Linear and nonlinear analysis of heart rate variability in healthy subjects and after acute myocardial infarction in patients

The objectives of this study were to evaluate and compare the use of linear and nonlinear methods for analysis of heart rate variability (HRV) in healthy subjects and in patients after acute myocardial infarction (AMI). Heart rate (HR) was recorded for 15 min in the supine position in 10 patients with AMI taking β-blockers (aged 57 ± 9 years) and in 11 healthy subjects (aged 53 ± 4 years). HRV was analyzed in the time domain (RMSSD and RMSM), the frequency domain using low- and high-frequency bands in normalized units (nu; LFnu and HFnu) and the LF/HF ratio and approximate entropy (ApEn) were determined. There was a correlation (P < 0.05) of RMSSD, RMSM, LFnu, HFnu, and the LF/HF ratio index with the ApEn of the AMI group on the 2nd (r = 0.87, 0.65, 0.72, 0.72, and 0.64) and 7th day (r = 0.88, 0.70, 0.69, 0.69, and 0.87) and of the healthy group (r = 0.63, 0.71, 0.63, 0.63, and 0.74), respectively. The median HRV indexes of the AMI group on the 2nd and 7th day differed from the healthy group (P < 0.05): RMSSD = 10.37, 19.95, 24.81; RMSM = 23.47, 31.96, 43.79; LFnu = 0.79, 0.79, 0.62; HFnu = 0.20, 0.20, 0.37; LF/HF ratio = 3.87, 3.94, 1.65; ApEn = 1.01, 1.24, 1.31, respectively. There was agreement between the methods, suggesting that these have the same power to evaluate autonomic modulation of HR in both AMI patients and healthy subjects. AMI contributed to a reduction in cardiac signal irregularity, higher sympathetic modulation and lower vagal modulation.

Avaliação da modulação autonômica da freqüência cardíaca nas posturas supina e sentada de homens jovens sedentários / Evaluation of autonomic heart rate modulation among sedentary young men, in seated and supine postures

OBJETIVO: Avaliar e comparar a modulação autonômica da freqüência cardíaca (FC) em repouso em relação à postura corporal em jovens sedentários. MÉTODOS: Foram estudados 20 homens jovens (22,6 ± 2,5 anos), saudáveis e sedentários. A FC e os intervalos das ondas R (iR-R em ms) do eletrocardiograma (ECG) foram captados em tempo real na derivação DII modificada, com os voluntários em repouso nas posturas supina e sentada, durante 15 minutos. Os dados dos iR-R foram analisados, no domínio do tempo (DT), pelos índices RMSSD, RMSM e pNN50 ( por cento); e no domínio da freqüência (DF) pela análise espectral, transformada rápida de Fourier (FFT), pelas bandas de baixa freqüência (BF) e alta freqüência (AF), expressas em unidades normalizadas (un) e a razão BF/AF. Para análise estatística foi utilizado o teste de correlação Spearman e o teste de Wilcoxon para amostras pareadas com significância de alfa= 5 por cento. RESULTADOS: No DT, os índices RMSSD e pNN50 apresentaram diferenças estatisticamente significantes na comparação entre as posturas supina e sentada (p< 0,05), e o RMSM não apresentou diferença estatisticamente significante na comparação entre as posturas (p> 0,05). No DF, as bandas de BF, AF e a razão BF/AF apresentaram diferença estatisticamente significante na comparação entre as posturas supina e sentada (p< 0,05). CONCLUSÕES: Os resultados mostraram que, com a mudança postural, ocorreram ajustes autonômicos do sistema nervoso parassimpático e simpático sobre o controle da FC, o que pode ser atribuído à integridade do sistema neurocárdico.

