Cardiovascular Autonomic System Research Articles

Differences in the cardiovascular hemodynamic response between the Valsalva and Reverse Valsalva Maneuvers in healthy subjects.

The Valsalva Maneuver (VM) is the first-line treatment for paroxysmal supraventricular tachycardia, but a recent, novel, and efficient tool to restore sinus rhythm has been described, i.e., the Reverse Valsalva (RV). This study aims to compare changes in cardiovascular hemodynamics and autonomic system activity (ANS) based on heart rate variability (HRV) analysis during both maneuvers. Fifteen healthy participants performed the VM and RV maneuvers three times in a sitting position for durations of 15 s and 10 s, respectively. Blood pressure (BP) and heart rate (HR) were continuously monitored before, during and after the tests. Autonomic system activity was evaluated using frequency-domain analysis of HRV. The decrease in HR from baseline to the lowest values, expressed as a ratio, was similar during both maneuvers (0.81 during the RV vs. 0.79 during the VM, p = 0.27). However, the final lowest HR in response to the RV was higher than that in response to the VM, 70/min vs. 59/min (p <0.001). The activation of the autonomic nervous system during the most bradycardic phase of the RV (phase II) and VM (phase IV) showed that the total power of HRV was less prominent during the RV than during the VM (p <0.012), with similar levels of parasympathetic activation. Our results showed less HR slowdown during the RV than during the VM. The changes in HRV parameters during both procedures in particular phases of the RV and VM suggest that the autonomic nervous system is activated alternately, so these tests can be used complementarily in a clinical setting with different results.

Orexinergic neurons contribute to autonomic cardiovascular regulation for locomotor exercise.

While the hypothalamic orexinergic nervous system is established as having a pivotal role in the long-term regulation of various organismic functions, including wakefulness, metabolism and hypertensive states, whether this system contributes to the rapid autonomic cardiovascular regulation during physical activity remains elusive. This study aimed to elucidate the role of the orexinergic nervous system in transmitting volitional motor signals, i.e. central command, to drive somatomotor and sympathetic cardiovascular responses. We first found that this system is activated by voluntary locomotor exercise as evidenced by an increased expression of Fos, a marker of neural activation, in the orexinergic neurons of Sprague-Dawley rats engaged in spontaneous wheel running. Next, using transgenic Orexin-Cre rats for optogenetic manipulation of orexinergic neurons, we found that optogenetic excitation of orexinergic neurons caused sympathoexcitation on a subsecond timescale under anaesthesia. In freely moving conscious rats, this excitatory stimulation rapidly elicited exploration-like behaviours, predominantly locomotor activity, along with pressor and tachycardiac responses. Meanwhile, optogenetic inhibition of orexinergic neurons during spontaneous wheel running immediately suppressed locomotor activities and blood pressure elevation without affecting basal cardiovascular homeostasis. Taken together, these findings demonstrate the essential role of the orexinergic nervous system in the central circuitry that transmits central command signals for locomotor exercise. This study not only offers insights into the brain circuit mechanisms precisely regulating autonomic cardiovascular systems during voluntary exercise but also likely contributes to our understanding of brain mechanisms underlying abnormal cardiovascular adjustments to exercise in pathological conditions, such as hypertension. KEY POINTS: The hypothalamic orexinergic nervous system plays various roles in the long-term regulation of autonomic and endocrine functions, as well as motivated behaviours. We present a novel, rapid role of the orexinergic nervous system, revealing its significance as a crucial substrate in the brain circuit mechanisms that coordinate somatomotor and autonomic cardiovascular controls for locomotor exercise. Our data demonstrate that orexinergic neurons relay volitional motor signals, playing a necessary and sufficient role in the autonomic cardiovascular regulation required for locomotor exercise in rats. The findings contribute to our understanding of how the brain precisely regulates autonomic cardiovascular systems during voluntary exercise, providing insights into the central neural mechanisms that enhance physical performance moment-by-moment during exercise.

Effects of COVID-19 on the Autonomic Cardiovascular System: Heart Rate Variability and Turbulence in Recovered Patients.

