The invention provides a multi-sensor system that uses an algorithm based on adaptive filtering to monitor a patient's respiratory rate. The system features an impedance pneumography sensor and a motion sensor (e.g., an accelerometer) configured to attach to the patient's torso and measure therefrom a motion signal. The system further comprises a processing system, configured to operably connect to the impedance pneumography sensor and motion sensor, and to determine a respiration rate value by applying filter parameters obtained from the impedance pneumography sensor signals to the motion sensor signals.