Changes In Autonomic Activity Research Articles

Effects of unconscious tactile stimuli on autonomic nervous activity and afferent signal processing

Autonomic nervous system (ANS) is a mechanism that regulates our internal environment. In recent years, the interest in how tactile stimuli presented directly to the body affect ANS function and cortical processing in humans has been renewed. However, it is not yet clear how subtle tactile stimuli below the level of consciousness affect human heart rate and cortical processing. To examine this, subthreshold electrical stimuli were presented to the left forearm of 43 participants during an image-viewing task, and electrocardiogram (ECG) and electroencephalogram (EEG) data were collected. The changes in the R-wave interval of the ECG immediately after the subthreshold electrical presentation and heartbeat-evoked potential (HEP), the afferent signal processing of cardiac activity, were measured. The results showed that heart rate decelerated immediately after the presentation of subthreshold electrical stimuli. The HEP during stimulus presentation was amplified for participants with greater heart rate acceleration immediately after this deceleration. The magnitude of these effects depended on the type of the subthreshold tactile stimuli. The results suggest that even with subthreshold stimulation, the changes in autonomic activity associated with orienting response and related afferent signal processing differ depending on the clarity of the tactile stimuli.

Robust and time-resolved estimation of cardiac sympathetic and parasympathetic indices.

The time-resolved analysis of heart rate (HR) and heart rate variability (HRV) is crucial for the evaluation of the dynamic changes of autonomic activity under different clinical and behavioral conditions. Standard HRV analysis is performed in the frequency domain because the sympathetic activations tend to increase low-frequency HRV oscillations, while the parasympathetic ones increase high-frequency HRV oscillations. However, a strict separation of HRV in frequency bands may cause biased estimations, especially in the low frequency range. To overcome this limitation, we propose a robust estimator that combines HR and HRV dynamics, based on the correlation of the Poincaré plot descriptors of interbeat intervals from the electrocardiogram. To validate our method, we used electrocardiograms gathered from open databases where standardized paradigms were applied to elicit changes in autonomic activity. Our proposal outperforms the standard spectral approach for the estimation of low- and high-frequency fluctuations in HRV, and its performance is comparable to newer methods. Our method constitutes a valuable, robust, time-resolved, and cost-effective tool for a better understanding of autonomic activity through HR and HRV in healthy state and potentially for pathological conditions.

Neuroregulatory Effects of Microcone Patch Stimulation on the Auricular Branch of the Vagus Nerve and the Prefrontal Cortex: A Feasibility Study.

Background: The primary purpose of this study was to preliminarily examine the effects of autonomic nervous system activity on the dorsolateral prefrontal cortex. Recent studies have examined approaches to modulating autonomic activity using invasive and non-invasive methods, but the effects of changes in autonomic activity during cognitive tasks on the dorsolateral prefrontal cortex have not been fully investigated. The purpose of this preliminary investigation was to examine changes in autonomic activity and blood oxygen saturation in the dorsolateral prefrontal cortex during reading tasks induced by vagus nerve stimulation using a microcone patch. Methods: A cohort of 40 typically developing adults was enrolled in this study. We carefully examined changes in autonomic nervous system activity and blood oxygen saturation in the dorsolateral prefrontal cortex during a reading task in two conditions: with and without microcone patch stimulation. Results: Significant changes in brain activation in the dorsolateral prefrontal cortext due to microcone patch stimulation were confirmed. In addition, hierarchical multiple regression analysis revealed specific changes in reading task-related blood oxygen saturation in the dorsolateral prefrontal region during microcone patch stimulation. Conclusions: It should be recognized that this study is a preliminary investigation and does not have immediate clinical applications. However, our results suggest that changes in autonomic nervous system activity induced by external vagal stimulation may affect activity in specific reading-related regions of the dorsolateral prefrontal cortex. Further research and evaluation are needed to fully understand the implications and potential applications of these findings.

