RESUMO
In studies of autonomic regulation during orthostatic challenges only a few nonlinear methods have been considered without investigating the effect of gender in young controls. Especially, the temporal development of the autonomic regulation has not yet been explicitly analyzed using short-term segments in supine position, transition and orthostatic phase (OP). In this study, nonlinear analysis of cardiovascular and respiratory time series was performed to investigate how nonlinear indices are dynamically changing with respect to gender during orthostatic challenges. The analysis was carried out using shifted short-term segments throughout a head-up tilt test in 24 healthy subjects, 12 men (26 ± 4 years) and 12 age-matched women (26 ± 5 years), at supine position and during OP at 70°. The nonlinear methods demonstrated statistical differences in the autonomic regulation between males and females. Orthostatic stress caused significantly decreased heart rate variability due to increased sympathetic activity mainly in men, already at the beginning and during the complete OP, revealed by (a) increased occurrence of specific word types with constant fluctuations as pW111 from symbolic dynamics, (b) augmented fractal correlation properties by the short-term index alpha1 from detrended fluctuation analysis, (c) increased slope indices (21ati and 31ati) from auto-transinformation and (d) augmented time irreversibility indices demonstrating more temporal asymmetries and nonlinear dynamics in men than in women. After tilt-up, both men and women increased their sympathetic activity but in a different way. Time-dependent gender differences during orthostatic challenge were shown directly between men and women or indirectly comparing baseline and different temporal stages of OP. The proposed dynamical study of autonomic regulation has the advantage of screening the fluctuations of the sympathetic and vagal activities that can be quantified by the temporal behavior of nonlinear indices. The findings in this paper strongly suggest the need for gender separation in studies of the dynamics of autonomic regulation during orthostatic challenge.
Assuntos
Sistema Nervoso Autônomo/fisiologia , Caracteres Sexuais , Teste da Mesa Inclinada , Adulto , Algoritmos , Entropia , Feminino , Frequência Cardíaca/fisiologia , Hemodinâmica , Humanos , Masculino , Dinâmica não LinearRESUMO
The cardiovascular and respiratory autonomic nervous regulation has been studied mainly by hemodynamic responses during different physical stressors. In this study, dynamics of autonomic response to an orthostatic challenge was investigated by hemodynamic variables and by diverse linear and nonlinear indices calculated from time series of beat-to-beat intervals (BBI), respiratory cycle duration (RESP), systolic (SYS) and diastolic (DIA) blood pressure. This study included 16 young female patients (SYN) with vasovagal syncope and 12 age-matched female controls (CON). The subjects were enrolled in a head-up tilt (HUT) test, breathing normally, including 5min of baseline (BL, supine position) and 18min of 70° orthostatic phase (OP). To increase the time resolution of the analysis the time series were segmented in five-minute overlapping windows with a shift of 1min. Hemodynamic parameters did not show any statistical differences between SYN and CON. Time domain linear analysis revealed increased respiratory frequency and increased blood pressure variability (BPV) in patients during OP meaning increased sympathetic activity and vagal withdrawal. Frequency domain analysis confirmed a predominance of sympathetic tone by steadily increased values of low over high frequency power in BBI and of low frequency power in SYS and DIA in patients during OP. The nonlinear analysis by symbolic dynamics seemed to be highly suitable for differentiation of SYN and CON in the early beginning of OP, i.e., 5min after tilt-up. In particular the index SYS_plvar3 showed less patterns of low variability in patients reflecting a steadily increase in both BPV and sympathetic activity. The proposed dynamical analysis could lead to a better understanding of the temporal underlying mechanisms in healthy subjects and patients under orthostatic stress.
Assuntos
Postura , Síncope Vasovagal/etiologia , Adulto , Estudos de Casos e Controles , Feminino , Humanos , Modelos Lineares , Adulto JovemRESUMO
Early treatment by thyroid hormone in congenital hypothyroidism (CH) prevents for mental retardation, but the autonomic condition could well remain impaired. The aim of this study was to get insights about the cardiovascular regulation of CH children by analysing their heart rate variability (HRV) data. RR-interval data of 34 early treated CH children, 24 to 48 months of age, were collected at rest in a clinical environment. In all these cases, CH resulted from an abnormal development of thyroid gland. Data from 29 age matched-controls were also collected in a scholar environment. Short time series were then analysed in time and frequency domains. Detrended fluctuation analysis (DFA) was also applied to obtain the scaling exponent α(1). We found that the HRV obtained from children with CH is diminished as suggested by statistical differences (p<0.05) in the following parameters: RMSDD, pNN20, total power, LF and HF. However, no significant differences were found in the LF/HF ratio, the central frequencies of the LF and HF bands, as well as in α(1). Given that the significant differences were basically reflected in static parameters rather than in the frequency distribution or scale-invariant behaviour of the studied data, we consider that the analysis points toward the effect of treatment on rising heart rate by the thyroid hormone, and not necessarily toward any residual autonomic dysfunction, as the dominant underlying cause of the diminished HRV exhibited by CH children.