COVID-19 may be a risk factor for developing cardiovascular autonomic dysfunction. Data are limited, however, on the association between heart rate variability, heart rate turbulence, and COVID-19. The aims of this study were to evaluate the effect of COVID-19 on the cardiovascular autonomic system in patients with persistent symptoms after recovering from COVID-19 and to determine whether these patients showed changes in ambulatory electrocardiography monitoring. Fifty-one adults who had confirmed SARS-CoV-2 infection and presented with persistent symptoms to the cardiology outpatient clinic after clinical recovery between April and June 2021 were included. Patients were prospectively followed for 6 months. The patients were evaluated at the time of first application to the cardiology outpatient clinic and at 6 months after presentation. Ambulatory electrocardiography monitoring and echocardiographic findings were compared with a control group of 95 patients. Patients in the post-COVID-19 group had significantly higher mean (SD) turbulence onset (0.39% [1.82%] vs -1.37% [2.93%]; P < .001) and lower heart rate variability than those in the control group at both initial and 6-month evaluations. The post-COVID-19 group had no significant differences in echocardiographic findings compared with the control group at 6 months, except for right ventricle late diastolic mitral annular velocity (P = .034). Furthermore, turbulence onset was significantly correlated with turbulence slope (r = -0.232; P = .004), heart rate variability, and the parameters of left (r = -0.194; P=.049) and right (r = 0.225; P = .02) ventricular diastolic function. COVID-19 may cause cardiovascular autonomic dysfunction. Heart rate variability and turbulence parameters can be used to recognize cardiovascular autonomic dysfunction in patients who have recovered from COVID-19 but have persistent symptoms.

Cardiovascular Autonomic Dysfunction and its association with Aortic Stenosis

Aortic stenosis remains the most common valvular abnormality that requires intervention and is becoming more prevalent with an ageing population. Untreated symptomatic severe aortic stenosis is associated with a mortality of 50-60% within two years. Valve replacement either surgical or transcatheter remains the only effective treatment. The autonomic nervous system involuntarily controls many basic cardiac, respiratory, gastrointestinal and genitourinary functions and plays a central role in the regulation of heart rate and blood pressure. Cardiovascular autonomic dysfunction has shown to be a marker of increased mortality. We discuss current methods to assess autonomic function, alongside abnormalities noted in common cardiac conditions and their correlation to mortality, and review current literature available that confirms severe aortic stenosis is associated with dysregulation of cardiovascular autonomic system.

Coexistence of fibromyalgia syndrome and inflammatory rheumatic diseases, and autonomic cardiovascular system involvement in fibromyalgia syndrome.

The spectrum of symptoms represented by fibromyalgia syndrome (FMS) has a profound effect on daily activities and impairs the quality of life. A considerable proportion of patients with inflammatory rheumatic diseases (IRDs) fulfill the FMS criteria, which can complicate the diagnosis, treatment, and follow-ups of IRD. In addition, the coexistence of FMS may cause unnecessary laboratory and radiological assessments. Several mechanisms have been proposed that may have a role in the etiopathogenesis of FMS, one of which is autonomic dysregulation. In studies evaluating cardiac autonomic dysfunction based on heart rate variability (HRV), there has been found to be a decrease in HRV and dominance of the sympathetic nervous system. Autonomic reactivity reflects modulations of several functions to overcome the existing state and conditions. Blunted autonomic reactivity has been found in some FMS patients, which makes it difficult for these patients to respond appropriately to unexpected stress sources that occur during daily living activities. Baroreceptor signals have an inhibitory influence on the central nervous system, and these impulses cause pain suppression. From this perspective, there are studies that have suggested the involvement of diminished baroreflex sensitivity in the etiology of FMS. The risk of endothelial dysfunction and increased arterial stiffness have been shown to occur in FMS patients due to autonomic dysfunction, sympathetic nervous system dominance, chronic stress, and pain. There is also evidence linking FMS with the risk of atrial and ventricular arrhythmias. Considering all these cardiovascular autonomic dysfunctions, tests that can confirm abnormalities should be performed when suspicion arises. There is a need for specific pharmacological and non-pharmacological treatment alternatives to be identified for subgroups of patients with cardiovascular system abnormalities. Key points • The frequency of FMS accompanying inflammatory rheumatic diseases is considerable and this coexistence leads to troubles in evaluating treatment response and determining appropriate medical treatment options in inflammatory rheumatic diseases. • Various cardiovascular autonomic abnormalities have been described in FMS patients. Among these, the most emphasized are autonomic dysfunction, the disruption of the balance between the sympathetic-parasympathetic nervous systems, blunted autonomic reactivity to acute stress, changes in baroreflex sensitivity, increased arterial stiffness, and electrophysiological alterations. • Autonomic cardiovascular dysfunction may be involved in the complex etiopathogenesis of the fibromyalgia syndrome and may trigger at least some symptoms.

