protocol 2. history of traumatic brain injury (tbi) or any other non covid brain pathology 3. active malignancy 4. substance use at baseline 5. severe or unstable physical disorders or major cognitive deficits at baseline 6. hbot for any reason prior to study enrolment 7. chest pathology incompatible with pressure changes (including moderate to severe asthma) 8. ear or sinus pathology incompatible with pressure changes 9. an inability to perform an awake brain mri 10. active smoking

inability to attend scheduled clinic visits and/or comply with the study protocol history of traumatic brain injury (tbi) or any other non covid brain pathology active malignancy substance use at baseline severe or unstable physical disorders or major cognitive deficits at baseline hbot for any reason prior to study enrolment chest pathology incompatible with pressure changes (including moderate to severe asthma) ear or sinus pathology incompatible with pressure changes an inability to perform an awake brain mri active smoking

inability to attend scheduled clinic visits and/or comply with the study protocol history of traumatic brain injury (tbi) or any other non covid brain pathology active malignancy substance use at baseline severe or unstable physical disorders or major cognitive deficits at baseline hbot for any reason prior to study enrolment chest pathology incompatible with pressure changes (including moderate to severe asthma) ear or sinus pathology incompatible with pressure changes an inability to perform an awake brain mri active smoking

inability to attend scheduled clinic visits and/or comply with the study protocol history of tbi or any other non covid brain pathology active malignancy substance use at baseline severe or unstable physical disorders or major cognitive deficits at baseline hbot for any reason prior to study enrolment chest pathology incompatible with pressure changes (including moderate to severe asthma) ear or sinus pathology incompatible with pressure changes an inability to perform an awake brain mri active smoking

inability to attend scheduled clinic visits and/or comply with the study protocol history of tbi or any other non covid brain pathology active malignancy substance use at baseline severe or unstable physical disorders or major cognitive deficits at baseline hbot for any reason prior to study enrolment chest pathology incompatible with pressure changes (including moderate to severe asthma) ear or sinus pathology incompatible with pressure changes an inability to perform an awake brain mri active smoking

1. inability to attend scheduled clinic visits and/or comply with the study protocol 2. history of tbi or any other non covid brain pathology 3. active malignancy 4. substance use at baseline 5. severe or unstable physical disorders or major cognitive deficits at baseline 6. hbot for any reason prior to study enrolment 7. chest pathology incompatible with pressure changes (including moderate to severe asthma) 8. ear or sinus pathology incompatible with pressure changes 9. an inability to perform an awake brain mri 10. active smoking

1. inability to attend scheduled clinic visits and/or comply with the study protocol 2. history of tbi or any other non covid brain pathology 3. active malignancy 4. substance use at baseline 5. severe or unstable physical disorders or major cognitive deficits at baseline 6. hbot for any reason prior to study enrolment 7. chest pathology incompatible with pressure changes (including moderate to severe asthma) 8. ear or sinus pathology incompatible with pressure changes 9. an inability to perform an awake brain mri 10. active smoking