MREG enables critical sampling of human brain physiology. This study reveals novel pulsation changes during repeated breatholds of 32 seconds. Cardiorespiratory control centers in the brain stem show increased pulsation amplitude during the end of the breathold. Also the overall cardiac pulse propagation in the brain alters markedly by breathold, especially when repeated. The findigs show that the MREG data enables spatially accurate estimation of the status of the cardiovascular pulsation which is the primary driver of glymphatic brain clearance.