Influence on the autonomic cardiovascular system regulation in the treatment of hypertension, arrhythmias and heart failure

Cardiovascular diseases are widespread and are the leading death cause in most countries, despite the creation and improvement of strategies to reduce cardiovascular risk. A significant role in the development and evolution of cardiovascular diseases belongs to sympathetic nervous system hyperactivity, and therefore the methods of effecting it are relevant for the prevention and treatment of cardiovascular pathology. The article discusses modern approaches to interventional and conservative regulation of the autonomic nervous system and neuromodulation in the prevention and treatment of hypertension, heart failure, tachyarrhythmias, as well as reflects a conjoint expert judgment on these issues.

Autonomic cardiovascular response during and after a graded exercise test in concussed athletes and healthy controls

Objective Dysfunction of the autonomic cardiovascular system after a concussion is known to cause exercise intolerance due to symptoms exacerbation. The aim of this study was to compare athletes with symptoms of a sport-related concussion and healthy controls with regard to their heart rate during a graded exercise test and their heart rate recovery during the 5 min cool-down after the graded exercise test. Methods Sport-related concussion patients ( N = 61; 31% female) and controls ( N = 16; 50% female) participated in a graded exercise test on a cycle ergometer followed by 5 min active cool-down. Based on the results of graded exercise tests they were divided into four groups: (1) patients who reached the symptom threshold and had to stop the graded exercise test (symptom threshold; N = 39; 33.3% female), (2) patients with symptoms who finished the graded exercise test (S; N = 16; 25% female), (3) patients without symptoms (NS; N = 6; 33.3% female), (4) controls ( N = 16; 50% female). Main outcome measures Heart rate, severity of headache and dizziness during graded exercise test, heart rate recovery (median (heart rate recoveries/maximal heart rate) ± median absolute deviation (MAD)) 30, 60 and 300 s after the start of cool-down. Results Heart rate recovery at 30 s was significantly slower in symptom (0.95 ± 0.01) compared to all other groups ( p &lt; 0.002; symptom threshold: 0.92 ± 0.02, NS: 0.91 ± 0.02, controls: 0.93 ± 0.02). Heart rate recovery at 60 s was significantly slower in symptom (0.90 ± 0.02) compared to the symptom threshold and controls ( p &lt; 0.041; 0.86 ± 0.03, 0.85 ± 0.04). Heart rate recovery at 300 s was significantly slower in symptom threshold (0.72 ± 0.05) compared to controls ( p = 0.003; 0.66 ± 0.02). Conclusions Heart rate measurements in athletes with symptoms of sport-related concussion should be continued during cool-down after the graded exercise test, as dysfunction of the autonomic cardiovascular system might manifest also during cool-down.

Delayed association of acute particulate matter 2.5 air pollution exposure with loss of complexity in cardiac rhythm dynamics: insight from detrended fluctuation analysis.

