Abstract Analysis of beat-to-beat heart rate variability (HRV) provides information of cardiac vagal outflow to the sinus node. Some methodological problems might, however, be involved in the analysis of cardiac vagal outflow from ambulatory Holter recordings, such as saturation, physical activity, and abrubt prolongations of R-R intervals unrelated to respiration. The purpose of this thesis was to assess the physiological basis of beat-to-beat HRV and to develop and assess new methods for the quantification of cardiac autonomic modulation from ambulatory Holter recordings. The study population consisted of 89 healthy volunteers (age 24 ± 4 years) and 590 patients with a recent acute myocardial infarction (AMI, age 61 ± 10 years). The relationship between R-R interval length and the high-frequency (HF) spectral power of the R-R intervals was assessed in 76 healthy subjects and 82 post-AMI patients. The effects of aerobic exercise training on the dynamics between R-R interval and HF power were evaluated by means of a controlled 8-week training intervention (n = 17). The effects of sympathetic activation and concomitant sympathetic and vagal outflow on beat-to-beat HR dynamics were studied in laboratory conditions (n = 13). A new method for quantifying beat-to-beat HRV from the R-R interval lengths where the relationship between HF power and R-R interval is most linear was developed to avoid the confounding effects of possible saturation, physical activity, and random R-R interval dynamics. The clinical significance of the new method was assessed in a series of 590 post-AMI patients. Saturated HF R-R interval dynamics, expressed as a lack of increase in HF power despite an increased R-R interval, was observed in 35 healthy subjects and 9 post-AMI patients. In the training study, 7 subjects out of a total of 17 had saturated HF power before the intervention. After the training period, 5 new cases of saturated HF power were observed. In laboratory conditions, co-activation of sympathetic and vagal outflow resulted in random R-R interval dynamics. In post-AMI patients, HF power analyzed exclusively from the R-R intervals where the relationship between the R-R interval and HF power was most linear (Vindex) predicted independently the occurrence of SCD among post-AMI patients, while traditionally analyzed HF power did not. In conclusion, the saturation of beat-to-beat HRV in ambulatory conditions is a common phenomenon. The prevalence of saturated HF power increases due to enhanced cardiac vagal outflow induced by aerobic training. Finally, the novel analysis of vagally mediated HRV (Vindex) provides unique information that cannot be obtained by traditional analysis of HF R-R interval dynamics.

Submitted by isabela.moljf@hotmail.com (isabela.moljf@hotmail.com) on 2017-05-16T13:02:47Z No. of bitstreams: 1 luiziralbertodesouzalimajunior.pdf: 1017703 bytes, checksum: f428c0dd46d8e916774da450732d3c28 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-05-17T16:14:41Z (GMT) No. of bitstreams: 1 luiziralbertodesouzalimajunior.pdf: 1017703 bytes, checksum: f428c0dd46d8e916774da450732d3c28 (MD5) / Made available in DSpace on 2017-05-17T16:14:41Z (GMT). No. of bitstreams: 1 luiziralbertodesouzalimajunior.pdf: 1017703 bytes, checksum: f428c0dd46d8e916774da450732d3c28 (MD5) Previous issue date: 2012-03-27 / Durante o repouso, a atividade colinérgica predomina sobre o nódulo sinoatrial. Assim o mecanismo de controle da Frequência Cardíaca pela atividade vagal, juntamente com a diminuída demanda energética, irão determinar a frequência cardíaca de repouso (FCR) de um indivíduo fisiologicamente íntegro. A FCR possui importância reconhecida como indicador independente de saúde cardiovascular, relação com doenças não cardiovasculares, além da sua utilização em fórmulas, questionários e protocolos relacionados ao exercício físico. Apesar da reconhecida notoriedade da FCR na prática clínica e física, ainda não foi estabelecido um modo de medição com evidências científicas, que sustentam a existência de um padrão. Desta forma o presente estudo procurou investigar, através de dois artigos, de que forma a FCR vem sendo utilizada na prática profissional de profissionais de Educação Física, no que tange as formas de medição (tempo, posição), cuidados pré e durante (substâncias interferentes e condições ambientais) e objetivos da medição. Além disso, testar e propor aplicações práticas da FCR mediante tempo e postura corporal de medição. No primeiro estudo foram entrevistados profissionais de Educação Física, através de um questionário composto por oito questões sobre a forma de utilização da FCR, tais como, importância da variável, período de repouso antes e durante a mensuração, posição corporal, equipamento, e condições ambientais (temperatura, luminosidade, substâncias interferentes). De acordo com os resultados apresentados pelas respostas dos questionários, pôde-se concluir que o uso da FCR pelos profissionais de Educação Física, não possui uma padronização para sua medição, havendo divergências estatisticamente significativas nos critérios de utilização e avaliação. No segundo estudo foram avaliados 39 indivíduos jovens (21 homens e 18 mulheres), submetidos a avaliações em repouso em duas posições, supina e sentada, cada uma com a duração de 60 minutos. Os resultados mostraram que as medições realizadas em apenas cinco minutos não eram diferentes estatisticamente das medições realizadas nos 60 minutos. Além disso, na posição sentada a FCR é 12% maior que na posição supina, retratando diferença estatística. Estes resultados se repetiram entre gêneros e entre indivíduos mais e menos ativos. Portanto, de acordo com os resultados dos estudos, pôde- se verificar a inexistência de consensos para a medição da FCR entre os profissionais de educação física. Entretanto o presente estudo propõe a medição para homens e mulheres jovens mais e menos ativos, utilizando 5 minutos de repouso, registrandose a média deste período e observando a posição medida para as devidas correções. / During rest, cholinergic activity predominates over the sympathetic system. Thus the control mechanism of Heart Rate by vagal activity, together with the reduced energy requirements, will determine the frequency resting heart rate (RHR) of an individual physiologically intact. The RHR has recognized as important independent predictor of health cardiovascular disease compared with non-cardiovascular, beyond its use in formulas, questionnaires and protocols related to exercise physical. Despite the notoriety of the RHR recognized in clinical practice and physical not yet established a method of measuring with scientific evidence that support the existence of a pattern. Thus the present study sought investigate, by means of two articles, how the RHR has been used in professional practice of physical education professionals, regarding the forms of measurement (time, location), and during antenatal care (substances interference and environmental conditions) and objective measurement. Furthermore, test and propose practical applications of RHR through time and body posture measurement. In the first study were interviewed education professionals Physics, through a questionnaire consisting of eight questions on how to use of the RHR, such as importance of the variable, rest period before and during the measurement, body position, equipment, and conditions environmental (temperature, light, interfering substances). According with the results presented by the questionnaire responses, we conclude that the use of RHR by physical education professionals, has no a standard for its measurement, with differences statistically significant use and the criteria for evaluation. In the second study were studied 39 young subjects (21 men and 18 women) who underwent evaluations at rest in two positions, supine and sitting positions, each with for 60 minutes. The results show that measurements made on only five minutes were not statistically different measurements performed in 60 minutes. Furthermore, in the sitting position is 12% higher HRH that in the supine position, portraying statistical difference. These results repeated between genders and between more and less active individuals. Therefore the According to the results of the studies, it was possible to verify the absence of consensus for the measurement of HRH among physical education teachers. However the present study proposes to measure for young men and women more and less active, using 5-minute rest, recording the average this period and noting the position measured for the corrections.