Cardiac Parasympathetic Nervous Activity Research Articles

Autonomic Nerve Activity Features According to Dry Eye Type.

The purpose of this study was to investigate the association between autonomic nerve activity and symptom intensity according to the type of dry eye (DE). This prospective, cross-sectional, comparative study included 25 eyes of 25 patients with short tear break-up time DE (sBUTDE; mean age = 57.4 ± 11.4 years, range = 30-74 years) and 24 eyes of 24 patients with aqueous tear-deficient DE (ADDE; mean age = 62.3 ± 10.7 years, range = 29-76 years) were studied. Autonomic nerve activity was examined, and the Japanese version of the Ocular Surface Disease Index (J-OSDI) and a stress check questionnaire were administered. Autonomic nerve activity was continuously measured for 10 minutes. The parameters were low-frequency (LF) and high-frequency (HF) components of heart rate variability, reflecting cardiac sympathetic and parasympathetic nerve activity, and parasympathetic nerve activity alone, respectively; and the coefficient of variation of R wave-to-R wave (RR) interval (cvRR), component coefficient of variation of LF (ccvLF), and component coefficient of variation of HF (ccvHF), reflecting fluctuation of RR interval, LF, and HF, respectively. Higher J-OSDI scores were associated with higher HF, ccvHF, and subjective stress in sBUTDE, showing a significant correlation (r = 0.53, P < 0.01; r = 0.55, P = 0.01; and r = -0.66, P = 0.01); no correlations were observed between the J-OSDI score and autonomic parameters and stress in ADDE. DE symptoms were significantly associated with the magnitude and fluctuation of parasympathetic activity in sBUTDE. Thus, among the autonomic parameters, parasympathetic activity is involved in the development of symptoms in sBUTDE, whereas the involvement of the autonomic nervous system may be minimal in ADDE.

Temporal relationships among changes in the RR-interval and the powers of the low- and high-frequency components of heart rate variability in normal subjects.

Spectral analysis of heart rate variability (HRV) is widely used as a non-invasive method to assess the cardiovascular autonomic function. Of the two main frequency components of HRV, namely low-frequency (LF, 0.04-0.15 Hz) and high-frequency (HF, 0.15-0.4Hz) components, it is generally accepted that the HF power reflects modulation of heart rate which is mediated by cardiac parasympathetic (vagal) nerve activity. In contrast, the origin and functional correlates of the LF component are still controversial. Although several lines of evidence have indicated a close correlation between LF power and the baroreflex modulation of autonomic outflows, the detailed mechanisms underlying the genesis of the LF component remain unclarified. In this study, we conducted an ultra-short-term (UST) spectral analysis of R-R interval (RRI) time series using Fast Fourier Transform (FFT) with 5- and 25-s windows to clarify the temporal relationships among transient changes in the RRI and, LF and HF powers in healthy subjects. We found that during active standing, transient RRI increases occurred sporadically. The UST spectral analysis revealed that this RRI increase was associated with a simultaneous increase in HF power which was closely linked to the prominent LF power increase. These results indicate that during active standing, increases in LF and HF powers occur simultaneously, and they may reflect enhanced cardiac vagal activity which generates transient bradycardia.

Dissecting the Roles of the Autonomic Nervous System and Physical Activity on Circadian Heart Rate Fluctuations in Mice.

Heart rate (HR) and blood pressure as well as adverse cardiovascular events show clear circadian patterns, which are linked to interdependent daily variations in physical activity and cardiac autonomic nerve system (ANS) activity. We set out to assess the relative contributions of the ANS (alone) and physical activity to circadian HR fluctuations. To do so, we measured HR (beats per minute, bpm) in mice that were either immobilized using isoflurane anesthesia or free-moving. Nonlinear fits of HR data to sine functions revealed that anesthetized mice display brisk circadian HR fluctuations with amplitudes of 47.1±7.4bpm with the highest HRs in middle of the dark (active) period (ZT 18: 589±46bpm) and lowest HRs in the middle of the light (rest) period (ZT 6: 497±54bpm). The circadian HR fluctuations were reduced by ~70% following blockade of cardiac parasympathetic nervous activity (PNA) with atropine while declining by <15% following cardiac sympathetic nerve activity (SNA) blockade with propranolol. Small HR fluctuation amplitudes (11.6±5.9bpm) remained after complete cardiac ANS blockade. Remarkably, circadian HR fluctuation amplitudes in freely moving, telemetrized mice were only ~32% larger than in anesthetized mice. However, after gaining access to running wheels for 1week, circadian HR fluctuations increase to 102.9±12.1bpm and this is linked directly to increased O2 consumption during running. We conclude that, independent of physical activity, the ANS is a major determinant of circadian HR variations with PNA playing a dominant role compared to SNA. The effects of physical activity to the daily HR variations are remarkably small unless mice get access to running wheels.