There is a delayed (lag 1 to 2days) correlation between acute PM 2.5 (particulate matter < 2.5μm in aerodynamic diameter) exposure and cardiovascular events, but the underlying mechanism remained unclear. We aimed to investigate the delayed impact of acute PM 2.5 exposures on cardiac autonomics through linear and nonlinear heart rate variability (HRV) analyses. Among 6912 patients who had received 24-h Holter ECG between October 1, 2015, to October 31, 2016, 56 patients (31 males, 70.3 ± 12.7years old) were enrolled. We classified the patients as high (> 35.4μg/m3) or low (< 35.4μg/m3) PM 2.5 groups according to their PM 2.5 exposures on the day of Holter recordings (day 0) lag 1 and lag 2days. Linear and nonlinear HRV parameters〔Detrended fluctuation analysis (DFA) slopes 1 and 2〕were compared. Baseline characteristics were similar between groups. Linear and nonlinear HRV parameters were similar between high- and low-exposure groups on day 0 and lag 1day, respectively. However, DFA slope 1 was significantly lower in the high-exposure group on lag 2days (0.784 ± 0.201 vs. 0.964 ± 0.274, p = 0.021). DFA slope 1 of the high-exposure group was significantly lower on daytime periods (9 am to 9 pm, 8 am to 4 pm and 4 pm to 12 pm) but not on nighttime periods. High lag 2days PM 2.5 exposure is associated with low DFA slope 1 and the relationship is diurnal. This suggests that air pollution might have a delayed impact on the cardiovascular autonomic system.

Cardiovascular autonomic neuropathy as a cause of fatigue in chronic hypoparathyroidism.

Hypoparathyroidism (hypoPT) results in an impairment of quality of life (QoL), an increase in fatigue and a higher risk of mortality. Cardiovascular autonomic neuropathy (CAN) is an impairment of the cardiovascular autonomic system and is associated with increased mortality and fatigability. Patients with hypoPT show an increased risk of CAN. However, no previous studies have investigated the association between CAN and QoL in hypoPT. To test whether CAN is associated with fatigue and impaired QOL in hypoPT patients. We enrolled 48 subjects with postsurgical hypoPT treated with calcium and calcitriol and 38 healthy subjects who underwent thyroidectomy. Subjects completed the RAND 36-Item Short Form (SF-36) Health Survey, evaluating physical (PCS) and mental (MCS) health, and fatigue score. CAN was assessed using cardiovascular autonomic reflex tests (CARTs). Participants were considered to have "early CAN" (EC) if they had one abnormal CART and "definite CAN" (DC) with two or more abnormal CARTs. Compared with controls, hypoPT population had lower fatigue scores (44.5 IQRː9 vs 38.5 IQRː12.3, P = 0.031). In the hypoPT group, only participants with DC had a lower fatigue score than subjects without CAN (DC: β: -9.55, P = 0.005) after adjusting for age, duration of disease, calcium concentration, TSH, calcitriol and calcium supplementation. No differences were found in the PCS and MCS scores in the hypoPT group. CAN may explain fatigue, a common complaint of postsurgical hypoPT patients. Further larger and prospective investigations are needed to confirm our findings.

MON-527 Cardiovascular Autonomic Neuropathy As A Cause Of Quality Of Life Impairment In Subjects With Chronic Hypoparathyroidism.

Background: Post-surgical hypoparathyroidism (hypoPT) increases fatigue and seems to affect the risk of mortality. Hypoparathyroid patients on conventional treatment with calcium and vitamin D supplementation show a reduction of Quality of life (QoL). Cardiovascular autonomic neuropathy (CAN) is an impairment of the cardiovascular autonomic system and it represents a cause of increased mortality and fatigability. Recently, we have demonstrated that patient with chronic post-surgical hypoparathyroidism show an increased risk of CAN. No previous studies have investigated the association between CAN and QoL in hypoparathyroidism. Aim: We tested the hypothesis that CAN would be associated with impaired QOL measures in subjects with chronic post-surgical hypoparathyroidism. Study population and design: We enrolled 49 post-surgical hypoparathyroid patients treated with calcium and calcitriol. Subjects completed the RAND 36-Item Short Form (SF-36) Health Survey, a measure of health-related QOL covering eight domains of physical and mental health. QOL has also been evaluated using Fatigue score (version 4). CAN was assessed by heart rate (HR) response to deep breathing, HR response to the lying-to-standing test, HR response to the Valsalva maneuver and blood pressure response to standing. Participants were considered to have “early CAN” (EC) if they had one abnormal result in the HR tests and “definite CAN” (DC) with two or more abnormal results. Results: the prevalence of EC was 39% (n=19), the prevalence of DC was 39% (n=19), the prevalence of patients without CAN (WC) was 22% (n=11). Only DC subjects had a statistically significant lower fatigue score compared to WC(35.1±5.8 vs 44.4±4.6, P=0.004). These results have been confirmed after adjustment for age, calcium concentration, calcitriol and calcium supplementation (β:-9.31, P=0.004). No statistically significant differences between groups were found for mental and physical component summary scores. Role limitation due to physical problem represents the only domain that showed a significant reduction between groups (WC: 82.6±33.4, EC: 72.4±33.2, DC: 50±38.2, ANOVA P=0.044). Conclusion: definite CAN may represent a cause of impaired QoL in patient with chronic post-surgical hypoparathyroidism. The presence of cardiovascular autonomic neuropathy could explain the fatigue, a common complaint in patient with hypoparathyroidism.