Modulation of cardio-respiratory activity in mice via transcranial focused ultrasound

Objective: The objective of this study was to investigate the effect of FUS on autonomic nervous system activity, including heart and respiratory rates, and to separate the thermal modulation from combined thermal and mechanical FUS effects.Methods: The thalamus and hypothalamus of wild-type mice were sonicated with a continuous-wave, 2 MHz FUS transducer at pressures of 425 and 850 kPa for 60 seconds. Cardiac and respiratory rates were monitored as signs of autonomic nervous activity. FUS-induced changes in autonomic activity were compared to FUS targeted to a spatially-distant motor region and to laser-induced heating.Results: FUS delivered to the primary target over the thalamus and hypothalamus at 850 kPa reversibly increased the respiratory rate by 6.5±3.2 breaths per minute and decreased the heart rate by 3.2±1.8 beats per minute. No significant changes occurred in this region at 425 kPa or when targeting the motor regions at 850 kPa. Laser heating with the same temperature rise profile produced by 850 kPa sonication resulted in cardiorespiratory modulation similar to that of FUS.Conclusions: FUS is capable of reversibly and non-invasively modulating cardiorespiratory activity in mice. Localized changes in temperature may constitute the main cause for this activity, though further investigation is warranted into the distinct and complementary mechanisms of mechanically- and thermally-induced FUS neuromodulation. Close monitoring of vital signs during FUS neuromodulation may be warranted to monitor systemic responses to stimulation.

Child emotion lability is associated with within-task changes of autonomic activity during a mirror-tracing task.

Adaptive biological and emotional stress responding are both critical for healthy human development. However, the complex associations between the two are not fully understood. The current study addresses this gap in research by studying associations of child emotion regulation and lability with within-task changes in the biological stress response during a mirror-tracing task. Participants were 59 families including two parents and a child between 5 and 12 years old (52.2% female). Parents reported on family demographics and completed the Emotion Regulation Checklist. Child skin conductance level (SCL) and respiratory sinus arrhythmia (RSA) were recorded during a baseline task and during a 3-minute mirror-tracing task. Within-task patterns of SCL and RSA during the task were estimated with multilevel modeling (measures within persons). The emotion regulation subscale was unrelated to any facet of SCL/RSA time courses. However, lower emotion lability was related to SCL patterns that changed less during the task and were overall lower. For RSA, lower emotion lability was related to higher initial RSA that significantly decreased during the task. These findings suggest that higher child emotion lability may promote increased physiological arousal of target organs during challenging activities.

Device-based neuromodulation for cardiovascular diseases and patient' s age.

The autonomic nervous system plays an important role in the pathogenesis of cardiovascular diseases. With aging, autonomic activity changes, and this impacts the physiological reactions to internal and external signals. Both sympathetic and parasympathetic responses seem to decline, reflecting functional and structural changes in nervous regulation. Although some investigators suggested that both the sympathetic and parasympathetic activities were suppressed, others found that only the parasympathetic activity was suppressed while the sympathetic activity increased. In addition, cardiac innervation progressively diminishes with aging. Therefore, one may suggest that neuromodulation interventions may have different effects, and older age groups can express an attenuated response. This article aims to discuss the effect of device-based neuromodulation in different cardiovascular diseases, depending on the patient's age. Thus, we cover renal denervation, pulmonary artery denervation, baroreceptor activation therapy, vagus nerve stimulation, spinal cord stimulation, ganglionated plexi ablation for the management of arterial and pulmonary hypertension, heart failure, angina and arrhythmias. The results of many clinical studies appeared to be unconvincing. In view of the low rate of positive findings in clinical studies incorporating neuromodulation approaches, we suggest the underestimation of advanced age as a potential contributing factor to poorer response. Analysis of outcomes between different age groups in clinical trials may shed more light on the true effects of neuromodulation when neutral/ambiguous results are obtained.

Autonomic nerve activity and cardiovascular changes during discrete seizures in rats.