OBJECTIVE: To evaluate and compare the autonomic heart rate (HR) modulation, under resting conditions in relation to body posture, in sedentary young adults. METHODS: Twenty young healthy and sedentary men aged 22.6 ± 2.5 years participated in the study. The HR and R-R intervals (in ms) of the electrocardiogram (EKG) were obtained in real time using the modified DII derivation, with the volunteers at rest in the supine and seated positions, for 15 minutes. The R-R data were analyzed in the time domain, by means of the RMSSD, RMSM and pNN50 ( percent) indices; and in the frequency domain, by means of spectral analysis and fast Fourier transforms (FFT), using low frequency (LF) and high frequency (HF) bands expressed as normalized units and as the LF/HF ratio. The statistical analysis consisted of the Spearman test for correlation analyses and the Wilcoxon test for paired samples, with significance of alpha= 5 percent. RESULTS: In the time domain, the RMSSD and pNN50 indices demonstrated statistically significant differences between the supine and seated positions (p< 0.05). The RMSM index did not showed any statistically significant difference between the positions (p> 0.05). In the frequency domain, the LF and HF bands and the LF/HF ratio demonstrated statistically significant differences between the supine and seated positions (p< 0.05). CONCLUSIONS: The results demonstrated that, by changing the posture, autonomic adjustments were produced to the parasympathetic and sympathetic nervous systems with regard to HR control. This can be attributed to the integrity of the neurocardiac system.

Autonomic modulation of heart rate of young and postmenopausal women undergoing estrogen therapy

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.

Estudo da modulação autonômica da freqüência cardíaca em repouso de pacientes idosos com doença pulmonar obstrutiva crônica / Study on autonomic heart rate modulation at rest among elderly patients with chronic obstructive pulmonary disease

OBJETIVO: Avaliar a variabilidade da freqüência cardíaca (VFC) de pacientes idosos com doença pulmonar obstrutiva crônica (DPOC) e de idosos saudáveis frente à mudança postural. MÉTODOS: Foram estudados 9 indivíduos com DPOC (70 anos) e 8 saudáveis (68 anos). A freqüência cardíaca e os intervalos R-R (iR-R) do eletrocardiograma foram registrados durante 360 s nas posturas supina e sentada. A VFC foi analisada no domínio do tempo (DT) (índice RMSSD - raiz quadrada da média dos quadrados das diferenças entre os iR-R sucessivos e SDNN - desvio-padrão da média dos iR-R normais em ms) e no domínio da freqüência (DF), pelas bandas de baixa (BF) e alta freqüência (AF) em unidades absolutas (ua) e normalizadas (un), e da razão BF/AF. Para análise intergrupo e intragrupo foram utilizados os testes de Mann-Whitney e Wilcoxon, respectivamente, com nível de significância de p< 0,05 (valores em mediana). RESULTADOS: No DT, o grupo controle (GC) apresentou valores significativamente maiores do RMSSD (14,6 versus 8,3ms) e SDNN (23,0 versus 13,5ms) na postura sentada, quando comparado ao grupo DPOC (GD). No DF, o GC apresentou valores significativamente maiores dos componentes de AF, na posição supina (39,0 versus 7,8 ua) e dos componentes de BF (146,7 versus 24,4 ua) e AF (67,6 versus 22,7 ua), na posição sentada, bem como do espectro total de potência (552,5 versus 182,9ms²). CONCLUSÃO: Pacientes portadores de DPOC apresentaram redução da VFC com diminuição da atividade simpática e vagal e não apresentaram ajustes autonômicos frente à mudança postural, assim como os idosos saudáveis.

OBJECTIVE: To evaluate heart rate variability (HRV) among elderly patients with chronic obstructive pulmonary disease (COPD) and healthy elderly individuals, during postural change. METHOD: Nine individuals with COPD (70 years old) and eight healthy individuals (68 years old) were studied. Heart rate and electrocardiographic R-R intervals (iR-R) were recorded for 360 seconds in the supine and seated positions. HRV was analyzed in the time domain (TD) (RMSSD index, i.e. the root mean square of the squares of the differences between successive iR-R records, and the SDNN index, i.e. the mean standard deviation of normal iR-R in ms) and in the frequency domain (FD), from the low-frequency (LF) and high-frequency (HF) bands in absolute units (au) and normalized units (nu), and the LF/HF ratio. The Mann-Whitney and Wilcoxon Tests respectively were utilized for inter--group and intra-group analysis, with a significant level of p< 0.05 (median values). RESULTS: In TD, the control group (CG) presented significantly higher values for the RMSSD index (14.6 versus 8.3 ms) and the SDNN index (23 versus 13.5 ms) in the seated position, in comparison with the COPD group (DG). In FD, the CG presented significantly higher values for HF components, in the supine position (39 versus 7.8 au), and for LF components (146.7 versus 24.4 au) and HF (67.6 versus 22.7 au), in the seated position, as well as for the total power spectrum (552.5 versus 182.9 ms²). CONCLUSION: Patients with COPD presented reduced HRV with decreased sympathetic and vagal activity. Additionally, neither the COPD patients nor the healthy elderly participants presented autonomic alterations with postural change.