Determinants of exercise limitation in contemporary paediatric Fontan patients with an extra cardiac conduit

BackgroundAlthough various determinants of exercise limitation in Fontan patients have been studied, most research has been performed in patients who underwent different surgical procedures with differing haemodynamic characteristics. The aim of the current study was to evaluate non-invasively measured cardiovascular parameters and their influence on exercise performance in paediatric Fontan patients with an extracardiac conduit and moderate-good systolic ventricular function. MethodsFontan patients, between 8 and 18 years of age, with moderate to good systolic ventricular function and an extracardiac conduit were included. Exercise performance and cardiovascular assessment, comprising echocardiography, aortic stiffness measurement and ambulatory measurement of cardiac autonomous nervous activity were performed on the same day. Healthy subjects served as controls. ResultsThirty-six Fontan patients (age 14.0 years) and thirty-five healthy subjects (age 12.8 years) were included. Compared to controls, Fontan patients had reduced diastolic ventricular function and increased arterial stiffness. No differences were found in heart rate (HR) and cardiac parasympathetic nervous activity. In Fontan patients, maximal as well as submaximal exercise capacity was impaired, with the percentage of predicted capacity ranging between 54 and 72%. Chronotropic competence, however, was good with a peak HR of 174 (94% of predicted). Lower maximal and submaximal exercise capacity was correlated with a higher HR at rest, higher pulse wave velocity of the aorta and a lower ratio of early and late diastolic flow velocity. ConclusionContemporary paediatric Fontan patients have an impaired exercise capacity with preserved chronotropic competence. Exercise performance correlates with heart rate at rest, diastolic function and aortic stiffness.

Abstract 16157: Catheter Ablation Induces an Increase in Heart Rate With Discordant With a Decrease in Sympathetic Nerve Activity in Patients With Paroxysmal Atrial Fibrillation

Background/Introduction: Paroxysmal atrial fibrillation (PAF) is the most common arrhythmia and catheter ablation (CA) is selected with the aim of rhythm control. CA was reported to increase heart rate (HR), which explains the modulation on the cardiac autonomic nervous system. However, little is known about the relationship between heart rate, sympathetic nerve activity and parasympathetic nerve activity in patient with PAF. Purpose: The purpose of this study was to evaluate the effect of CA on direct recording of muscle sympathetic nerve activity (MSNA) and heart rate variability (HRV), and these influences on HR. Methods: This study was conducted as a prospective, observational study. Patients with PAF who were scheduled for CA were enrolled. We measured blood pressure, HR, body weight, brain natriuretic peptide (BNP), echocardiogram parameters, high frequency component as cardiac parasympathetic nerve activity and low frequency component as cardiac sympathetic nerve activity in HRV, and MSNA before and 12 weeks after CA. Results: 21 PAF patients participated in this study. After CA, E/e’ and Ln BNP were significantly reduced(10.6±2.9 to 9.2±2.6, p&lt;0.05. 3.8±1.3 to 3.3±1.6 log/pg/ml, p&lt;0.05, respectively) while no significant changes were observed in EF, SV, left atrial diameter, left ventricular end diastolic and systolic diameters. HR was significantly increased (61.3±7.8 to 71.1±7.6 beats/min, p&lt;0.05, respectively). However, the MSNA burst incidence and frequency were significantly decreased (65.4±12.6 to 41.3±13.4 bursts/100beats, p&lt;0.01, n=21. 39.8±8.8 to 28.1±9.6 bursts/min, p&lt;0.01, n=21. respectively). Also, the reduction in MSNA burst frequency was correlated with the increase in HR (r=0.57, 95%CI 0.183-0.804, p=0.00702). Ln Low frequency component in HRV was significantly decreased (5.72±1.75 to 3.85±2.13 log/ms 2 , p&lt;0.05, n=12), but Ln high frequency (HF) component was not changed . No significant relationship observed between increased HR and HF component. Conclusion: CA induced paradoxical increasing heart rate with the reduction in sympathetic nerve activity in patient with PAF. These findings suggest that CA might modulate autonomic interaction between sinus nodes and in left atrium with denervated in ganglionated plexi.

