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  • Author or Editor: Mary M. Durando x
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Objective—To compare cardiac output (CO) obtained by the lithium dilution method (LiDCO) with CO calculated from the Fick principle (FickCO), in horses maximally exercising on a high-speed treadmill.

Animals—13 Thoroughbreds.

Procedures—In part 1 of the study, 5 horses performed a warm-up (walk, trot, and canter) and exercise test (walk, trot, canter, and gallop [90% to 100% maximum oxygen consumption [{O2max}]) with measurements of LiDCO and FickCO obtained simultaneously after 60 seconds at each exercise level, for a total of 7 measurements. In part 2 of the study, 8 horses performed a warm-up (walk, trot, and canter) followed by an exercise test (walk and gallop [90% to 100% O2max], repeated twice). Measurements of LiDCO and FickCO were obtained 60 seconds into the first walk and each gallop of the exercise tests, for a total of 3 measurements.

Results—Cardiac output increased significantly with increasing speeds by use of both methods. In part 1, lithium dilution significantly overestimated CO, compared with the Fick principle, during the exercise test (as both injection number and exercise intensity increased). Mean ± SD bias was 246 ± 264 mL of blood/min/kg in part 1 and 67 ± 100mLof blood/kg/min in part 2. Three injections of lithium (part 2) did not result in the same degree of overestimation of LiDCO that was observed with 7 injections (part 1).

Conclusions and Clinical Relevance—Lithium dilution may be an acceptable substitute for the Fick principle as a means to measure CO in maximally exercising client-owned horses.

Full access
in American Journal of Veterinary Research


Objective—To determine whether echocardiographic variables differed between successful (elite) and less successful (nonelite) Arabian endurance horses.

Animals—34 Arabian horses that competed in endurance racing.

Procedures—Horses were assigned to either an elite or nonelite group on the basis of results of a previous competition, and a standardized echocardiographic examination was performed on each horse within 1 to 4 weeks after that competition. Multivariable logistic regression with backward stepwise elimination was used to create a prediction model for the determination of horse status (elite or nonelite) as a function of the measured echocardiographic variables.

Results—The elite and nonelite groups consisted of 23 and 11 horses, respectively. One horse in the nonelite group had a frequent ventricular dysrhythmia that could have negatively affected its performance and rider's safety, whereas none of the horses in the elite group had remarkable cardiac abnormalities. The left ventricular internal diameter during systole and diastole and left ventricular mass and stroke volume were significantly greater for horses in the elite group, compared with those for horses in the nonelite group. The final logistic regression model correctly predicted the horse status for all of the horses in the elite group and 8 of 11 horses in the nonelite group.

Conclusions and Clinical Relevance—Results indicated that heart size was significantly associated with performance for Arabian endurance horses in a manner similar to findings for Thoroughbred and Standardbred racehorses in active competition.

Full access
in American Journal of Veterinary Research