Effect of different recumbent positions on spectral indices of autonomic modulation of the heart during the acute phase of myocardial infarction

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 Cardiac Sympathetic Nerve Activity in the Elderly Is Attenuated in the Right Lateral Decubitus Position

Objectives: The aim of this study was to evaluate the effect of the supine, left lateral decubitus, and right lateral decubitus positions on autonomic nervous activity in elderly adults by using spectral analysis of heart rate variability (HRV). Method: Forty-five adults aged 73.6 ± 5.7 years were enrolled. After lying in the supine position, all participants moved to the lateral decubitus positions in a random order and maintained the positions for 10 min, while electrocardiographic data were recorded to measure HRV. Results: The lowest heart rate continued for 10 min when participants were in the left lateral decubitus position compared with the other two positions (p < .001), while the HRV indexes remained unchanged. The low-frequency HRV to high-frequency HRV ratio (LF/HF) for the right lateral decubitus position was significantly lower than that for the other positions. Discussion: The right lateral decubitus position may attenuate sympathetic nerve activity in elderly adults.

Left Recumbent Position Decreases Heart Rate without Alterations in Cardiac Autonomic Nervous System Activity in Healthy Young Adults

Some studies have reported that recumbent position may have advantages in patients with heart disease and in pregnancy. However, it remains controversial whether recumbent position affects autonomic nervous system activity and hemodynamics in healthy adults. The aim of this study was to evaluate alterations in heart rate variability (HRV) and hemodynamics in the supine, left recumbent and right recumbent positions in healthy young adults. A total of 80 participants aged 22.8 ± 3.1 years were enrolled in this observational study. Fifty-eight volunteers (29 men and 29 women) maintained the supine position followed by the left and right recumbent positions, while electrocardiographic data were recorded for spectral analysis of HRV to assess cardiac vagal nerve and sympathetic nerve activities. The heart rate (HR) was significantly lower in the left recumbent position than in the other positions. There were no statistically significant differences in HRV among the three positions. Considering the possibility that the echographic procedure affects autonomic nervous system (ANS) activity, the other 22 participants (11 men and 11 women) underwent an echographic evaluation of hemodynamics in the heart and inferior vena cava (IVC) across the three positions. Although a low HR was also observed, there were no statistically significant differences in the IVC or the heart blood volume between the supine and the left recumbent positions. A postural change to the left recumbent position does not affect the cardiac blood circulation or ANS activity, though it does decrease HR in healthy young adults. This finding indicates that the lower HR in the left recumbent position is not attributable to the ANS activity.

The Glymphatic-Lymphatic Continuum: Opportunities for Osteopathic Manipulative Medicine

The brain has long been thought to lack a lymphatic drainage system. Recent studies, however, show the presence of a brain-wide paravascular system appropriately named the glymphatic system based on its similarity to the lymphatic system in function and its dependence on astroglial water flux. Besides the clearance of cerebrospinal fluid and interstitial fluid, the glymphatic system also facilitates the clearance of interstitial solutes such as amyloid-β and tau from the brain. As cerebrospinal fluid and interstitial fluid are cleared through the glymphatic system, eventually draining into the lymphatic vessels of the neck, this continuous fluid circuit offers a paradigm shift in osteopathic manipulative medicine. For instance, manipulation of the glymphatic-lymphatic continuum could be used to promote experimental initiatives for nonpharmacologic, noninvasive management of neurologic disorders. In the present review, the authors describe what is known about the glymphatic system and identify several osteopathic experimental strategies rooted in a mechanistic understanding of the glymphatic-lymphatic continuum.

Increased first and second pulse harmonics in Tai Chi Chuan practitioners

Background

Tai Chi Chuan (TCC) is known to be a good calisthenics for people. This study examined the relationship between pulse harmonics and autonomic nervous modulation in TCC practitioners.

