1. A computer-implemented method of determining a blood flow characteristic, the method comprising: receiving image data of one or more blood vessels of a patient, the image data being obtained while the patient's body is at a first physiological state; generating a patient-specific vascular model of the one or more blood vessels from the image data obtained while the patient's body is at the first physiological state; determining a mechanical response of a portion of a vessel wall associated with a second physiological state, the second physiological state caused by a change from the first physiological state at a location other than the location of the portion of the vessel wall, the mechanical response of the portion of the vessel wall including at least one of a response to a change in blood flow associated with the second physiological state, a response to a change in blood pressure associated with the second physiological state, or a response to medication associated with the second physiological state; updating the patient-specific vascular model of the one or more blood vessels based on the determined mechanical response; and determining a blood flow characteristic through the one or more blood vessels of the patient based on the updated patient-specific vascular model.