Use of the Wasserman equation in optimization of the duration of the power ramp in a cardiopulmonary exercise test: a study of Brazilian men

This study aimed to analyze the agreement between measurements of unloaded oxygen uptake and peak oxygen uptake based on equations proposed by Wasserman and on real measurements directly obtained with the ergospirometry system. We performed an incremental cardiopulmonary exercise test (CPET), which was applied to two groups of sedentary male subjects: one apparently healthy group (HG, n=12) and the other had stable coronary artery disease (n=16). The mean age in the HG was 47±4 years and that in the coronary artery disease group (CG) was 57±8 years. Both groups performed CPET on a cycle ergometer with a ramp-type protocol at an intensity that was calculated according to the Wasserman equation. In the HG, there was no significant difference between measurements predicted by the formula and real measurements obtained in CPET in the unloaded condition. However, at peak effort, a significant difference was observed between oxygen uptake (V˙O2)peak(predicted)and V˙O2peak(real)(nonparametric Wilcoxon test). In the CG, there was a significant difference of 116.26 mL/min between the predicted values by the formula and the real values obtained in the unloaded condition. A significant difference in peak effort was found, where V˙O2peak(real)was 40% lower than V˙O2peak(predicted)(nonparametric Wilcoxon test). There was no agreement between the real and predicted measurements as analyzed by Lin’s coefficient or the Bland and Altman model. The Wasserman formula does not appear to be appropriate for prediction of functional capacity of volunteers. Therefore, this formula cannot precisely predict the increase in power in incremental CPET on a cycle ergometer.

Respostas cardiovasculares a mudança postural e capacidade aeróbia em homens e mulheres de meia-idade antes e após treinamento físico aeróbio / Cardiovascular responses to postural change and aerobic capacity among middle-aged men and women before and after aerobic physical training

OBJETIVO: Comparar respostas cardiovasculares a Manobra Postural Passiva (Tilt Test) e capacidade cardiorrespiratória em homens e mulheres de meia-idade antes e após treinamento físico aeróbio. MATERIAIS E MÉTODOS: Sete homens - GH (44,6±2,1 anos) e sete mulheres - GM (51,7±4,8 anos), participaram de treinamento físico aeróbio por 12 semanas. Foi realizado protocolo de Tilt Test (cinco minutos supino, dez minutos inclinado 70º, cinco minutos supino), com monitoração da pressão arterial e freqüência cardíaca. Para mensuração da capacidade cardiorrespiratória foi realizado protocolo em cicloergômetro. RESULTADOS: Na condição sedentária, GH mostrou maior influência parassimpática no controle da freqüência cardíaca evidenciada por maior intervalo RR (iRR) durante Tilt Test. Na condição treinada, os valores de iRR de ambos os grupos se assemelham, tendo as mulheres iRR maior em supino, mas na inclinação os homens mantêm iRR mais elevado. Para pressão arterial, as mulheres permanecem com valores superiores após treino, mas a freqüência cardíaca tende a se assemelhar em ambos. Já na capacidade cardiorrespiratória, homens e mulheres têm um padrão de comportamento semelhante após treino. Com exceção dos valores absolutos da freqüência cardíaca, sem diferenças entre os grupos, para todas as outras variáveis os homens obtiveram valores superiores aos das mulheres. Observa-se ainda que, após o treinamento, houve redução significativa dos valores de pressão arterial no GM, mesmo continuando superiores aos dos homens. CONCLUSÃO: O treinamento parece ter reduzido os níveis pressóricos nas mulheres, além de serem observadas melhorias na capacidade cardiorrespiratória de ambos os grupos, permanecendo os homens com melhor desempenho do que as mulheres.

OBJECTIVE: To compare the cardiovascular responses to passive postural maneuvers (tilt test) and the cardiorespiratory capacity in middle-aged men and women, before and after aerobic physical training. METHODS: Seven men (44.6±2.1 years old) and seven women (51.7±4.8 years old) participated in aerobic physical training for 12 weeks. The tilt test protocol (five minutes supine, ten minutes tilted at 70º and five minutes supine) was followed, with arterial blood pressure and heart rate monitoring. A cycle ergometer protocol was used to measure cardiorespiratory capacity. RESULTS: In the sedentary condition, men showed greater parasympathetic influence in heart rate control, as demonstrated by their higher RR interval (iRR) during the tilt test. After training, the iRR values became more similar in the two groups, although the women had higher iRR in the supine position and the men continued to present higher iRR under tilted conditions. The women's blood pressures continued to be higher after training, but heart rate tended to become similar in the two groups. The cardiorespiratory capacity patterns in the two groups were similar after training. Except for absolute heart rate values, for which there were no differences between the groups, the men's values were higher than those of the women for all other variables. It was also observed that, after the training, the women's blood pressures were significantly lower, even though their pressures remained higher than the men's. CONCLUSIONS: The training seemed to reduce the women's arterial blood pressure levels and improve both groups' cardiorespiratory capacity, but the men continued to present better performance than the women.

