An extracorporeal hemodialysis circuit comprising: a) arterial tube (110) for receiving unfiltered blood from a patient； b) venous line (190) to provide filtered blood to the patient； and c) a dialyzer and an apparatus for controlling the pressure differential located within the extracorporeal hemodialysis circuit so that blood flows from the patient, through the arterial tube, through the dialyzer, through the apparatus for controlling differential pressure, and towards the venous line, in which the apparatus for controlling the pressure differential controls the pressure differential through a semipermeable membrane that seals a 3-way outlet from a gas collection chamber (530), the apparatus for controlling the differential pressure comprising: i) a first pressure sensor (561) that detects the pressure along the outlet path from the gas collection chamber； ii) a second pressure sensor (521, 511) that detects an inlet or outlet pressure of the gas collection chamber； iii) a semipermeable membrane (542) disposed between the gas collection chamber and the exit path； iv) a valve (572) operatively connected to a gas source, the exit path from the gas collection chamber, and the atmosphere； and v) a control device connected to the first pressure sensor and the valve； wherein the control apparatus may vary the pressure provided by the source of pressurized gas in order to vary the amount of back pressure applied through the semipermeable membrane.Un circuito de hemodiálisis extracorpóreo que comprende: a) tubo (110) arterial para recibir sangre no filtrada de un paciente； b) línea (190) venosa para proporcionar sangre filtrada al paciente； y c) un dializador y un aparato para controlar el diferencial de presión localizado dentro del circuito de hemodiálisis extracorpóreo para que la sangre fluya desde el paciente, a través del tubo arterial, a través del dializador, a través del aparato para controlar la presión diferencial ,y hacia la línea venosa, en el que el aparato
