ABSTRACT
The aim of the present study was to determine whether estrogen therapy (ET) reduces alterations of the autonomic control of heart rate (HR) due to hypoestrogenism and aging. Thirteen young (24 ± 2.6 years), 10 postmenopausal (53 ± 4.6 years) undergoing ET (PM-ET), and 14 postmenopausal (56 ± 2.6 years) women not undergoing ET (PM) were studied. ET consisted of 0.625 mg/day conjugated equine estrogen. HR was recorded continuously for 8 min at rest in the supine and sitting positions. HR variability (HRV) was analyzed by time (SDNN and rMSSD indices) and frequency domain methods. Power spectral components are reported as normalized units (nu) at low (LF) and high (HF) frequencies, and as LF/HF ratio. Intergroup comparisons: SDNN index was higher in young (median: supine, 47 ms; sitting, 42 ms) than in PM-ET (33; 29 ms) and PM (31; 29 ms) women (P < 0.05). PM showed lower HFnu, higher LFnu and higher LF/HF ratio (supine: 44, 56, 1.29; sitting: 38, 62, 1.60) than the young group in the supine position (61, 39, 0.63) and the PM-ET group in the sitting position (57, 43, 0.75; P < 0.05). Intragroup comparisons: HR was lower in the supine than in the sitting position for all groups (P < 0.05). The HRV decrease from the supine to the sitting position was significant only in the young group. These results suggest that HRV decreases during aging. ET seems to attenuate this process, promoting a reduction in sympathetic activity on the heart and contributing to the cardioprotective effect of estrogen hormones.
Subject(s)
Adult , Female , Humans , Middle Aged , Autonomic Nervous System/drug effects , Estrogen Replacement Therapy , Estrogens, Conjugated (USP)/administration & dosage , Heart Rate/drug effects , Heart/innervation , Postmenopause/physiology , Autonomic Nervous System/physiology , Cross-Sectional Studies , Cardiovascular Diseases/prevention & control , Heart Rate/physiology , PostureABSTRACT
Several methods are used to estimate anaerobic threshold (AT) during exercise. The aim of the present study was to compare AT obtained by a graphic visual method for the estimate of ventilatory and metabolic variables (gold standard), to a bi-segmental linear regression mathematical model of Hinkley's algorithm applied to heart rate (HR) and carbon dioxide output (VCO2) data. Thirteen young (24 ± 2.63 years old) and 16 postmenopausal (57 ± 4.79 years old) healthy and sedentary women were submitted to a continuous ergospirometric incremental test on an electromagnetic braking cycloergometer with 10 to 20 W/min increases until physical exhaustion. The ventilatory variables were recorded breath-to-breath and HR was obtained beat-to-beat over real time. Data were analyzed by the nonparametric Friedman test and Spearman correlation test with the level of significance set at 5 percent. Power output (W), HR (bpm), oxygen uptake (VO2; mL kg-1 min-1), VO2 (mL/min), VCO2 (mL/min), and minute ventilation (VE; L/min) data observed at the AT level were similar for both methods and groups studied (P > 0.05). The VO2 (mL kg-1 min-1) data showed significant correlation (P < 0.05) between the gold standard method and the mathematical model when applied to HR (r s = 0.75) and VCO2 (r s = 0.78) data for the subjects as a whole (N = 29). The proposed mathematical method for the detection of changes in response patterns of VCO2 and HR was adequate and promising for AT detection in young and middle-aged women, representing a semi-automatic, non-invasive and objective AT measurement.
