Air impeller devices for providing assisted ventilation during spontaneous breathing are described. The devices include a motor a fan driven by the motor, and a casing defining a housing for the fan. The housing is connectable through a single inlet and outlet port to a respiratory mask, wherein a pressure inside the housing is adjustable according to a rotational speed of the fan such that, in use, an inspiration air flow and an exhalation air flow circulate substantially through the inlet and outlet port. A kit including such an air impeller device and a respiratory mask is also disclosed.
