Marcos Bezerra de Almeida

Effects of aerobic training on heart rate

ABSTRACTRegular physical exercise is an important factor to re-duce the indexes of cardiovascular and all causes morbi-mortality. However, there is, a pparently, additional and in-dependent benefits of the regular practice of physicalexercise and the improvement of the level of aerobic con-dition. Heart rate ( HR ) is mediated primarily by the directactivity of the autonomic nervous system ( ANS ), specifi-cally through the sympathetic and parasympathetic branch-es activities over the sinus node autorhythmicity, with pre-dominance of the vagal activity (parasympathetic) at rest,that is progressively inhibited since the onset of the exer-cise. The HR behavior has been widely studied during dif-ferent conditions and protocols associated to the exercise.A reduction of the cardiac vagal tone (parasympatheticfunction) and consequently a diminished HR variability inrest, independently of the protocol of measurement used,is related to an autonomic dysfunction, chronic-degenera-tive diseases and increased mortality risk. Individuals withhigh levels of aerobic condition have a lower resting

Validação do Teste de Exercício de 4 Segundos em Posição Ortostática

OBJECTIVE: To test the operational viability of and validate the 4-second exercise test (4sET) protocol in the orthostatic position (ORTHO). METHODS: The ORTHO protocol, an alternative to the conventional protocol (CYCLO), was used. The ORTHO protocol consists of performing sudden exercise in the orthostatic position - accelerated stationary walking (alternate upward flexion of the thighs) - from the fourth to the eighth second of a 12-second maximum inspiratory apnea, instead of rapid cycling without load. The adimensional cardiac vagal index (CVI) was calculated using the ratio between the longest RR interval (RRB) - the one immediately before, or the first during exercise - and the shortest RR interval during exercise - usually the last (RRC) - measured on electrocardiographic tracings at a 10-ms resolution. Forty-seven individuals (40±17 years, 169±9 cm, 72±14 kg) of both sexes, healthy or unhealthy, randomly underwent 3 consecutive repetitions of the 2 protocols, the first being performed only to acquaint patients with the procedure. RESULTS: Although differences in the CVI were found in both protocols (1.48±0.04 vs 1.42±0.04; P<0.001), no physiological relevance was observed. In 5 (11%) cases, a clinically significant difference between the ORTHO and CYCLO protocols was observed for CVI. The results of RRB, RRC, and CVI in the 2 protocols were strongly correlated, being 0.84, 0.85, and 0.93, respectively (P<0.001). CONCLUSION: The 4sET performed in the orthostatic position proved to be a valid option for assessing the vagal cardiac tonus in laboratories lacking a cycloergometer, without jeopardizing clinical interpretation. In addition to simplicity and applicability, the procedure also provides low operational costs.

Intra and interdays reliability of the 4-second exercise test

The 4-second exercise test (T4s) is pharmacologically validated to assess cardiac vagal tone, and consists in pedaling, as fast as possible, a cycle-ergometer unloaded, from the 4th to the 8th second of a 12-second maximum inspiratory apnea. An dimensionless cardiac vagal index (CVI) is calculated from the ratio of the duration of the cardiac cycles (RR intervals at the electrocardiogram) from immediately before the exercise and the shorter of the exercise. Our objective was to determine T4s intra and interdays reliability, and the actual need for two trials, as described on the original protocol. In study 1, the interday reliability of the results was assessed prospectively from 15 asymptomatic subjects (28 ± 6 years) submitted to T4s for five consecutive days, being two trials carried out at each day. To determine CVI intraday reliability, in one of the five days, randomly selected, nine T4s consecutive trials were made. In study 2, the CVI intraday reliability was calculated from 1699 subjects (47 ± 17 years) in two trials. CVI presented high intraday and interday reliability (ri = 0.92; 95%CI = 0.84 to 0.97 and ri = 0.77; 95%CI = 0.49 to 0.92, respectively) for study 1 and for study 2 (ri = 0.89; 95%CI = 0.88 to 0.90). In spite of high reliability, there were some minor differences between the means (mean ± SEM = 1.32 ± 0.01 vs 1.37 ± 0.01; p < 0.001), and in only 15% of the cases this difference was higher than 0.20, thus not representing major clinical meaning. It was also observed that in 65% of the cases, the second trial was considered the best and, with only one trial, clinical misinterpretation could occur in 27% of the data. In summary, this study evidenced high CVI reliability assessed by T4s, and confirmed the need for two consecutive trials, as prescribed in its protocol.

Fidedignidade intra e interdias do teste de exercício de quatro segundos

The 4-second exercise test (T4s) is pharmacologically validated to assess cardiac vagal tone, and consists in pedaling, as fast as possible, a cycle-ergometer unloaded, from the 4th to the 8th second of a 12-second maximum inspiratory apnea. An dimensionless cardiac vagal index (CVI) is calculated from the ratio of the duration of the cardiac cycles (RR intervals at the electrocardiogram) from immediately before the exercise and the shorter of the exercise. Our objective was to determine T4s intra and interdays reliability, and the actual need for two trials, as described on the original protocol. In study 1, the interday reliability of the results was assessed prospectively from 15 asymptomatic subjects (28 ± 6 years) submitted to T4s for five consecutive days, being two trials carried out at each day. To determine CVI intraday reliability, in one of the five days, randomly selected, nine T4s consecutive trials were made. In study 2, the CVI intraday reliability was calculated from 1699 subjects (47 ± 17 years) in two trials. CVI presented high intraday and interday reliability (ri = 0.92; 95%CI = 0.84 to 0.97 and ri = 0.77; 95%CI = 0.49 to 0.92, respectively) for study 1 and for study 2 (ri = 0.89; 95%CI = 0.88 to 0.90). In spite of high reliability, there were some minor differences between the means (mean ± SEM = 1.32 ± 0.01 vs 1.37 ± 0.01; p < 0.001), and in only 15% of the cases this difference was higher than 0.20, thus not representing major clinical meaning. It was also observed that in 65% of the cases, the second trial was considered the best and, with only one trial, clinical misinterpretation could occur in 27% of the data. In summary, this study evidenced high CVI reliability assessed by T4s, and confirmed the need for two consecutive trials, as prescribed in its protocol.