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Abstract

A pressure sensor for indicating pressure in the animal or human body, such as intracranial pressure, including a housing, a bellows contained within the housing, a body pressure sensing tambour for placing the bellows in communication with pressure in the body so that the pressure will cause the bellows to move as a function of the pressure, output means, such as a radioactive source and associated shielding, contained within the housing and associated with the bellows for providing an output which is a function of the movement of the bellows, and a receiver, such as a radiation detector, located external to the body to receive the output and provide data indicative of the pressure in the body. The pressure sensor includes means associated with the bellows to enable in vivo calibration of the pressure sensor after implantation by establishing a preselected output condition during calibration. An ambient pressure sensing tambour is associated with the bellows for compensating for ambient pressure variations. The bellows is resilient, made of a material which has essentially 100% memory of position and has particular critical dimensions in order to provide linear movement in response to the range of pressures to be monitored, and to provide a sufficient movement, or deflection, in order to provide a sufficient readout. The bellows has a spring rate which is substantially greater than the spring rate of the pressure sensing and ambient pressure compensating tambours thereby making the pressure sensor essentially insensitive to temperature variations.

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