Residual heart rate variability measures can better differentiate patients with acute myocardial infarction from patients with patent coronary artery.

PURPOSE: It has been shown that the power spectral density (PSD) of heart rate variability (HRV) can be decomposed into a power-law function and a residual PSD (rPSD) with a more prominent high-frequency component than that in traditional PSD. This study investigated whether the residual HRV (rHRV) measures can better discriminate patients with acute myocardial infarction (AMI) from patients with patent coronary artery (PCA) than traditional HRV measures. MATERIALS AND METHODS: The rHRV and HRV measures of 48 patients with AMI and 69 patients with PCA were compared. RESULTS: The high-frequency power of rHRV spectrum was significantly enhanced while the low-frequency and very low-frequency powers of rHRV spectrum were significantly suppressed, as compared to their corresponding traditional HRV spectrum in both groups of patients. The normalized residual high-frequency power (nrHFP = residual high-frequency power/residual total power) was significantly greater than the corresponding normalized high-frequency power in both groups of patients. Between-groups comparison showed that the nrHFP in AMI patients was significantly smaller than that in PCA patients. Receiver operating characteristic curve analysis showed that the nrHFP or nrHFP + normalized residual very low-frequency power (residual very low-frequency power/rTP) had better discrimination capability than the corresponding HRV measures for predicting AMI. CONCLUSIONS: Compared with traditional HRV measures, the rHRV measures can slightly better differentiate AMI patients from PCA patients, especially the nrHFP or nrHFP + normalized residual very low-frequency power.

The use of heart rate variability measures as indicators of autonomic nervous modulation must be careful in patients after orthotopic heart transplantation.

The precise relation between heart rate variability (HRV) and autonomic re-innervation has not been established explicitly in patients after orthotopic heart transplantation (OHT), but can be inferred from the fact that the HRV is reduced immediately after OHT and may increase gradually with time. The aim of this study was to investigate the residual HRV in patients about 1-2 years after OHT, as compared with patients after coronary artery bypass graft (CABG) surgery. Thirteen patients who had received OHT and 14 patients who had received CABG surgery were recruited. HRV analysis was performed and the HRV measures in supine position were compared between these two groups of patients. We found that the mean (mRRI), standard deviation and coefficient of variation of RR intervals, total power, very low frequency power (VLFP), low frequency power, high frequency power (HFP), normalized VLFP (nVLFP) and low-/high-frequency power ratio in the OHT group were all significantly decreased, while the heart rate (HR) and normalized HFP (nHFP) were significantly increased, as compared with the CABG group. The decrease in HRV was more severe in the VLFP region. A smaller nVLFP and a greater nHFP were associated with a smaller mRRI and a larger HR in the OHT patients. The slope of the power law relation of HRV became positive in OHT patients, instead of negative in CABG patients. We conclude that patients after OHT have residual HRV which were characterized by severely depressed time and frequency domain HRV, increased HR and nHFP, decreased nVLFP, and positive slope of the power-law relation of HRV. The use of nHFP as the indicator of vagal modulation and the use of nVLFP as the indicator of renin-angiotensin modulation, thermoregulation and vagal withdrawal must be careful in the OHT patients.

Poincaré plot analysis of autocorrelation function of RR intervals in patients with acute myocardial infarction.

The Poincaré plot of RR intervals (RRI) is obtained by plotting RRIn+1 against RRIn. The Pearson correlation coefficient (ρRRI), slope (SRRI), Y-intercept (YRRI), standard deviation of instantaneous beat-to-beat RRI variability (SD1RR), and standard deviation of continuous long-term RRI variability (SD2RR) can be defined to characterize the plot. Similarly, the Poincaré plot of autocorrelation function (ACF) of RRI can be obtained by plotting ACFk+1 against ACFk. The corresponding Pearson correlation coefficient (ρACF), slope (SACF), Y-intercept (YACF), SD1ACF, and SD2ACF can be defined similarly to characterize the plot. By comparing the indices of Poincaré plots of RRI and ACF between patients with acute myocardial infarction (AMI) and patients with patent coronary artery (PCA), we found that the ρACF and SACF were significantly larger, whereas the RMSSDACF/SDACF and SD1ACF/SD2ACF were significantly smaller in AMI patients. The ρACF and SACF correlated significantly and negatively with normalized high-frequency power (nHFP), and significantly and positively with normalized very low-frequency power (nVLFP) of heart rate variability in both groups of patients. On the contrary, the RMSSDACF/SDACF and SD1ACF/SD2ACF correlated significantly and positively with nHFP, and significantly and negatively with nVLFP and low-/high-frequency power ratio (LHR) in both groups of patients. We concluded that the ρACF, SACF, RMSSDACF/SDACF, and SD1ACF/SD2ACF, among many other indices of ACF Poincaré plot, can be used to differentiate between patients with AMI and patients with PCA, and that the increase in ρACF and SACF and the decrease in RMSSDACF/SDACF and SD1ACF/SD2ACF suggest an increased sympathetic and decreased vagal modulations in both groups of patients.

