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PubMed2002

Heart rate recovery after exercise: relations to heart rate variability and complexity.

Physical exercise is associated with parasympathetic withdrawal and increased sympathetic activity resulting in heart rate increase. The rate of post-exercise cardiodeceleration is used as an index of cardiac vagal reactivation. Analysis of heart rate variability (HRV) and complexity can provide useful information about autonomic control of the cardiovascular system. The aim of the present study was to ascertain the association between heart rate decrease after exercise and HRV parameters. Heart rate was monitored in 17 healthy male subjects (mean age: 20 years) during the pre-exercise phase (25 min supine, 5 min standing), during exercise (8 min of the step test with an ascending frequency corresponding to 70% of individual maximal power output) and during the recovery phase (30 min supine). HRV analysis in the time and frequency domains and evaluation of a newly developed complexity measure - sample entropy - were performed on selected segments of heart rate time series. During recovery, heart rate decreased gradually but did not attain pre-exercise values within 30 min after exercise. On the other hand, HRV gradually increased, but did not regain rest values during the study period. Heart rate complexity was slightly reduced after exercise and attained rest values after 30-min recovery. The rate of cardiodeceleration did not correlate with pre-exercise HRV parameters, but positively correlated with HRV measures and sample entropy obtained from the early phases of recovery. In conclusion, the cardiodeceleration rate is independent of HRV measures during the rest period but it is related to early post-exercise recovery HRV measures, confirming a parasympathetic contribution to this phase.

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PubMed1979

Reduced heart rate response to exercise in ischemic heart disease: the fallacy of the target heart rate in exercise testing.

When exercise testing 159 patients with prior myocardial infarction, we identified 39 who were limited by fatigue. This group was all in sinus rhythm; none were taking drugs likely to impair the chronotropic response of the heart; none experienced chest pain or developed ischemic ECG changes. In 18 of this group, maximal heart rate achieved with exercise was 2SD or more below the age predicted value, and their heart rate response to exercise was reduced compared to that of the other 21 whose maximal exercise heart rates were within 2SD of age predicted values. A subgroup of 8 subjects with reduced exercise heart rates was studied before and after vagal blockade. In the 4 subjects whose infarction was inferior, the reduction in heart rate response was more profound and persisted after vagal blockade, suggesting either reduced pacemaker responsivness, due to ischemia or infarction, or autonomic imbalance as possible mechanisms. All 8 showed alinear increases in ventilation at higher power outputs and mean blood lactate postexercise was 7.5 mM/I without vagal blockade. Our findings suggest that a reduced heart rate response to exercise, already shown to imply added coronary risk, may be subdivided aetiologically and possibly prognostically. The use of a "Target Heart Rate" in such patients offers no safety margin, and maximal exercise capacity will be grossly over-estimated if extrapolated from the submaximal heart rate response. A cardiovascular limitation to exercise may be detected by an alinear increase in ventilation.

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PubMed1989

The effect of stress inoculation training on self-reported stress, observer's rating of stress, heart rate and gymnastics performance.

Eighteen volunteer female subjects received preliminary instruction in a simple gymnastics bench sequence. They were then given a pre-intervention test on a bench at ground level. Self-reported distress, an independent observer's ratings of distress and heart rates were monitored immediately prior to performance of the sequence. Performances were also videotaped and formally scored by a qualified gymnastics judge. Subjects were then randomly assigned to a stress inoculation training group or a 'no stress management' training control group. Stress inoculation group subjects then received seven sessions of training in relaxation, imagery and making self-statements in order to develop a set of coping skills. Control group subjects also received seven training sessions during which they practised a series of coordination exercises, but no psychological stress management training was given to this group. All subjects were then re-tested on the bench sequence but this time at a height of 1.52 m. Self-reported stress, observer's ratings of distress and heart rate were recorded as before. Performance was again videotaped for scoring. The stress inoculation group reported significantly less stress prior to the test on the elevated beam than the control group. However, the groups did not differ in terms of heart rate. Further, the stress inoculation group performed reliably better than the control group on the elevated bench.

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PubMed1988

Spectral analysis of heart rate indicates reduced baroreceptor-related heart rate variability in elderly persons.

Spectral analysis of the cardiac interbeat interval was used to examine baroreceptor-related supine and standing heart rate variability (HRV) in young (less than 40 years of age) and elderly (greater than 60 years of age) healthy volunteers. Heart rates and blood pressures were examined also. When supine, average heart rate, systolic and diastolic blood pressure, and HRV for the young volunteers were 66.5 bpm, 113.0/64.3 mmHg, and 5.74 log units of relative power, respectively. The same values for the elderly group were 65.4 bpm, 126.3/74.0 mmHg, and 4.43 log units. Statistical analysis revealed that, compared to the young volunteers, supine elderly volunteers had similar heart rates, higher blood pressures, and lower baroreceptor HRV. There was little change in blood pressure in either group upon standing. However, upon standing, heart rate increased 17.7 bpm and baroreceptor HRV increased to 6.58 (+ 14.6%) in the younger volunteers. This was significantly different from the elderly volunteers, whose heart rate increased by only 10.9 bpm and their HRV to 4.72 (+ 6.5%). These results indicate that much of the reduction in HRV in old age results from decreases in baroreceptor modulation of heart rate. In addition, the difference between young and old persons is greatest in the standing position because elderly individuals exhibit less recruitment of baroreceptor activity with postural change.

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PubMed1985

Effect of acute hypoxia on human fetal heart rate. The significance of increased heart rate variability.

The fetal heart rate response to acute hypoxemia was observed during an accidental drop in oxygen concentration inspired by the mother in labor. There was a marked increase in FHR variability in the early stage of hypoxia and also during the recovery phase. While an increase in fetal heart variability is generally considered to be a normal physiological event, it may also indicate a state of fetal hypoxemia associated with an intact fetal circulation, and should be treated with caution during labor.

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