Pressure telemetry implant

Apparatus for monitoring pressure changes in a subject comprising:

• a piezoresistive transducer mounted to said subject;
• a metal package for said transducer, said package including access means for routing a fluid whose pressure is to be measured inside said package to the vicinity of said transducer and further defining a pathway for allowing communicating signals inside said package;
• circuitry mounted inside said package, said circuitry including a low power analog to digital converter integrated circuit for converting electrical signals from said transducer into pulse code modulated communications signals for transmission to a remote receiver;
• and a second low power integrated circuit coupled to said analog to digital converter, said second integrated circuit having means for activating said circuitry in response to a signal external to said package from a quiescent low power state to a higher power transmitting state, amplifier means for amplifying an output from the transducer, and means for generating said pulse code modulated communications signals;
• and
• a battery within the metal package for powering said circuitry in both said quiescent and transmitting states.

Apparatus for monitoring pressure in a subject comprising:

• sensing means for monitoring pressure variations in a fluid, said sensing means including a piezoresistive pressure sensing diaphragm electrostatically bonded to a glass tube said tube having a center cavity in pressure communication with a region in said subject, said diaphragm partially bounding said cavity;
• circuitry mounted to the diaphragm for converting diaphragm response to pressure into an analog signal, and conversion circuitry for converting said analog signal into a digital communications signal suitable for transmission to a remote receiver;
• means responsive to the temperature in the vicinity of said sensing means to vary a frequency with which said digital communications signal is transmitted to said remote receiver thereby giving an indication of said temperature;
• a titanium package for hermetically encapsulating said transducer and said transmitter means within said subject, said package including a titanium adapter thermally sealed to said glass tube to couple fluid from the subject to the inside cavity of said glass tube.

Apparatus for monitoring a pressure level in a subject comprising:

• a pressure transducer mounted inside a hermetically sealed corrosion resistant package, said package including access means for coupling said transducer to a region inside said subject;
• circuitry mounted inside said package and coupled to said transducer for converting an analog pressure signal from said transducer into a digital pressure signal;
• transmitter means coupled to said circuitry for transmitting said digital signal from the subject to a remote receiving station;
• a battery mounted inside said package for powering said circuitry and said transmitter means;
• power control means mounted inside said package to switch said circuitry and transmitter means from a quiescent state where power drawn from said battery is relatively low to an active state during periods of data transmission where power drawn from said battery is relatively higher;
• and
• a temperature sensor mounted inside said package for measuring fluid temperature at the site of the pressure transducer;
• said temperature sensor coupled to said transmitter means which transmits both temperature and pressure data to said remote station.

Apparatus for monitoring intracranial pressure in a subject comprising:

• a silicon substrate etched to form a piezoresistive diaphragm for monitoring pressure variations;
• a glass tube having a center cavity for routing a fluid from an intracranial cavity to a diaphragm surface;
• said tube electrostatically bonded to a non-etched region of said substrate;
• circuitry coupled to the diaphragm for converting movement of the diaphragm into a communication signal proportional to the pressure on the diaphragm suitable for transmission to a remote receiver;
• and
• a titanium package for encapsulating said diaphragm, glass tube and circuitry while isolating said glass tube from said circuitry, said package including a titanium adapter for routing fluid through said package to said center cavity, said package having an outer covering of silicon rubber to reduce discomfort to said subject.

Apparatus for monitoring intracranial fluid pressure in a subject comprising:

• pressure sensing means for monitoring pressure variations in a fluid routed from an intracranial cavity to the pressure sensing means and producing an electronic output related to said pressure variations;
• temperature sensing means for monitoring the temperature in the vicinity of said pressure sensing means;
• means for transmitting a digital pressure communications signal corresponding to the pressure and for varying the frequency of transmission to give an indication of said temperature;
• a remote receiver for receiving said digital communications signal;
• and;
• programmable controller means for storing digital representations of said pressure and temperature and for monitoring atmospheric pressure at the vicinity of said programmable control means, said programmable controller means including demodulating means for calibrating the intracranial pressure reading with changes in temperature by monitoring changes in said digital pressure signal with calibration pressure and temperature conditions and calculating polynominal calibration co-efficiencies which define a relation between intracranial pressure, said pressure signal and the temperature indicated by said frequency.