Abstract

A wireless, surgically implantable pressure transducer for measuring pressure of fluid or tissue in a body chamber such as a brain ventricle of a patient suffering hydrocephalus or a head injury. The transducer includes an inductor and a capacitor connected in parallel to form a resonant L-C circuit. One of these reactive components is variable, and a bellows (or similar pressure-sensitive force-summing device) is mechanically connected to the variable component to vary the value of capacitance or inductance and hence the resonant frequency of the L-C circuit in response to pressure changes of the fluid in which the bellows is immersed. The transducer is electromagnetically coupled to an external source of variable-frequency energy such as a grid-dip oscillator, enabling external detection of the transducer resonant frequency which is a measure of the fluid pressure being sensed. An antenna coil is inductively coupled to the transducer inductor, and is positioned in the transducer to be just beneath the skin when the housing is implanted to provide efficient coupling of the external oscillator and internal resonant circuit. A second bellows or analogous device may be coupled to a reference-pressure side of the transducer to provide improved compensation of variations in ambient temperature and atmospheric pressure.

Other References

• Atkinson, J. R., et al., Journ. of Neurosurgery, vol. 27, No. 5, 1967, pp. 428-432
• Medical Engineering, Ch. 15, C. R. Ray, Yearbook Publishing, Chicago, 1974, p. 156