Introduction: The autonomic nervous system has been related to an increase in heart rate, blood pressure and cardiac output in situations of stress.

Objective: To determine the modifications that the non-linear parameters undergo in the autonomic cardiovascular regulation of the heart rate variability subjected to mental stress through the mental arithmetic test.

Material and Method: A non-observational quasi-experimental study of before-after type without control group was conductedin  the  Biomedical  Basic  Sciences  Laboratory  at  Medical  school  1, University  of Santiago  de Cuba, from March 2016 to August 2018. A group of 10 Medical Students constituted the population and sample.

Results: Statistically significant differences between means were found in Heart rate values (p = 0.000), SD1 (p = 0.002), SD2/SD1rate (p = 0.000), Sample Entropy (p = 0.026), Short-term fluctuations α 1 (p = 0.000), CorrelationDimension (p = 0.020), Max line length (p = 0.017), Recurrence rate (p = 0.007), Determinism (p = 0.003), Multiscale Entropy minimum(p = 0.001), Multiscale Entropy maximum(p = 0.000) and MultiscaleEntropyAverage (p = 0.001).

Conclusions: The non-linear parameters in the cardiovascular autonomic regulation of Heart rate, SD1, SD2/SD1 rate, Sample Entropy, Short-term fluctuations α 1, Correlation Dimension, Max line length, Recurrence rate, Determinism, Multiscale Entropy Minimum, Multiscale Entropy Maximum and Multiscale Entropy Average experienced variations in patients subjected to mental stress through the arithmetic calculation test.

Introduction:  In recent  years,  the relationship  between  the systematic  practice  of physical  exercise,  cardiovascular  dynamics  and  the  functioning  of  the  autonomic nervous system has been recognized.

Objective: To determine the modifications that non-linear parameters undergo in the autonomic cardiovascular regulation of the heart rate variability with the systematic practice of physical exercise.

Methods: A retrospective cohort analytical study was conducted from February 2016 to August 2018. Population and sample: 36 individuals (Group 1: 18 high- performance baseball athletes; Group 2:  18 medical students). The  data  were collected  in  the  Biomedical  Basic  Sciences  Laboratory  at  Medical  school  1, University  of Santiago  de Cuba,  through  the 8-channel  PowerLab  polygraph,  and stored using the Kubios Software version 3.0.4 Premium.

Results: Statistically significant differences between means were found in heart rate values (p = 0.000); SD1 (p = 0.025); SD2/SD1 ratio (p = 0.007); sample entropy (p = 0.011); short-term fluctuations α 1 (p = 0.019); mean line length (p = 0.016); max line length (p = 0.001); recurrence rate (p = 0.034); determinism (p = 0.010) and Shannon entropy (p = 0.015). The parameters of SD1 (C = 0.906) and sample entropy (C = 0.712) were significantly associated with a heart rate ≤ 70 beats per minute.

Introduction: the autonomic nervous system plays an important role in cardiovascular readjustments to exercise. In cardiovascular hyperreactivity there is a greater sensitivity of the sympathetic system to different stressors.  Objective: to determine the characteristics of cardiac autonomic control in young adults with different degrees of cardiovascular reactivity at rest and during isometric exercise. Material and Methods: the sample consisted of 97 individuals of both sexes, it was divided into three groups; normorreactives, hyperreactive and with hypertensive response according to the pressor response to the sustained weight test. All individuals underwent a variability study of heart rate at rest and during the isometric test. Variables in the frequency domain were studied: HF, LF, resting LF/HF ratio and the parameters of the Poincaré diagram SD1, SD2 and the SD1/SD2 ratio at rest and during exercise.  Results: At the basal state, hyperreactive individuals and with a hypertensive response had a sympathetic predominance over cardiac function and a lower variability of heart rate. During isometric exercise the values of the SD1 and SD2 axes decreased in all groups and the SD1/SD2 ratio decreased in normorreactive individuals and with hypertensive response, but it was only significantly in the hyperreactive ones. Conclusions: In individuals with cardiovascular hyperreactivity, an autonomic imbalance is already present in the basal state and there is a reduction in autonomic vagal modulation during exercise that may contribute to the development of hypertension.

Introduction: The nervous system is divided into voluntary nervous system and autonomic nervous system. The latter has been related to situations of stress and struggle usually results in an increase in heart rate, blood pressure and cardiac output. Objective: To determine the modifications that the non-linear parameters undergo in the autonomic cardiovascular regulation of the heart rate variability subjected to mental stress through the arithmetic calculation test. Material and Method: A non-observational quasi-experimental study was performed without control group before and after; the population constituted by 10 patients and the sample occupied the total of the population, in the Laboratory of Basic Sciences of the University of Medical Sciences of Santiago de Cuba Faculty No. 1 (March 2016-August 2018. The statistical analysis was performed by means of a set of statisticians contained in the SSPS version 21 package. Nonparametrictechniques are used when checking the small size of the sample. Results: Within the non-linear parameters that were modified with the stressor were SD1 (26.64 ± 15.33), SD2 / SD1 ratio (2.53 ± 0.68), Sample entropy (1.43±0) , 25), short-term fluctuation (1.28 ± 0.16), CorrelationDimension (2.41±1.52), maximum linear length (190.10 ± 120.12), recurrent frequency (27,10 ± 5,26), determinism (97.61 ± 1.28), multiscale entropy, minimum value (1.41 ± 0.65) and multiscale entropy, maximum value (2.08 ± 0.30). Conclusions: The nonlinear parameters in the autonomic cardiovascular regulation of the SD2 / SD1 relationship, short-term fluctuation, maximum linear length, recurrent frequency, determinism and multiscale entropy experienced an increase in patients subjected to mental stress through the arithmetic calculation test. . The SD1, Correlationdimension and Simple Entropy parameters experienced a decrease in patients subjected to mental stress through the arithmetic calculation test.

Introduction: In recent years the relationship between the systematic practice of physical exercise, cardiovascular dynamics and the functioning of the autonomic nervous system has been recognized. Objective: To determine the modifications that nonlinear parameters undergo in the autonomic cardiovascular regulation of the heart rate variability with the systematic practice of physical exercise. Methodological Design: Retrospective cohort analytical study in the period from February 2016 to August 2018. Universe and sample of 36 individuals (Group 1: 18 high performance baseball athletes, Group 2: 18 students from the University of Medical Sciences of Santiago de Cuba). The data were collected in the Biomedical Basic Sciences Laboratory of the University's Faculty 1, through the 8-channel PowerLab polygraph, and stored using the Kubios Software version 3.0.4 Premium.
Results: Statistically significant differences were found in heart rate values (p = 0.000); SD1 (p = 0.025); SD2 / SD1 ratio (p = 0.007); sample entropy (p = 0.011); short-term fluctuations alpha 1 (p = 0.019); linear average length (p = 0.016); linear maximum length (p = 0.001); recurrence rate (p = 0.034); determinism (p = 0.010) and Shannon entropy (p = 0.015). The parameters of SD1 (C = 906) and sample entropy (C = 712) were significantly associated with a heart rate ≤ 70 beats / min. Conclusions: With the systematic practice of physical exercise, the non-linear dynamics of the autonomic cardiovascular regulation of the heart rate variability undergoes modifications that respond to a better adaptability of the autonomic nervous system, and to a greater capacity to regulate cardiovascular function.