Rationale and design of the EMPYREAN study.

AimsA sodium glucose cotransporter 2 (SGLT2) inhibitor was recently found to reduce heart failure hospitalization in the EMPA‐REG OUTCOME trial. We have hypothesized that autonomic nerve activity may be modulated by SGLT2 inhibition. The current study aims to investigate the impact of empagliflozin on sympathetic and parasympathetic nerve activity in patients with type 2 diabetes mellitus.Methods and resultsThis ongoing study is a prospective, randomized, open‐label, multicentre investigation of 134 patients with type 2 diabetes mellitus. The patients are randomly allocated to receive either empagliflozin or sitagliptin with the treatment goal of the Japan Diabetes Society guidelines. Ambulatory electrocardiographic monitoring is performed at the baseline and at 12 and 24 weeks of treatment. Analyses of heart rate variability are conducted using the MemCalc method, which is a combination of the maximum entropy method for spectral analysis and the non‐linear least squares method for square analysis. The primary endpoint is the change in the low‐frequency (0.04–0.15 Hz)/high‐frequency (0.15–0.4 Hz) ratio from baseline to 24 weeks.ConclusionsThis investigation on the effect of EMPagliflozin on cardiac sYmpathetic and parasympathetic neRve activity in JapanEse pAtieNts with type 2 diabetes (EMPYREAN study) offers an important opportunity to understand the impact of SGLT2 inhibition on autonomic nerve activity in patients with type 2 diabetes.

Do sprinters and distance runners have the same autonomic nervous system activity and hemodynamic responses?

The autonomic nervous system (ANS) has an important role in physical performance. However, the cardiac ANS activity between sprinters (SPR) and distance runners (DR) has been poorly explored. Not much research has been conducted to determine the differences between sprinters (SPR) and distance runners (DR). We aimed to investigate the influences of ANS activity and circulatory dynamics on different types of exercise training. For this study, five male SPR and seven male DR, aged 18–24 years old (21.2±2.0 years), were recruited from Tohoku University sports club. They had trained using the same exercise type for more than 3 years. We measured weight, height, body mass index, muscle mass, bone mass, visceral fat rating, basal metabolic rate, and part fat percentage and part muscle mass. We also measured blood pressure (BP) and heart rate variability (HRV) at rest and during the postural change from the supine position to the sitting position. Spectral analysis of HRV was performed to evaluate low‐frequency power (LF), high‐frequency power (HF), and the LF/HF ratio to observe the changes in cardiac sympathetic and parasympathetic nerve activity. Data regarding type, duration, and content of the training were obtained using questionnaires after the measurements. Significant differences were observed between both groups with regards to bone mass and left‐hand muscle mass. SPR had significantly higher HRV in supine position compared with DR. The HF of SPR was significant higher than DR in all positions. During postural change from the supine to the sitting position, LF/HF was significantly higher in DR compared with the SPR. Systolic BP in SPR was observed to significantly increase during postural change from the supine position to sitting position, while the systolic BP during postural change was reduced in the DR group. We thus observed different responses in both groups suggesting significant differences in ANS activity and circulatory dynamics between SPR and DR.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

May a unitary autonomic index help assess autonomic cardiac regulation in elite athletes? Preliminary observations on the national Italian Olympic committee team.

Long term endurance training, as occurring in elite athletes, is associated to cardiac neural remodeling in favor of cardioprotective vagal mechanisms, resulting in resting bradycardia and augmented contribution of cardiac parasympathetic nerve activity. Autonomic assessment can be performed by way of heart rate variability. This technique however provides multiple indices, and there is not yet complete agreement on their specific significance. Purpose of the study was to assess whether a rank transformation and radar plot could provide a unitary autonomic index, capable to show a correlation between intensity of individual work and quality of autonomic regulation. We studied 711 (23.6±6.2 years) elite athletes that took part in the selection procedure for the 2016 Rio Olympic Games for the National Italian Olympic Committee (CONI). Indices from Heart Rate Variability HRV obtained at rest, during standing up and during recovery from an exercise test were used to compute a percent ranked unitary autonomic index for sport (ANSIs), taken as proxy of quality of autonomic regulation. Within the observed wide range of energy expenditure, the unitary autonomic index ANSIs appears significantly correlated to individual and discipline specific training workloads (r=0.25, P<0.001 and r=0.78, P<0.001, respectively), correcting for possible age and gender bias. ANSIs also positively correlates to lipid profile. Estimated intensity of physical activity correlates with quality of cardiac autonomic regulation, as expressed by a novel unitary index of cardiac autonomic regulation. ANSIs could provide a novel and convenient approach to individual autonomic evaluation in athletes.

