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Heart rate variability as a tool for monitoring anesthetized animals: indicators of its age variables

The article is dedicated to outcomes as for the method of analysis of heart rate variability (HRV) among dogs to improve evaluation of monitoring of anesthetized animals.

The statistical parameters of HRV are: Mo (distribution mode of RR-intervals, ms) – the description of the most repetitive values of RR-intervals; Amo (amplitude of distribution mode) –it is a percentage of RR interval that characterizes a proportion of distribution mode to the sample size, reflecting the stabilizing effect of centralization of  the heart rate control, which is mainly caused by the degree of activation of the sympathetic division of ANS; SDNN, ms - standard deviation of the mean duration of RR-intervals for 5 min, describes the state of regulatory mechanisms, indicates the overall effects upon the sinus node sympathetic and parasympathetic divisions of ANS; Cv - coefficient of variation, which is a normalized estimate of SDNN; RMSSD, ms - standard deviation of the values of successive pairs of heart rate, and is a measure of the activity of the parasympathetic autonomic regulation level; PNN50,% - similar to RMSSD, the percentage number of pairs of successive RR-intervals that differ more than 50 ms, reflecting the degree of preference parasympathetic regulation of the sympathetic level.

Spectral analysis allows to divide into 3 main components of power spectral density of heart rate fluctuations: high-frequency waves - HF (0,15-0,4 Hz), determined by parasympathetic impact on the heart (vagal activity); Low-frequency waves - LF (0,04-0,15 Hz) mainly related to sympathetic and to a lesser extent – parasympathetic influences, as well as pressoreceptor reflex; waves of very low frequency - VLF (less than 0.04 Hz), reflecting the effect of many factors, including vascular tone, thermoregulation system and the rennin-angiotensin-aldosterone system (central energotropic contribution). In addition to the amplitude of the components, determine the ratio of low frequency power to high power (LF / HF), which value indicates the balance of sympathetic and parasympathetic influences. This index within 0.85-1,15 indicates normotonia that is more than 1.15 - the sympathicotonia, and less than 0.85 - the parasympathicotonia.

According to the research the mode of the distribution (Mo) was highest among dogs older than 8 years, and lowest - of the age of 2 months (p<0.001). That is, these dogs during the myocardium de- and repolarization significantly shorter. At this time excitement sinus node, the passage of nerve impulses and recovery potential of cell membrane attack faster. With age, Mo increases. Amo lowest index (p<0.01) at the age of 4-6 months, that is, there is a significant variation of excitation, conduction and recovery in the myocardium, and from a clinical point of view - the instability of ANS.

The total effect of autonomic regulation of circulation (SDNN) was the lowest in 2-month-old dogs and over 8 years. The rest was significantly higher, indicating a wide variation limits in the processes of excitation in the heart of ANS. The coefficient of variation (Cv) is least among dogs over 8 years old (p<0.01). But it average in size (p<0.05) in the 3rd group animals, RR- intervals sufficiently stable. PNN50 index was the highest in the 2nd, 3rd and 4th groups, and in the 1st and 5th - lower (p <0.01) than the other groups. RMSSD also was greater in the 2 nd, 3 rd and 4 th groups, but the highest - in the 4-6-month-old and 5-7-year-old dogs. Thus, the level PNN50 and RMSSD suggest, their electrophysiological correlates significantly higher impact on the regulation of the parasympathetic component of heart rate in dogs found in the age range from 4 months to 7 years.

It is established that in dogs 5-7 years neurohumoral activity (VLF) in 1,3-2 times (p <0.001) higher than in other age groups. The lowest level of VLF in 2-month-old dog indicates a shortage of energy and metabolic reserves to maintain stability of heart rate, while high at the age of 5-7 years - a state hyper adaptation. The activity of the parasympathetic modulation (HF) in 2-month-old dogs and over 8 years was lowest (p<0.01). They found normotonia - 0.9, and the rest parasympathicotonia - 0.7.

Consequently, anesthesia requires the consideration of age features of ANS influence on cardiovascular activity in dogs.

Key words: heart rate variability, autonomic nervous system, normotonia, sympathicotonia, parasympathicotonia, dogs.

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