Association of long-term exposure to traffic-related PM10 with heart rate variability and heart rate dynamics in healthy subjects

BackgroundEpidemiological evidence on the influence of long-term exposure to traffic-related particulate matter (TPM10) on heart rate variability (HRV) is weak. ObjectiveTo evaluate the association of long-term exposure (10 years) with TPM10 on the regulation of the autonomic cardiovascular system and heart rate dynamics (HRD) in an aging general population, as well as potential modifying effects by the a priori selected factors sex, smoking status, obesity, and gene variation in selected glutathione S-transferases (GSTs). MethodsWe analyzed data from 1593 SAPALDIA cohort participants aged ≥ 50 years. For each participant, various HRV and HRD parameters were derived from 24-hour electrocardiogram recordings. Each parameter obtained was then used as the outcome variable in multivariable mixed linear regression models in order to evaluate the association with TPM10. Potential modifying effects were assessed using interaction terms. ResultsNo association between long-term exposure to TPM10 and HRV/HRD was observed in the entire study population. However, HRD changes were found in subjects without cardiovascular morbidity and both HRD and HRV changes in non-obese subjects without cardiovascular morbidity. Subjects without cardiovascular morbidity with homozygous GSTM1 gene deletion appeared to be more susceptible to the effects of TPM10. ConclusionThis study suggests that long-term exposure to TPM10 triggers adverse changes in the regulation of the cardiovascular system. These adverse effects were more visible in the subjects without cardiovascular disease, in whom the overall relationship between TPM10 and HRV/HRD could not be masked by underlying morbidities and the potential counteracting effects of related drug treatments.

Cardiovascular Autonomic Neuropathy as a New Complication of Postsurgical Chronic Hypoparathyroidism.

Postsurgical hypoparathyroidism (hypoPT) increases fatigue and seems to affect the risk of mortality. Cardiovascular autonomic neuropathy (CAN) is an impairment of the cardiovascular autonomic system, a cause of increased mortality, and associated with increased fatigability. The aim of this study is to evaluate CAN in hypoPT and its relationship with hypocalcemia, PTH levels, and hyperphosphatemia. This is a cross-sectional study comparing 51 postsurgical hypoPT patients treated with calcium and calcitriol and 43 control subjects without any PTH/calcium/phosphate disorders who underwent thyroidectomy. CAN was assessed by heart rate (HR) response to deep breathing, HR response to the lying-to-standing test, HR response to the Valsalva maneuver, and blood pressure response to standing. Participants were considered to have "early CAN" if they had one abnormal result in the HR tests and "definite CAN" with two or more abnormal results. The prevalence of CAN was 23% in the control group and 78% in the hypoPT group (OR 11.48; 95% CI, 4.48 to 32.17). Patients with hypoPT and serum calcium (sCa) ≥8.5 mg/dL had a prevalence of early CAN of 72.4% and the prevalence was 86.4% in those with sCa <8.5 mg/dL. Definite CAN was found in 2.3% of the control group, 24.1% of the hypoPT group without hypocalcemia, and 59.1% of the hypoPT group with hypocalcemia. In the hypoPT group, the OR for definite CAN in the patients with hypocalcemia compared to the patients with normocalcemia was 4.54 (95% CI, 1.36 to 15.11). The association between low sCa and definite CAN was confirmed after adjustment for confounders with OR 13.62 (95% CI, 2.12 to 149.84). No association was found between definite CAN and PTH levels or high phosphate levels. HypoPT is associated with CAN and hypocalcemia seems to affect its severity. Larger and prospective studies are needed to confirm our findings. © 2018 American Society for Bone and Mineral Research.

