Comparison of daily heart rate variability in old and young horses: a preliminary study

Abstract This study analysed heart rate variability (HRV) parameters in selected intervals of a 24-hour recording session. The study was conducted with eight young and eight old, clinically-healthy geldings. HRV measurements were taken with Polar RS800CX instruments. The recordings were then analysed with Kubios HRV software. The following time intervals were identified: 24 hours, 15 hours of the day (light period), 9 hours of the night in total, and in subsequent hours of the night. During each interval, the following time analysis parameters were investigated: heart rate (beats per minute; HR), verified beat-to-beat times (NN), standard deviation of the NN intervals (SDNN), and the square radical of the mean sum of the squares of differences between the adjacent NN intervals (rMSSD). The following HRV frequency parameters were also investigated: total power of the spectrum (TP), high-frequency spectrum (HF), low-frequency spectrum (LF) and LF/HF ratio. It was found that geriatric horses had higher HRs, but reduced some HRV parameters compared to young horses. Noticeable changes were least evident after midnight, especially between 01h00 and 04h00.