Methods

Power spectral measures of right pulse wave and heart rate variability (HRV) measures were compared between TCC practitioners and control subjects. Correlation analyses between pulse harmonics and HRV measures were performed using linear regression analysis.

Results

At baseline, the total power of pulse (TPp), powers of all individual pulse harmonics, normalized power of the 1^st harmonics (nPh1) of TCC practitioners were greater, while the normalized power of the 4^th pulse harmonics (nPh4) of TCC practitioners was smaller, than those of the controls. Similarly, the baseline standard deviation (SD_RR), coefficient of variation (CV_RR), and normalized high-frequency power (nHFP) of RR intervals were smaller, while the normalized very low-frequency power (nVLFP) and low-/high- frequency power ratio (LHR) were larger in the TCC practitioners. The TCC age correlated significantly and negatively with nPh1, and nearly significantly and negatively with nPh2 in the TCC practitioners. Thirty min after TCC exercise, the percentage changes in mRRI, SD_RR, TP, VLFP were decreased, while the percentage changes in HR, ULFP, nLFP, and Ph2 were increased, relative to the controls. Correlation analysis shows that the %Ph2 correlates significantly and negatively with %mRRI and significantly and positively with %HR.

Conclusion

The TCC practitioners had increased baseline total power of pulse and the 1^st and 2^nd pulse harmonics, and decreased power of the 4^th pulse harmonics, along with decreased vagal modulation and increased sympathetic modulation. After TCC exercise, the power of the 2^nd harmonics of TCC practitioners was increased which might be related to the increase in HR due to decreased vascular resistance after TCC exercise.

The Effect of Body Posture on Brain Glymphatic Transport

The glymphatic pathway expedites clearance of waste, including soluble amyloid β (Aβ) from the brain. Transport through this pathway is controlled by the brain's arousal level because, during sleep or anesthesia, the brain's interstitial space volume expands (compared with wakefulness), resulting in faster waste removal. Humans, as well as animals, exhibit different body postures during sleep, which may also affect waste removal. Therefore, not only the level of consciousness, but also body posture, might affect CSF-interstitial fluid (ISF) exchange efficiency. We used dynamic-contrast-enhanced MRI and kinetic modeling to quantify CSF-ISF exchange rates in anesthetized rodents' brains in supine, prone, or lateral positions. To validate the MRI data and to assess specifically the influence of body posture on clearance of Aβ, we used fluorescence microscopy and radioactive tracers, respectively. The analysis showed that glymphatic transport was most efficient in the lateral position compared with the supine or prone positions. In the prone position, in which the rat's head was in the most upright position (mimicking posture during the awake state), transport was characterized by "retention" of the tracer, slower clearance, and more CSF efflux along larger caliber cervical vessels. The optical imaging and radiotracer studies confirmed that glymphatic transport and Aβ clearance were superior in the lateral and supine positions. We propose that the most popular sleep posture (lateral) has evolved to optimize waste removal during sleep and that posture must be considered in diagnostic imaging procedures developed in the future to assess CSF-ISF transport in humans.

SIGNIFICANCE STATEMENT

The rodent brain removes waste better during sleep or anesthesia compared with the awake state. Animals exhibit different body posture during the awake and sleep states, which might affect the brain's waste removal efficiency. We investigated the influence of body posture on brainwide transport of inert tracers of anesthetized rodents. The major finding of our study was that waste, including Aβ, removal was most efficient in the lateral position (compared with the prone position), which mimics the natural resting/sleeping position of rodents. Although our finding awaits testing in humans, we speculate that the lateral position during sleep has advantage with regard to the removal of waste products including Aβ, because clinical studies have shown that sleep drives Aβ clearance from the brain.

The effect of bedding system selected by manual muscle testing on sleep-related cardiovascular functions

BACKGROUND

Different types of mattresses affect sleep quality and waking muscle power. Whether manual muscle testing (MMT) predicts the cardiovascular effects of the bedding system was explored using ten healthy young men.