A comparative study of pulse rate variability and heart rate variability in healthy subjects.

Both heart rate variability (HRV) and pulse rate variability (PRV) are noninvasive means for the assessment of autonomic nervous control of the heart. However, it is not settled whether or not the PRV obtained from either hand can be the surrogate of HRV. The HRV measures obtained from electrocardiographic signals and the PRV measures obtained from the pulse waves recorded from the index fingers of both hands were compared in normal subjects by using linear regression analysis and Bland and Altman method. Highly significant correlations (P < 0.001, 0.89 < r < 1.0) were found between all HRV measures and the corresponding PRV measures of both hands. However, there were insufficient agreements in some measures between pairwise comparisons among HRV, right PRV and left PRV except heart rate and ultra-low frequency power (ULFP). The PRV of either hand is close to, but not the same as the HRV in healthy subjects. The HRV, right PRV and left PRV are not surrogates of one another in normal subjects except heart rate and ULFP. Since HRV is generally accepted as the standard method for the assessment of the autonomic nervous modulation of a subject, the PRV of either hand may not be suitable for the assessment of the cardiac autonomic nervous modulation of the subject.

Power spectral analysis of plethysmographic pulse waveform in pregnant women.

OBJECTIVE: To investigate the effect of pregnancy on the pulse wave of the mother. PATIENTS AND METHODS: Pulse waveforms recorded via a pulse oximeter from the left index finger of non-pregnant women and pregnant women in the three trimesters of pregnancy were Fourier transformed into power spectra. Spectral indices of the power spectra of pulse waveform were obtained and compared among non-pregnant women and pregnant women in the three trimesters of pregnancy. RESULTS: The power of harmonics of pulse wave decayed exponentially with respect to the order of harmonics. The exponent and initial value of exponential decay for the power of harmonics and the power of the 2nd harmonic were increased, whereas the total power of pulse and the powers of higher order harmonics were decreased during pregnancy. CONCLUSION: The power of harmonics of pulse wave can be described by an exponential decay function with respect to the order of harmonics in both non-pregnant and pregnant women. The effects of pregnancy on the pulse wave are the reduction in the total power of pulse and the power of higher order harmonics, and the increase in the power of lower order harmonics in the power spectrum of pulse wave. This effect of pregnancy on the pulse wave might be caused by the decrease in vascular resistance during pregnancy, the increase in workload on the heart due to increased demand of the growing fetus, and the aortocaval compression caused by the progressively enlarged gravid uterus and fetus.

A multicenter study of the association of serum uric acid, serum creatinine, and diuretic use in hypertensive patients.

BACKGROUND: Individuals with hypertension and hyperuricemia have an increased risk of coronary artery disease and cerebral vascular disease as compared to patients with normal uric acid levels. Our aim is to determine the prevalence of hyperuricemia in hypertensive patients in Taiwan, and whether serum uric acid (SUA) is associated with changes in renal function in patients with hypertension. METHODS: We studied 2145 hypertensive patients receiving medical treatment, assessed the prevalence of hyperuricemia, and determined the independent risk factors for SUA. Simple correlation and multiple regression analyses were applied to identify the independent risk factors for SUA increase. Logistic regression analysis was used to estimate the association between 4 quartiles of SUA level and correspondent serum creatinine (SCr) concentrations. RESULTS: Hypertensive subjects had a high prevalence of hyperuricemia (men, 35%; women, 43%). SUA was significantly associated with the independent risk factors of SCr, diuretic usage, and diabetes (inversely related) in both genders, whereas ß-blocker usage and body mass index were only associated in men. Multiple logistic regression models showed that in the non-diuretic user group the highest SUA quartile entailed >4 times greater risk for SCr elevation than the lowest. In the diuretic user group, a >2 times greater risk was noted. CONCLUSIONS: Hyperuricemia hypertensive subjects demonstrated a corresponding elevation of SUA and SCr irrespective of diuretic use. Elevation of SUA, in addition to SCr, may represent a progression of renal function impairment.

