Please assess the completion status of the following clinical trial:

Trial Title: Non-invasive Measurement of Cerebrovascular Reactivity After Traumatic Brain Injury

Study Design Characteristics:
- Allocation: None
- Intervention Model: None
- Observational Model: COHORT
- Primary Purpose: None
- Time Perspective: PROSPECTIVE
- Masking: None
- Phase: None
- Number of Arms: None

Eligibility Criteria:
Inclusion Criteria:~1. Men and women, aged ≥18~2. CT evidence of TBI-linked abnormality~   * Traumatic subarachnoid hemorrhage~  * Intracerebral hemorrhage/contusion~  * Subdural/epidural hematoma~3. Ability to undergo fNIRS testing with hypercapnia challenge~4. Subject able to provide informed consent~5. Attending of record agrees to include subject in study~Exclusion Criteria:~1. Unstable respiratory or hemodynamic status~2. Evidence of penetrating brain injury~3. TBI requiring craniotomy or craniectomy~4. Evidence or risk of ICP crisis~5. History of disabling pre-existing neurologic disorder (e.g. dementia, uncontrolled epilepsy, multiple sclerosis, strokes, brain tumors, prior severe TBI, or other disorder that confounds interpretation of NIRS testing or neuropsychological results)~6. History of pre-existing disabling mental illness (e.g. major depression or schizophrenia)~7. Exclusion criteria for sildenafil administration:~   * History of melanoma~  * current use of organic nitrate vasodilators~  * current use of ritonavir (HIV-protease inhibitor)~  * current use of erythromycin, ketoconazole, or itraconazole; current use of cimetidine~  * current use of alpha-blockers such as doxazosin (Cardura), tamsulosin (Flomax), and terazosin (Hytrin) prazosin (Minipres)~  * resting hypotension (systolic BP \<90)~  * severe renal insufficiency~  * hepatic cirrhosis~  * acute ischemic stroke within past 2 months~  * acute myocardial infarction within past 2 months~  * unstable angina pectoris~  * acute or chronic heart failure~  * retinitis pigmentosa~  * pregnant or breastfeeding female~  * known hypersensitivity or allergy to sildenafil~8. Unstable cardiac status that constitutes a contraindication to sexual activity~9. Inability to read and communicate in English (necessary to obtain reliable neuropsychometric data)~10. Nursing mothers

- Gender: ALL
- Minimum Age: 18 Years
- Maximum Age: None
- Healthy Volunteers: t

Study Arms:
- Acute TBI (Type: None): Subjects will be recruited from the neurointensive care unit within 72 hours of their injury. At the time of informed consent, the investigators will perform fNIRS testing with a hypercapnia challenge, fNIRS with hypercapnia challenge 60 minutes after a single oral dose of 50mg sildenafil citrate, outcome qustionaires and symptom checklists (including: Glasgow Outcomes Scale-Extended, Rivermead Post-Concussive Symptom Questionnaire, Brief Symptom Inventory, Alcohol Consumption Questionnaire, Patient Health Questionnaire, and Insomnia Severity Index). This will all be administered again at 14 days, 90 days, 180 days, 1 year, 2 years, 3 years, and 4 years after injury.
- Sub-acute/Chronic TBI (Type: None): Subjects who suffered a TBI previously and have now entered a subacute or chronic phase of their TBI will be approached by the research team at their clinic visit with a TBI specialist. In those subjects, study timing will be based on the time of their original injury, therefore will start study visits at the next possible time point.
- Healthy Controls (Type: None): The investigators will also enroll healthy peer controls. These control subjects will be family members and friends of TBI subjects. These peer controls are likely to have similar environmental and socioeconomic exposures/support which may impact recovery after TBI and may also impact CVR. These control subjects will meet the same inclusion/exclusion criteria as TBI subjects without the requirement for an injury or acute brain imaging. These subjects will be tested in the same way as both TBI groups, but will only have one visit.

Based on this trial design, predict the completion outcome and termination type (if applicable).

Answer: outcome: terminate
termination_type: enrollment issues