Cardiovascular coupling during graded postural challenge: comparison between linear tools and joint symbolic analysis

ABSTRACT Background A joint symbolic analysis (JSA) is applied to assess the strength of the cardiovascular coupling from spontaneous beat-to-beat variability of the heart period (HP) and the systolic arterial pressure (SAP) during an experimental protocol inducing a gradual baroreflex unloading evoked by postural change (i.e. graded head-up tilt). Method: The adopted JSA can quantify the degree of association between the HP and SAP variabilities as a function of the time scale of the HP and SAP patterns. Traditional linear tools assessing the HP-SAP coupling strength, such as squared correlation coefficient, squared coherence function, and percentage of baroreflex sequences, were computed as well for comparison. Results: We found that: i) JSA indicated that the strength of the cardiovascular coupling at slow temporal scales gradually increased with the magnitude of the orthostatic challenge, while that at fast temporal scales gradually decreased; ii) the squared correlation coefficient and percentage of baroreflex sequences did not detect this behavior; iii) even though squared coherence function could measure the magnitude of the HP-SAP coupling as a function of the time scale, it was less powerful than JSA owing to the larger dispersion of the frequency domain indexes. Conclusion: Due to its peculiar features and high statistical power, JSA deserves applications to pathological groups in which the link between HP and SAP variabilities is lost or decreased due to the overall depression or impairment of the cardiovascular control.

The relationship between dual-task and cognitive performance among elderly participants who exercise regularly

BACKGROUND: The dual-task performance is associated with the functionality of the elderly and it becomes more complex with age. OBJECTIVE: To investigate the relationship between the Timed Up and Go dual task (TUG-DT) and cognitive tests among elderly participants who exercise regularly. METHOD: This study examined 98 non-institutionalized people over 60 years old who exercised regularly. Participants were assessed using the TUG-DT (i.e. doing the TUG while listing the days of the week in reverse order), the Montreal Cognitive Assessment (MoCA), the Clock Drawing Test (CDT), and the Mini Mental State Examination (MMSE). The motor (i.e. time and number of steps) and cognitive (i.e. number of correct words) data were collected from TUG-DT . We used a significance level of α=0.05 and SPSS 17.0 for all data analyses. RESULTS: This current elderly sample featured a predominance of women (69.4%) who were highly educated (median=10 years of education) compared to Brazilian population and mostly non-fallers (86.7%). The volunteers showed a good performance on the TUG-DT and the other cognitive tests, except the MoCA, with scores below the cutoff of 26 points. Significant and weak correlations were observed between the TUG-DT (time) and the visuo-spatial/executive domain of the MoCA and the MMSE. The cognitive component of the TUG-DT showed strong correlations between the total MoCA performance score and its visuo-spatial/executive domain. CONCLUSIONS: The use of the TUG-DT to assess cognition is promising; however, the use of more challenging cognitive tasks should be considered when the study population has a high level of education. .

The relationship between cardiac autonomic function and clinical and angiographic characteristics in patients with coronary artery disease / Relação entre a modulação autonômica cardíaca e as características clínicas e angiográficas de pacientes com doença arterial coronariana

BACKGROUND: A reduction in heart rate variability (HRV) is considered an important indicator of autonomic dysfunction. OBJECTIVES: The aims of this study were to evaluate the presence of autonomic dysfunction measured by HRV in patients with coronary artery disease (CAD) and to compare them with normal subjects. METHODS: A sample of 52 men (mean age 54±5.39 years) was allocated into three groups: obstructive CAD ≥50 percent (CAD+ n=18), obstructive CAD <50 percent, (CAD- n=17) and apparently healthy controls (CG n=17). Heart rate (HR) was measured at rest using a Polar®S810i for 15 min. HRV was analyzed via Shannon entropy (SE) and symbolic analysis (0V and 2ULV), which relate to sympathetic and vagal predominance, respectively. Statistical analysis included the Kruskal-Wallis test and multivariate analysis (p<0.05). RESULTS: The CAD+ group presented lower SE and 2ULV percent values and higher 0V percent compared to CAD- and control groups (p<0.05). In the multivariate analysis, the presence of the clinical characteristics such as myocardial infarction and revascularization in the CAD+ group lead to a lower SE and higher 0V compared to the CAD- group. The use of angiotensin converting enzymes led to a higher SE in the CAD- group compared to the CAD+ (p<0.05). CONCLUSION: In uncomplicated CAD+ patients the patterns of HRV have a lower complexity, a greater sympathetic modulation and a lower parasympathetic modulation compared to CAD- and control groups in supine resting conditions. These results indicate that autonomic heart dysfunction is related to the degree of coronary occlusion and cardiac compromise.

