Orthostatic Cerebral Hypoperfusion Syndrome

Abstract

Objective: Orthostatic dizziness without orthostatic hypotension is common but underlying pathophysiology is poorly understood. This study describes orthostatic cerebral hypoperfusion syndrome (OCHOs). OCHOs is defined by (1) abnormal orthostatic drop of cerebral blood flow velocity (CBFv) during the tilt test and (2) absence of orthostatic hypotension, arrhythmia, vascular abnormalities, or other causes of abnormal orthostatic CBFv.

Methods: This retrospective study included patients referred for evaluation of unexplained orthostatic dizziness. Patients underwent standardized autonomic testing, including 10 min of tilt test. The following signals were monitored: heart rate, end tidal CO2, blood pressure, and CBFv from the middle cerebral artery using transcranial Doppler. Patients were screened for OCHOs. Patients who fulfilled the OCHOs criteria were compared to age- and gender-matched controls.

Results: From 1279 screened patients, 102 patients (60/42 women/men, age 51.1 ± 14.9, range 19-84 years) fulfilled criteria of OCHOs. There was no difference in baseline supine hemodynamic variables between OCHOs and the control group. During the tilt, mean CBFv decreased 24.1 ± 8.2% in OCHOs versus 4.2 ± 5.6% in controls (p < 0.0001) without orthostatic hypotension in both groups. Supine mean blood pressure (OCHOs/controls, 90.5 ± 10.6/91.1 ± 9.4 mmHg, p = 0.62) remained unchanged during the tilt (90.4 ± 9.7/92.1 ± 9.6 mmHg, p = 0.2). End tidal CO2 and heart rate responses to the tilt were normal and equal in both groups.

Conclusion: OCHOs is a novel syndrome of low orthostatic CBFv. Two main pathophysiological mechanisms are proposed, including active cerebral vasoconstriction and passive increase of peripheral venous compliance. OCHOs may be a common cause of orthostatic dizziness.

Keywords: OCHOs; OH; POTS; QASAT; hypoperfusion; hypotension; orthostatic.

Figure 1

Representative examples of normal orthostatic blood pressure and cerebral blood flow velocity (CBFv) (left panel), orthostatic hypotension (OH) with stable CBFv during tilt test (middle panel), and orthostatic cerebral hypoperfusion syndrome (OCHOs) (right panel). A patient with OH was asymptomatic and had stable CBFv during tilt test indicating preserved cerebral autoregulation. Patient with OCHOs had stable orthostatic blood pressure but reduced CBFv during the tilt test. He was dizzy during the tilt test. HR, heart rate; BP, blood pressure.

Figure 2

Example of severe OCHOs. 72-year-old man had diabetes for 2 years and hypertension for 12 years. For last year, he experienced orthostatic dizziness and multiple presyncopal episodes. He was not orthostatic at the office visits and psychogenic or cardiac cause of orthostatic symptoms has been suspected. Left panel shows the baseline supine period before and after the tilt and the tilt responses. Right panel shows one cardiac cycle of blood pressure and cerebral blood flow velocity (CBFv) at the supine baseline and at the end of the tilt. The baseline CBFv gradually declined during tilt test. After the 5th minute of tilt, patient became progressively dizzy, confused, and disoriented that coincided with drop of CBFv. He recovered shortly after returning to the supine position when also the CBFv returned to the baseline value. There was no evidence cardiac dysrhythmia throughout the testing. There was no orthostatic hypotension during the tilt test, in fact, the blood pressure was elevated at the second half of the tilt that corresponds to a period when patient experienced orthostatic symptoms. HR, heart rate; BP, blood pressure.

Figure 3

Details of cerebral blood flow velocity (CBFv) in OCHOs (right) and in a control subject with normal response to tilt (left). OCHOs subject is 61-year-old man with history of orthostatic dizziness and neuropathy. During tilt, patient complained on dizziness with headache and he became very tired at the end of the tilt. Note progressive decline in CBFv during the tilt pointed by black arrows. Both resistance index (RI) and cerebrovascular resistance (CVR) increased in OCHOs while they remained unchanged in control subject during the tilt. The mean blood pressure was stable in both control and OCHOs subject during tilt. The heart responses to tilt were preserved in both subjects.