Abstract 3402: Use of Near-Infrared Spectroscopy during Breath Holding Test in Patients with Carotid Stenosis

Background: Breath-holding index (BHI) defined with transcranial doppler (TCD) is a risk marker for stroke in asymptomatic carotid stenosis. Near-infrared spectroscopy (NIRS) is a non-invasive method that can measure changes in cerebral microvasculature hemodynamics with the use of different light wavelengths. In the present study, we correlated the cerebral hemodynamic response using NIRS to BHI in patients with carotid stenosis. Methods: We studied 15 patients (9 men) with the mean age of 66 years (range, 55 - 75 years). Carotid stenosis was defined by carotid duplex (1 with 50-70%, 10 with 70-99% and 4 with occlusion). Patients were instructed to hold their breath for 30 seconds after a normal inspiration for dynamic acquisition. Changes in oxygenated hemoglobin (HbO), deoxygenated hemoglobin (HbR) and total hemoglobin (HbT) concentrations on the temporoparietal regions corresponding to the territory of the middle cerebral artery of both hemispheres were recorded using NIRS (28 channels, CW6, TechEn Inc. Milford, MA). BHI was calculated in a separate session with the same procedure. We correlated changes in NIRS defined parameters to BHI using the Spearman’s correlation test. Results: The NIRS parameters HbO, HbR and HbT showed a bimodal distribution ( fig. 1 ). There was a weak correlation between BHI and HbO, HbR and HbT (r = 0.16, 0.17, 0.19, respectively) with all the subjects. When the population heterogeneity was separated, there was a strong correlation between BHI and HbR (r = 0.87) and a moderate correlation with HbO and HbT (r = 0.77 and 0.73, respectively) in the patients with carotid occlusion. Conclusion: NIRS was capable of identifying robust hemodynamic changes due to breath holding test. The relationship between microvascular oxygenation from NIRS and macrovascular flow from BHI was found to be quite low, potentially due to the heterogeneity of the population studied. Our results suggest that NIRS could potentially be used as a useful tool to assess the physiological state of patients with carotid stenosis.