Aging modifies the effect of cardiac output on middle cerebral artery blood flow velocity.

An association between cerebral blood flow (CBF) and cardiac output (CO) has been established in young healthy subjects. As of yet it is unclear how this association evolves over the life span. To that purpose, we continuously recorded mean arterial pressure (MAP; finger plethysmography), CO (pulse contour; CO-trek), mean blood flow velocity in the middle cerebral artery (MCAV; transcranial Doppler ultrasonography), and end-tidal CO partial pressure (PetCO) in healthy young (19-27 years), middle-aged (51-61 years), and elderly subjects (70-79 years). Decreases and increases in CO were accomplished using lower body negative pressure and dynamic handgrip exercise, respectively. Aging in itself did not alter dynamic cerebral autoregulation or cerebrovascular CO reactivity. A linear relation between changes in CO and MCAV was observed in middle-aged ( < 0.01) and elderly ( = 0.04) subjects but not in young ( = 0.45) subjects, taking concurrent changes in MAP and PetCO into account. These data imply that with aging, brain perfusion becomes increasingly dependent on CO.