Análise dos índices espectrais da variabilidade da freqüência cardíaca em homens de meia idade e mulheres na pós-menopausa / Analysis of spectral indexes for heart rate variability in middle-aged men and postmenopausal women

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.

Comparação das respostas cardiorrespiratórias entre exercício de carga constante e incremental abaixo, acima e no limiar de anaerobiose ventilatório / Comparison of cardiorespiratory responses between constant and incremental load exercises below, above and at the ventilatory anaerobic threshold

OBJETIVO: Aplicar diferentes metodologias de análise aos dados dos testes contínuo em rampa (TCR) e descontínuo em degrau (TDD) e comparar as respostas das variáveis cardiorrespiratórias. MÉTODOS: 8 homens realizaram teste ergoespirométrico em bicicleta: TCR com incremento de 20 a 25W.min-1 e TDD em degraus de 15min cada baseado no limiar de anaerobiose ventilatório (LAV) do TCR, sendo degrau 1 (70 por centoLAV), degrau 2 (100 por centoLAV) e degrau 3 (130 por centoLAV). O LAV foi determinado pela perda do paralelismo entre consumo de oxigênio (VO2) e produção de dióxido de carbono (VCO2). A freqüência cardíaca (FC bpm),VCO2, VO2, (ml.min-1), VO2, (ml.kg-1.min-1), ventilação (VE L.min-1) do TCR foram analisadas em médias móveis de 8 ciclos respiratórios, respiração-a-respiração e pela regressão linear. No TDD, a média foi aplicada do 3° ao 15°min dos degraus. Na análise estatística foram utilizados o teste de Kolmogorov-Smirnov, ANOVA, post hoc de Tukey-Kramer e regressão linear, p<0,05. RESULTADOS: No pico do exercício houve diferença estatisticamente significante entre respiração-a-respiração e demais metodologias. Na comparação de protocolos: VO2, VCO2, V E foram similares entre LAV e degrau 1 (p>0,05), porém VO2 relativo foi diferente (p<0,05) entre LAV e todos os degraus; a FC mostrou diferença (p<0,05) entre LAV e degrau 3, e na análise entre os três degraus houve diferença (p<0,05). CONCLUSÃO: Os resultados indicam que a regressão linear foi eficaz para estimar as variáveis cardiorrespiratórias. Em relação aos protocolos, verificou-se que para a obtenção no TDD de valores cardiorrespiratórios similares ao LAV do TCR foi necessário diminuir a potência em 30 por cento.

Effects of age and physical activity on the autonomic control of heart rate in healthy men

The effects of the aging process and an active life-style on the autonomic control of heart rate (HR) were investigated in nine young sedentary (YS, 23 ± 2.4 years), 16 young active (YA, 22 ± 2.1 years), 8 older sedentary (OS, 63 ± 2.4 years) and 8 older active (OA, 61 ± 1.1 years) healthy men. Electrocardiogram was continuously recorded for 15 min at rest and for 4 min in the deep breathing test, with a breath rate of 5 to 6 cycles/min in the supine position. Resting HR and RR intervals were analyzed by time (RMSSD index) and frequency domain methods. The power spectral components are reported in normalized units (nu) at low (LF) and high (HF) frequency, and as the LF/HF ratio. The deep breathing test was analyzed by the respiratory sinus arrhythmia indices: expiration/inspiration ratio (E/I) and inspiration-expiration difference (deltaIE). The active groups had lower HR and higher RMSSD index than the sedentary groups (life-style condition: sedentary vs active, P < 0.05). The older groups showed lower HFnu, higher LFnu and higher LF/HF ratio than the young groups (aging effect: young vs older, P < 0.05). The OS group had a lower E/I ratio (1.16) and deltaIE (9.7 bpm) than the other groups studied (YS: 1.38, 22.4 bpm; YA: 1.40, 21.3 bpm; OA: 1.38, 18.5 bpm). The interaction between aging and life-style effects had a P < 0.05. These results suggest that aging reduces HR variability. However, regular physical activity positively affects vagal activity on the heart and consequently attenuates the effects of aging in the autonomic control of HR.

