Cheryl C.H. Yang

Effect of aging on gender differences in neural control of heart rate

To clarify the influence of gender on sympathetic and parasympathetic control of heart rate in middle-aged subjects and on the subsequent aging process, heart rate variability (HRV) was studied in normal populations of women ( n = 598) and men ( n = 472) ranging in age from 40 to 79 yr. These groups were divided into eight age strata at 5-yr intervals and were clinically diagnosed as having no hypertension, hypotension, diabetic neuropathy, or cardiac arrhythmia. Frequency-domain analysis of short-term, stationary R-R intervals was performed, which reveals very-low-frequency power (VLF; 0.003-0.04 Hz), low-frequency power (LF; 0.04-0.15 Hz), high-frequency power (HF; 0.15-0.40 Hz), the ratio of LF to HF (LF/HF), and LF and HF power in normalized units (LF% and HF%, respectively). The distribution of variance, VLF, LF, HF, and LF/HF exhibited acute skewness, which was adjusted by natural logarithmic transformation. Women had higher HF in the age strata from 40 to 49 yr, whereas men had higher LF% and LF/HF between 40 and 59 yr. No disparity in HRV measurements was found between the sexes in age strata ≥60 yr. Although absolute measurements of HRV (variance, VLF, LF, and HF) decreased linearly with age, no significant change in relative measurements (LF/HF, LF%, and HF%), especially in men, was detected until age 60 yr. We conclude that middle-aged women and men have a more dominant parasympathetic and sympathetic regulation of heart rate, respectively. The gender-related difference in parasympathetic regulation diminishes after age 50 yr, whereas a significant time delay for the disappearance of sympathetic dominance occurs in men.To clarify the influence of gender on sympathetic and parasympathetic control of heart rate in middle-aged subjects and on the subsequent aging process, heart rate variability (HRV) was studied in normal populations of women (n = 598) and men (n = 472) ranging in age from 40 to 79 yr. These groups were divided into eight age strata at 5-yr intervals and were clinically diagnosed as having no hypertension, hypotension, diabetic neuropathy, or cardiac arrhythmia. Frequency-domain analysis of short-term, stationary R-R intervals was performed, which reveals very-low-frequency power (VLF; 0.003-0.04 Hz), low-frequency power (LF; 0.04-0.15 Hz), high-frequency power (HF; 0.15-0.40 Hz), the ratio of LF to HF (LF/HF), and LF and HF power in normalized units (LF% and HF%, respectively). The distribution of variance, VLF, LF, HF, and LF/HF exhibited acute skewness, which was adjusted by natural logarithmic transformation. Women had higher HF in the age strata from 40 to 49 yr, whereas men had higher LF% and LF/HF between 40 and 59 yr. No disparity in HRV measurements was found between the sexes in age strata >/=60 yr. Although absolute measurements of HRV (variance, VLF, LF, and HF) decreased linearly with age, no significant change in relative measurements (LF/HF, LF%, and HF%), especially in men, was detected until age 60 yr. We conclude that middle-aged women and men have a more dominant parasympathetic and sympathetic regulation of heart rate, respectively. The gender-related difference in parasympathetic regulation diminishes after age 50 yr, whereas a significant time delay for the disappearance of sympathetic dominance occurs in men.

Relationship between electroencephalogram slow-wave magnitude and heart rate variability during sleep in humans

To explore whether depth of sleep is related to changes in autonomic control, continuous power-spectral analysis of the electroencephalogram (EEG) and heart rate variability (HRV) was performed in ten normal subjects during nocturnal sleep. Quiet sleep (QS) was associated with an increase in high-frequency power (HF) of HRV (0.15-0.4 Hz) but a decrease in low-frequency power (LF) (0.04-0.15 Hz) to HF ratio (LF/HF) compared with awakening. During QS, LF/HF was significantly and negatively correlated with delta power of EEG (0.5-4.0 Hz), whereas mean R-R interval and HF were not. We conclude that during QS, cardiac sympathetic regulation is negatively related to the depth of sleep, although vagal regulation is not. Our methodology offers a quantitative analysis to study the interaction between cerebral cortical and autonomic functions.

