The present disclosure concerns a method for determining a heart-lung interaction factor of a subject, comprising: measuring a heart activity-related signal comprising heart activity-related information from the heart activity-related signal, calculating a frequency of cardiac cycle and a frequency of respiratory cycle from the heart activity-related signal, determining a cardiac cycle energy at the frequency of cardiac cycle, determining a respiratory cycle energy at the frequency of respiratory cycle, and determining a heart-lung interaction energy at an intermodulation frequency corresponding to the difference between the frequency of respiratory cycle and the frequency of cardiac cycle, or the sum of the frequency of respiratory cycle and the frequency of cardiac cycle and determining a heart-lung interaction factor from the ratio of the heart-lung interaction energy and one of the cardiac cycle energy and the respiratory cycle energy. The heart-lung interaction factor can be determined non-invasively.
