Effects of sodium bicarbonate on cardiorespiratory measurements and exercise capacity in thoroughbred horses.

We examined the effects of sodium bicarbonate in 6 Thoroughbred horses during submaximal and maximal treadmill exercise. Cardiorespiratory function was assessed together with the effect on exercise capacity by determining the run time to fatigue at maximal intensities. To discriminate between sodium bicarbonate's alkalinising effects and the fluid shifts that could result from the high osmotic load, we administered an equimolar solution of sodium chloride as a control. The horses were given sodium bicarbonate (1 g/kg bwt) or an equivalent number of moles of sodium chloride by nasogastric tube. Arterial blood samples were collected before exercise and 5 h after treatment, resulting in mean standard bicarbonate values of 39.6 mmol/l in horses treated with sodium bicarbonate compared with 24.2 mmol/l in horses that received saline. The horses were exercised on a treadmill at 40, 60 and 80% of their VO2max for 4, 2 and 2 mins respectively. The horses were walked for 3 mins and accelerated rapidly to a speed approximately equivalent to 110% VO2max and run until fatigued. The horses ran for 170 +/- 20 secs (mean +/- sem) after administration of sodium bicarbonate compared with 128 +/- 13 secs after receiving sodium chloride (P < 0.02). At rest and throughout submaximal and maximal exercise, the bicarbonate-treated horses had significantly lower arterial oxygen tensions and higher arterial carbon dioxide tensions. There were no differences in cardiac output, heart rate, oxygen uptake or carbon dioxide production between the saline and bicarbonate treatments.(ABSTRACT TRUNCATED AT 250 WORDS)