An alternative method to enhance vagal activities and suppress sympathetic activities in humans

Vagal withdrawal and/or sympathetic overactivity is always accompanied by various kinds of stress and is dangerous to the body. We proposed that mild acupuncture on the Sishencong points may effectively enhance vagal activities but suppress sympathetic regulations of the heart in humans. Experiments were carried out on nine healthy male volunteers, while they were lying in a quiet room during 2-4 P.M. Acupuncture was applied 2 mm deep into the skin using standard stainless acupuncture needles at the Sishencong points, which are located on the vertex of the head, each 1 cm away from Baihui (GV 20) in four directions. Four points around the temporal area were selected as control points. Forty minutes of precordial ECG signals before, during, and after acupuncture were recorded continuously. Frequency-domain analysis of the stationary RR intervals was performed to evaluate the total variance, high-frequency power (HF, 0.15-0.40 Hz) and low-frequency power (LF, 0.04-0.15 Hz) in normalized units (LF%). Acupuncture on the Sishencong points resulted in an increased HF but a decreased LF% compared with the before acupuncture stage. Such effects did not occur when manual acupuncture was applied to the control points. The differences in the heart rate dynamics between Sishencong and the control groups took place 10 min after initiation of acupuncture and persisted even after the removal of the needles. Based on these results, we concluded that manual acupuncture on the Sishencong points enhanced cardiac vagal and suppressed sympathetic activities in humans. The underlying mechanisms and potential applications warrant further investigations.

Sleep-Related Changes in Cardiovascular Neural Regulation in Spontaneously Hypertensive Rats

Background—Sleep has significant effects on cardiovascular neural regulation. The aim of this study is to explore the possible change in sympathetic vasomotor activity and baroreflex sensitivity associated with spontaneous hypertension during each stage of the sleep-wake cycle. Methods and Results—Polysomnographic analysis was performed in freely moving spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) during their normal daytime sleep. Continuous spectral analyses of electroencephalogram and electromyogram were performed to define active waking, quiet sleep, and paradoxical sleep. Low-frequency power of the arterial pressure variability (BLF) was quantified to provide an index of sympathetic vasomotor activity. Spontaneous baroreflex sensitivity was assessed (1) by the slopes of the regression lines of the mean arterial pressure and R-R intervals pairs that ascended (BrrA) or descended (BrrD) successively and (2) by the magnitudes of the arterial pressure and R-R intervals transfer functions in the high-frequency (BrrHF) or low-frequency (BrrLF) ranges. SHR had significantly higher mean arterial pressure during each of the sleep-wake states. Although the values of BLF, BrrA, BrrD, BrrHF, and BrrLF in SHR did not differ from those of WKY during active waking, SHR had a significantly higher BLF and lower BrrA, BrrD, BrrHF, and BrrLF compared with WKY during quiet sleep and paradoxical sleep. Conclusions—SHR had enhanced sympathetic vasomotor activity but attenuated baroreflex sensitivity during sleep although each phenomenon was not evident when awake.

