Semi-invasive fiber-optic tonometer

A semi-invasive method for the instantaneous and continuous measurement of absolute blood pressure in small arteries is developed using the principle of arterial tonometry. This is accomplished with a miniature implantable fiber-optic sensor enclosed in an applanation ring and positioned around the artery. A reflective stainless-steel diagram (0.005 mm) bonded to a stainless-steel block is used to deflect the artery. Light is conveyed through a cable to the vibrating diaphragm by a method that causes the intensity of the reflected light to vary proportionally to the displacement of the diaphragm. Measures of reflected light are obtained by a phototransistor amplifier. Operating stability is 4 mm Hg/h with a signal-to-noise ratio of 42.4 dB (resolution is 0.59 mm Hg). The measured external pressure was found to have nearly unity correlation with the internal pressure. Animal studies were performed to determine the accuracy of the method utilizing the invasive methods as a reference. The errors found were 6.16% for systolic, -7.53% for diastolic, and -2.26% for mean pressure. The tonometer is indirectly calibrated and can be applied to vessels of varying sizes