A fluid analysing system comprises: a pneumatic system for fluid analysis of expiratory and/or inspiratory breath, wherein said pneumatic system comprises a pneumatic manifold comprising: a connection interface (12, 23) for a fluid analyser unit; a connection interface for a pump unit (11, 20); and a buffer volume arranged between said connection interface (12, 23) for the fluid analyser unit and said connection interface (11, 20) for the pump unit, and wherein said buffer volume is configured to act as a constant flow cavity, a pump capacity improving cavity and as a ripple cancellation cavity; wherein said pneumatic system further comprises: a flow sensor and/or a pressure sensor; and a control unit; said fluid analysing system further comprising a pump unit connected to said connection interface (11, 20) for a pump unit; and a fluid analyser unit connected to said connection interface (12, 23) for a fluid analyser unit; wherein said control unit is configured to regulate a pump stroke force and/or pump frequency of said pump unit based on measurements from said flow sensor and said pressure sensor for obtaining a constant flow through said pneumatic system during a breath cycle with dynamic pressure, such as an inhale and/or an exhale. a pneumatic system for fluid analysis of expiratory and/or inspiratory breath, wherein said pneumatic system comprises a pneumatic manifold comprising: a connection interface (12, 23) for a fluid analyser unit; a connection interface for a pump unit (11, 20); and a buffer volume arranged between said connection interface (12, 23) for the fluid analyser unit and said connection interface (11, 20) for the pump unit, and wherein said buffer volume is configured to act as a constant flow cavity, a pump capacity improving cavity and as a ripple cancellation cavity; a connection interface (12, 23) for a fluid analyser unit; a connection interface for a pump unit (11, 20); and a buffer volume arranged between said connection interface (12, 23) for the fluid analyser unit and said connection interface (11, 20) for the pump unit, and wherein said buffer volume is configured to act as a constant flow cavity, a pump capacity improving cavity and as a ripple cancellation cavity; wherein said pneumatic system further comprises: a flow sensor and/or a pressure sensor; and a control unit; said fluid analysing system further comprising a pump unit connected to said connection interface (11, 20) for a pump unit; and a fluid analyser unit connected to said connection interface (12, 23) for a fluid analyser unit; wherein said control unit is configured to regulate a pump stroke force and/or pump frequency of said pump unit based on measurements from said flow sensor and said pressure sensor for obtaining a constant flow through said pneumatic system during a breath cycle with dynamic pressure, such as an inhale and/or an exhale. a flow sensor and/or a pressure sensor; and a control unit; said fluid analysing system further comprising a pump unit connected to said connection interface (11, 20) for a pump unit; and a fluid analyser unit connected to said connection interface (12, 23) for a fluid analyser unit; wherein said control unit is configured to regulate a pump stroke force and/or pump frequency of said pump unit based on measurements from said flow sensor and said pressure sensor for obtaining a constant flow through said pneumatic system during a breath cycle with dynamic pressure, such as an inhale and/or an exhale.