A variety of medical devices are used for chronic, e.g., long-term, delivery of therapy to patients suffering from a variety of conditions, such as chronic pain, tremor, Parkinson's disease, epilepsy, urinary or fecal incontinence, sexual dysfunction, obesity, or gastroparesis.  As examples, electrical stimulation generators are used for chronic delivery of electrical stimulation therapies such as cardiac pacing, neurostimulation, muscle stimulation, or the like.  Pumps or other fluid delivery devices may be used for chronic delivery of therapeutic agents, such as drugs.  Typically, such devices provide therapy continuously or periodically according to parameters contained within a program.  A program may comprise respective values for each of a plurality of parameters, specified by a clinician. 
Initially, a clinician uses an external device, e.g., a clinician programmer, to provide a set, or multiple sets, of stimulation parameters that instruct the medical device how to deliver the therapy to the patient.  In the case of an implantable medical device, this “programming” task usually occurs once the medical device is implanted in the patient and ready for operation.  In some cases, the initial stimulation parameters are the best estimate of the clinician as to what type of therapy will alleviate the patient of their physiological symptoms or conditions.  The patient may thus need to visit the clinician periodically to subsequently adjust the stimulation parameters for more effective treatment. 
In some cases, the patient may be allowed to activate and/or modify the therapy delivered by the medical device.  For example, a patient may be provided with a patient programming device.  The patient programming device communicates with a medical device to allow the patient to activate therapy and/or adjust therapy parameters.  For example, an implantable medical device (IMD), such as an implantable neurostimulator, may be accompanied by an external patient programmer that permits the patient to activate and deactivate neurostimulation therapy and/or adjust the intensity of the delivered neurostimulation.  The patient programmer may communicate with the IMD via wireless telemetry to control the IMD and/or retrieve information from the IMD.