Assessment of muscle oxygenation in the horse by near infrared spectroscopy.
Authors: Pringle J, Roberts C, Art T, Lekeux P
Journal: Equine veterinary journal
Summary
# Editorial Summary: Assessment of Muscle Oxygenation in the Horse by Near Infrared Spectroscopy Near infrared spectroscopy (NIRS) offers a non-invasive means of monitoring real-time changes in muscle oxygen availability, a capability that could prove valuable for assessing equine athletic performance and metabolic stress during work. Pringle and colleagues tested NIRS reliability in two experimental models: anaesthetised horses subjected to controlled limb ischaemia and systemic hypoxaemia, and conscious horses exposed to hypoxic gas inhalation followed by limb ischaemia, measuring haemoglobin and myoglobin deoxygenation alongside arterial and venous oxygen saturation. Limb ischaemia consistently produced marked muscle deoxygenation signals (P<0.01 in anaesthetised horses; P<0.05 in awake horses), whereas systemic hypoxaemia generated only modest deoxygenation in anaesthetised subjects (3.2% of the ischaemia signal) and proved undetectable in conscious animals despite significant reductions in arterial oxygen saturation. Notably, neither experimental condition induced measurable cytochrome aa3 reduction, suggesting peripheral oxygen availability rather than cellular respiration became the limiting factor within the timeframes examined. For practitioners, these findings indicate that NIRS can reliably distinguish between different hypoxic mechanisms and could provide a non-invasive tool for detecting exercise-induced muscle hypoperfusion in working horses, though further validation during genuine athletic performance is warranted.
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Practical Takeaways
- •NIRS can be used as a non-invasive monitoring tool to assess muscle oxygenation in horses during anaesthesia and recovery, with clear differentiation between ischaemic and hypoxaemic states
- •Limb ischaemia produces far more dramatic muscle deoxygenation changes than systemic hypoxia, which may inform clinical interpretation of NIRS readings during lameness or surgical cases
- •Movement artefact does not prevent detection of ischaemia-induced deoxygenation signals, suggesting NIRS could be applied to working horses to assess muscle oxygenation during exercise or performance
Key Findings
- •NIRS reliably detected marked muscle deoxygenation during 8 min limb ischaemia in anaesthetised horses (P<0.01), with haemoglobin/myoglobin saturation changes of clinically significant magnitude
- •Systemic hypoxaemia induced only 3.2% of the deoxygenation signal seen with ischaemia in anaesthetised horses, demonstrating distinct physiological responses between the two conditions
- •Awake horses showed rapid and significant muscle deoxygenation during ischaemia (P<0.05) but no detectable deoxygenation during hypoxia despite arterial saturation dropping to 86.8%
- •No evidence of cytochrome aa3 reduction was detected in either group despite up to 8 min of complete ischaemia, suggesting anaerobic metabolism does not reach the mitochondrial electron transport chain in these conditions