Foot reflexology can increase vagal modulation, decrease sympathetic modulation, and lower blood pressure in healthy subjects and patients with coronary artery disease.

OBJECTIVE: Complementary and alternative medicine (CAM) has long been used by people to postpone the aging process and to reverse disease progression. Reflexology is a CAM method that involves massage to reflex areas in the feet and hands. This study investigated the effect of foot reflexology (FR) on the autonomic nervous modulation in patients with coronary artery disease (CAD) by using heart rate variability analysis. STUDY METHODS: Seventeen people with angiographically patent coronary arteries and 20 patients with CAD scheduled for coronary artery bypass graft surgery were recruited as the control and CAD groups, respectively. The normalized high-frequency power (nHFP) was used as the index of vagal modulation and the normalized very low-frequency power (nVLFP) as the index of vagal withdrawal and renin-angiotensin modulation. RESULTS: In both control and CAD groups, the nHFP was increased significantly whereas the nVLFP was decreased significantly 30 and 60 minutes after FR, as compared with those before FR. The systolic, diastolic, mean arterial, and pulse pressures were significantly decreased after FR in both groups of participants. In the CAD group, the percentage change in heart rate 30 and 60 minutes after FR was smaller than that in the control, and the percentage change in nVLFP 60 minutes after FR was smaller than that in the control. In conclusion, a higher vagal modulation, lower sympathetic modulation, and lower blood pressure can be observed following 60 minutes of FR in both controls and CAD patients. The magnitude of change in the autonomic nervous modulation in CAD patients was slightly smaller than that in the controls. CONCLUSION: FR may be used as an efficient adjunct to the therapeutic regimen to increase the vagal modulation and decrease blood pressure in both healthy people and CAD patients.

The effect of ice water ingestion on autonomic modulation in healthy subjects.

OBJECTIVE: Drinking ice water is a common daily activity. The safety of ice water ingestion has been questioned due to its possible deleterious effect on heart rate or cardiac rhythm, especially in patients with acute myocardial infarction. Thus, we investigated the heart rate variability (HRV) before and after ice water ingestion in normal subjects to delineate the possible effect of ice water ingestion on autonomic nervous modulation. METHODS: Subjects were volunteers who came to the hospital to receive routine health examination. They were randomly assigned to drinking 250 ml of ice water or room temperature water. Twenty-eight subjects in the room temperature water ingestion group and 25 subjects in the ice water ingestion group were studied. The relationships between the change in HRV measures before and after water ingestion and clinical parameters were assessed by correlation analysis. RESULTS: After ice water ingestion, the percentage change in mean RR intervals (RRIs) (4 ± 4 vs. -1 ± 4, P < 0.001), standard deviation of RRIs (19 ± 35 vs. 0 ± 21, P = 0.018), high-frequency power (64 ± 90 vs. -3 ± 41, P < 0.001), and normalized high-frequency power (39 ± 99 vs. -5 ± 31, P = 0.038) were higher, while the percentage change in low-/high-frequency power ratio (3 ± 92 vs. 44 ± 97, P = 0.017) was lower, when compared with those after the room temperature water ingestion. INTERPRETATION: Ice water ingestion can decrease heart rate through temperature stimulus-mediated vagal enhancement in healthy subjects.

Detrended fluctuation analysis of short-term heart rate variability in late pregnant women.

Spectral analysis of heart rate variability using short or long time series is a common method in the assessment of autonomic nervous activity. Nonlinear method such as detrended fluctuation analysis was proposed and proved to be useful for the possible non-stationary and nonlinear characteristics in the time series of heart period. In this study, we investigated the detrended fluctuation analysis and conventional heart rate variability measures in 16 late pregnant women before and 3 months after delivery and in 16 healthy controls. Global and discrete, short-term (< or =11 beats, alpha1) and long-term (>11 beats, alpha2), scaling exponent were calculated in detrended fluctuation analysis. We found that the late pregnant women have elevated global scaling exponent, elevated short-term scaling exponent and lower heart rate variability measures in the low and high frequency ranges than those of the healthy controls and 3 months after delivery. The deranged measures recovered 3 months after delivery. In addition, the detrended fluctuation scaling exponent did not correlate with most conventional time and frequency domain measures of heart rate variability. Our study suggested that the global and short-term detrended fluctuation scaling exponents might be new and independent measures of heart rate variability in late pregnancy, in addition to those conventional time and frequency domain measures.

