Techniques for evaluation of right ventricular relaxation rate in horses and effects of inhalant anesthetics with and without intravenous administration of calcium gluconate.

The study aims to identify the best approach to measure right ventricular relaxation rate in horses and assesses the impact of anesthesia and calcium gluconate administration on the rate.

Study Design and Methods

• The study involved the participation of six Thoroughbred horses aged between two and four years.
• Researchers tested six models which use monoexponential decay to calculate the right ventricular relaxation rate- two with zero asymptote, three with variable asymptote, and one with biexponential decay under both conscious and anesthetized conditions.
• The two most reliable methods were then used in a study to analyze ventricular relaxation rates in horses that were anesthetized either with isoflurane or halothane, and the observational periods included the phases before, during, and after the intravenous administration of calcium gluconate.
• Ventricular pressure was monitored using a high-fidelity pressure transducer catheter tip, digitizing the results at 500 Hz from the minimum rate of the ventricular pressure change.

Findings of the Study

• Of all assessed models, the ones that used monoexponential decay with zero asymptote consistently provided an estimate for the relaxation rate.
• Both types of anesthesia— isoflurane and halothane — prolonged the right ventricular relaxation rate, with halothane exhibiting a more prominent effect.
• When calcium gluconate was administered intravenously, it reduced the prolongation of right ventricular relaxation rate caused by anesthesia.
• The recovery was greater in horses anesthetized with isoflurane as compared to those under halothane.

Study Conclusions

• The research concluded that the reliable and effective strategy to assess right ventricular relaxation rate in horses involves application of a monoexponential decay model with zero asymptote and non-linear regression.
• Administering calcium gluconate via an intravenous route can mitigate the anesthesia-induced-lengthening of the right ventricular relaxation rate more effectively in horses anesthetized with isoflurane.