Changes in cerebral blood flow after acetazolamide: an experimental study comparing near-infrared spectroscopy and SPECT

Abstract

Background and purpose: It is important to find a reliable and bedside method, which can estimate the cerebral blood flow (CBF) of patients in clinical settings. Estimation of CBF by calculating a blood flow index (BFI) using continuous wave near-infrared spectroscopy (CW-NIRS) and indocyanine green (ICG) as an i.v. tracer has been proposed to be a feasible and promising method. To validate if the BFI method can detect relative changes in CBF we compared data with the established method (133)Xenon single photon emission computer tomography ((133)Xe-SPECT).

Methods: Ten healthy subjects were investigated before and after a bolus of acetazolamide. NIRS data were obtained using a multi source detector separation configuration in order to assess a corrected BFI (BFI(corr)) value, which attempts to eliminate contamination of skin blood flow.

Results: Data obtained showed no significant correlation between CBF changes measured by (133)Xe-SPECT and BFI(corr) (0.133, P = 0.732). After acetazolamide, a 49% increase in CBF was detected using the (133)Xe-SPECT method, whereas no changes in any ICG variables were observed after acetazolamide.

Conclusion: The study shows that it is not possible to obtain reliable BFI data, which reflect changes in CBF after acetazolamide infusion, using the CW-NIRS and ICG method.

Figure 1

Increase in per cent from baseline for CBF_MCA (■), BFI (○), BFI_corr (□), ICG_max (▲) and rise time () after infusion of acetazolamide. A significant increase in CBF_MCA was found 15 min (48.9 ± 6.6, *** P < 0.001) and 60 min (26.0 ± 6.8, ** P = 0.003) after acetazolamide bolus.

Figure 2

Changes over time for CBF_MCA and BFI_corr (in optical density, OD/s) individual measurements. Thick grey bars shown mean values. ANOVA showed now changes over time for BFI_corr values (P = 0.319). CBF_MCA showed changes from baseline after acetazolamide over time (P < 0.001). Post hoc analysis showed a 48.9 ± 6.8% increase in CBF_MCA after the acetazolamide challenge at T₁₅ (P < 0.001) and 26.0 ± 6.8% increase at T₆₀ (P = 0.003).

Figure 3

Scatter diagram with changes of BFI_corr and CBF_MCA from baseline in per cent 15 min after acetozolamide infusion. Correlation coefficient 0.133 (P = 0.732).

Figure 4

Optical density curve after an ICG bolus. Coloured lines show source detector of different distances. Y axis: ΔOD = delta optical density.

Figure 5

Example of corrected blood flow index (BFI_corr, in optical density, OD/s) at seven consecutive measurements calculated at source detector distances of 3, 4 and 5 cm. Acetozolamide bolus given at time = 0.