Relationship between VO2max, heart score and echocardiographic measurements obtained at rest and immediately following maximal exercise in thoroughbred horses.

This research article delves into the analysis of the relationship between the heart score, echocardiographic measures, and maximal oxygen consumption (VO2max) in thoroughbred horses, while also considering maximal cardiac output and maximal stroke volume. The key findings include the lack of a correlation between heart score and VO2max, Qmax, or SVmax, and no significant difference in pre-and post-exercise measurements of left ventricular diameter, interventricular septal thickness, and left ventricular free wall thickness.

Study Setup and Methodology

• The study involved six mature, fit Thoroughbred horses, who were put through exercises on an inclined treadmill. Each run consisted of a three-minute warm-up and an incremental exercise test, culminating when VO2max was achieved.
• The researchers used an ATL HDI 3000 ultrasound system and a 3.5 MHz phased array transducer to carry out echocardiographic measurements before and within two minutes of completing the run.
• Blood samples (arterial and mixed venous) were collected during the last 15 seconds of the exercise to determine the arteriovenous oxygen content difference.
• From the echocardiographic recordings, measurements of the left ventricular diameter (LVD), interventricular septal thickness (IVS), and left ventricular free wall thickness (LVFW) were made. For further evaluation, the heart rate was recorded using a cardiotachometer, and the heart score was calculated on non-exercise days.
• The study used the Fick equation to calculate maximum cardiac output and SVmax based on the determined maximum heart rate (HRmax).

Results and Analysis

• The findings of the study revealed a mean pre-exercise heart rate of around 54.7 beats/minute and post-exercise rate of roughly 111.7 beats/minute. The mean VO2max was approximately 150.4 ml/(kg.min).
• Through a backward stepwise regression analysis, the researchers related the pre- and post-exercise echocardiographic measurements to VO2, Q, and SV at the time of the measurement, and to VO2max, Qmax, and SVmax. The left ventricular diastolic diameter (LVDD) was identified as a significant variable in these relationships.
• Interestingly, the research concluded that the heart score, an index expected to have a correlation with the parameters, showed no correlation with VO2max, Qmax, or SVmax.
• Additionally, the study noted no significant variation in the pre- and post-exercise measurements about the left ventricular diameter, interventricular septal thickness, and left ventricular free wall thickness.