A device (7) monitors a blood path from a blood vessel access (3) of a human subject through an extracorporeal blood processing apparatus and back to the blood vessel access (3). A pumping device (4) in the blood path is operable to pump blood through the blood path from the blood withdrawal device (2') to the blood return device (2"). The monitoring device (7) obtains pressure data from a pressure sensor (6a) arranged upstream of the pumping device (4) in the blood path, and processes the pressure data for detection of a disruption of the blood path downstream of the pumping device (4), e.g. caused by VND (Venous Needle Dislodgement). The disruption is detected by evaluating presence/absence of cross-talk pulses at the pressure sensor (6a), where the cross-talk pulses originate from one or more pulse generators in the extracorporeal blood processing apparatus (80) and have propagated on a propagation path (P2) in a direction downstream of the pumping device (4) through the blood return device (2"), the blood vessel access (3) and the blood withdrawal device (2') to the pressure sensor (6a).