Resting EEG Microstates and Autonomic Heart Rate Variability Do Not Return to Baseline One Hour After a Submaximal Exercise.

Recent findings suggest that an acute physical exercise modulates the temporal features of the EEG resting microstates, especially the microstate map C duration and relative time coverage. Microstate map C has been associated with the salience resting state network, which is mainly structured around the insula and cingulate, two brain nodes that mediate cardiovascular arousal and interoceptive awareness. Heart rate variability (HRV) is dependent on the autonomic balance; specifically, an increase in the sympathetic (or decrease in the parasympathetic) tone will decrease variability while a decrease in the sympathetic (or increase in the parasympathetic) tone will increase variability. Relying on the functional interaction between the autonomic cardiovascular activity and the salience network, this study aims to investigate the effect of exercise on the resting microstate and the possible interplay with this autonomic cardiovascular recovery after a single bout of endurance exercise. Thirty-eight young adults performed a 25-min constant-load cycling exercise at an intensity that was subjectively perceived as “hard.” The microstate temporal features and conventional time and frequency domain HRV parameters were obtained at rest for 5 min before exercise and at 5, 15, 30, 45, and 60 min after exercise. Compared to the baseline, all HRV parameters were changed 5 min after exercise cessation. The mean durations of microstate B and C, and the frequency of occurrence of microstate D were also changed immediately after exercise. A long-lasting effect was found for almost all HRV parameters and for the duration of microstate C during the hour following exercise, indicating an uncompleted recovery of the autonomic cardiovascular system and the resting microstate. The implication of an exercise-induced afferent neural traffic is discussed as a potential modulator of both the autonomic regulation of heart rate and the resting EEG microstate.

75. Absent cardiac and muscle sympathetic nerve activities involvement in Ross syndrome: A follow-up study

Ross syndrome (RS) is a rare disorder characterized by selective involvement of post-ganglionic skin sympathetic nerve fibres with absent cholinergic sudomotor fibres as hallmark of the disease. It is still not well defined whether autonomic dysfunction remain localized to skin fibres or it affects also cardiovascular autonomic system. To clarify this aspect, we report a cardiovascular autonomic system follow-up study in 4 patients affected by Ross syndrome. We studied 4 patients affected by RS for a follow-up mean period of 5 years (range 1–10 years). All patients complained of anhydrosis with heat intolerance and showed areflexia and tonic pupil on neurological examination and absent cholinergic sudomotor fibres on skin biopsy. All patients underwent cardiovascular reflexes (CVR, head-up tilt test, Valsalva maneuver, deep breathing, isometric handgrip) and microneurography recording of muscle sympathetic nerve activity (MSNA) from common peroneal nerve. CVR and MSNA resulted normal at baseline and unchanged over the follow-up in all patients although anhydrosis was usually widespread on patient’s clinical re-evaluation. Our preliminary study shows that cardiovascular autonomic system is not affected in Ross syndrome differently from skin autonomic activity dysfunction which tend to progress over time.

Absent cardiac and muscle sympathetic nerve activities involvement in Ross syndrome: A follow-up study.

Ross syndrome (RS) is characterized by selective involvement of post-ganglionic skin sympathetic nerve fibres. We report a follow-up study in 4 patients to clarify whether in RS autonomic dysfunction spreads affecting also cardiovascular system. The patients underwent cardiovascular reflexes (CVR) and microneurography recording of muscle sympathetic nerve activity (MSNA) for a follow-up mean period of 5years. CVR and MSNA were normal at baseline and unchanged over the follow-up. Cardiovascular autonomic system is spared in RS differently from skin autonomic activity dysfunction which progress over time. However, before drawing any definite conclusion, a large cohort of patients needs to be studied.