Activity in both divisions of the autonomic nervous system (ANS) can increase during seizures and result in tachy- or bradyarrhythmias. We sought to determine the patterns of ANS activity that led to heart rate (HR) changes and whether the character of ANS and HR changes can impact the seizures themselves. Simultaneous recordings of vagus nerve and cervical sympathetic ganglionic or nerve activity, EEG, ECG, and blood pressure were acquired from 16 urethane-anesthetized rats that received systemic kainic acid to induce seizures. After initial continuous seizure activity, discrete seizures were observed in 11/16 rats. Individual seizures were classified based on HR changes as tachycardic (n=3), bradycardic (n=17), or one of two more severe categories in which (a) the seizure appeared to be terminated by severe bradyarrhythmia (n=5) or (b) the animal died (n=6). Interestingly, even simple bradycardic seizures had episodes of dramatically increased respiratory effort, which we interpret as evidence of airway occlusion based on muscle artifacts in the recordings with transient blood pressure decreases. In the severe outcomes, ANS activity increased during seizures until it caused a drastic HR reduction (>50%), in which case seizure and ANS activity decreased dramatically. Sympathetic activity during this late vulnerable period was important for survival. We conclude that individual seizures produce (a) stereotypical changes in autonomic activity and HR, (b) persistence of sympathetic tone helps to protect against death, and (c) bradycardic seizures may indicate increased risk for seizure-associated obstructive apnea.

Longitudinally Tracking Maternal Autonomic Modulation During Normal Pregnancy With Comprehensive Heart Rate Variability Analyses.

Changes in the maternal autonomic nervous system are essential in facilitating the physiological changes that pregnancy necessitates. Insufficient autonomic adaptation is linked to complications such as hypertensive diseases of pregnancy. Consequently, tracking autonomic modulation during progressing pregnancy could allow for the early detection of emerging deteriorations in maternal health. Autonomic modulation can be longitudinally and unobtrusively monitored by assessing heart rate variability (HRV). Yet, changes in maternal HRV (mHRV) throughout pregnancy remain poorly understood. In previous studies, mHRV is typically assessed only once per trimester with standard HRV features. However, since gestational changes are complex and dynamic, assessing mHRV comprehensively and more frequently may better showcase the changing autonomic modulation over pregnancy. Subsequently, we longitudinally (median sessions = 8) assess mHRV in 29 healthy pregnancies with features that assess sympathetic and parasympathetic activity, as well as heart rate (HR) complexity, HR responsiveness and HR fragmentation. We find that vagal activity, HR complexity, HR responsiveness, and HR fragmentation significantly decrease. Their associated effect sizes are small, suggesting that the increasing demands of advancing gestation are well tolerated. Furthermore, we find a notable change in autonomic activity during the transition from the second to third trimester, highlighting the dynamic nature of changes in pregnancy. Lastly, while we saw the expected rise in mean HR with gestational age, we also observed increased autonomic deceleration activity, seemingly to counter this rising mean HR. These results are an important step towards gaining insights into gestational physiology as well as tracking maternal health via mHRV.

Causality of cortical and cardiovascular activity during cyclic alternating pattern in non-rapid eye movement sleep.

The dynamic interplay between central and autonomic nervous system activities plays a pivotal role in orchestrating sleep. Macrostructural changes such as sleep-stage transitions or phasic, brief cortical events elicit fluctuations in neural outflow to the cardiovascular system, but the causal relationships between cortical and cardiovascular activities underpinning the microstructure of sleep are largely unknown. Here, we investigate cortical-cardiovascular interactions during the cyclic alternating pattern (CAP) of non-rapid eye movement sleep in a diverse set of overnight polysomnograms. We determine the Granger causality in both 507 CAP and 507 matched non-CAP sequences to assess the causal relationships between electroencephalography (EEG) frequency bands and respiratory and cardiovascular variables (heart period, respiratory period, pulse arrival time and pulse wave amplitude) during CAP. We observe a significantly stronger influence of delta activity on vascular variables during CAP sequences where slow, low-amplitude EEG activation phases (A1) dominate than during non-CAP sequences. We also show that rapid, high-amplitude EEG activation phases (A3) provoke a more pronounced change in autonomic activity than A1 and A2 phases. Our analysis provides the first evidence on the causal interplay between cortical and cardiovascular activities during CAP. Granger causality analysis may also be useful for probing the level of decoupling in sleep disorders. This article is part of the theme issue 'Advanced computation in cardiovascular physiology: new challenges and opportunities'.

Prediction of viral symptoms using wearable technology and artificial intelligence: A pilot study in healthcare workers.

