Operation of a patient's lungs may be analyzed by transmitting ultrasound energy into the patient's lung, and obtain power and velocity Doppler data while a vibration is being induced in the lung. At least one portion of the power and velocity data that corresponds to a fundamental harmonic is then identified. In some embodiments, portions of the power and velocity data that corresponds to higher order harmonics are also identified. The power observed in the fundamental harmonic and optionally the higher order harmonics can then be used to determine the condition of the lungs.