Effects of behavior responses on the vasovagal tonus index in healthy dogs

The vasovagal tonus index (VVTI) is a time-domain analysis method of heart rate variability acquired over a short period. It is a useful measurement for evaluating severity and prognosis heart failure in dogs. Behavior responses can be used to evaluate stress in each dog individually. Stress during clinical examination may interfere with the VVTI since it influences the sympathetic nervous system. The aim of this study was to investigate the effect of behavior responses during clinical examination on the VVTI. Data set obtained from physical examination, systolic blood pressure measurement, electrocardiography, VVTI calculation, and video recording were collected from 50 healthy dogs. Behavior scores were analyzed from video recording and dogs were classified into three groups; group 1 (passive), group 2 (quite active), and group 3 (highly active). The results showed that the VVTI was not different between the three groups (p=0.77). Medians and interquartiles of the VVTI in group 1, 2, and 3 were 8.45 (6.86-9.05), 7.65 (6.82-8.94), and 7.26 (5.80-8.90) respectively. There was a negative correlation between VVTI and heart rate (Pearson's r= -0.68, p<0.001). Therefore, the effect of behavior responses during clinical examination did not affect the VVTI measurement in healthy dogs.