METHODS

For each participant, two bedding systems, one inducing the strongest limb muscle force (strong bedding system) and the other inducing the weakest limb force (weak bedding system), were identified using MMT. Each bedding system, in total five mattresses and eight pillows of different firmness, was used for two continuous weeks at the participant's home in a random and double-blind sequence. A sleep log, a questionnaire, and a polysomnography were used to differentiate the two bedding systems.

RESULTS AND CONCLUSION

Heart rate variability and arterial pressure variability analyses showed that the strong bedding system resulted in decreased cardiovascular sympathetic modulation, increased cardiac vagal activity, and increased baroreceptor reflex sensitivity during sleep as compared to the weak bedding system. Different bedding systems have distinct cardiovascular effects during sleep that can be predicted by MMT.

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.

Effect of body position on bilateral EEG alterations and their relationship with autonomic nervous modulation in normal subjects

This study investigated the effect of body position on the electroencephalogram (EEG) and autonomic nervous modulation, and the relationship between them using spectral analysis of EEG and heart rate variability (HRV). All healthy volunteers recruited had their electrocardiogram and EEG recorded for power spectral analysis. We found that when changing position from supine to upright, the EEG spectral components below the α band, such as δ and θ bands, were significantly decreased while the EEG spectral components above the α band, such as β, γ and ω bands, were significantly increased in both scalps. Correlation analysis showed that the θ rhythm of both scalps might be associated with the control of HR, the α and β rhythms of right scalp might be associated with vagal modulation, and the γ rhythm of left scalp might be associated with sympathetic modulation of the subject. Thus, some EEG components might be associated with the autonomic nervous modulation of the subject during positional change. There might be a mechanism located in the brain-stem which jointly controls both autonomic influences on heart rate and EEG activation.

Characteristics of heart rate variability can predict impending septic shock in emergency department patients with sepsis

OBJECTIVES

To determine whether heart rate variability (HRV) measures can be used to predict which septic patients in the emergency department (ED) will progress to septic shock.

METHODS

The authors prospectively enrolled consecutive patients who met the 2001 International Sepsis Definitions Conference criteria of sepsis and visited the ED of a university teaching hospital over a six-month period. In addition to the septic workup, a continuous 10-minute electrocardiogram recording was performed at the same time. The HRV measures were calculated off-line and correlated with the outcome of the patients.

RESULTS

Eighty-one patients aged 30-84 years who met the inclusion criteria were enrolled. The patients were classified as those with no septic shock (n = 60) and those with septic shock (n = 21), according to their outcome within six hours. The baseline root mean square successive difference, high-frequency power, and normalized high-frequency power of the septic shock group were significantly higher than those of the no septic shock group. The low-frequency power, normalized low-frequency power, and low-/high-frequency power ratio of the septic shock group were significantly lower than those of the no septic shock group. Multiple logistic regression analysis identified root mean square successive difference as the best predictor of impending septic shock for septic ED patients.

CONCLUSIONS

HRV measures may be used to identify septic ED patients with impending septic shock. Among those HRV measures, root mean square successive difference seems to be the best indicator to predict the occurrence of septic shock.

Position-dependent changes in vagal modulation after coronary artery bypass grafting

Reduced cardiac vagal modulation increases propensity to arrhythmias. Right decubitus position is a vagal enhancer in coronary and congestive heart disease. We evaluated vagal modulation before and after coronary artery bypass grafting (CABG) in 30 patients. Heart rate variability (HRV) indexes in frequency domain were calculated from 10-min digital electrocardiograms. Kolmogorov-Smirnov and paired t-tests were applied, p<0.05 was considered significant. The HRV indexes decreased after CABG. Higher LF/HF ratio and shorter mean RR were observed in right recumbent position postoperatively. Right lateral decubitus position did not give rise to higher vagal modulation after heart surgery.