Influences of torque and joint angle on heart rate responses during isometric exercise in young men

OBJECTIVE: To evaluate the influence of joint angle on heart rate (HR) responses induced by isometric exercise. METHODS: Ten healthy men (23.8 ± 2.5 years old) underwent isometric maximum voluntary contraction (MVC) tests lasting 10 sec using an electronic dynamometer under the following experimental conditions: knee extension at angles of 60º and 90º and knee flexion at angles of 30º and 90º angles. Their HR was recorded at rest (65 sec), during MVC (10 sec) and during the recovery period (120 sec). The data on mean maximum torque (MMT) and HR variation (deltaHR) were analyzed using the Friedman test with the Dunn post-hoc test, and their correlation was analyzed using the Spearman test (alpha= 0.05). RESULTS: 1) MMT was significantly higher at 60º and 90º knee extension than at 30º and 90º knee flexion (p< 0.05), while no significant differences were found between the two extension angles or between the two flexion angles; 2) deltaHR was similar under all the experimental conditions; 3) No correlation was found between MMT and deltaHR. CONCLUSION: The data suggest that the rapid increase in HR during the 10 sec of isometric MVC does not depend on the joint angle or the morphofunctional differences between the two muscle groups studied.

OBJETIVO: Avaliar a influência do ângulo articular nas respostas da freqüência cardíaca (FC) induzida pelo exercício isométrico. MÉTODOS: Dez homens saudáveis (23,8 ± 2,5 anos) foram submetidos a testes de contração voluntária máxima (CVM) isométrica, durante 10s, em um dinamômetro eletrônico, nas seguintes condições experimentais: extensão do joelho nos ângulos de 60º e 90º e flexão do joelho nos ângulos de 30º e 90º. A freqüência cardíaca foi registrada durante o repouso (65s), durante a CVM (10s) e durante o período de recuperação (120s). Os dados de torque médio máximo (TMM) e de variação da FC (deltaFC) foram analisados usando teste de Friedman, com pós-teste de Dunn, e sua correlação foi analisada usando o teste de Spearman (alfa= 0,05). RESULTADOS: 1) TMM foi significativamente maior nos ângulos de 60º e 90º de extensão em relação aos ângulos de 30º e 90º de flexão (p< 0,05), enquanto entre os dois ângulos de flexão e entre os dois de extensão não foram encontradas diferenças significativas; 2) deltaFC foi similar em todas as condições experimentais; 3) Não foi encontrada correlação entre TMM e deltaFC. CONCLUSÕES: Os dados sugerem que a elevação rápida da FC, durante os 10 s de CVM isométrica, independe do ângulo articular e das diferenças morfofuncionais entre os dois grupos musculares estudados.

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.

Comparison of anaerobic threshold determined by visual and mathematical methods in healthy women

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.

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.

Identification of anaerobic threshold using heart rate response during dynamic exercise

The objective of the present study was to characterize the heart rate (HR) patterns of healthy males using the autoregressive integrated moving average (ARIMA) model over a power range assumed to correspond to the anaerobic threshold (AT) during discontinuous dynamic exercise tests (DDET). Nine young (22.3 ± 1.57 years) and 9 middle-aged (MA) volunteers (43.2 ± 3.53 years) performed three DDET on a cycle ergometer. Protocol I: DDET in steps with progressive power increases of 10 W; protocol II: DDET using the same power values as protocol 1, but applied randomly; protocol III: continuous dynamic exercise protocol with ventilatory and metabolic measurements (10 W/min ramp power), for the measurement of ventilatory AT. HR was recorded and stored beat-to-beat during DDET, and analyzed using the ARIMA (protocols I and II). The DDET experiments showed that the median physical exercise workloads at which AT occurred were similar for protocols I and II, i.e., AT occurred between 75 W (116 bpm) and 85 W (116 bpm) for the young group and between 60 W (96 bpm) and 75 W (107 bpm) for group MA in protocols I and II, respectively; in two MA volunteers the ventilatory AT occurred at 90 W (108 bpm) and 95 W (111 bpm). This corresponded to the same power values of the positive trend in HR responses. The change in HR response using ARIMA models at submaximal dynamic exercise powers proved to be a promising approach for detecting AT in normal volunteers.

