Abstract: (EN) Respiration of a patient can be monitored by means of a device (ASD) that has the following characteristics. An inlet (IL) receives a pressurized airflow of breathable air from an airflow source. An outlet (OL) applies the pressurized airflow to a mask worn by the patient. An airflow path (AFP) is arranged between the inlet (IL) and the outlet (OL). The airflow path (AFP) has an axis (AX) and exhibits a decrease (??D) in diameter followed by an increase (+?D) in diameter in a direction from the inlet (IL) to the outlet (OL). The increase (+?D) in diameter comprises an initial portion (WI) in which the diameter increases according to a slope (?) of less than 10° with respect to the axis (AX). A pressure measurement arrangement (PS1, PS2) provides an indication (SO) of a pressure difference in the pressurized airflow between two sections (IN, T) of the airflow path that have different diameters.