CONTEXTUALIZAÇÃO: A redução da variabilidade da frequência cardíaca (VFC) é considerada como um importante marcador de disfunção autonômica. OBJETIVOS: Avaliar a VFC em pacientes com doença arterial coronariana (DAC) e compará-los com sujeitos saudáveis. MÉTODOS: Cinquenta e dois homens (53±7,2 anos), divididos em três grupos, sendo dois grupos com obstrução coronariana (DAC+ com obstrução ≥50 por cento, n=17 e DAC+ com obstrução ≥50 por cento, n=18) e um grupo controle (GC, n=17). A frequência cardíaca (FC) foi captada batimento a batimento, a partir do Polar®S810i, em repouso supino, durante 15 minutos. A análise da VFC foi feita pelos cálculos da entropia de Shannon (ES) e pelos padrões da análise simbólica (0V e 2ULV por cento), relacionados à predominância simpática e vagal, respectivamente. A análise estatística incluiu o teste de Kruskal-Wallis e a análise multivariada (p<0,05) RESULTADOS:O grupo DAC+ apresentou menores valores de ES e 2ULV por cento e maior 0V quando comparado aos grupos DAC- e CG. Na análise multivariada, observou-se menor ES e maior 0V na presença das características clínicas prévias, como infarto e revascularização do miocárdio no grupo DAC+ comparado ao grupo DAC-. O uso de inibidores da enzima conversora de angiotensina contribuiu para maior ES do grupo DAC- comparado ao DAC+. CONCLUSÃO: Na DAC+ não complicada, os padrões da VFC apresentam menor complexidade, maior modulação autonômica simpática e menor modulação parassimpática comparativamente ao DAC- e ao GC em repouso supino. Esses resultados indicam que a disfunção autonômica cardíaca está relacionada ao grau de oclusão coronariana e ao comprometimento cardíaco.

Torque, myoeletric sygnal and heart rate responses during concentric and eccentric exercises in older men / Torque, sinal eletromiográfico e respostas da frequência cardíaca durante exercícios concêntrico e excêntrico em homens idosos

BACKGROUND: The literature reports that the eccentric muscular action produces greater force and lower myoelectric activity than the concentric muscular action, while the heart rate (HR) responses are bigger during concentric contraction. OBJECTIVES: To investigate the maximum average torque (MAT), surface electromyographic (SEMG) and the heart rate (HR) responses during different types of muscular contraction and angular velocities in older men. METHODS: Twelve healthy men (61.7±1.6years) performed concentric (C) and eccentric (E) isokinetic knee extension-flexion at 60º/s and 120º/s. SEMG activity was recorded from vastus lateralis muscle and normalized by Root Mean Square - RMS (µV) of maximal isometric knee extension at 60º. HR (beats/min) and was recorded at rest and throughout each contraction. The data were analyzed by the Friedman test for repeated measures with post hoc Dunn's test (p<0.05). RESULTS: The median values of MAT (N.m/kg) was smaller and the RMS (µV) was larger during concentric contraction (C60º/s=2.80 and 0.99; C120º/s=2.46 and 1.0) than eccentric (E60º/s=3.94 and 0.85; E120º/s=4.08 and 0.89), respectively. The HR variation was similar in the four conditions studied. CONCLUSION: The magnitude of MAT and RMS responses in older men were dependent of the nature of the muscular action and independent of the angular velocity, whereas HR response was not influenced by these factors.

CONTEXTUALIZAÇÃO: A literatura refere que a ação muscular excêntrica produz maior força e menor atividade mioelétrica que a concêntrica, enquanto a resposta da frequência cardíaca (FC) é maior durante a contração concêntrica que durante a excêntrica. OBJETIVOS: Investigar as respostas de torque médio máximo (TMM), eletromiografia de superfície (EMGs) e FC durante diferentes tipos de contração muscular e velocidades angulares em homens idosos. MATERIAIS E MÉTODOS: Doze homens saudáveis (61,7±1,6 anos) realizaram flexões e extensões do joelho concêntrica (C) e excêntrica (E) em 60º/s e 120º/s. Registrou-se a atividade EMGs do músculo vasto lateral e normalizou-se pela RMS (µV) da extensão isométrica máxima do joelho em 60º. A FC (bpm) foi registrada em repouso e durante cada contração. Os dados foram analisados utilizando-se o teste de Friedman para medidas repetidas com post hoc de Dunn (p<0,05). RESULTADOS: Os valores médios de TMM (N.m/kg) foram menores e os de RMS (µV) foram maiores (p<0,05) nas contrações concêntricas (C60º/s=2,80 e 0,99; C120º/s=2,46 e 1,0) comparativamente com as excêntricas (E60º/s=3,94 e 0,85; E120º/s=4,08 e 0,89), respectivamente. Já a variação da FC foi semelhante nas quatro condições estudadas. CONCLUSÃO: A magnitude das respostas de TMM e RMS em homens idosos foi dependente da natureza da ação muscular e independente da velocidade angular, enquanto as respostas da FC não foram influenciadas por esses fatores.