Comparação dos niveis de potencia e da frequencia cardiaca no limiar de anaerobiose determinado por dois metodos indiretos / Comparasion of power output and heart rate levels in anaerobic threshold determinations by two indirect methods

Analisar se protocolos individualizados do tipo rampa podem ser melhor que os do tipo degrau na determinacao do limiar de anaerobiose (LA). Metodo: 10 homens de meia idade (54+-3,25 anos) saudaveis e sedentarios foram submetidos a 2 testes de exercicio fisico dinamico em cicloergometro de frenagem eletromagnetica (Quinton Corival 400). O primeiro teste foi continuo do tipo rampa (TC-R), com incrementos de 15 W/min, ate a exaustao fisica. O segundo teste foi descontinuo do tipo degrau (TD-D). A frequencia cardiaca (FC) foi captada batimento a batimento e as variaveis ventilatorias e metabolicas, respiracao a respiracao, em tempo real. No TC-R o LA foi determinado pela metodlogia visual (media de 3 observadores) de analise das variaveis ventilatorias e metabolicas. Para determinacao do LA no TD-D foi aplicado o modelo matematico e estatistico semiparametrico ao conjunto de dados da FC. Analise estatistica Teste de wilcoxon para amostras pareadas com nivel de significancia (= 5 por cento). Resultados: foi observada diferenca estatisticamente significativa (p< 0,05) entre os valores de potencia no LA determinando no TC-R (66,5w) e no TD-D (45w). Os valores de FC nao foram estatisticamente diferentes (p > 0,05) entre 2 protocolos. Conclusoes: nossos dados mostram que no protocolo com cargas descontinuas, os voluntarios atingem o LA em niveis de potencia inferiores, porem com resposta do trabalho ardiaco similar a do exercicio realizado com protocolo continuo do tipo rampa. Isso sugere que a carga de trabalho durante o treinamento fisico para esses voluntarios devem ser a do protocolo descontinuo

Heart rate variability in athletes and nonathletes at rest and during head-up tilt

The purpose of the present study was to determine if autonomic heart rate modulation, indicated by heart rate variability (HRV), differs during supine rest and head-up tilt (HUT) when sedentary and endurance-trained cyclists are compared. Eleven sedentary young men (S) and 10 trained cyclists (C) were studied. The volunteers were submitted to a dynamic ECG Holter to calculate HRV at rest and during a 70° HUT. The major aerobic capacity of athletes was expressed by higher values of VO2 at anaerobic threshold and peak conditions (P < 0.05). At rest the athletes had lower heart rates (P < 0.05) and higher values in the time domain of HRV compared with controls (SD of normal RR interval, SDNN, medians): 59.1 ms (S) vs 89.9 ms (C), P < 0.05. During tilt athletes also had higher values in the time domain of HRV compared with controls (SDNN, medians): 55.7 ms (S) vs 69.7 ms (C), P < 0.05. No differences in power spectral components of HRV at rest or during HUT were detected between groups. Based on the analysis of data by the frequency domain method, we conclude that in athletes the resting bradycardia seems to be much more related to changes in intrinsic mechanisms than to modifications in autonomic control. Also, HUT caused comparable changes in sympathetic and parasympathetic modulation of the sinus node in both groups.

Avaliação da variabilidade da frequencia cardíaca em repouso de homens saudáveis sedentários e de hipertensos e coronariopatias em treinamento físico / Resting heart rate variability in sedentary healthy men and in in trained men with hipertension and coronary heart disease

O objetivo deste estudo foi avaliar e comparar a variabilidade da frequencia cardiaca(VFC) em repouso supino e sentado de 10 homens de meia idade saudaveis (SA), 9 hipertensos (HA) e 9 com infarto do miocardio (IM), com idade media de 52, 62 e 56 anos, respectivamente. Os voluntarios SA nao praticavam atividade fisica frequentemente e os voluntarios HA e IM participavam de um programa de treinamento fisico aerobico (TFA) ha aproximadamente 3 anos. A frequencia cardiaca (FC) e os intervalos R-R(iR-R - ms) foram coletdos durante 900 s nas posicoes supina e sentada, e os voluntarios foram orientados a manter-se em repouso. Para a analise dos dados de dominio do tempo (DT), foi utilizado o indice RMSSD dos iR-R (ms). Para o dominio da frequencia (DF), foi aplicado um modelo auto-regressivo e obtidas as bandas de frequencia muito baixa (MBF), baixa (BF) e alta (AF), sendo os componentes BF e AF expressos em unidades normalizadas e na razao BF/AF. Foram utilizados os testes estatisticos nao-parametricos de Wilcoxon, de kruskall-Wallis e pos-hoc de Dunn. O nivel de significancia foi de a=5(por cento). Nao foram observadas diferencas estatisticamente significativas nos indices de VFC, avaliados no DT e no DF nas condicoes supino e sentado, nas comparacoes inter e intragrupo. Os resultados que a ausencia de diferencas entre os grupos estudados pode estar relacionada aos efeitos do do TFA realizadopelos HA e IM, comparativamente aos SA

