title: Evaluation of potential factors affecting the measurement of cerebrovascular reactivity by near-infrared spectroscopy.
abstract: 1.Near-infrared (IR) spectroscopy is based on the relative transparency of skin, skull and brain to the light in the near-IR region (700-1100 nm) and on the oxygen-dependent tissue absorption changes of haemoglobin.2. We evaluated the most relevant factors (reproducibility, venous return, age and sex) that might affect reliability of near-IR spectroscopy to test CO2 cerebrovascular reactivity.3.Thirty-four healthy volunteers were enrolled in the study. The protocol consisted of a 3-min baseline, a 3-min hypercapnia (5% CO2 in air) and a 2-min recovery. Transcranial Doppler sonography measurements were simultaneously performed. The CO2 reactivity test was repeated on 27 subjects after 1 h to assess reproducibility. CO2 reactivity was also evaluated at different body positions (supine, 35 degrees Trendelenburg and 35 degrees reverse Trendelenburg), and over a gradual increase of the inspired CO2.4. Changes in near-IR spectroscopy and transcranial Doppler sonography parameters were significantly correlated with variations of end-tidal CO2 (P<0.005). A significant correlation between the reactivity indexes of near-IR spectroscopy parameters and flow velocity was also found (P<0.01). A high reproducibility was also found for deoxyhaemoglobin (rI=0.76), oxyhaemoglobin (rI=0.68) and flow velocity (rI=0.60) reactivity indexes. No significant differences between the reactivity indexes of different body positions were found (P>0.05). The reactivity index of oxyhaemoglobin and deoxyhaemoglobin decreased (P<0.05) and increased (P<0.01) with age respectively.5. We found that near-IR spectroscopy is a reliable and reproducible method for the evaluation of cerebrovascular reactivity and might be considered, after appropriate validation, for the assessment of patients with cerebrovascular disease.
authors.affiliation: Dipartimento di Medicina Interna e Sanità Pubblica, Università degli Studi di L'Aquila, 67100 L'Aquila-Coppito, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Totaro
authors.forename: G
authors.initials: G
authors.lastname: Barattelli
authors.forename: V
authors.initials: V
authors.lastname: Quaresima
authors.forename: A
authors.initials: A
authors.lastname: Carolei
authors.forename: M
authors.initials: M
authors.lastname: Ferrari
mesh_terms: D000293:Adolescent; D000328:Adult; D001783:Blood Flow Velocity / Q000187:drug effects; D002245:Carbon Dioxide; D002536:Cerebral Arteries / Q000000981:diagnostic imaging; D002560:Cerebrovascular Circulation / Q000187:drug effects*; D002561:Cerebrovascular Disorders / Q000175:diagnosis; D005069:Evaluation Studies as Topic; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010108:Oxyhemoglobins / Q000032:analysis*; D011187:Posture; D015203:Reproducibility of Results; D019265:Spectroscopy, Near-Infrared; D018709:Statistics, Nonparametric; D017585:Ultrasonography, Doppler, Transcranial
chemical_list: D010108:Oxyhemoglobins; D002245:Carbon Dioxide