Martí et al assert that a 50% increase in ventricular volume in older compared with younger subjects would “compensate” for a 50% reduction in the CSF flow rate so that the observed lack of change in the CSF HVA concentration in the older group demonstrates unchanged brain delivery of HVA to CSF. In contrast, we concluded in our ARCHIVES article that brain delivery of HVA to CSF is reduced by about 50% in the elderly.1 Our conclusion is supported by the discussion below, which also shows that the CSF HVA concentration is independent of ventricular volume at the steady state (the condition under which measurements were made).
Rapoport SI, Schapiro MB, May C. Brain Delivery of Homovanillic Acid to Cerebrospinal Fluid During Human Aging—Reply. Arch Neurol. 2005;62(4):690-691. doi:10.1001/archneur.62.4.690-b