Biomedical subjects

L E Martins

Publications and source records attributed to L E Martins.

12 recordsLinked to original sources

PubMed1998

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% of the peak HR). The contribution of sympathetic and para-sympathetic 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 (delta 0-10 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 (delta 1-4 min) related to a sympathetic-dependent mechanism was observed in T; 3) the VO2 AT (S = 1.06 and T = 1.33 l/min) and VO2 peak (S = 1.97 and T = 2.47 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.

Adaptation, Physiological↗

PubMed1989

Evaluation of the autonomic nervous system of the heart in male patients with mitral valve prolapse syndrome using respiratory sinus arrhythmia and dynamic exercise.

The autonomic nervous system of the heart was evaluated in two male groups composed of 11 patients with mitral valve prolapse and of 10 normal subjects, using the heart rate response in two types of tests: respiratory sinus arrhythmia at rest and dynamic exercise. Sinus arrhythmia was of higher magnitude in patients with mitral valve prolapse when compared to the control group; however, the differences reached statistical significance only at a respiratory frequency of 7 cycles/min. With respect to dynamic exercise (25, 50, 100, 150 W during 4 min), the heart rate response, either in terms of the early, vagus-dependent fast tachycardia (first 10 s), or the late, sympathetic-dependent tachycardia (1-4 min) was normal in both groups studied, the same occurring with aerobic exercise capacity evaluated by measurement of the anaerobic threshold. Thus, our results show that in the group of male patients with mitral valve prolapse studied here, the parasympathetic abnormalities, if present, are of questionable physiological significance and do not affect the sympathetic and parasympathetic control of heart rate during dynamic exercise.

Adult↗

PubMed1989

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

1. Seven healthy young men 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 (HR). 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 13 sedentary individuals and to 7 athletes (medium distance runners) who showed a VO2max of 39.4 and 53.8 ml/kg, respectively. HR was continuously monitored throughout 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 withdrawal, 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 lesser magnitude. 3. During 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 sedentary individuals, and the same response pattern 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 not changed by training of the sedentary subjects. 4. These results suggest that aerobic training decreases the slow sympathetic and increases the fast parasympathetic contribution to HR during dynamic exercise at the same absolute workloads. 5. These functional 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 response.

Adaptation, Physiological↗

PubMed1989

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 exercise. 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 coefficient 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.

Anaerobic Threshold↗

PubMed1989

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

1. Heart rate (HR) response to isometric exercise (handgrip) was investigated in 7 normal males of sedentary habits before and after endurance training involving the muscles of the lower limbs. Thirteen additional sedentary individuals and 7 middle-distance runners were also studied. Isometric exercise was performed at 100, 75 and 50% of maximum voluntary contraction (MVC) during 10, 20 and 40 s, respectively. Training produced a 15.6 +/- 1.4% (mean +/- SEM) increase in VO2max and a reduction in resting HR from 69 +/- 1.9 to 58 +/- 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 mainly mediated by vagal release. After the first 10 s, when the sympathetic influence on tachycardia becomes evident, athletes and trained individuals showed a slight 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.

Adaptation, Physiological↗

PubMed1988

The use of isometric exercise as a means of evaluating the parasympathetic contribution to the tachycardia induced by dynamic exercise in normal man.

Fourteen normal subjects were submitted to isometric exercise (IE), dynamic exercise (DE) and a combination of the two (IE + DE). The main purpose of the present study was to use IE as a means of evaluating the mechanism of the heart rate (HR) increase induced by DE. To this end, the magnitude of the IE (handgrip) was standardized so as to cause an elevation of HR almost exclusively by vagal withdrawal: IE was performed using a dynamometer strain-gauge system with a linear response at 75% of maximum voluntary contraction (MVC) for 10 s, repeated at 1 min intervals. The change in HR evoked by IE under control conditions was compared with that evoked during DE, and during the corresponding recovery period. DE was performed by the legs, with the subject in the seated position for 4 min, at workloads of 55 and 105 watts, separated by a rest period. In the combined protocol, IE was performed at the beginning of DE, as well as at 1, 2 and 3 min during DE, and at 0, 1, 2, 3 and 5 min during recovery period. The following results were obtained: (1) IE associated with DE always induced smaller increase in heart rate than IE alone, and this effect was more marked at 105 than at 55 W; this finding suggested a workload-dependent vagal withdrawal at the very beginning of DE that was sustained until the end of effort.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1988

Autonomic control of heart rate during dynamic exercise in human hyperthyroidism.

1. The relative contribution of the sympathetic and parasympathetic components of the autonomic nervous system to the regulation of the chronotropic response to dynamic exercise was evaluated indirectly in nine patients with thyrotoxicosis and in seven normal volunteers. All subjects were women, with equivalent ages in both groups. Six of the nine patients with hyperthyroidism were reevaluated after clinical compensation of the disease with propylthiouracil. 2. Heart rate responses were evaluated during discontinuous dynamic effort maintained for 4 min on a bicycle ergometer at levels of 5, 15, 25 and 50 W, and also of 75 W in normal individuals. The study was also performed under conditions of sympathetic pharmacological blockade with propranolol (0.2 mg/kg body weight). 3. Even though the magnitude of the total increase in heart rate evoked by each level of dynamic exercise was equivalent in normal and hyperthyroid patients, the tachycardiac response occurring at the beginning of the exercise, which depends on a predominantly vagal mechanism, was substantially different from that observed after 30 s of effort, when sympathetic contribution becomes more important. The hyperthyroid patients showed considerably lower increases in heart rate than the normal individuals during the initial 30 s of effort, with the opposite occurring from this moment onward. 4. In the hyperthyroid patients, beta-adrenergic blockage depressed tachycardia after 30 s of effort at the 15 and 50 W levels, whereas in normal individuals this effect was only manifested at 50 and 75 W. 5. The patients who obtained clinical compensation showed a pattern of chronotropic response which tended to be close to that shown by normal subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Autonomic Nervous System↗

PubMed1988

Inadequacy of first and second order models to characterize the heart rate response induced by dynamic exercise.

