An objective method to identify non-responders in neurovascular coupling testing.

BACKGROUND: Neurovascular coupling (NVC) can be assessed using transcranial Doppler (TCD) measured task-activation of cerebral blood flow velocity (CBFv). However, not all individuals show consistent responses. The aim of this study was to develop a robust, objective, method to identify non-responders to task-activation. NEW METHOD: Using five-minute seated resting (non-stimulated), bilateral CBFv data from 135 healthy participants, the cross-correlation function peak (CCF) between the population coherent average and each individual was obtained for a randomly selected segment of data (40 s) for both hemispheres (n = 270). The variance ratio (VR) was calculated by comparing the variance in CBFv data pre- and post-random mark. The 90th percentile for non-stimulated data was used to determine the upper confidence limit of normal variation in the CCF peak value (0.53), and VR (2.59). These criteria were then applied to task-activated CBFv from 69 healthy participants for five cognitive tasks (attention, verbal fluency, language, visuospatial, memory). RESULTS: Data were accepted as responders if either CCF ≥ 0.53 or VR ≥ 2.59. The number of cases accepted as responders for each task were as follows: attention, 54-59 (78-86%); verbal fluency, 42-48 (60-70%); language, 51-53 (74-77%); visuospatial, 54 (78%); memory, 40-47 (58-68%). COMPARISON WITH EXISTING METHOD: Currently, there are no objective criteria for the identification of non-responders in studies of NVC. This is a new method to objectively classify non-responders to task-activation. CONCLUSIONS: Using a large sample of resting CBFv data, we have set objective criteria to differentiate between responders and non-responders in task activation protocols.