Conventional testing and diagnostic methods for infections like SARS-CoV-2 have limitations for population health management and public policy. We hypothesize that daily changes in autonomic activity, measured through off-the-shelf technologies together with app-based cognitive assessments, may be used to forecast the onset of symptoms consistent with a viral illness. We describe our strategy using an AI model that can predict, with 82% accuracy (negative predictive value 97%, specificity 83%, sensitivity 79%, precision 34%), the likelihood of developing symptoms consistent with a viral infection three days before symptom onset. The model correctly predicts, almost all of the time (97%), individuals who will not develop viral-like illness symptoms in the next three days. Conversely, the model correctly predicts as positive 34% of the time, individuals who will develop viral-like illness symptoms in the next three days. This model uses a conservative framework, warning potentially pre-symptomatic individuals to socially isolate while minimizing warnings to individuals with a low likelihood of developing viral-like symptoms in the next three days. To our knowledge, this is the first study using wearables and apps with machine learning to predict the occurrence of viral illness-like symptoms. The demonstrated approach to forecasting the onset of viral illness-like symptoms offers a novel, digital decision-making tool for public health safety by potentially limiting viral transmission.

Thermoregulation and Sleep: Functional Interaction and Central Nervous Control.

Each of the wake-sleep states is characterized by specific changes in autonomic activity and bodily functions. The goal of such changes is not always clear. During non-rapid eye movement (NREM) sleep, the autonomic outflow and the activity of the endocrine system, the respiratory system, the cardiovascular system, and the thermoregulatory system seem to be directed at increasing energy saving. During rapid eye movement (REM) sleep, the goal of the specific autonomic and regulatory changes is unclear, since a large instability of autonomic activity and cardiorespiratory function is observed in concomitance with thermoregulatory changes, which are apparently non-functional to thermal homeostasis. Reciprocally, the activation of thermoregulatory responses under thermal challenges interferes with sleep occurrence. Such a double-edged and reciprocal interaction between sleep and thermoregulation may be favored by the fact that the central network controlling sleep overlaps in several parts with the central network controlling thermoregulation. The understanding of the central mechanism behind the interaction between sleep and thermoregulation may help to understand the functionality of thermoregulatory sleep-related changes and, ultimately, the function(s) of sleep. © 2021 American Physiological Society. Compr Physiol 11:1591-1604, 2021.

Sympathetic hyperactivity, hypertension, and tachycardia induced by stimulation of the ponto-medullary junction in humans

ObjectiveThe purpose of this study is to investigate changes in autonomic activities and systemic circulation generated by surgical manipulation or electrical stimulation to the human brain stem. MethodsWe constructed a system that simultaneously recorded microsurgical field videos and heart rate variability (HRV) that represent autonomic activities. In 20 brain stem surgeries recorded, HRV features and sites of surgical manipulation were analyzed in 19 hypertensive epochs, defined as the periods with transient increases in the blood pressure. We analyzed the period during electrical stimulation to the ponto-medullary junction, performed for the purpose of monitoring a cranial nerve function. ResultsIn the hypertensive epoch, HRV analysis showed that sympathetic activity predominated over the parasympathetic activity. The hypertensive epoch was more associated with surgical manipulation of the area in the caudal pons or the rostral medulla oblongata compared to controls. During the period of electrical stimulation, there were significant increases in blood pressures and heart rates, accompanied by sympathetic overdrive. ConclusionsOur results provide physiological evidence that there is an important autonomic center located adjacent to the ponto-medullary junction. SignificanceA large study would reveal a candidate target of neuromodulation for disorders with autonomic imbalances such as drug-resistant hypertension.

The influence of low-intensity resistance training combined with neuromuscular electrical stimulation on autonomic activity in healthy adults: A randomized controlled cross-over trial

Background:Low-intensity resistance training (RT) combined with neuromuscular electrical stimulation (NMES) is one method of exercise to improve the deterioration of physical function. However, it is unclear whether low-intensity RT combined with NMES (RT + NMES) can be safely implemented.Objective:This study aimed to examine the influence of low-intensity RT + NMES on autonomic activity and cardiovascular responses in healthy adults.Methods:This study was an open-label, randomized controlled cross-over trial. The exercise intensity of isometric knee extension RT was set to 40% of the maximum voluntary contraction (peak torque). NMES was adjusted to a biphasic asymmetrical waveform with the frequency maintained at 50 Hz and a phase duration of 300 s. The difference in the change in autonomic activity and cardiovascular responses was compared by assessing heart rate variability, blood pressure, and heart rate during RT and .Results:Twenty healthy male college students (mean age years) participated in this study. The ratio of low- and high-frequency components of heart rate variability, systolic blood pressure, and heart rate increased during exercise in the RT and sessions (0.05). There were no significant differences in autonomic activity and cardiovascular responses throughout the sessions during RT and .Conclusion:In conclusion, our results demonstrated that low-intensity was safe and did not induce excessive autonomic and cardiovascular responses in healthy adults.

