Biotelemetry: adjustment of a telemetry system for simultaneous measurements of acute heart rate changes and behavioral events in unrestrained rats.

The radiotelemetry system described in this paper consists of an implantable transmitter and a receiver, connected to a microcomputer. The hardware and software belonging to Mini-Mitters, for the collection and analysis of heart rate (HR), core temperature (CT), and gross activity data, do not possess the flexibility to detect acute changes in HR nor to discriminate among simultaneously occurring different types of behavior. In order to study short-term changes in HR in response to stress or drugs, in relation to behavioral responses, an inexpensive computer interface and a software program (CARDIAQ) were developed to collect data from Mini-Mitters. The interface conveys the QRS signal, which is converted to a TTL pulse train, to the parallel printer adapter (LPT1) of an IBM-compatible computer. Heart rate is determined by measuring single interbeat intervals (IBI). The software controls the sampling schedule and stores the collected data in a format compatible with a commercial spreadsheet package. The program calculates the median IBI per s, mean +/- SD IBI, variance, skewness, and kurtosis of the IBI distribution. In addition, it enables simultaneous recording of behavior by entering data through the keyboard at the occurrence of each event. In this paper, we describe the CARDIAQ program and provide examples of its application together with the implantable transmitters in freely moving rats.