Cerebrovascular reactivity (CVR), the blood flow response to a vasodilatory stimulus, is changed in many pathologies. CVR can be estimated without gas challenges by performing breathing tasks or by analyzing natural CO2 fluctuations at rest. We added two short breathing tasks (hypercapnic: breath hold, hypocapnia: cued deep breathing) to the start of two resting state fMRI scans. When using all the data, or just the breathing segments, adequate CVR maps could be estimated; this was not the case when just using the resting portions. This paradigm can provide an estimate of CVR, and help improve analysis of resting state data.