Cardiac parasympathetic outflow during dynamic exercise in humans estimated from power spectral analysis of P-P interval variability.

What is the central question of this study? Should we use the high-frequency (HF) component of P-P interval as an index of cardiac parasympathetic nerve activity during moderate exercise? What is the main finding and its importance? The HF component of P-P interval variability remained even at a heart rate of 120-140 beats min(-1) and was further reduced by atropine, indicating incomplete cardiac vagal withdrawal during moderate exercise. The HF component of R-R interval is invalid as an estimate of cardiac parasympathetic outflow during moderate exercise; instead, the HF component of P-P interval variability should be used. The high-frequency (HF) component of R-R interval variability has been widely used as an indirect estimate of cardiac parasympathetic (vagal) outflow to the sino-atrial node of the heart. However, we have recently found that the variability of the R-R interval becomes much smaller during dynamic exercise than that of the P-P interval above a heart rate (HR) of ∼100 beats min(-1). We hypothesized that cardiac parasympathetic outflow during dynamic exercise with a higher intensity may be better estimated using the HF component of P-P interval variability. To test this hypothesis, the HF components of both P-P and R-R interval variability were analysed using a Wavelet transform during dynamic exercise. Twelve subjects performed ergometer exercise to increase HR from the baseline of 69 ± 3 beats min(-1) to three different levels of 100, 120 and 140 beats min(-1). We also examined the effect of atropine sulfate on the HF components in eight of the 12 subjects during exercise at an HR of 140 beats min(-1) . The HF component of P-P interval variability was significantly greater than that of R-R interval variability during exercise, especially at the HRs of 120 and 140 beats min(-1). The HF component of P-P interval variability was more reduced by atropine than that of R-R interval variability. We conclude that cardiac parasympathetic outflow to the sino-atrial node can be estimated better by the HF component of P-P interval variability during exercise and that cardiac parasympathetic nerve activity exists during moderate dynamic exercise.

Cardiac autonomic regulation during hypoxic exercise

autonomic nervous system regulation of the heart and vasculature plays a key role in enabling the tight coupling between oxygen consumption of exercising skeletal muscles and oxygen delivery. The withdrawal of cardiac parasympathetic nerve activity and elevation in cardiac sympathetic nerve activity

The Treatment Benefit of Ghrelin on a Mouse Model of Inherited Dilated Cardiomyopathy Caused by Troponin Mutation

The therapeutic effect of ghrelin has been reported in humans as well as in animal models of chronic heart failure. However, little is known about the therapeutic efficacy of ghrelin for the treatment of inherited forms of dilated cardiomyopathy (DCM). We aim to examine whether ghrelin is beneficial for the treatment of inherited DCM with a deletion mutation ΔK210 in the cardiac troponin T (cTnT) gene using a knock-in mouse model. Ghrelin (150 μg/kg/day) was administered subcutaneously to the mouse model of inherited DCM. The therapeutic effects were examined on the basis of survival and myocardial remodeling. Ghrelin administration prolonged the life span of DCM mice compared to the saline-treated controls. Echocardiography data showed that ghrelin reduced left ventricular (LV) end-diastolic dimensions and increased LV ejection fraction. Moreover, histoanatomical data revealed that ghrelin decreased the heart-to-body weight ratio, prevented cardiac remodeling and fibrosis, and markedly decreased the expression of brain natriuretic peptide. Telemetry recording and heart rate variability analysis showed that ghrelin suppressed the excessive cardiac sympathetic nerve activity (CSNA) and recovered the cardiac parasympathetic nerve activity. Ghrelin has therapeutic benefits for the treatment of DCM with ΔK210 mutation in cTnT. Importantly, these cardiovascular benefits of ghrelin are likely linked to the suppression of CSNA and recovery of cardiac parasympathetic nerve activity.

