There is disclosed on external programmer for use with heart pacers of two different types. Depending on the reed orientations in the two types of pacers, the magnetic flux generated by the programmed has to be in one of two orthogonal directions through the pacers. A pair of parallel coils is provided. A switching circuit switches the current direction through one of the coils so that the two coil fluxes aid or oppose each other, thus giving rise to orthogonal fluxes through pacers to be adjusted. A pacer of either type can thus be adjusted without the physician having any concern for the reed/programmer orientations.

A hand-held, portable, battery-powered test instrument for evaluating the performance of cardiac pacer devices prior to the implantation thereof and afterwards. To test R-wave sensitivity of a pacer device, a series of simulated R-waves, each of a predetermined greater amplitude, is applied to the pacer unit under test, each such simulated R-wave occurring at a time following a preceding pacer pulse sufficient to ensure that the pacer's refractory period has elapsed. This process is continued until a succeeding pacer pulse does not occur at the time it would otherwise be due, thus indicating that the R-wave had just reached the amplitude sufficient to cause the resetting of the pacer pulse generator. A count is maintained of the number of cycles needed to cause resetting of the pacer pulse generator and this value is displayed to indicate, in terms of voltage, the minimum amplitude of the R-wave just sufficient to result in pacer resetting.

A complete system for telemetering and monitoring the functioning of an implanted pacemaker as well as controlling the testing of the functions from a remotely located central facility is disclosed specifically comprising the provision of capabilities for directly and simultaneously transmitting from the pacer, electrical signals indicative of multiple pacer functions such as pacer rate, cell voltage, refractory period, heart rate with pacer inhibited, R-wave level and sensing margin, sensing circuit and other component failure, cardiac electrode, lead break, and hermetic integrity. The indicative signals are picked up at the patient's location for local analysis and/or telephonically communicated to a remote central monitoring station. The central station may control testing of the pacemaker functions by transmitting command signals back telephonically for coupling through cooperating external and implanted inductances or mangetically controlled switches to the implanted pacer circuitry. Systems of particular value in pacers with single cell lithium iodide power sources are also provided for integrating pacer output pulse current and voltage and producing indicative signals which are telemetered to permit monitoring of cell and electrode pacing impedance. Additionally, provision is made for avoiding sensing of the electrode "after potential" and for differentiating the refractory signal to produce a marker pulse in the telemetered signal. Improvements in the telemetry oscillator are also disclosed.

A system consisting of a multiplicity of separate modules which collectively perform a useful biomedical purpose; the modules communicating with each other without the use of interconnecting wires. All modules may be intracorporeal or body mounted extracorporeal or some modules may be intracorporeal with others being body mounted extracorporeal. Signals are sent from one module to another by electromagnetic waves, by electrical signals using the body as an electrical conductor, or by acoustic waves. Physiologic sensor measurements sent from a first module causes a second module to perform some function in a closed-loop manner. One extracorporeal module can provide electrical power to an intracorporeal module; which power operates means for transferring data from the intracorporeal module to the body mounted extracorporeal module.

An external pacer having a plurality of user-selectable output current levels includes a user-actuable push button switch for reducing the selected output current level by a factor of 10. By observing the absence or presence of an R-wave while operating at the reduced current level the stimulation threshold level of the heart can be determined without the need for additional level selections, and without subjecting the heart to sustained periods of low current. In the illustrated embodiment of the invention for typical output current levels of 2-20 milliamperes threshold levels of 0.2-2.0 milliamperes are obtained.