Age-related changes of cardiac control function in man. With special reference to heart rate control at rest and during exercise

Assessment of the Effects of Age, Gender, and Exercise Training on the Cardiac Sympathetic Nervous System Using Positron Emission Tomography Imaging

BACKGROUND

Using positron emission tomography (PET) imaging, we sought to determine whether normal age or exercise training cause changes in the cardiac sympathetic nervous system function in male or female healthy volunteers.

METHODS

Healthy sedentary participants underwent PET studies before and after 6 months of supervised exercise training. Presynaptic uptake by the norepinephrine transporter-1 function was measured using PET imaging of [(11)C]-meta-hydroxyephedrine, a norepinephrine analog, and expressed as a permeability-surface area product (PSnt in mL/min/mL). Postsynaptic function was measured as β-adrenergic receptor density (β'max in pmol/mL tissue) by imaging the β-receptor antagonist [(11)C]-CGP12177. Myocardial blood flow (MBF in mL/min/mL tissue) was measured by imaging [(15)O]-water.

RESULTS

At baseline, there was no age difference in β'max or MBF but PSnt declined with age (1.12±0.11 young vs 0.87±0.06 old, p = .036). Before training, women had significantly greater MBF (0.87±0.03 vs 0.69±0.03, p < .0001) and PSnt (1.14±0.08 vs 0.75±0.07, p < .001) than men. Training increased VO2 max by 13% (p < .0001), but there were no training effects on β'max, PSnt, or MBF. Greater MBF in females and a trend to increased PSnt post-training persisted.

CONCLUSION

With age, presynaptic uptake as measured by PSnt declines, but there were no differences in β'max. Endurance training significantly increased VO2 max but did not cause any changes in the measures of cardiac sympathetic nervous system function. These findings suggest that significant changes do not occur or that current PET imaging methods may be inadequate to measure small serial differences in a highly reproducible manner.

Blunted cardiac autonomic responsiveness to hypoxemic stress in healthy older adults

Supine resting cardiac dynamics and responses to steady-state hypoxemia were investigated in six healthy older (59-72 yrs) adults using coarse-graining spectral analysis of heart rate variability (HRV) and were compared to six young (22-29 yrs) adults studied previously (Lucy et al., 2000). End-tidal carbon dioxide pressure (PETCO2) was clamped at 1-2 mmHg above the usual resting value for 11 min of euoxia (PETO2 100 mmHg), followed by 22 min of hypoxia (PETO2 55 mmHg). During euoxia, vagally mediated harmonic and fractal power of HRV of older adults was minimal. Hypoxia induced an increase in ventilation, p < 0.01, and heart rate, p < 0.05. The heart rate increase (mean +/- SE) of 0.23 +/- 0.08 beats.min-1 per 1% decrease in arterial O2 saturation was 25% of that demonstrated previously by young subjects, p < 0.001. In older adults, HRV spectral power remained unchanged during hypoxia, providing further evidence of an age-related blunting of cardiac autonomic function.

Accelerated plethysmogram in nursing home residents

To investigate the peripheral blood circulation, 24 young volunteers, 28 nursing home residents with cerebrovascular diseases (CVD) and 42 residents without them were studied for accelerated plethysmogram (APG). Both residents were rated by the modified Stockton geriatric rating scale (modified SGRS) which have four aspects of impairments; physical disability, socially irritating behavior, communication failure and apathy. As to the waveform patterns of APG, the majority of the young volunteers and both the residents showed patterns B and G, respectively. Coefficient of APG (Co-APG) of the former was significantly larger than that of the latter. In the residents without CVD, Co-APG was significantly negatively correlated with physical disability and apathy of the modified SGRS. But, Co-APG did not correlate with the modified SGRS in the residents with CVD.

Relationship between common carotid arterial flow and age in nursing home residents

Heart rate and carotid blood flow were measured in 82 elderly nursing home residents in both supine and sitting positions. The subjects had been divided into two groups according to whether or not they had had an episode of chronic cerebrovascular disease. In subjects with chronic cerebrovascular disease, the heart rate in the sitting position was significantly (P less than 0.01) faster than that in the supine position but there were no significant differences in total carotid blood flow volume or in mean carotid blood flow velocity between the positions. In subjects with chronic cerebrovascular disease, there were also no significant correlations between heart rate, total blood flow volume, or mean blood flow velocity, in either position, and age. In subjects without chronic cerebrovascular disease, the results for postural change were the same as those in subjects with chronic cerebrovascular disease but in both positions there was a significant negative correlation between age and both total carotid blood flow volume and mean carotid blood flow velocity.

The beat-to-beat blood pressure response to postural change in young and elderly healthy adult males

Heart rate and blood pressure were studied with the beat-to-beat tracking cuff system in two groups (n = 20 per group) of healthy, unmedicated males, one between 60 and 75 years of age and the second between 18 and 29 years of age. The study confirms the previously reported blunted heart rate response to standing and the fact that, when blood pressure is recorded by conventional means, the response exhibited during orthostasis does not differ in healthy groups of young and elderly subjects. With the tracking cuff system, however, the elderly exhibited a smaller immediate systolic and diastolic drop in response to the change to upright posture and less variability in beat-to-beat blood pressure changes. The results have implications for cardiovascular studies, where age and posture can influence both blood pressure and heart rate.