Heart rate variability in children with refractory generalized epilepsy

OBJECTIVE Repetitive seizures can alter the regulation of cardiac activity by the autonomic nervous system (ANS), and ANS dysregulation is thought to be associated with higher morbidity and mortality in epileptic patients, especially from sudden unexpected death. Few studies of interictal dysregulation of cardiac activity in children with epilepsy have been performed. In this study we characterize heart rate variability (HRV) in children with refractory generalized epilepsy. METHODS Fifteen male and 15 female children, average age = 10.9+/-0.6 years, all with refractory generalized epilepsy were enrolled into the study group. A control group consisted of 15 males and 15 females with average age = 10.6+/-0.6 years. A lead I ECG was recorded for 5 min in the interictal period during daylight hours from each subject while awake. Frequency-domain analysis of HRV was performed using a non-parametric method of fast Fourier transformation. Changes of HRV were categorized into high frequency power (HF; 0.15-0.45 Hz), which represented vagal regulation, and low frequency power (LF; 0.04-0.15 Hz). LF/(HF+LF) expressed in normalized units (LF%) was considered to mirror sympathetic regulation. RESULTS There were significant reductions in RR, LF, and HF in the study group when compared to controls. There was no significant difference in LF% between the two groups. CONCLUSIONS We postulate that the lower HRV in our patients results from parasympathetic or vagal reduction. This suggests that decreased HRV in epileptic children occurs by a different mechanism than in adults with epilepsy.

Heart rate variability in patients with frontal lobe epilepsy

OBJECTIVE To identify autonomic dysregulation in frontal lobe epilepsy (FLE). METHODS We studied 14 male and 11 female subjects with FLE and an equal number of matched healthy control subjects. Lead I electrocardiograms were obtained for 5 min in the interictal state during daytime. Frequency-domain analysis of heart rate variability was performed and the data subsequently converted to heart rate interval and high frequency (HF; 0.15-0.45 Hz) power which representing vagal or parasympathetic regulation, as well as low frequency (LF; 0.04-0.15 Hz) power and LF/(HF+LF) expressed in normalized units (LF%) (considered to mirror sympathetic regulation). Differences in data between groups were compared using t-test. RESULTS The epilepsy group had a lower mean heart rate interval and a lower high frequency power. CONCLUSIONS Patients with FLE have interictally faster heart rates, attributed to lower parasympathetic drive, which may contribute to the higher incidence of sudden death that is seen in this group of patients. This suggests that the mechanism of decreased HRV in patients with FLE is probably different from that in patients with temporal lobe epilepsy.

Assessment of cardiac sympathetic regulation by respiratory-related arterial pressure variability in the rat

1 Mechanical ventilation evokes a corresponding arterial pressure variability (APV) which is decreased by β‐adrenoceptor antagonism. Therefore, in this study we set out to determine whether the respiratory‐related APV can be used to assess cardiac sympathetic tone. 2 Computer‐generated broad‐band mechanical ventilation (0–3 Hz) was applied to Sprague‐Dawley rats that had been anaesthetized with ketamine and paralysed with pancuronium. APV and its relationship to lung volume variability (LVV–APV) was systematically quantified with auto‐ or cross‐spectral frequency domain analysis. 3 APV and LVV–APV transfer magnitudes between 0.5 and 1.5 Hz showed dose‐dependent suppression by propranolol from 0.01 to 1 mg kg−1, while the static value of arterial pressure remained unchanged. Stroke volume variability, assessed by the use of a pulse contour method, exhibited a similar pattern of suppression by propranolol. In contrast, heart rate variability was not lowered with propranolol. 4 The effect of propranolol on respiratory‐related APV persisted even in the presence of combined α‐adrenoceptor and muscarinic receptor blockade by phentolamine and atropine. 5 The frequency range of 0.5–1.0 Hz was optimal for LVV–APV transfer magnitude to correlate with cardiac sympathetic tone. 6 We conclude that respiratory‐related APV may provide a valid assessment of cardiac sympathetic regulation which is independent of parasympathetic and vascular sympathetic influences in ketamine‐anaesthetized and positive pressure‐ventilated rats.

