Effects of repeated atropine injection on heart rate variability in Thoroughbred horses.

This study investigates the impact of repeated atropine injection on the heart rate variability in resting Thoroughbred horses. The researchers found that administration of atropine decreases parasympathetic nervous activity progressively, providing valuable insights on autonomic nervous activity in Thoroughbred horses.

Research Objectives

• The purpose of this study was to determine the effects of routine atropine injection on the variability of heart rate in resting Thoroughbred horses.

Methods and Procedures

• The researchers used a dosage of two micrograms per kilogram of atropine, which acts as a blocker to the parasympathetic nervous system. This was administered intravenously every six minutes, to a total of eight micrograms per kilogram.
• Prior to the atropine administration, the horses received an intravenous dose of 0.2 milligrams per kilogram of propranolol, which serves as a sympathetic nervous block.
• During the process, the scientists recorded electrocardiograms and measured the heart rate.

Assessment of Heart Rate Variability

• The investigators evaluated the variation of heart rate utilizing the power spectrum.
• They measured this in terms of low frequency (LF, 0.01-0.07 Hz) power and high frequency (HF, 0.07-0.6 Hz) power.

Findings

• The researchers found that the administration of atropine decreased parasympathetic nervous activity in a dose-dependent manner.
• Initially, the LF power was affected. This was followed by alterations in the HF power, and finally changes in the heart rate itself.

Significance

• The responses observed in this study might provide valuable information for evaluating the autonomic nervous activity in Thoroughbred horses. Understanding these effects could influence both the approach to training these animals and their health care management.