A patient monitoring apparatus for monitoring and/or measuring a physiological characteristic of said patient. A user interface having an interior portion communicates with an airway of a user such that substantially all gas inhaled and exhaled by the user enters the interior portion of the user interface. At least one vent element is associated with the user interface and communicates the interior portion of the user interface with an ambient atmosphere outside the user interface. The vent element and user interface define a flow element across which a pressure differential is created during inhalation and exhalation. The pressure differential is the pressure difference between the pressure within the interior portion of the user interface and the pressure of the ambient atmosphere outside the user interface. A sensor communicates with the interior portion of the user interface and measures a fluid characteristic resulting from this pressure differential and outputs a first signal indicative of the measured fluid characteristic. The output from the sensor is used alone or in combination with the output from other sensors that detect other physiological characteristics to provide a variety of information about the patient.