There is increasing evidence that patients with Alzheimer’s disease (AD) dementia have decreased cerebrovascular reactivity (CVR) in response to a vasodilatory challenge, also denoted as the cerebrovascular reserve (Glodzik et al., 2013, for a review). However, this is less clear for patients during the prodromal mild cognitive impairment (MCI) stage of AD. Some studies show positive findings [Richiardi et al., 2014; Glodzik et. al., 2011; Cantin et al.; 2011; Zavoreo et al., 2010], while other do not [Shim et al., 2015; Fromm et al., 2013; Anzola et al., 2011]. This question is becoming important in AD research. CVR alterations, especially at microvascular level, affect the neurovascular coupling during neural activation [Pillai and Mikulis, 2015], which could have implications for early diagnosis and treatment of AD.