The association between heart rate, heart rate variability, endocrine and behavioural pain measures in horses suffering from laminitis.
Authors: Rietmann, Stauffacher, Bernasconi, Auer, Weishaupt
Journal: Journal of veterinary medicine. A, Physiology, pathology, clinical medicine
Summary
# Editorial Summary Assessing pain severity in acute and chronic laminitis cases presents a clinical challenge, particularly when determining treatment efficacy beyond observable lameness. Rietmann and colleagues examined whether heart rate variability (HRV) analysis could serve as an objective pain marker by measuring cardiac autonomic function alongside traditional orthopaedic assessment, behavioural indicators, and stress hormones in 19 laminitic horses before and seven days after NSAID treatment. Low-frequency HRV components (reflecting sympathetic dominance) decreased significantly with treatment and analgesia, whilst high-frequency components (parasympathetic tone) increased correspondingly; notably, these HRV parameters correlated with clinical lameness scores (Obel grade plus hoof tester response) and weight-shifting behaviour better than circulating cortisol, adrenaline or noradrenaline levels. The findings suggest that power spectral HRV analysis offers a quantifiable, non-invasive window into the autonomic nervous system's response to pain, potentially providing equine practitioners—particularly those managing acute laminitis cases—with a supplementary objective measure of treatment response when clinical signs remain ambiguous or borderline.
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Practical Takeaways
- •Heart rate variability analysis may provide objective assessment of pain response to treatment in laminitic horses, complementing clinical lameness scoring
- •The sympathetic-parasympathetic balance shift (declining LF/HF ratio) with NSAID treatment could help monitor analgesic efficacy when clinical signs are difficult to assess
- •Cortisol measurement alone is insufficient for pain monitoring in laminitis; HRV-based assessment may be more reliable than single hormone measurements
Key Findings
- •Low-frequency heart rate variability (normalized units) decreased significantly from 60.41 to 51.12 after NSAID treatment, indicating reduced sympathetic activity with pain relief
- •High-frequency heart rate variability increased from 35.07 to 43.14 normalized units following treatment, reflecting increased parasympathetic tone
- •Clinical pain index (Obel grade plus hoof tester score) correlated with sympatho-vagal balance (R=0.57) and individual HRV components, suggesting HRV reflects pain severity
- •Plasma cortisol showed poor association with pain measures and treatment response, whereas catecholamines (adrenalin/noradrenalin) correlated with HF components (R=-0.47 and 0.33 respectively)