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

Modulacao do sistema nervoso autonomico na resposta da frequencia cardiaca em repouso e a manobra de valsalva com o incremento da idade / Modulation of autonomic nervous system in the heart rate responseto rest and the valsalva maneuver with increasing age

A Manobra de Valsalva (MV) provoca sobrecarga no sistema cardiovascular, ativando barorreceptores arteriais, quimiorreceptores e receptores cardiopulmonares. Ha interacao entre os receptores e o sistema nervoso central, desencadeando respostas autonomicas que modulam a resposta da frequencia cardiaca (FC). O objetivodo presente estudo foi verificar o controle autonomico do coracao nas seguintes condicoes: a)durante a MV; b)em repouso, nas condicoes supina e sentada; c)antes e apos a MV, na posicao supina em homens jovens de meia idade. Dezesseis voluntarios jovens (mediana=22,5 anos) e 11 de meia idade (mediana=43 anos) foram submetidos a uma avaliacao clinica e cardiovascular. A FC foi captada batimento a batimento em tempo real: a) durante 900s em repouso, na posicao supina sentada; b) durante 60sem repouso, com respiracao espontanea, e 20s em MV, mantendo pressao oral de 40mmHg e apos, por 280s, com respiracao espontanea. Os dados foram analisados por meio do indicede Valsava, da variacao dos intervalos RR e da variabilidade da FC (VFC) por meio do indice RMSSD dos intervalos RR em milissegundos. Os resultados mostram que a VFC, o indice de Valsavae a variacao dos intervalos RR foram menores nos voluntarios de meia idade comparativamente aos jovens (p<0,05). Tais resultados sugerem diminuicao da atividade parassimpatica atuante sobre o nodulo sinoatrial com o incremento de idade

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

Pulmonary function, cholinergic bronchomotor tone, and cardiac autonomic abnormalities in type 2 diabetic patients

This prospective study analyzed the involvement of the autonomic nervous system in pulmonary and cardiac function by evaluating cardiovascular reflex and its correlation with pulmonary function abnormalities of type 2 diabetic patients. Diabetic patients (N = 17) and healthy subjects (N = 17) were evaluated by 1) pulmonary function tests including spirometry, He-dilution method, N2 washout test, and specific airway conductance (SGaw) determined by plethysmography before and after aerosol administration of atropine sulfate, and 2) autonomic cardiovascular activity by the passive tilting test and the magnitude of respiratory sinus arrhythmia (RSA). Basal heart rate was higher in the diabetic group (87.8 ± 11.2 bpm; mean ± SD) than in the control group (72.9 ± 7.8 bpm, P<0.05). The increase of heart rate at 5 s of tilting was 11.8 ± 6.5 bpm in diabetic patients and 17.6 ± 6.2 bpm in the control group (P<0.05). Systemic arterial pressure and RSA analysis did not reveal significant differences between groups. Diabetes intragroup analysis revealed two behaviors: 10 patients with close to normal findings and 7 with significant abnormalities in terms of RSA, with the latter subgroup presenting one or more abnormalities in other tests and clear evidence of cardiovascular autonomic dysfunction. End-expiratory flows were significantly lower in diabetic patients than in the control group (P<0.05). Pulmonary function tests before and after atropine administration demonstrated comparable responses by both groups. Type 2 diabetic patients have cardiac autonomic dysfunction that is not associated with bronchomotor tone alterations, probably reflecting a less severe impairment than that of type 1 diabetes mellitus. Yet, a reduction of end-expiratory flow was detected

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

Heart rate variability under resting conditions in postmenopausal and young women

The aim of the present study was to compare the modulation of heart rate in a group of postmenopausal women to that of a group of young women under resting conditions on the basis of R-R interval variability. Ten healthy postmenopausal women (mean Ý SD, 58.3 Ý 6.8 years) and 10 healthy young women (mean Ý SD, 21.6 Ý 0.82 years) were submitted to a control resting electrocardiogram (ECG) in the supine and sitting positions over a period of 6 min. The ECG was obtained from a one-channel heart monitor at the CM5 lead and processed and stored using an analog to digital converter connected to a microcomputer. R-R intervals were calculated on a beat-to-beat basis from the ECG recording in real time using a signal-processing software. Heart rate variability (HRV) was expressed as standard deviation (RMSM) and mean square root (RMSSD). In the supine position, the postmenopausal group showed significantly lower (P<0.05) median values of RMSM (34.9) and RMSSD (22.32) than the young group (RMSM: 62.11 and RMSSD: 49.1). The same occurred in the sitting position (RMSM: 33.0 and RMSSD: 18.9 compared to RMSM: 57.6 and RMSSD: 42.8 for the young group). These results indicate a decrease in parasympathetic modulation in postmenopausal women compared to young women which was possibly due both to the influence of age and hormonal factors. Thus, time domain HRV proved to be a noninvasive and sensitive method for the identification of changes in autonomic modulation of the sinus node in postmenopausal women