Comparison of effect of 5 recumbent positions on autonomic nervous modulation in patients with coronary artery disease.

BACKGROUND: This study compared the effect of 5 recumbent positions on cardiac autonomic nervous modulation in patients with coronary artery disease (CAD). METHODS AND RESULTS: Spectral heart rate variability analysis was performed on 33 CAD patients and 17 patients with patent coronary arteries in random order in 5 positions; namely, supine, right lateral decubitus, left lateral decubitus, left prone and right prone positions. In the right lateral decubitus position, the vagal modulation was the highest and the sympathetic modulation was the lowest among the 5 recumbent positions in the control group. In the CAD patients, the vagal modulation in the supine position was significantly lower than that in the other 4 positions. The lower the normalized high-frequency power (nHFP) in the supine position, the larger the percent age increase in nHFP when the position was changed from supine to another recumbent position in both CAD patients and controls. There was no significant change in the respiratory rate when the position was changed from supine to any of the other 4 positions. CONCLUSIONS: Right lateral decubitus position leads to the highest vagal modulation in the controls, whereas the supine position leads to the lowest vagal modulation in the CAD patients. In addition to the right lateral decubitus position, both the right and left prone positions can be used as a vagal enhancer in patients with CAD as compared with supine, especially for those patients who have severely reduced cardiac vagal modulation while supine.

Abdominal obesity is associated with autonomic nervous derangement in healthy Asian obese subjects.

BACKGROUND & AIMS: Subjects with obesity had autonomic nervous abnormalities. This study investigated autonomic nervous modulation in subjects with obesity and its association with the indices of obesity, especially the body mass index and waist circumference, by heart rate variability analysis. METHODS: Forty-seven adults with a body mass index (in kg/m(2)) greater than 28 were recruited as the obese group and 30 subjects with a body mass index less than 23 were recruited as the control group. Anthropometric measures and heart rate variability measures were obtained for both groups. The correlation between heart rate variability measures and the anthropometric measures was assessed in subjects with obesity. RESULTS: Subjects with obesity had lower normalized low-frequency power and normalized high-frequency power than those of the control group. The body height, body weight, waist circumference and waist-to-hip ratio correlated significantly with the spectral heart rate variability measures in Asian subjects with obesity, whereas the body mass index did not. CONCLUSIONS: Abdominal obesity, rather than general obesity, was related to autonomic nervous derangement in Asian subjects with obesity. The close relation between abdominal obesity and autonomic derangement may partially account for the close relationship between abdominal obesity and higher risk of mortality and morbidity in subjects with obesity.

Effect of disease activity and position on autonomic nervous modulation in patients with systemic lupus erythematosus.

Patients with systemic lupus erythematosus (SLE) are known to have lower heart rate variability and impaired vagal modulation, and right lateral position has been shown to lead to a higher vagal modulation than supine position in healthy subjects and patients with cardiovascular diseases. This study evaluated the effect of disease activity and different recumbent positions on cardiac autonomic nervous modulation by heart rate variability analysis in patients with SLE. Thirty-five female patients with SLE and 33 female controls were enrolled in this study. Electrocardiogram was recorded during supine, left lateral, and right lateral positions for 15 min. Both time and frequency domains heart rate variability measures were calculated. The normalized high-frequency power was used as the index of vagal activity, and the low-/high-frequency power ratio as the index of sympathovagal balance. We found that patients with SLE had lower indices of time domain heart rate variability measures and lower low-frequency power, high-frequency power, and normalized high-frequency power than control subjects. SLE patients with lower serum albumin had lower normalized high-frequency power and higher low-/high-frequency power ratio. In patients with SLE, right lateral position could lead to higher high-frequency power, normalized high-frequency power, and lower low-/high-frequency power ratio than supine position. In addition, the lower the normalized high-frequency power in supine position the patient had, the greater the increase in normalized high-frequency power when the position of the patient was changed from supine to right lateral. Thus, serum albumin level might be used as a potential disease severity index of SLE, and right lateral position can lead to higher vagal modulation and lower sympathetic modulation, renin-angiotensin-aldosterone modulation, and vagal withdrawal than supine position in patients with SLE. Right lateral position can be used as an efficient and physiological vagal enhancer in SLE patients with depressed vagal modulation.

