Abstract: A stereotactic navigation system for navigating an instrument to a target within a patient may include a stereotactic head frame, an imaging device, a tracking device, a controller and a display. The stereotactic head frame is coupled to the patient and is used to assist in guiding the instrument to the target. The imaging device captures image data of the patient and of the stereotactic head frame. The tracking device is used to track the position of the instrument relative to the stereotactic head frame. The controller receives the image data from the imaging device and identifies the stereotactic head frame in the image data and automatically registers the image data with navigable patient space upon identifying the stereotactic head frame, while the display displays the image data.

Abstract: A body-implantable rate-responsive cardiac pacemaker is provided with circuitry for sensing a plurality of physiologic parameters known to be indicative of a patient's metabolic demand for increased cardiac output. In one embodiment, a rate-responsive pacemaker is provided with an activity sensor for detecting the patient's level of physical activity, and is further provided with an impedance sensing circuit for detecting the patient's level of minute ventilation by monitoring cardiac impedance. A rate-response transfer function, implemented by the pacemaker's control circuitry, periodically computes a rate-responsive pacing rate as a function of the outputs from both physiologic sensing circuits. The pacemaker's pacing rate is variable within a rate range defined by predetermined (programmable) upper and lower limits. In the preferred embodiment, the influence of activity sensing and minute ventilation parameters varies in accordance with the current pacing rate.