Subject(s)
Adult , Female , Humans , Middle Aged , Anaerobic Threshold/physiology , Carbon Dioxide/metabolism , Exercise Test/methods , Heart Rate/physiology , Algorithms , Electrocardiography , Models, TheoreticalABSTRACT
OBJETIVO: Analisar e comparar a variabilidade da freqüência cardíaca (VFC), em repouso, de homens e mulheres de meia-idade. MÉTODOS: Foram estudados 10 homens (54 ± 3,2 anos) e 14 mulheres na pós-menopausa (56 ± 2,6 anos) que não faziam uso de terapia hormonal. A freqüência cardíaca (FC) e os intervalos R-R foram obtidos a partir do eletrocardiograma, batimento a batimento, durante 8 minutos em repouso, nas posições supina e sentada. A VFC foi analisada no domínio da freqüência, usando a transformada rápida de Fourier, por meio da qual foram obtidas as bandas de baixa (BF) e alta freqüência (AF), as quais foram expressas em unidades normalizadas (AFun) e (BFun) e na razão BF/AF. Foram utilizados os testes estatísticos não-paramétricos de Mann-Whitney e de Wilcoxon, com nível de significância de alfa= 5 por cento. RESULTADOS: Na comparação intergrupo, as mulheres apresentaram maiores valores da banda AFun e menores valores da banda BFun e da razão BF/AF em relação aos homens, diferenças essas significativas (p<0,05). Na comparação intragrupo, não foram observadas diferenças significativas nos índices de VFC entre as posições supina e sentada para os 2 grupos estudados. CONCLUSÃO: Nossos resultados mostram uma maior modulação vagal e menor simpática no controle autonômico da FC para as mulheres em comparação aos homens de mesma idade, o que sugere que as diferenças autonômicas relacionadas ao gênero não se devem unicamente aos níveis hormonais de estrogênio, uma vez que as mulheres estudadas já se encontravam na fase pós-menopausa. Outros fatores podem estar contribuindo para essas diferenças.
OBJECTIVE: To analyze and compare heart rate variability (HRV) in middle-aged men and women under resting conditions. METHOD: Ten men (54 ± 3.2 years) and fourteen postmenopausal women (56 ± 2.6 years) who were not using hormonal therapy were studied. Heart rates (HR) and R-R intervals (iR-R) on a beat-to-beat basis were obtained from electrocardiograms over an eight-minute period under resting conditions, in the supine and sitting positions. The HRV was analyzed in the frequency domain by means of fast Fourier transforms and the low (LF) and high (HF) frequency bands were obtained and presented as normalized units (LFnu and HFnu) and the LF/HF ratio. Wilcoxon and Mann-Whitney non-parametric statistical tests were used, with the significance level set at 5 percent. RESULTS: Comparing between the groups, the women presented significantly higher HFnu and lower LFnu and LF/HF ratios than did the men (p<0.05). Comparing within the groups, no significant differences (p>0.05) were found in the HRV indexes between the supine and sitting positions for either study group. CONCLUSION: Our results show greater vagal modulation and lower sympathetic activity in autonomic heart rate control among women than among men of similar age. This suggests that the gender-related autonomic differences are not solely dependent on estrogen levels, since the women studied were already postmenopausal. Other factors may be contributing towards these differences.
ABSTRACT
O controle autonomico do coracao pode ser investigado a partir da analise da variabilidade da requencia cardiaca (VFC). Sabe-se que o aparecimento de doencas cardiovasculares (DCV) em mulheres aumenta com a idade, principalmente apos a menopausa, quando o risco torna-se similar ao observado em homens. Assim, o objetivo deste trabalho e analisar e comparar a VFC de homens de meia-idade e de mulheres pos-menopausa em condicoes de repouso. Foram estudados dois grupos saudaveis e sedentarios, sendo 10 homens de meia-idade (52,6 +- 2,63 anos) e 10 mulheres pos-menopausa (56,8+-5,09 anos) que nao faziam uso de terapia de reposicao hormonal. A frequencia cardiaca e os intervalos R-R (iR-R) foram obtidos a partir de eletrocardiograma em tempo real, batimento a batimento, durante 6 minutos em condicoes de repouso, nas posicoes supina(S) e sentada(SE). Para analise da VFC foram calculados os indices RMSM e RMSSD dos iR-R em milissegundo(ms). Nao foram observadas diferencas estatisticamente significativas nos valores dos indices RMSM e RMSSD entre os homens e as mulheres e entre as posicoes supina e sentada de ambos os grupos. A reducao da VFC observada em ambos os grupos estudados sugere similar decrescimo da modulacao parasimpatica sobre o coracao, fato que pode contribuir para o aumento do risco de DCV observado nessa faixa etaria em ambos os sexos