Assuntos
Sistema Nervoso Autônomo/fisiopatologia , Hipotireoidismo Congênito/fisiopatologia , Frequência Cardíaca/fisiologia , Pré-Escolar , Interpretação Estatística de Dados , Eletrocardiografia , Feminino , Hemodinâmica/fisiologia , Humanos , Lactente , Masculino , Dinâmica não Linear , Glândula Tireoide/crescimento & desenvolvimento , Glândula Tireoide/fisiopatologiaRESUMO
PURPOSE: This study examines the effect of static and dynamic leg exercises on heart rate variability (HRV) and blood pressure variability (BPV) in humans. METHODS: 10 healthy male subjects were studied at rest, during static exercise performed at 30% of maximal voluntary contraction (SX30), and during dynamic cycling exercises done at 30% of VO2max (DX30) and at 60% of VO2max (DX60). Respiration, heart rate, and blood pressure signals were digitized to analyze temporal and spectral parameters involving short and overall indexes (SD, deltaRANGE, RMSSD, Total power), power of the low (LF), middle (MF), and high (HF) frequency components, and the baroreceptor sensitivity by the alphaMF index. RESULTS: During SX30, indexes of HRV as SD, deltaRANGE, Total power, and MF in absolute units increased in relation with rest values and were significantly higher (P < 0.001) than during DX30 and DX60; HF during SX30, in normalized and absolute units, was not different of the rest condition but was higher (P < 0.001) than HF during DX30 and DX60. Parameters of BPV as SD and deltaRANGE increased (P < 0.001) during both type of exercises, and significant (P < 0.01) increments were observed on MF during SX30 and DX30; systolic HF was attenuated during DX30 (P < 0.05), whereas diastolic HF was augmented during DX60 (P < 0.001). Compared with rest condition, the alphaMF index decreased (P < 0.01) only during dynamic exercises. CONCLUSION: Because HRV and BPV response is different when induced by static or dynamic exercise, differences in the autonomic activity can be advised. Instead of the vagal withdrawal and sympathetic augmentation observed during dynamic exercise, the increase in the overall HRV and the MF component during static exercise suggest an increased activity of both autonomic branches.
Assuntos
Pressão Sanguínea/fisiologia , Exercício Físico , Frequência Cardíaca/fisiologia , Adulto , Eletrocardiografia , Teste de Esforço , Humanos , Perna (Membro) , Masculino , Pressorreceptores/fisiologia , RespiraçãoRESUMO
Body density by hydrostatic method and anthropometric variables were measured in 29 young males, natives of Mexico City, in order to test the validity of nine currently used equations for predicting body composition. Tested equations were those reported for body density by Sloan, Wilmore, Jackson and Pollock, Durnin and Womersley, Lohman, and Pollock et al.; for lean body weight by Wilmore, and Hume-Rathbun; and for fat percentage by Yuhasz. Mean values for body density, fat percentage and lean body weight obtained by hydrostatic weighing were 1.0560 +/- 0.0149 kg/l, 18.9 +/- 6.7%, and 52.6 +/- 5.3 kg, respectively, while the means for predicted body density using the six regression equations varied from 1.0538 to 1.0654 kg/l, with a range of correlation from 0.846 to 0.900, and total errors from 0.0077 to 0.0124 kg/l. Mean lean body weight predicted by Wilmore was 55.7 +/- 5.9 kg, with an R of 0.902 and a total error of 4.0 kg, while values given in the same order by Hume-Rathbun were 52.8 +/- 4.8 kg, R of 0.892 and total error of 2.3 kg. Mean fat percentage predicted by Yuhasz was 17.8 +/- 5.6%, R of 0.869 and total error of 3.5%. Although by analysis of variance there were no significant differences among the means of the models, statistical analysis of individual differences between predicted and measured values were significant in six of them.(ABSTRACT TRUNCATED AT 250 WORDS)