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.

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

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