Physicochemical Analysis of Mixed Venous and Arterial Blood Acid-Base State in Horses at Core Temperature during and after Moderate-Intensity Exercise.
Authors: Lindinger Michael I, Waller Amanda P
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary During moderate-intensity exercise, horses maintain blood pH stability through intricate physiological compensation rather than succumbing to metabolic acidosis, despite substantial rises in blood lactate and venous carbon dioxide. Lindinger and Waller studied six horses fitted with arterial and pulmonary artery catheters over 37 minutes of exercise at approximately 50% maximum heart rate and 60 minutes of recovery, analysing plasma ion concentrations and blood gases whilst accounting for core temperature changes of +4.5°C. Venous blood pH remained essentially unchanged because increased PCO2 (an acidifying factor) was precisely counterbalanced by rises in strong ion difference (an alkalizing factor), whilst arterial blood showed mild alkalosis driven primarily by decreased PCO2 and elevated strong ion difference. The temperature-induced increase in arterio-venous oxygen difference enhancement of oxygen delivery to working muscle, challenging the conventional practice of correcting blood gas values to a standard 37°C laboratory temperature rather than actual core body temperature. For practitioners evaluating equine performance and recovery, this research underscores that standard blood gas analysis may misrepresent the actual acid-base status of exercising horses and suggests that temperature-corrected values provide more physiologically relevant interpretation of blood work during and after exercise.
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Practical Takeaways
- •Standard laboratory acid-base measurements at 37°C do not reflect the actual acid-base status of exercising horses; temperature-corrected values provide clinically relevant information for assessing exercise physiology
- •Horses maintain blood pH stability during moderate exercise despite lactate accumulation, suggesting efficient compensatory mechanisms that should be considered when interpreting post-exercise blood work
- •The increased arterio-venous oxygen difference during exercise (driven by temperature effects on PO2) facilitates oxygen delivery to working muscles, supporting the physiological adequacy of moderate-intensity work
Key Findings
- •Core temperature increased by 4.5°C during 37 min of moderate-intensity exercise (~50% heart rate max), significantly increasing PO2, PCO2, and [H+] without affecting [TCO2]
- •No acidosis occurred during exercise or recovery despite significant increases in lactate and venous PCO2, indicating complex multilevel acid-base control
- •Arterial blood showed mild alkalosis during exercise due to decreased PCO2 and increased strong ion difference (SID)
- •Venous blood [H+] remained nearly unchanged because acidifying effects of increased PCO2 were offset by alkalizing effects of increased SID
- •Temperature correction of acid-base variables revealed markedly different physiological responses compared to variables measured at standard instrument temperature of 37°C