Gender-Specific Association Between Self-reported Sleep Duration and Falls in High-Functioning Older Adults

BACKGROUND Prior studies have shown that sleep disturbances are related to falling and its risk factors, such as poorer cognition, depression, and physical function. However, little is know about the gender-specific associations between falling and sleep duration. METHODS Study participants were from the annual Health Examination for the Elderly Program in the National Taiwan University Hospital (135 women and 121 men, mean age 72.2 years). Self-reported sleep duration was grouped into three categories: less than 5, 5-7.9, and 8 or more hours. Short sleep duration was defined as sleep duration less than 5 hours. Falling during the previous 12 months was ascertained by self-report questionnaire. The association of sleep duration with falling was examined by using multiple logistic regression. We approximated risk ratio (RR) of falls from the adjusted odds ratio (OR) after correction of falls incidence in the previous year. RESULTS Sleep duration was inversely associated with falling among women. After adjusting for multiple confounding factors including use of antihypertensives and psychotropic medications, the OR of falls for each hour decrease in sleep duration was 1.95 (95% confidence interval [CI] 1.24-3.06). Moreover, women with sleep deprivation had a greater odds of falls within the last year than those with longer sleep durations. The estimated RR of falls comparing women with short sleep duration (sleep <5 hours) with those without was 2.98 (95% CI 1.32-4.62). We did not find an association among men. CONCLUSION Sleep deprivation is independently associated with falls in women but not in men. Short sleep duration may be an indicator to identify women at risk for falling.

The relationship of subjective sleep quality and cardiac autonomic nervous system in postmenopausal women with insomnia under auricular acupressure.

Objective:The aim of this study is to examine the relationship between the changes in self-reported sleep symptoms and cardiac sympathovagal activity among women with postmenopausal insomnia (PI) who received auricular acupressure (AA) therapy. Methods:A pretest/posttest study design was conducted at Taipei Veterans General Hospital, Taiwan, from August 2008 to July 2009. Forty-five women (mean ± SD age, 56.2 ± 5.4 years) with PI (4.9 ± 3.5 years of insomnia) received an AA therapy course on five auricular points every night before going to sleep for 4 weeks. Heart rate variability (HRV), the Chinese version of the Pittsburgh Sleep Quality Index, and the Menopause Rating Scale were measured before and after AA treatment. Results:The total sleep duration and sleep efficiency were increased, and the sleep latency was shortened significantly (P < 0.01) after AA therapy. The total Menopause Rating Scale and somatovegetative subscale scores were reduced significantly (P < 0.05) after the intervention. A greater percentage change in Pittsburgh Sleep Quality Index was moderately correlated with both a lower percentage change in high-frequency power of HRV (r = −0.660, P < 0.001) and a greater percentage change in normalized low-frequency power (nLF) of HRV (r = 0.599, P < 0.001). An elevation of high-frequency power and a reduction of nLF of HRV were observed in the responder group, whereas a raise in nLF of HRV was noted in the nonresponder group. Conclusions:This study suggests that AA intervention leads to more cardiac parasympathetic and less cardiac sympathetic activity, which contributes to the improvement of PI.

Combined cardiac sympathetic excitation and vagal impairment in patients with non-organic erectile dysfunction.

OBJECTIVE Patients with non-organic erectile dysfunction (ED) frequently present with syndromes involving systemic sympathovagal dysfunction. The linkage of ED to cardiac autonomic regulation is not well understood. METHODS Forty-four men with non-organic ED and 38 healthy age-matched control subjects with ages ranging from 40 years to 69 years were recruited. These two groups were divided into three distinct age categories at 10-year intervals. Patients were divided into three different severity categories, among whom 35 patients received a two-month oral treatment of trazodone. Power spectral analysis of successive R-R intervals (RR) was performed to evaluate the variance (variance of RR-interval values), the high-frequency power (HF), and the ratio of low-frequency power to HF (LF/HF) of their heart rate variability (HRV). RESULTS Patients exhibited a significantly lower variance and HF, but a higher LF/HF compared to the control group across all age categories. The changes in variance and HF were severity dependent. In addition, all the HRV parameters of the patients with a satisfactory response after treatment have significantly improved. CONCLUSION The results indicate that patients with non-organic ED had significant cardiac sympathetic hyperactivity and severity-dependent cardiac vagal impairment. SIGNIFICANCE Non-organic ED may be accompanied by an abnormality in cardiac autonomic regulation.