Effect of ghrelin on autonomic activity in healthy volunteers

Ghrelin is a novel growth hormone (GH)-releasing peptide originally isolated from the stomach. Recently, we have shown that ghrelin suppresses cardiac sympathetic activity and prevents early left ventricular remodeling in rats with myocardial infarction. In the present study, we evaluated the effect of ghrelin on autonomic nerve activity in healthy human subjects. An intravenous bolus of human synthetic ghrelin (10μg/kg) was administered to 10 healthy men (mean age, 33 years). Holter monitoring assessment was performed before and during 2h after the ghrelin therapy. The standard deviation of normal RR intervals (SDNN), square root of the mean of the sum of the squares of differences between adjacent RR intervals (rMSSD), high-frequency power (HF), and low-frequency power (LF) were analyzed. Blood samples were also obtained before and after the therapy. A single administration of ghrelin decreased both heart rate and blood pressure. Interestingly, ghrelin significantly decreased the LF and LF/HF ratio of heart rate variability and increased the SDNN, rMSSD, and HF. Ghrelin also elicited a marked increase in circulating GH, but not insulin-like growth factor-1. These data suggest that ghrelin might suppress cardiac sympathetic nerve activity and stimulate cardiac parasympathetic nerve activity.

Survival benefit of ghrelin in the heart failure due to dilated cardiomyopathy.

Although ghrelin has been demonstrated to improve cardiac function in heart failure, its therapeutic efficacy on the life expectancy remains unknown. We aim to examine whether ghrelin can improve the life survival in heart failure using a mouse model of inherited dilated cardiomyopathy (DCM) caused by a deletion mutation ΔK210 in cardiac troponin T (cTnT). From 30 days of age, ghrelin (150 μg/kg) was administered subcutaneously to DCM mice once daily, control mice received saline only. The survival rates were compared between the two groups for 30 days. After 30-day treatment, functional and morphological measurements were conducted. Ghrelin-treated DCM mice had significantly prolonged life spans compared with saline-treated control DCM mice. Echocardiography showed that ghrelin reduced left ventricular (LV) end-diastolic dimensions and increased LV ejection fraction. Moreover, histoanatomical data revealed that ghrelin decreased the heart-to-body weight ratio, prevented cardiac remodeling and fibrosis, and markedly decreased the expression of brain natriuretic peptide. Telemetry recording and heart rate variability analysis showed that ghrelin suppressed the excessive cardiac sympathetic nerve activity (CSNA) and recovered the cardiac parasympathetic nerve activity. These results suggest that ghrelin has therapeutic benefits for survival as well as for the cardiac function and remodeling in heart failure probably through suppression of CSNA and recovery of cardiac parasympathetic nerve activity.

Consciously controlled breathing decreases the high-frequency component of heart rate variability by inhibiting cardiac parasympathetic nerve activity.

Heart rate variability (HRV), the beat-to-beat alterations in heart rate, comprises sympathetic and parasympathetic nerve activities of the heart. HRV analysis is used to quantify cardiac autonomic regulation. Since respiration could be a confounding factor in HRV evaluation, some studies recommend consciously controlled breathing to standardize the method. However, it remains unclear whether controlled breathing affects HRV measurement. We compared the effects of controlled breathing on HRV with those of spontaneous breathing. In 20 healthy volunteers, we measured respiratory frequency (f), tidal volume, and blood pressure (BP) and recorded electrocardiograms during spontaneous breathing (14.8 ± 0.7 breaths/min) and controlled breathing at 15 (0.25 Hz) and 6 (0.10 Hz) breaths/min. Compared to spontaneous breathing, controlled breathing at 0.25 Hz showed a higher heart rate and a lower high-frequency (HF) component, an index of parasympathetic nerve activity, although the f was the same. During controlled breathing at 0.10 Hz, the ratio of the low frequency (LF) to HF components (LF/HF), an index of sympathetic nerve activity, increased greatly and HF decreased, while heart rate and BP remained almost unchanged. Thus, controlled breathing at 0.25 Hz, which requires mental concentration, might inhibit parasympathetic nerve activity. During controlled breathing at 0.10 Hz, LF/HF increases because some HF subcomponents are synchronized with f and probably move into the LF band. This increment leads to misinterpretation of the true autonomic nervous regulation. We recommend that the respiratory pattern of participants should be evaluated before spectral HRV analysis to correctly understand changes in autonomic nervous regulation.

