• Meeri N Kim, Brian L Edlow, Turgut Durduran, Suzanne Frangos, Rickson C Mesquita, Joshua M Levine, Joel H Greenberg, Arjun G Yodh, and John A Detre.
• Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA, 19104, USA, meeri@alumni.upenn.edu.
• Neurocrit Care. 2014 Jun 1;20(3):443-53.

IntroductionHead-of-bed manipulation is commonly performed in the neurocritical care unit to optimize cerebral blood flow (CBF), but its effects on CBF are rarely measured. This pilot study employs a novel, non-invasive instrument combining two techniques, diffuse correlation spectroscopy (DCS) for measurement of CBF and near-infrared spectroscopy (NIRS) for measurement of cerebral oxy- and deoxy-hemoglobin concentrations, to monitor patients during head-of-bed lowering.MethodsTen brain-injured patients and ten control subjects were monitored continuously with DCS and NIRS while the head-of-bed was positioned first at 30° and then at 0°. Relative CBF (rCBF) and concurrent changes in oxy- (ΔHbO2), deoxy- (ΔHb), and total-hemoglobin concentrations (ΔTHC) from left/right frontal cortices were monitored for 5 min at each position. Patient and control response differences were assessed.ResultsrCBF, ΔHbO2, and ΔTHC responses to head lowering differed significantly between brain-injured patients and healthy controls (P < 0.02). For patients, rCBF changes were heterogeneous, with no net change observed in the group average (0.3 ± 28.2 %, P = 0.938). rCBF increased in controls (18.6 ± 9.4 %, P < 0.001). ΔHbO2, ΔHb, and ΔTHC increased with head lowering in both groups, but to a larger degree in brain-injured patients. rCBF correlated moderately with changes in cerebral perfusion pressure (R = 0.40, P < 0.001), but not intracranial pressure.ConclusionDCS/NIRS detected differences in CBF and oxygenation responses of brain-injured patients versus controls during head-of-bed manipulation. This pilot study supports the feasibility of continuous bedside measurement of cerebrovascular hemodynamics with DCS/NIRS and provides the rationale for further investigation in larger cohorts.

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