Method and device for monitoring a blood treatment unit of an extracorporeal blood treatment device

A device for monitoring a blood treatment unit for an extracorporeal blood treatment apparatus comprising:

• a blood treatment unit divided by a semipermeable membrane into a blood chamber and a dialysing fluid chamber;
• an extracorporeal blood circuit with an arterial branch that leads to the blood chamber, and a venous branch that leads away from the blood chamber, and a dialysing fluid system in which the dialysing fluid chamber is disposed;
• an ultrafiltration device for withdrawing ultrafiltrate at a preset ultrafiltration rate from the blood flowing in the extracorporeal blood circuit via the semipermeable membrane of the blood treatment unit;
• and
• a device for supplying substituate at a preset substituate rate upstream or downstream of the blood treatment unit to the blood flowing in the extracorporeal blood circuit;
• at least one device configured for measuring oscillating pressure signals in the extracorporeal blood circuit or in the dialysing fluid system, wherein the at least one device configured for measuring the oscillating pressure signals is configured such that, in the extracorporeal blood circuit or in the dialysing fluid system, an oscillating pressure signal is measured at a first time when at least one of the following occurs:
• substituate is provided at a preset first substituate rate upstream or downstream of the blood treatment unit to the extracorporeal blood circuit, or ultrafiltrate is withdrawn at a preset first ultrafiltration rate via the semipermeable membrane of the blood treatment unit, and an oscillating pressure signal is measured at a second time when at least one of the following occurs:
• substituate is fed at a preset second substituate rate to the extracorporeal blood circuit, or ultrafiltrate is withdrawn at a preset second ultrafiltration rate via the membrane of the blood treatment unit,
• wherein the preset second substituate rate differs from the preset first substituate rate, and the preset second ultrafiltration rate differs from the preset first ultrafiltration rate, and
• a unit configured for analyzing the pressure signals measured in the extracorporeal blood circuit or in the dialysing fluid system, wherein the unit configured for analyzing is configured such that, on a basis of the measured oscillating pressure signals before and after a change in at least one of the substituate rate and the ultrafiltration rate a quantity correlating with a change in flow resistance of the blood treatment unit is calculated.