Heart rate variability analysis: a tool to assess cardiac autonomic function

Heart rate monitoring is commonly used to provide an acute indicator of an individual's cardiovascular status and responsiveness. An increasingly popular technique involves quantifying the very small amounts by which the heart rate changes from one cardiac cycle to the next. This "heart rate variability (HRV) analysis" provides a substantial amount of additional information about the cardiovascular system and enables quantification of cardiac regulatory influences on the autonomic nervous system. The autonomic nervous system consists of two main components: the sympathetic system and the parasympathetic system. The relative influence of these two components on the sino-atrial node of the heart determines the heart rate. A number of physiological factors, including blood pressure and respiratory rate, can have a profound effect on this autonomic "balance." HRV analysis therefore provides a noninvasive method for investigating the dynamic influence of changing physiological parameters on cardiac regulation.

Short-term effect of transdermal estrogen on autonomic nervous modulation in postmenopausal women

OBJECTIVE

To evaluate the effect of short-term transdermal estradiol-l7b on cardiac autonomic nervous modulation in postmenopausal women.

DESIGN

Prospective study.

SETTING

A tertiary medical center.

PATIENT(S)

Twenty-one postmenopausal women.

INTERVENTION(S)

Transdermal estradiol or placebo therapy for 3 weeks in randomized, double-blinded, crossover fashion.

MAIN OUTCOME MEASURE(S)

Heart rate variability measures in both time and frequency domains, serum biochemistry, and climacteric symptoms were compared among baseline, placebo and transdermal estrogen therapies.

RESULT(S)

Plasma concentration of estradiol rose significantly from 11.0 +/- 5.2 pg/ml to 48.2 +/- 34.0 pg/ml after transdermal estrogen. The standard deviation of RR-interval increased significantly from 30.3 +/- 9.9 ms (placebo) to 31.3 +/- 7.4 ms (transdermal estrogen), and the coefficient of variation of RR-interval increased significantly as compared with the baseline session. The total power was marginally increased as compared among baseline, placebo, and transdermal estrogen sessions. The irritability symptom decreased significantly after transdermal estrogen therapy, as compared with baseline and placebo treatment.

CONCLUSION(S)

Transdermal estradiol for 3 weeks could significantly increase the global heart rate variability and reduce the irritability symptom in the postmenopausal women. Short-term transdermal estrogen for 3 weeks could improve cardiac autonomic nervous modulation and climacteric symptoms, and might have some cardioprotective effect in postmenopausal women.

Electroacupuncture on PC6 (Neiguan) attenuates ischemia/reperfusion injury in rat hearts

The use of somato-visceral regulation has been proposed as a treatment for a wide range of diseases. The aim of this study was to test the hypothesis that through somato-visceral regulation, ischemia-reperfusion (I/R) injury to the myocardium can be avoided by electroacupuncture (EA) on PC6 (Neiguan). Electroacupuncture on PC6 (Neiguan) was brought about by the application of metal needles over the bilateral median nerve at a point 1.5 cm proximal to the palm crease in male Spraque-Dawley rats. The animals were randomized into two groups: (1) prevention group with preconditioning by the application of EA on PC6 (n = 13); and (2) treatment group with EA on PC6 during I/R injury (n = 10). The protection against myocardial injury was blocked by different mechanisms: (1) severing of the bilateral median nerve (n = 10), (2) bilateral vagotomy (n = 10), and (3) intravenous naloxone injection (n = 10). The hemodynamic parameters (mean artery pressure and heart rate), duration of arrhythmia, mortality rate and cardiac enzymes were evaluated in these groups. The results showed that there were significant reductions in cardiac enzymes, the duration of arrhythmia and mortality rate in rats that were either preconditioned or treated with EA on PC6, compared with those that did not undergo EA on PC6 (P < 0.05). The cardioprotective effects were blocked by different procedures (P > 0.05). We conclude that EA on bilateral PC6 (Neiguan) prevents and attenuates I/R injury to the heart, and that this approach may provide an applicable and preventative alternative for patients with ischemic heart disease.