Hypoxemia and autonomic nervous dysfunction in patients with chronic obstructive pulmonary disease.

OBJECTIVE: Hypoxemia is known to be associated with abnormal heart rate variability (HRV) that can reflect the severity of the illness and may have prognostic value in patients with chronic obstructive pulmonary disease (COPD). The aim of this study was to examine the relationship between the derangements in cardiac autonomic nervous function and the oxygenation status or degree of airflow obstruction in COPD patients by using HRV analysis. METHODS: Thirty clinically stable COPD patients and 18 age-matched normal subjects were included in this study. The normalized high-frequency power (nHFP) and the low-/high-frequency power ratio (LFP/HFP) were used as indices of vagal activity and sympathovagal balance, respectively. RESULTS: Although global HRV measures were all significantly decreased, the nHFP and LFP/HFP of COPD patients were not significantly different from those of normal controls. There was a negative correlation between nHFP and arterial partial pressure of O2 (PaO2) and a positive correlation between LFP/HFP and PaO2 in COPD patients. No correlation existed between forced expiratory volume in 1.0 s/forced vital capacity (FEV1/FVC), % predicted of FEV1 (%FEV1) and nHFP or LFP/HFP in COPD patients. CONCLUSIONS: The resting autonomic nervous function of COPD patients is not different from that of normal controls. Though the degree of airway narrowing is not related to the cardiac autonomic nervous function, chronic hypoxemia can lead to enhanced cardiac vagal activity and depressed sympathetic activity in COPD patients. A worse oxygenation status is associated with increased cardiac vagal and decreased cardiac sympathetic activities in COPD patients.

Increase in the vagal modulation by acupuncture at neiguan point in the healthy subjects.

Acupuncture at the Neiguan (P6) point has been shown to lessen nausea and vomiting which are related to vagal modulation. This study investigated whether acupuncture at the P6 point could improve vagal modulation by using heart rate variability analysis. We compared the heart rate variability measures of 39 subjects receiving acupuncture at the P6 point, 38 subjects receiving sham acupuncture, and 34 subjects receiving no treatment at all. The normalized high-frequency power was used as the index of vagal modulation, and the low-/high-frequency power ratio was used as the index of sympathovagal balance. The normalized high-frequency power after acupuncture increased significantly from 28.1 +/- 12.6 nu (mean +/- SD) to 30.7 +/- 14.1 nu in the P6 acupuncture group, but not in the sham acupuncture (30.6 +/- 13.7 nu versus 31.8 +/- 13.8 nu) or no-treatment group (30.1 +/- 15.0 nu versus 30.1 +/- 15.7 nu). In both the P6 and sham acupuncture groups, the mean RR interval (the intervals between consecutive R waves in the electrocardiogram) increased significantly after acupuncture. In the no-treatment group, there was no statistical difference in all heart rate variability measures in the initial and later sessions. In conclusion, acupuncture at the P6 point can increase vagal modulation of the subjects. This result may be helpful in the understanding of the mechanism underlying the effect of acupuncture or acupressure at P6 on the lessening of nausea and vomiting in clinic.

Characterization and quantification of the return map of RR intervals by Pearson coefficient in patients with acute myocardial infarction.

The return map is the plot that displays the relationship between a point and its consecutive point in a time series. This study tried to characterize and quantify the return map of RR intervals (RRI) in subjects with patent coronary arteriogram and in patients with acute myocardial infarction (AMI) by using some parameters of linear regression between RRI(n+1) and RRI(n), and compared the newly introduced parameters with the time- and frequency-domain indices of heart rate variability (HRV) obtained from the same RRI. Three quantitative measures were introduced to quantify the return map of RRI: the Pearson coefficient, slope and Y-intercept of linear regression between RRI(n+1) and RRI(n). We found that the Pearson coefficient was almost identical to the slope of linear regression, and correlated significantly and negatively with Y-intercept in controls and patients with AMI. The Pearson coefficient and the slope in patients with AMI were significantly larger while the Y-intercept was significantly smaller than those of controls. The Pearson coefficient was also found to correlate significantly and negatively with the indices of vagal modulation and positively with the indices of sympatho-vagal balance and rennin-angiotensin-aldosterone modulation in both normal controls and patients with AMI. Our results suggested that the return map of RRI could be characterized and quantified by Pearson coefficient, which was related to the autonomic nervous modulation of the subject.