The validity and reliability of continuous-wave near-infrared spectroscopy for the assessment of leg blood volume during an orthostatic challenge

Near-infrared spectroscopy (NIRS) can potentially be used to assess the cardiovascular autonomic system by monitoring orthostatic challenge-induced shifts in lower limb blood volume. However, in order to be of clinical utility the test must be valid, reliable, and relatively simple to conduct. PurposeTo induce lower limb blood volume shifts using a 10 min 70° head-up tilt, and: (1) in the soleus, determine the validity of an inexpensive continuous wave (cw)-NIRS device by comparing to a criterion frequency-domain (fd-) NIRS device, (2) determine the between-day reliability of soleus assessments obtained from cw-NIRS and fd-NIRS; and, (3) compare the between-day reliability for fd-NIRS assessments obtained at the soleus (standard) and gastrocnemius (simpler alternative). MethodsFifteen non-smoking healthy adults were tested on 3 different mornings, under standardized conditions, separated by a maximum of 7 days. Total haemoglobin concentration (tHb) was continuously monitored bi-laterally in the medial soleus using cw-NIRS and fd-NIRS. For site comparison, tHb was measured in the medial gastrocnemius using fd-NIRS. Results(1) The area under the curve (AUC) for cw-NIRS and fd-NIRS assessments at the soleus were not significantly different (p = 0.619). (2) The criterion (0.75) intra-class correlation coefficient (ICC) was exceeded for both cw-NIRS and fd-NIRS. (3) The criterion ICC was exceeded for both soleus and gastrocnemius assessments. ConclusionContinuous-wave NIRS can be used to monitor orthostatic stress-induced shifts in lower leg blood volume with acceptable validity and reliability. This orthostatic test may present a relatively simple and inexpensive approach for assessing the cardiovascular autonomic nervous system.

Intrinsic cardiovascular autonomic regulatory system of astronauts exposed long-term to microgravity in space: observational study

The fractal scaling of the long-term heart rate variability (HRV) reflects the ‘intrinsic’ autonomic regulatory system. Herein, we examine how microgravity on the ISS affected the power-law scaling β (beta) of astronauts during a long-duration (about 6 months) spaceflight. Ambulatory electrocardiographic (ECG) monitoring was performed on seven healthy astronauts (5 men, 52.0±4.2 years of age) five times: before launch, 24±5 (F01) and 73±5 (F02) days after launch, 15±5 days before return (F03), and after return to Earth. The power-law scaling β was calculated as the slope of the regression line of the power density of the MEM spectrum versus frequency plotted on a log10–log10 scale in the range of 0.0001–0.01 Hz (corresponding to periods of 2.8 h to 1.6 min). β was less negative in space (−0.949±0.061) than on Earth (−1.163±0.075; P<0.025). The difference was more pronounced during the awake than during the rest/sleep span. The circadian amplitude and acrophase (phase of maximum) of β did not differ in space as compared with Earth. An effect of microgravity was detected within 1 month (F01) in space and continued throughout the spaceflight. The intrinsic autonomic regulatory system that protects life under serious environmental conditions on Earth is altered in the microgravity environment, with no change over the 6-month spaceflight. It is thus important to find a way to improve conditions in space and/or in terms of human physiology, not to compromise the intrinsic autonomic regulatory system now that plans are being made to inhabit another planet in the near future.

Long-term smoking cessation and heart rate dynamics in an aging healthy cohort: Is it possible to fully recover?