Six normal subjects were submitted to dynamic exercise at workloads of 25, 50, 100 and 150 w for 4 min, intercalated by periods of rest, before and after an aerobic training period of 10 weeks. The heart rate response was fitted to 2 mathematical models, a 1st-order model and a 2nd-order model. The results indicate that these 2 models were not adequate to characterize the physiological response of heart rate induced by dynamic exercise.

Exercise Test↗

PubMed1987

Autonomic nervous control of the heart rate during isometric exercise in normal man.

The relative contribution of the efferent components of the autonomic nervous system to the regulation of tachycardia induced by isometric exercise was assessed in 23 normal males. The isometric exercise (handgrip) was performed at the maximum intensity tolerated by the individual over a period of 10 s (maximal voluntary contraction-MVC) and at levels equivalent to 75, 50 and 25% of MVC for 20, 40 and 10 s, respectively. The study was performed both under control conditions and after pharmacological blockade with atropine (12 individuals) or propranolol (11 individuals). Under control conditions, the heart rate (HR) responses to isometric effort were dependent on the intensity and duration of the exercise, showing a tendency towards progressive elevation with the maintenance of muscular contraction at the levels studied. The tachycardia evoked by this effort was of considerable magnitude and of rapid onset, especially at the more intense levels of activity. Parasympathetic blockade markedly decreased tachycardia, which manifested itself during the first 10 s of exercise at all levels of intensity, whereas sympathetic blockade markedly modified the HR response after 10 s of effort at the 75 and 50% MVC levels. A slight depression of the tachycardiac response could be observed already after 10 s of maximum effort after propranolol. The present results suggest that the autonomic regulation of these responses is based on a biphasic mechanism, with the initial phase depending on the rapid withdrawal of the parasympathetic influence, followed by a marked sympathetic contribution to the induction of tachycardia after 10 s of isometric contraction or even a little before at maximum exertion.

Adult↗

PubMed1987

Functional evaluation of sympathetic and parasympathetic system in Chagas' disease using dynamic exercise.

Ten normal subjects and 14 patients with chronic Chagas' disease (seven with and seven without heart disease) underwent dynamic exercise on a cycle ergometer. Heart rate (HR), pulmonary ventilation (V), oxygen consumption (VO2), carbon dioxide production (VCO2), and respiratory quotient (RQ) were measured. Increasing workloads (25, 50, 100, and 150 W) were applied for 4 min and intercalated with resting periods. The main objective of this protocol was to analyse heart rate response in relation to the other cardiorespiratory variables in order to evaluate the functional conditions of the sympathetic and parasympathetic cardiac efferents. Analysis of the results showed that (a) the group of chagasic patients with heart disease had lower heart rates (p less than 0.05) than normal subjects during the initial 10 s (delta HR 0-10 s) of effort (fast component); (b) the difference between the normal subjects and chagasic patients without heart disease was not statistically significant; (c) the abnormalities in heart rate response were due to depression of parasympathetic efferent action on the sinus node; (d) the slow heart rate response (delta HR 1-4 min), which expresses the degree of sympathetic stimulation of the sinus node, was comparable in the three groups studied, thus showing unimpaired adrenergic responses during dynamic exercise in Chagas' disease; and (e) the V, VO2, VCO2, and RQ values were normal at all workloads in each group, suggesting that vagal dysfunction does not affect oxygen transport at these submaximal levels of dynamic exercise.

Adult↗

PubMed1986

Autonomic nervous control of the heart rate during dynamic exercise in normal man.

The relative contribution of the efferent components of the sympathetic and parasympathetic nervous systems to the heart rate (HR) response to dynamic physical exercise was evaluated in 23 normal males. The dynamic exercise was performed on a bicycle ergometer at work loads of 25, 50 and 100 W, before and after pharmacological blockade with atropine (13 individuals) or propranolol (10 individuals). Parasympathetic blockade significantly depressed the rapid HR response at the beginning of the exercise period at all levels of intensity, whereas sympathetic blockade only affected the slow-response phase (1-4 min), especially at the highest level of effort. The present results suggest that the tachycardia evoked by dynamic exercise is mediated by a biphasic mechanism initially depending on rapid vagal release, which increases progressively with increasing effort. An increased sympathetic activity manifests itself in a more delayed manner, especially at the higher levels of activity. Continuous monitoring of HR during the entire period of activity at different levels of intensity permits the utilization of dynamic exercise as a simple and non-invasive method for the functional evaluation of the two components of the autonomic nervous system of the heart.

Adult↗

PubMedDate not supplied

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.

Atropine↗