Analise da modulacao autonomica do coracao durante condicoes de repouso em homens de meia idade e mulheres pos-menopausa / Analysis of heart autonomic modulation during resting conditions in middle-aged men and postmenopausal women

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

Effects of aerobic exercise training on heart rate variability during wakefulness and sleep and cardiorespiratory responses of young and middle-aged healthy men

The purpose of the present study was to evaluate the effects of aerobic physical training (APT) on heart rate variability (HRV) and cardiorespiratory responses at peak condition and ventilatory anaerobic threshold. Ten young (Y: median = 21 years) and seven middle-aged (MA = 53 years) healthy sedentary men were studied. Dynamic exercise tests were performed on a cycloergometer using a continuous ramp protocol (12 to 20 W/min) until exhaustion. A dynamic 24-h electrocardiogram was analyzed by time (TD) (standard deviation of mean R-R intervals) and frequency domain (FD) methods. The power spectral components were expressed as absolute (a) and normalized units (nu) at low (LF) and high (HF) frequencies and as the LF/HF ratio. Control (C) condition: HRV in TD (Y: 108, MA: 96 ms; P<0.05) and FD - LFa, HFa - was significantly higher in young (1030; 2589 ms²/Hz) than in middle-aged men (357; 342 ms²/Hz) only during sleep (P<0.05); post-training effects: resting bradycardia (P<0.05) in the awake condition in both groups; VO2 increased for both groups at anaerobic threshold (P<0.05), and at peak condition only in young men; HRV in TD and FD (a and nu) was not significantly changed by training in either groups. The vagal predominance during sleep is reduced with aging. The resting bradycardia induced by short-term APT in both age groups suggests that this adaptation is much more related to intrinsic alterations in sinus node than in efferent vagal-sympathetic modulation. Furthermore, the greater alterations in VO2 than in HRV may be related to short-term APT

Cardiorespiratory adaptations induced by aerobic training in middle-aged men: the importance of a decrease in sympathetic stimulation for the contribution of dynamic exercise tachycardia

We investigated the effects of aerobic training on the efferent autonomic control of heart rate (HR) during dynamic exercise in middle-aged men, eight of whom underwent exercise training (T) while the other seven continued their sedentary (S) life style. The training was conducted over 10 months (three 1-h/sessions/week on a field track at 70-85 percent of the peak HR). The contribution of sympathetic and parasympathetic exercise tachycardia was determined in terms of differences in the time constant effects on the HR response obtained using a discontinuous protocol (4-min tests at 25,50,100 and 125 watts on a cycle ergometer), and a continuous protocol (25 watts/min until exhaustion allowed the quantification of the parameters (anaerobic threshold, VO2,AT; peak O2 uptake, VO2 peak; power peak) that reflect oxygen transport. The results obtained for the S and the T groups were: 1) a smaller resting HR in T (66 beats/min) when compared to S (84 beats/min); 2) during exercise, a small increase in the fast tachycardia (delta0-10 s) related to vagal withdrawal (P<0.05, only at 25 watts) was observed in T at all powers; at middle and higher powers a significant decrease (P<0.05 at 50, 100 and 125 watts) in the slow tachycardia (delta1-4 min) related to a sympathetic-dependent mechanism was observed in T; 3) VO2AT (S=1.06 and T=1.33 l/min) and VO2 peak (S=1.97 and T=2.37 l/min) were higher in T (P<0.05). These results demonstrate that aerobic training can induce significant physiological adaptations in middle-aged men, mainly expressed as a decrease in the sympathetic effects on heart rate associated with an increase in oxygen transport during dynamic exercise.