AimTo evaluate the long-term influence of smoking cessation on the regulation of the autonomic cardiovascular system in an aging general population, using the subpopulation of lifelong non-smokers as control group. MethodsWe analyzed 1481 participants aged ≥50 years from the SAPALDIA cohort. In each participant, heart rate variability and heart rate dynamics were characterized by means of various quantitative analyzes of the inter-beat interval time series generated from 24-hour electrocardiogram recordings. Each parameter obtained was then used as the outcome variable in multivariable linear regression models in order to evaluate the association with smoking status and time elapsed since smoking cessation. The models were adjusted for known confounding factors and stratified by the time elapsed since smoking cessation. ResultsOur findings indicate that smoking triggers adverse changes in the regulation of the cardiovascular system, even at low levels of exposure since current light smokers exhibited significant changes as compared to lifelong non-smokers. Moreover, there was evidence for a dose–response effect. Indeed, the changes observed in current heavy smokers were more marked as compared to current light smokers. Furthermore, full recovery was achieved in former smokers (i.e., normalization to the level of lifelong non-smokers). However, while light smokers fully recovered within the 15 first years of cessation, heavy former smokers might need up to 15–25 years to fully recover. ConclusionThis study supports the substantial benefits of smoking cessation, but also warns of important long-term alterations caused by heavy smoking.

Impact of type of intervention for aortic valve replacement on heart rate variability

BackgroundIt is known that coronary heart surgery leads to varying degrees of cardiac autonomic derangement, clinically detectable as depression of heart rate variability (HRV) parameters. Few studies report that also surgical replacement of the aortic valve (SAVR) may lead to HRV abnormalities, while very little is known about the autonomic effects obtained after less invasive aortic valve replacement techniques. The study aimed to evaluate HRV after SAVR and to compare it with two less invasive techniques, transapical (TaAVI) and tranfemoral (TfAVI) aortic valve implant. MethodsTime-domain heart rate variability (HRV) parameters have been studied by 24-h Holter ECG in 129 patients after SAVR, in 63 patients after TfAVI and in 19 patients after TaAVI. ResultsAll HRV parameters were significantly depressed in SAVR, while they were almost completely preserved in TfAVI patients; TaAVI cases showed a somehow intermediate behaviour [(SDNN respectively: 71.0±34.9 vs 95.9±29.5 (p<0.001) vs 84.4±32.6ms (p=ns)]. Mean heart rate during the 24-h Holter was 8% higher in SAVR patients than in both TfAVI and TaAVI patients. The reported results were not correlated with echocardiographic ejection fraction, or presence of abnormal glucose metabolism, or degree of anaemia or treatment with beta-blockers. ConclusionsSAVR leads to profound depression of some cardiac autonomic parameters, while less invasive procedures allow better preservation of HRV. In particular TfAVI does not induce any significant deterioration of HRV parameters and seems to be the strategy of valve implant with less impact on the cardiovascular autonomic system.

Cardiovascular autonomic function analysis using approximate entropy from 24-h heart rate variability and its frequency components in patients with type 2 diabetes.

Aims/IntroductionThe principal aim of the present study was to investigate the cardiovascular autonomic system status of diabetes patients using approximate entropy (ApEn) extracted from 24-h heart rate variability (HRV) and its frequency components.Materials and MethodsA total of 29 healthy controls and 63 type 2 diabetes patients were included. Participants’ 24-h HRV signals were recorded, and decomposed and reconstructed into four frequency components: high, low, very low and ultra low. The total 24-h HRV and its four components were divided into 24 1-h segments. ApEn values were extracted and statistically analyzed. Four traditional HRV indices, namely standard deviation of the RR intervals, root mean square of successive differences, coefficient of variance of RR intervals and ratio of low to high power of HRV, were also calculated.ResultsThe low-frequency component contained the most abundant non-linear information, so was potentially most suitable for studying the cardiovascular system status with non-linear methods. ApEn values extracted from low- and high-frequency components of healthy controls were higher than those of diabetes patients. Except for root mean square of successive differences, standard deviation of the RR intervals, low to high power of HRV and coefficient of variance of RR intervals of healthy controls were all higher than those of diabetes patients.ConclusionsThe results showed that ApEn contained information on disorders of autonomic system function of diabetes patients as traditional HRV indices in time and frequency domains. ApEn and three traditional indices showed accordance to some degree. Non-linear information in subcomponents of HRV was shown, which is potentially more effective for distinguishing healthy individuals and diabetes patients than that extracted from the total HRV. Compared with diabetes patients, the cardiovascular system of healthy controls showed information of higher complexity, and better regulation function in response to changes of environment.