Parasympathetic Nerve Function Status in Female with Rheumatoid Arthritis

Background: Sudden cardiac death in patients with Rheumatoid Arthritis has been attributed to the decreased vagal drive to the heart. Objective: To assess cardiac parasympathetic nerve function status in patients with Rheumatoid Arthritis (RA). Methods: This cross sectional study was conducted in the Department of Physiology, Bangabandhu Sheikh Mujib Medical University (BSMMU), Shahbag, Dhaka from January to December 2010. Sixty female RA patients aged 18-50 years were included in the study group. They were enrolled from the Out Patient Department of Rheumatology Wing of the Department of Medicine, BSMMU, Dhaka. For comparison age matched thirty apparently healthy females were also studied as control. To assess parasympathetic nerve function status, all the subjects were examined by three noninvasive cardiovascular reflex tests such as heart rate response to valsalva maneuver (valsalva ratio), heart rate response to deep breathing and heart rate response to standing (30th :15th ratio). For statistical analysis independent sample t test was used. Results: Mean values of valsalva ratio, deep breathing test and 30th :15th ratio were significantly (p&lt;0.001) lower in rheumatoid arthritis patients compared to those of healthy control. Conclusion: From this study it may be concluded that lower cardiac parasympathetic nerve activity characterized the autonomic nerve dysfunction in patients with Rheumatoid Arthritis. DOI: http://dx.doi.org/10.3329/jbsp.v8i1.16643 J Bangladesh Soc Physiol. 2013, June; 8(1): 21-25

Effects of Underwater Arm-Cranking Exercise on Cardiac Autonomic Nervous Activity

ABSTRACT The purpose of this study was to clarify the beneficial effect of an underwater environment on heart rate (HR) and cardiac autonomic nervous activity (HF) during arm-cranking exercise. Ten healthy young men participated in this study. The arm-cranking exercise (40% peakV̇O2) was performed for 10 minutes under two conditions: in water and in air. After the exercise, a recovery phase for 30 seconds followed. Changes in HR, V̇O2, and HF did not differ between the conditions. The time constant of the heart rate decay for the first 30 seconds after exercise in the water was less than in air. The results suggest that cardiac parasympathetic nervous activity influences earlier recovery of HR after exercise in water. The results of our study suggest underwater exercise may be applied to wider areas of health management for individuals returning from space travel or sedentary patients in simulated microgravity environments.

The LF/HF ratio does not accurately measure cardiac sympatho-vagal balance

Power spectral analysis of the beat-to-beat variations of heart rate or the heart period (R–R interval) has become widely used to quantify cardiac autonomic regulation (Appel et al., 1989; Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology, 1996; Berntson et al., 1997; Denver et al., 2007; Thayler et al., 2010; Billman, 2011). This technique partitions the total variance (the “power”) of a continuous series of beats into its frequency components, typically identifying two or three main peaks: Very Low Frequency (VLF) <0.04 Hz, Low Frequency (LF), 0.04–0.15 Hz, and High Frequency (HF) 0.15–0.4 Hz. It should be noted that the HF peak is shifted to a higher range (typically 0.24–1.04 Hz) in infants and during exercise (Berntson et al., 1997). The HF peak is widely believed to reflect cardiac parasympathetic nerve activity while the LF, although more complex, is often assumed to have a dominant sympathetic component (Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology, 1996; Berntson et al., 1997; Billman, 2011). Based upon these assumptions, Pagani and co-workers proposed that the ratio of LF to HF (LF/HF) could be used to quantify the changing relationship between sympathetic and parasympathetic nerve activities (i.e., the sympatho-vagal balance) (Pagani et al., 1984, 1986; Malliani et al., 1991) in both health and disease. However, this concept has been challenged (Kingwell et al., 1994; Koh et al., 1994; Hopf et al., 1995; Eckberg, 1997; Houle and Billman, 1999; Billman, 2011). Despite serious and largely under-appreciated limitations, the LF/HF ratio has gained wide acceptance as a tool to assess cardiovascular autonomic regulation where increases in LF/HF are assumed to reflect a shift to “sympathetic dominance” and decreases in this index correspond to a “parasympathetic dominance.” Therefore, it is vital to provide a critical assessment of the assumptions upon which this concept is based.

