Cerebral Vasomotor Reactivity Testing in the Middle Cerebral Artery Using Transcranial Doppler to Assess Brain Dysregulation in Long-haul COVID Patients

Introduction: COVID-19 has wide-ranging physiological effects, with many patients complaining of persistent asthenia following recovery from the acute phase of the infection. The frequent term for this is “Long-Haul COVID.” While we have tools to measure effects on general physiology in human subjects, a metric for cerebral dysregulation is lacking. Cerebral blood flow is closely regulated in a healthy young person. Cerebral vasomotor reactivity (CVR) was used as a tool to assess this dysregulation. Methods: A transcranial Doppler (TCD) study for CVR was performed under the influence of Carbogen gas. A questionnaire collected prior to the procedure provided additional details on subjects’ demographics and COVID history. Cases and controls were recruited using the self-reported questionnaire. Statistics involved assessing the reproducibility of the test, as well as discovering differences between cases and control groups. Results: Cerebral vasomotor reactivity was assessed in 26 subjects (10 cases and 16 controls). Mean flow velocity in the left middle cerebral artery was analyzed at baseline, at peak Carbogen gas exposure, and in the hypercapnic phase. The reproducibility of the test was established within the longitudinal repeated measures data. The case and control groups were insignificant in difference at the base level but significant when controlled for confounders. Cerebral vasomotor reactivity was found to increase by 3.8 units in cases compared to controls. Confounders like body mass index, gender, and age were found significantly different between cases and controls. The number of COVID episodes and symptom severity was significant for CVR. Conclusion: This simple TCD bedside test was found to be effective in assessing CVR among all the subjects and was homogenous in its effect irrespective of baseline subject differences. As a preliminary test, the test showed differences among cases and control groups. The sample for the test lacked sufficient power and observations. A bigger sample size and a subsequent longitudinal follow-up may help better understand the use of CVR to screen high-risk populations for cerebrovascular anomalies.