A device to assist pulmonary function, comprising: a fibre bundle having a first end and a second end, wherein the fibre bundle comprises a plurality of hollow fibres; a housing surrounding the fibre bundle, the housing comprising: an inlet nozzle in fluid communication with an inlet, and an outlet nozzle in fluid communication with an outlet, wherein a blood flow path is established from the inlet, through the inlet nozzle, through the fibre bundle, through the outlet nozzle, and to the outlet; a first gas distribution manifold surrounding the first end of the fibre bundle and attached to the housing and having a gas inlet; a second gas distribution manifold surrounding the second end of the fibre bundle and attached to the housing and having a gas outlet, wherein the second gas distribution manifold is in fluid communication with the first gas distribution manifold through an interior of at least a portion of the plurality of hollow fibres, wherein a gas flow path is established from the gas inlet, through the interior of at least a portion of the plurality of hollow fibres, to the gas outlet, characterised in that, in use, when the fibre bundle extends horizontally, the inlet nozzle expands in a horizontal plane and constricts in a vertical plane along the blood flow path. a fibre bundle having a first end and a second end, wherein the fibre bundle comprises a plurality of hollow fibres; a housing surrounding the fibre bundle, the housing comprising: an inlet nozzle in fluid communication with an inlet, and an outlet nozzle in fluid communication with an outlet, wherein a blood flow path is established from the inlet, through the inlet nozzle, through the fibre bundle, through the outlet nozzle, and to the outlet; an inlet nozzle in fluid communication with an inlet, and an outlet nozzle in fluid communication with an outlet, wherein a blood flow path is established from the inlet, through the inlet nozzle, through the fibre bundle, through the outlet nozzle, and to the outlet; a first gas distribution manifold surrounding the first end of the fibre bundle and attached to the housing and having a gas inlet; a second gas distribution manifold surrounding the second end of the fibre bundle and attached to the housing and having a gas outlet, wherein the second gas distribution manifold is in fluid communication with the first gas distribution manifold through an interior of at least a portion of the plurality of hollow fibres, wherein a gas flow path is established from the gas inlet, through the interior of at least a portion of the plurality of hollow fibres, to the gas outlet, characterised in that, in use, when the fibre bundle extends horizontally, the inlet nozzle expands in a horizontal plane and constricts in a vertical plane along the blood flow path. wherein the second gas distribution manifold is in fluid communication with the first gas distribution manifold through an interior of at least a portion of the plurality of hollow fibres, wherein a gas flow path is established from the gas inlet, through the interior of at least a portion of the plurality of hollow fibres, to the gas outlet, characterised in that, in use, when the fibre bundle extends horizontally, the inlet nozzle expands in a horizontal plane and constricts in a vertical plane along the blood flow path.