Cerebral Oximetry in Syncope and Syndromes of Orthostatic Intolerance

Figures

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  Figure 1. Measurement of cerebral tissue oxygenation with near infrared spectroscopy. The NIRS probe is attached to the forehead. Near infrared light from the emitter, passes through tissues such as skin and bone with minimal absorption whereas hemoglobin (Hb) has a well-defined absorption spectrum that is influenced by the binding of O2. Light attenuation is detected by the deep and shallow detectors as shown in this figure. Because oxygenated Hb and deoxygenated Hb have different absorption spectra, their proportion can be calculated. In healthy human normal cerebral tissue oxygenation is 60–80%. Edwards Lifesciences Corp, Irvine, CA, USA images archive.

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  Figure 2. Cerebral oximetry during head-up tilt in patients with syncope and orthostatic intolerance. In (A–D) two panels are shown: blood pressure in gray/black (BP—mmHg−0–200) and cerebral tissue oxygen oxygenation in blue and red (SctO2-%−0–100) are plotted above with time scale denoted. Heart rate shown in red (HR—bpm−0–200) is demonstrated simultaneously in the panel below. (A) 61-year-old woman with syncope while driving. There is a normal response to head up tilt and preserved cerebral tissue oxygenation (red arrow). (B) 20-year-old woman with history of recurrent syncope. Vasovagal syncope during head up tilt occurs when cerebral tissue oxygenation falls below 60% (red arrow). (C) 23-year-old man with orthostatic intolerance. This patient fulfills diagnostic criteria of postural orthostatic tachycardia syndrome with pronounced decrease in cerebral tissue oxygenation during head up tilt of more than 10% associated with subjective symptoms (dizziness, red arrow). (D) 77-year-old man with Parkinson's disease and orthostatic hypotension. The symptoms of cerebral hypoperfusion are intolerable when cerebral tissue oxygenation falls below 60% (red arrow). BP, blood pressure; SctO2,…