An airflow perturbation device for measuring respiratory resistance of a patient breathing with the use of a ventilator comprises a sealed housing having a first port and a second port each configured to couple to a ventilator hose, a perturbation mechanism to periodically alter air flow resistance between the first port and the second port, a pneumotachometer comprising a flow sensor to measure airflow between the first port and the second port, a pressure sensor to measure a difference in air pressure between the first port and the second port, and a computing system comprising at least one processor configured to receive data from the flow sensor and pressure sensor. The computing system determines an airflow resistance based on the received data. Embodiments of the present invention further include a method and computer program product for measuring respiratory resistance of a ventilated patient in substantially the same manners described above.