This data was submitted to the Santa Fe Time Series Competitionby in 1991 by our group. The heart rate was determined by measuring the time between the QRS complexes in the electrocardiogram, taking the inverse, and then converting this to an evenly sampled record by interpolation. There were no premature beats - sudden changes in the heart rate are not artifacts. They were converted from 250 Hz to 2 Hz data by averaging over a 0.08 second window at the times of the heart rate samples. Between roughly 4 hours 30 minutes and 4 hours 34 minutes from the start of the file the sensors were disconnected.
Sleep apnea is medically important because it leads to sleep deprivation and occasionally death.
Most importantly, there is interest in verifying and understanding the coupling between respiration and the heart rate. A successful analysis of these data must attempt to distinguish the presumed internal dynamics from changes in the patient's state.