Abstract: In the implantable cardiac pacer disclosed herein, a drop in battery voltage is signalled by a discrete change in the stimulation frequency of the pacer. Reliably distinct frequencies are obtained by digitally dividing, by two different integer factors, a stable high frequency pulse signal generated by a mechanically controlled oscillator, for example a piezoelectric crystal controlled oscillator.

Abstract: A flow rate controlled angiographic injection system is provided with an overspeed injection protection means. The injection system includes a motor driven syringe injector and a flow rate controller responsive to the overspeed protection means to drive the motor to inject a contrast medium from the syringe into a blood vessel at a desired flow rate when the actual flow rate from the syringe is less than or equal to the predetermined flow rate, and to disable the motor otherwise. The overspeed injection protection means includes a means for generating a signal representative of the actual flow rate of a contrast medium from the syringe by detecting the back emf induced in the motor armature, compensation being made for the resistive voltage drop in the armature windings and brushes.