Control of heart rate during exercise in health and disease

The authors present a review of their contributions over the last decade to the study of the autonomic control of heart rate during dynamic exercise under physiological and pathological conditions. These studies included the development of new methods for the evaluation of autonomic control of heart rate during dynamic exercise in man. Pharmacological blockade of sympathetic (propranolol) and parasympathetic (atropine) efferent nerves was used to demonstrate differences in time constants and power-dependent relative participation of each division of the autonomic nervous system, as predominant mechanisms responsible for the tachycardia occurring during dynamic exercise. These findings have permitted the use of properly standardized dynamic exercise (discontinuous protocol: step powers, seated position on a bicycle ergometer, 4-min duration), as a simple and noninvasive test for the evaluation of autonomic control of the sinus node. This test has proved to be useful for detecting physiological autonomic adaptations induced by aerobic training, as well as dysfunctions occurring in pathologic conditions such as Chagas' disease and hyperthyroidism.

Anaerobic threshold estimation by statistical modelling

Anaerobic threshold (AT) is usually estimated as a change point problem by visual analysis of the cardiorespiratory response to incremental dynamic exercice. In this study, two phase linear (TPL) models of the linear-linear and linear-quadratic type were used for the estimation of AT. The correlation coefficiente between the classical and statistical approaches was 0.88, and 0.89 after outlier exclusion. The TPL models provide a simple method for estimating AT that can be easily implemented using a digital computer for the automatic pattern recognition of AT

Leg endurance training has no effect on the autonomic control of hearth rate during isometric exercise

1. Heart rate (HR) response to isometric exercise (handgrp) was investigated in 7 normal males of sedentary habits befrore and after endurance training involving the muscles of the lower limbs. Thirteen additional sedentary individuals and 7 middle-distance renners were also studied. Isometric exercise was performed at 100, 75 and 50% of maximum voluntary contraction (MVC) during 10, 20 and 30 s, respectively. Training produced a 15.6 ñ 1.4% (mean ñ SEM) increase in VO2max and a reduction in resting HR from 69 ñ 1.9 to 58 ñ 1.7 bpm. HR was monitored throughout each period of isometric exercise. 2. The pattern of HR response to static effort performed by untrained muscles was comparable before and after training as well as in athletes and sedentary individuals during the first 10 s of contraction, a period during which tachycardia is aminly mediated by vagal release. after the first 10 s, when the sympathetic influence on tachycardia becomes evident, athlets and trained individuals showed a sligh but nonsignificant tendency toward lower HR increases. 3. These results do not demonstrate any appreciable alteration in the efferent activity of autonomic components induced by aerobic training of the leg muscles when isometric exercise is performed with untrained muscles

Sympathetic and parasympathetic changes in heart rate control during dynamic exercise induced by endurance training in man

1. Seven healthy young mean of sedentary habits were submitted to a 10-week period of endurance physical training on a cycle ergometer. The training program caused a 15% increase in maximal oxygen consumption (VO2max) and a 16% reduction in resting heart rate (RH). Before and after training, these volunteers performed dynamic exercise (DE) on a cycle ergometer at loads of 25, 50, 75, 100 and 150 w for 4 min at each level. The same exercise protocol was applied to 12 sedentary individuals and to 7 athletes (medium distance runners) who showed a VO2max of 39.4 and 53.8 ml/Kg, respectively. HR was cocntinuously monitored thoughoth the period of effort at each workload. 2. During the first 10 s of DE, a period when tachycardia is mediated almost exclusively by vagal eitdrawal, the athletes presented a more rapid increase in HR than sedentary subjects. The same tendency was observed in the sedentary individuals after the training period, although of a leser magnitude. 3. Dduring the DE phase in which sympathetic mediation plays an important role (between 30 s and 4 min), the athletes presented a lower HR increase than the sedentart individuals, and the same response patern was observed in the group submitted to physical training. Total HR increase (from 0 to 4 min) induced by DE was lower in athletes than in sedentary subjects and was changed by training of the sedentary subjects. 4. These results suggest that aerobic training decreases the slow sympathetic and increases the fast parasynpathetic contribution to HR during dynamic exercise at the same absolute workloads. 5. These function changes in the autonomic control of HR may or may not be associated with modifications of absolute HR values which increase from rest to the end of exercise. In contrast to what happens in athletes, the autonomic adaptations observed after short-term aerobic training may occur during DE without changes in the total HR rsponse