An intravascular sensor delivery device can have a sensor that is used to measure a physiological parameter of a patient, such as blood pressure, within a vascular structure or passage. In some embodiments, the device can be used in combination with a medical guidewire carrying another sensor also configured to measure a physiological parameter of the patient, such as blood pressure. Data generated from the intravascular sensor delivery device sensor and the guidewire sensor can be used to determine a characteristic of interest for the vascular structure under investigation. For example, the data can be used to calculate a pressure distal to pressure proximal ratio across a stenotic lesion in order to assess the severity of the lesion.