The main physical attribute of these sensors is the ability to be sterilized by autoclave equipments for high pressure and temperature too far beyond that which it was designed to operate in the human body. On medical equipments, what you say as "sensor", we could better technically define as a "probe", due consists of an apparatus encapsulating the sensor. Physiologically must be little aggressive, due it needs to be inserted into the patient.
Concerning the sensor itself can be something as a PT100 type, which offers a good linearity in small ranges of variation.
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