Assessment by autonomic blockade of age-related changes of the sinus node function and autonomic regulation in sick sinus syndrome

Age-related changes of the sinus node (SN) function and the autonomic influence on the SN function were evaluated in 65 patients with sick sinus syndrome (range 14 to 84 years). Heart rate (HR), corrected SN recovery time and sinoatrial conduction time were measured before (basic) and after (intrinsic) autonomic blockade (propranolol 0.2 mg/kg plus atropine 0.04 mg/kg intravenously). Percent of autonomic chronotropies of the SN function were calculated by the following formulas: (1)--(intrinsic HR--basic HR/intrinsic HR) X 100; (2) (intrinsic corrected SN recovery time--basic corrected SN recovery time/intrinsic corrected SN recovery time) X 100; (3) (intrinsic sinoatrial conduction time--basic sinoatrial conduction time/intrinsic sinoatrial conduction time) X 100. Basic HR, basic corrected SN recovery time and basic sinoatrial conduction time did not vary with age. Intrinsic HR decreased with age, but this correlation was weak (r = -0.54, p less than 0.001). Intrinsic corrected SN recovery time and intrinsic sinoatrial conduction time tended to increase with age (r = 0.26, p less than 0.05; r = 0.29, p less than 0.05, respectively). Percent chronotropies of HR, corrected SN recovery time and sinoatrial conduction time were negative values in younger patients and positive values in elderly patients; they correlated positively with age (r = 0.59, p less than 0.001; r = 0.60, p less than 0.001; r = 0.43, p less than 0.001, respectively). Thus, the basic SN function did not change with age, while the intrinsic SN function deteriorated with age.(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormal heart rate control in vasospastic angina: effects of calcium antagonists

We examined the effects of administration of calcium antagonists on the heart rate response to treadmill exercise in 11 patients with vasospastic angina and 8 healthy young volunteers. The exercise test was performed by walking on a treadmill at a constant speed and grade according to a scheme of pseudo-randomized sequence for 19 min. The dynamic property of heart rate response to exercise was evaluated by using a frequency analytic procedure. The exercise test was also studied in 21 age-matched normal controls without drug administration. Administration of calcium antagonists revealed no significant effects on heart rate and blood pressure at rest in young healthy subjects or in patients with vasospastic angina. Young volunteers showed the same normal properties of heart rate response to exercise before and after calcium antagonists. Vasospastic angina showed abnormal heart rate response to exercise and revealed characteristically different transfer function from that in normal controls. These characteristics were not affected by treatment with calcium antagonists except for a slight, uniform decrease of gain of the system over the whole frequency range. Accordingly, the present exercise test can feasibly be used in the diagnosis and management of vasospastic angina even when calcium antagonists are administered to the patients.

Poor responsiveness of heart rate to treadmill exercise in vasospastic angina

Heart rate response to submaximal graded treadmill exercise was measured in 45 patients with vasospastic angina, 31 with effort angina, and 40 normal controls. There was no difference of resting heart rate among the three groups. Vasospastic angina showed significantly poor responsiveness of heart rate to exercise at every stage: stage 1, 2.5 km/h (10%), stage 3, 4.5 km/h (10%), stage 5, 5.5 km/h (14%), stage 7, 5.5 km/h (22%), when compared with those in normal controls. The effort angina group also showed lower heart rates at stages 3 and 5 than those in control subjects, although their heart rate at stage 1 was not different from that in normals. When abnormal response suggesting vasospastic angina was defined as heart rate at each stage lower than values of mean heart rate +/- 1 SD in normal controls, positive test results were obtained in 15 of 45 patients (33%). The use of heart rate criteria in addition to ischemic criteria raises sensitivity from 27 to 51% (p less than 0.02).

Cardiovascular responses to acute footshock stress in adult and aged Fischer 344 male rats

Tail artery catheters were surgically implanted in Fischer 344 male rats to allow for measurement of mean arterial pressure (MAP, mm Hg) and heart rate (HR, beats/min) in conscious, unrestrained rats. Basal values of MAP and HR were similar for groups of 4, 12 and 24 month old rats. Increments in Map did not differ among rats of the 3 ages following handling and transfer to a shock chamber or immediately or 5 minutes after exposure to inescapable footshock (2.0 mA, 0.6 sec duration, every 6 sec for 1 min). In contrast, there was a significant age-related attenuation of the tachycardia following handling and transfer of rats to the shock chamber and at the end of footshock. These data are consistent with previous findings of a reduced sensitivity of the aged myocardium to stress-induced sympathetic stimulation.

Diagnosis of vasospastic angina by analysis of heart rate response to exercise: effects of different levels of work load

To examine alterations in control functions of the heart, which may account for the pathophysiologic conditions precipitating coronary arterial spasm, heart rate response to exercise in vasospastic angina was evaluated by using our previously developed method of frequency analysis. We also examined the effects of three different levels of work load on the heart rate response to treadmill exercise in 9 patients with vasospastic angina and 7 normal controls: stage 1 (2.5 Km/h, 10%), stage 3 (4.5 Km/h, 10%), and stage 5 (5.5 Km/h, 14%). The transfer function of heart rate control in vasospastic angina was characteristically different from that in normal controls: lower gain and more delayed phase angle of the system. Although this abnormality was observed in every test at 3 different levels of work load, the abnormality was more striking in tests at lower levels of work load: stage 1 or 3. The moderately light exercise test at stage 3 is most suitable as a test for detecting abnormal heart rate response to exercise in vasospastic angina because the exercise test at stage 1 had a poor S/N ratio.

Does aging differentially reduce heart rate variability related to respiration?

Segments of resting heart rate were submitted to spectral analysis in order to assess changes in spectral power with age. Different frequencies of heart rate variability have been related to vagal and sympathetic cardiac control. Data were from 56 male volunteers ranging in age between 18 and 65 years of age. Spectral results revealed that respiratory sinus arrhythmia declined less with age than lower (vasomotor) frequencies. Assessment of total (rather than relative) power at respiratory frequencies revealed the expected drop in power with age. Thus, the decline in heart rate variability with age may not be due predominantly to a decline in frequencies related to respiration.