Measurement of two new indicators of cardiac reserve in humans, rats, rabbits, and dogs

Abstract

Background: It is difficult to observe the phenomena of cardiac fatigue under a low or moderate workload test, and little was reported about cardiac fatigue under a heavy workload test because of the potential risk (sudden death) of prolonged strenuous exercise. Animal experiments would be helpful to resolve this problem. The objective of this study was to obtain baseline data of two new indicators of cardiac reserve in rats, rabbits, and dogs. Methods: Ten New Zealand White rabbits (1. 5 to 2 kg, 4 females), 10 male Wistar rats (2 months old), and 10 Golden Retriever dogs (40 days old, 5 females) were included in this study. Phonocardiogram of each animal was recorded. The basic points concerning heart sound quantitative analysis were: 1) measuring the duration and the amplitude of relevant heart sound components; 2) calculating and analyzing relevant indicators based on the data obtained from the above measurements, including the ratio of diastolic to systolic duration (D/S) and the ratio of the amplitude of the first heart sound to the amplitude of the second heart sound (S1/S2). Results: The baseline data of D/S ratio and S1/S2 ratio in rats, rabbits, and dogs were obtained. The swimming time to exhaustion for rabbits was several to a dozen minutes, and for rats, several hours. Conclusion: D/S ratio has an important biological implication, which is a safe and easy indicator for evaluating the cardiac health status of both animals and humans.