Evaluation of postural cerebral hemodynamics by near-infrared spectroscopy in patients with dizziness with or without orthostatic dysfunction

Introduction: Using the near-infrared spectroscopy (NIRS), we evaluated the central circulation of patients with either dizziness and orthostatic dysfunction or dizziness alone. Methods: We used the NIRO-200 NIRS instrument to monitor bilateral oxygenation changes in cerebellar hemoglobin levels in 57 subjects during an orthostatic exam. Of the 46 patients with dizziness, 8 had orthostatic dysfunction. To determine whether NIRS is useful for evaluating patients with dizziness, we compared blood pressure changes with orthostatic dysfunction test scores. Diagnostic criteria for orthostatic dysfunction were as follows: (1) a greater than 21 mmHg reduction in systemic blood pressure, (2) a greater than 16 mmHg reduction in pulse pressure, and (3) a greater than 21 beats per minute increase in pulse rate. Results: We observed four different types of changes in oxy-hemoglobin during the orthostatic test. In type I, a rapid temporal decline of oxy-hemoglobin was followed by rapid recovery. In type II, the decline of oxy-hemoglobin was followed by recovery of oxy-hemoglobin levels above the initial levels. In type III, the decline of oxy-hemoglobin was followed by recovery of oxy-hemoglobin levels below the initial levels. In type IV, the decline of oxy-hemoglobin persisted without recovery. Most of the control patients displayed type I changes. Patients with orthostatic hypertension more frequently displayed type II and IV changes. Nine of the dizzy patients had a positive orthostatic test. Of these patients, 3 displayed type II changes and 6 displayed type IV changes. Conclusions: In normal subjects, cerebellar circulation remains stable, at least if orthostatically induced changes in blood pressure remain within normal ranges due to autoregulation. We suspect that dysfunctional autoregulation was responsible for the reduced cerebellar circulation in patients with orthostatic dysfunction. We propose that NIRS is an excellent, non-invasive tool for evaluating patients with dizziness that present with orthostatic dysfunction.