A detection device for detecting variations in intravascular pressure indicating irregular blood flow in a blood circuit of a hemodialysis machine where blood is drawn from a patient for processing and then returned, said device comprising: a means of calculation that includes a microprocessor to automatically calculate the pressure in the venous access (VAP) upstream of an assumed place of a blood flow restriction by using an algorithm to automatically calculate a ratio of the pressure in the venous access (VAPR ) of said VAP at mean arterial pressure (MAP)； and a comparator to compare each of said calculated relationships, with a standard relationship contained within a repository of the central database, wherein said calculation means uses an empirical formula VAP>； = VDP - VDP0 where VDP is the pressure of the venous drip chamber in the blood circuit of the hemodialysis machine, VDP0 is the venous drip pressure for a hemodialysis machine, a tubing set and a needle size given when the pressure in the VAP venous access is zero, VDP0 that is calculated from the polynomial equation of the second degree of the form in whose equation Qb is the blood flow rate in ml / minute and Hct is the hematocrit expressed as a percentage.Un dispositivo de detección para detectar las variaciones en la presión intravascular que indican flujo sanguíneo irregular en un circuito sanguíneo de una máquina de hemodiálisis donde la sangre se extrae de un paciente para su procesamiento y después se retorna, dicho dispositivo que comprende: un medio de cálculo que incluye un microprocesador para calcular automáticamente la presión en el acceso venoso (VAP) corriente arriba de un lugar supuesto de una restricción del flujo de sangre mediante el uso de un algoritmo para calcular automáticamente una relación de la presión en el acceso venoso (VAPR) de dicha VAP a la presión arterial media (MAP)； y un comparador para comparar cada una de dichas relaciones calculadas, con una relación patrón co