Central command does not decrease cardiac parasympathetic efferent nerve activity during spontaneous fictive motor activity in decerebrate cats

To examine whether withdrawal of cardiac vagal efferent nerve activity (CVNA) predominantly controls the tachycardia at the start of exercise, the responses of CVNA and cardiac sympathetic efferent nerve activity (CSNA) were directly assessed during fictive motor activity that occurred spontaneously in unanesthetized, decerebrate cats. CSNA abruptly increased by 71 ± 12% at the onset of the motor activity, preceding the tachycardia response. The increase in CSNA lasted for 4-5 s and returned to the baseline, even though the motor activity was not ended. The increase of 6 ± 1 beats/min in heart rate appeared with the same time course of the increase in CSNA. In contrast, CVNA never decreased but increased throughout the motor activity, in parallel with a rise in mean arterial blood pressure (MAP). The peak increase in CVNA was 37 ± 9% at 5 s after the motor onset. The rise in MAP gradually developed to 21 ± 2 mmHg and was sustained throughout the spontaneous motor activity. Partial sinoaortic denervation (SAD) blunted the baroreflex sensitivity of the MAP-CSNA and MAP-CVNA relationship to 22-33% of the control. Although partial SAD blunted the initial increase in CSNA to 53% of the control, the increase in CSNA was sustained throughout the motor activity. In contrast, partial SAD almost abolished the increase in CVNA during the motor activity, despite the augmented elevation of 31 ± 1 mmHg in MAP. Because afferent inputs from both muscle receptors and arterial baroreceptors were absent or greatly attenuated in the partial SAD condition, only central command was operating during spontaneous fictive motor activity in decerebrate cats. Therefore, it is likely that central command causes activation of cardiac sympathetic outflow but does not produce withdrawal of cardiac parasympathetic outflow during spontaneous motor activity.

Decreased cardiac parasympathetic nerve activity of pregnant women during foot baths

This study aimed to examine the effect of foot baths on the cardiac parasympathetic outflow of five pregnant (31-32 weeks; mid-pregnancy) women and 16 non-pregnant women. The cardiac parasympathetic outflow was assessed by using the respiratory variability of the R-R interval under controlled breathing according to three different methods: (i) respiratory sinus arrhythmia; (ii) a respiratory-synchronized component of the power spectrum of R-R interval variability with a fast Fourier transform; and (iii) a high-frequency component (HF at 0.15-0.40 Hz) of the power spectrum of R-R interval variability with a maximum entropy method. The rate and amplitude of spontaneous respiration and arterial blood pressure at rest were the same between the non-pregnant and pregnant women. However, the baseline R-R interval was shorter and the respiratory-synchronized and HF components of the power spectrum of R-R interval variability were smaller in the pregnant women, indicating a decreased baseline cardiac parasympathetic outflow with mid-pregnancy. Although a foot bath for 15 min did not significantly affect the systemic hemodynamics and body temperature of both groups, the foot bath reduced the respiratory arrhythmia and the respiratory-synchronized and HF components of the power spectrum of R-R interval variability in both groups. The reduction in the respiratory R-R interval became more prominent in the pregnant group. A foot bath, used as part of midwives' daily nursing care, is able to decrease the cardiac parasympathetic outflow of pregnant women.

Influence of ageing on carotid baroreflex peak response latency in humans

The stability of a physiological control system, such as the arterial baroreflex, depends critically upon both the magnitude (i.e. gain or sensitivity) and timing (i.e. latency) of the effector response. Although studies have examined resting arterial baroreflex sensitivity in older subjects, little attention has been given to the influence of ageing on the latency of peak baroreflex responses. First, we compared the temporal pattern of heart rate (HR) and mean arterial blood pressure (BP) responses to selective carotid baroreceptor (CBR) unloading and loading in 14 young (22 +/- 1 years) and older (61 +/- 1 years) subjects, using 5 s pulses of neck pressure (NP, +35 Torr) and neck suction (NS, -80 Torr). Second, CBR latency was assessed following pharmacological blockade of cardiac parasympathetic nerve activity in eight young subjects, to better understand how known age-related reductions in parasympathetic nerve activity influence CBR response latency. In response to NP, the time to the peak increase in HR and mean BP were similar in young and older groups. In contrast, in response to NS the time to peak decrease in HR (2.1 +/- 0.2 vs. 3.8 +/- 0.2 s) and mean BP (6.7 +/- 0.4 vs. 8.3 +/- 0.2 s) were delayed in older individuals (young vs. older, P < 0.05). The time to peak HR and mean BP were delayed in young subjects following cardiac parasympathetic blockade (glycopyrrolate). Collectively, these data suggest that ageing is associated with delayed peak cardiovascular responses to acute carotid baroreceptor loading that may be, in part, due to age-related reductions in cardiac parasympathetic tone.