A pulsatile flow model for in vitro quantitative evaluation of prosthetic valve regurgitation

A pulsatile pressure-flow model was developed for in vitro quantitative color Doppler flow mapping studies of valvular regurgitation. The flow through the system was generated by a piston which was driven by stepper motors controlled by a computer. The piston was connected to acrylic chambers designed to simulate "ventricular" and "atrial" heart chambers. Inside the "ventricular" chamber, a prosthetic heart valve was placed at the inflow connection with the "atrial" chamber while another prosthetic valve was positioned at the outflow connection with flexible tubes, elastic balloons and a reservoir arranged to mimic the peripheral circulation. The flow model was filled with a 0.25 per cent corn starch/water suspension to improve Doppler imaging. A continuous flow pump transferred the liquid from the peripheral reservoir to another one connected to the "atrial" chamber. The dimensions of the flow model were designed to permit adequate imaging by Doppler echocardiography. Acoustic windows allowed placement of transducers distal and perpendicular to the valves, so that the ultrasound beam could be positioned parallel to the valvular flow. Strain-gauge and electromagnetic transducers were used for measurements of pressure and flow in different segments of the system. The flow model was also designed to fit different sizes and types of prosthetic valves. This pulsatile flow model was able to generate pressure and flow in the physiological human range, with independent adjustment of pulse duration and rate as well as of stroke volume. This model mimics flow profiles observed in patients with regurgitant prosthetic valves.

Role of bradykinin in postprandial hypotension in humans

A transient significant decrease in mean arterial blood pressure (MAP) from 107 + ou - 3 to 98 + ou - 3 mmHg (P<0.05) was observed in elderly (59-69 years of age), healthy volunteers 25-30 min following ingestion of a test meal. In young volunteers (22-34 years of age), a postprandial decrease of MAP from 88 + ou - 3 to 83 + ou - 4 mmHg was also noted but it was not statistically significant. A 40 per cent decrease in bradykinin (BK) content of circulatory high molecular weight kininogen had previously been observed in human subjects given the same test meal. We presently demonstrate by specific ELISA that the stable pentapeptide metabolite (1-5 BK) of BK increases from 2.5 + ou - 1.0 to 11.0 + ou - 2.5 pg/ml plasma (P<0.05) in elderly volunteers and from 2.0 + ou - 1.0 to 10.3 + ou - 3.2 pg/ml plasma (P<0.05) in young volunteers 3 h following food intake. This result suggests that ingestion of food stimulates BK release from kininogen in normal man. Postprandial splanchnic vasodilatation, demonstrated by a decrease of plasma half-life of intravenously administered indocyanine green (ICG), a marker of mesenteric blood flow to the liver, from 4.4 + ou - 0.4 to 3.0 + ou - 0.1 min (P<0.05) in young volunteers and from 5.2 + ou - 1.0 to 4.0 + ou - 0.5 min (P<0.05) in elderly volunteers, accompanied BK release. The participation of BK in this response was investigated in subjects given the BK-potentiating drug captopril prior to food intake. Postprandial decreases of ICG half-lives were not changed by this treatment in either young or elderly subjects, a result which may indicate that BK released following food intake plays no role in postprandial splanchnic vasodilatation in normal man.

Evaluation of electromyographic activity and heart rate responses to isometric exercise. The role played by muscular mass and type

The purpose of the present study was to examine the relationship between the electromyographic (EMG) activity and heart rate (HR) responses induced by isometric exercise performed by knee extension (KE) and flexion (KF) in men. Fifteen healthy male subjects, 21 1.3 years (mean SD), were submitted to KE and KF isometric exercise tests at 100 percent of maximal voluntary contraction (MVC). The exercises were performed with one leg (right or left) and with two legs simultaneously, for 10 s in the sitting position with the hip and knee flexed at 90o. EMG activity (root mean square values) and HR (beats/min) were recorded simultaneously both at rest and throughout the sustained contraction. The HR responses to isometric exercise in KE and KF were similar when performed with one and two legs. However, the HR increase was always significantly higher in KE than KF (P<0.05), whereas the EMG activity was higher in KE than in KF (P<0.05), regardless of the muscle mass (one or two legs) involved in the effort. The correlation coefficients between HR response and the EMG activity during KE (r = 0.33, P>0.05) and KF (r = 0.15, P>0.05) contractions were not significant. These results suggest that the predominant mechanism responsible for the larger increase in HR response to KE as compared to KF in our study could be dependent on qualitative and quantitative differences in the fiber type composition found in each muscle group. This mechanism seems to demand a higher activation of motor units with a corresponding increase in central command to the cardiovascular centers that modulate HR control

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.