Frequency domain analysis of heart rate variability in horses at rest and during exercise.

This study investigated the variability in heart rate in horses both at rest and during various levels of exercise. The researchers gathered data about the frequency and spectral power of heartbeats within various frequency ranges, and analyzed how these changed in relation to exercise intensity. The findings indicate that heart rate variability may be influenced by factors other than autonomic nervous system activity during intense exercise.

Methodology

• Data for this study were gathered by monitoring the heart rates of six Thoroughbred horses at rest and during three different treadmill exercise protocols.
• The researchers tracked the timings of individual heartbeats (RR intervals) to create time series data for analysis.
• The frequencies of the heartbeats were categorized into three bands: very low (VLF), low (LO), and high (HI). These bands represent different levels of physical stress on the heart.
• The study also calculated indicators of both sympathetic (SNSI) and parasympathetic (PNSI) nerve activity. These provide an understanding of how the autonomic nervous system (ANS) regulates heart rate.

Results

• The power in all frequency bands fell progressively with an increase in exercise intensity. This trend continued up to a trotting pace, but at a galloping pace, the power in the high frequency (HI) band increased.
• The sympathetic activity indicator (SNSI) increased from rest to walking pace, but fell with further increases in physical exertion, reaching its lowest at a galloping pace.
• The parasympathetic activity indicator (PNSI), meanwhile, fell from rest to a walking pace, then rose with increased physical exertion, peaking at a galloping pace.
• Results showed significant variation between individual horses, suggesting inter-horse variability in heart rate responses.

Conclusion

• You could conclude from the study that heart rate and heartbeat variability in horses changed in response to increasing levels of physical effort in ways that indicate both neural and non-neural influences acting on heart rate.
• There is a change in autonomic modulation once heart rate reaches high exercise intensities above 120-130 beats per minute.
• Variables such as respiratory-gait entrainment, energetics of locomotion and work of breathing could also have influenced heart rate variability during intense exercise.
• The study suggests that frequency domain analysis of heart rate variability could be a non-invasive means of assessing autonomic modulation of heart rate at low exercise intensities.