The effect of Tai Chi Chuan on the autonomic nervous modulation in older persons

PURPOSE

This study evaluated the effect of Tai Chi Chuan (TCC) on the autonomic nervous modulation in older persons.

METHODS

Twenty TCC practitioners and 20 normal controls were included in this study. The stationary state spectral heart rate variability (HRV) measures between TCC practitioners and normal controls, and the sequential changes in HRV measures after classical Yang's TCC were compared.

RESULTS

The total power, very low-frequency power, low-frequency power, normalized low-frequency power, and low-/high-frequency power ratios in TCC practitioners were all significantly higher than those of normal controls, whereas the heart rate and systolic and diastolic blood pressures were not different between these two groups of subjects. After TCC, the normalized high-frequency power increased significantly from 22.8 +/- 14.6 normalized units (nu) before TCC to 28.2 +/- 16.1 nu 30 min after TCC and to 30.6 +/- 18.4 nu 60 min after TCC. In contrast, the low-/high-frequency power ratio decreased significantly from 2.5 +/- 2.4 before TCC to 1.8 +/- 1.4 30 min after TCC and to 2.2 +/- 2.9 60 min after TCC. The heart rate, systolic blood pressure, diastolic blood pressure, mean arterial blood pressure, and pulse pressure also decreased sequentially after TCC.

CONCLUSION

The short-term effect of TCC was to enhance the vagal modulation and tilt the sympathovagal balance toward deceased sympathetic modulation in older persons. TCC might be good health-promoting calisthenics for older persons.

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.

Breathing rates and heart rate spectrograms regarding body position in normal subjects

The right lateral body position has been proposed as an effective vagal enhancer. However, the possibility of breathing affecting heart rate power spectra in different body positions has not been assessed. The level of vagal modulation in various body positions in normal subjects was estimated by calculating heart rate power spectra. The results suggest that the levels of vagal modulation do not necessarily reflect a change due to assuming different body position, but might be the consequence of changed breathing patterns. Before adopting the right lateral body position as vagal enhancing, the contribution of varying breathing pattern should be eliminated.

Comparison of heart rate variability in supine, and left and right lateral positions

In order to determine whether differences exist in cardiac autonomic tone between different body positions that may be used in unconscious subjects, we examined beat-to-beat heart rate variability (HRV) in volunteers lying supine, and in left lateral and right lateral positions. We studied 24 subjects, aged 20-35 years in each of the three positions on one study day, and 6 subjects in each of the three positions on each of six different study days. In both groups of subjects we observed no difference in heart rate, respiratory frequency, total power (0.02-0.45 Hz) of HRV or the proportion of power in the high (0.15-0.45 Hz), low (0.08-0.15 Hz) or very low (0.02-0.08 Hz) frequency bands among the three positions. These results suggest that there are no cardiac autonomic tone advantages to be gained by placing a person in the recovery position on one side compared with the other.

Autonomic dysfunction in the ICU patient

The sympathetic-parasympathetic balance may be altered in critically ill patients. Assessment of autonomic function provides information concerning prognosis, pathogenesis, and treatment strategies in ICU-relevant disorders. Proven tools are heart rate variability, baroreflex sensitivity, and, with limitations, cardiac chemoreflex sensitivity. New nonlinear methods are being evaluated that may predict risk more precisely in critically ill patients. This article summarizes application of these tools in the ICU. In addition, a model is introduced for investigating the impaired autonomic function in multiple organ dysfunction syndrome and sepsis, integrating extrinsic mechanisms and factors that are intrinsic to the cardiac tissue. By this combined approach, the authors hope to gain insight into the pathogenesis of multiple organ dysfunction syndrome. New pathophysiologic concepts are needed for the development of treatment strategies for this life-threatening disease.