Heart Rate Variability and Multi-Site Pulse Rate Variability for the Assessment of Autonomic Responses to Whole-Body Cold Exposure.

Heart rate variability (HRV) is a noninvasive marker of cardiac autonomic activity and has been used in different circumstances to assess the autonomic responses of the body. Pulse rate variability (PRV), a similar variable obtained from pulse waves, has been used in recent years as a valid surrogate of HRV. However, the effect that localized changes in autonomic activity have in the relationship between HRV and PRV has not been entirely understood. In this study, a whole-body cold exposure protocol was performed to generate localized changes in autonomic activity, and HRV and PRV from different body sites were obtained. PRV measured from the earlobe and the finger was shown to differ from HRV, and the correlation between these variables was affected by the cold. Also, it was found that PRV from the finger was more affected by cold exposure than PRV from the earlobe. In conclusion, PRV is affected differently to HRV when localized changes in autonomic activity occur. Hence, PRV should not be considered as a valid surrogate of HRV under certain circumstances.Clinical Relevance- This indicates that pulse rate variability is affected differently to heart rate variability when autonomic activity is modified and suggests that pulse rate variability is not always a valid surrogate of heart rate variability.

Insomnia is Associated with an Increased Carotid‐Femoral Pulse Wave Velocity in Healthy Young Adults during Awake Hours

Current literature indicates that those living with insomnia have an increased risk of developing and dying from cardiovascular disease (CVD). Previous studies have investigated cardiovascular measures such as baroreflex sensitivity (cvBRS), heart rate (HR), blood pressure (BP) and serum lipid levels in those with insomnia, however these studies focus on older adults and do not investigate early cardiovascular changes occurring in a young population. The purpose of this study was to examine differences across multiple cardiovascular measures that may be associated with insomnia in a young, healthy adult population. This cross‐sectional analysis of the midpoint sample of the Niagara Longitudinal Heart Study used data from 156 participants aged 19–25 years. Insomnia was classified using the SLEEP‐50 questionnaire and was compared across measures of BP, HR, cvBRS, and carotid‐femoral pulse wave velocity (cfPWV). HR and BP were measured using an automatic oscillometric device, cvBRS was measured using a beat‐by‐beat systolic BP and RR intervals, and cfPWV was measured using a hand‐held tonometer which measured pressure waveforms. Significantly higher cfPWV was found in those with insomnia (M=6.00± 0.89) versus those without (M=5.57 ±0.88) (p=0.013). There were no significant differences between those with and without insomnia for BP, HR or cvBRS (p>0.05), however, a non‐significant trend in HR was found between those with insomnia (M=79.93± 11.92) and those without (M=75.91± 11.18) (p=0.058). Literature suggests that insomnia may lead to CVD through mechanisms including changes in autonomic activity, systemic inflammation, and hormonal dysregulation. Previous insomnia studies have not investigated cfPWV, therefore these findings suggest that arterial stiffness may be an early indicator of CVD risk in those with insomnia. These results are especially novel since they are being detected in a young, otherwise healthy population suggesting that CVD risk may begin to develop early in those suffering with insomnia. The identification of these differences at a young age suggests that significant cardiovascular change occurs earlier than previously expected in those living with insomnia, thus prompting early intervention to help reduce the physiological burden of this sleeping disorder.Support or Funding InformationFunding source: The NLHS is funded by the Canadian Institutes of Health Research (CIHR #s 363774, 399332). KSD is funded by a CIHR Doctoral Research Award – Frederick Banting and Charles Best Canada Graduate Scholarship (RFN#167014)

Lying Awake at Night: Cardiac Autonomic Activity in Relation to Sleep Onset and Maintenance

Insomnia, i.e., difficulties initiating and/or maintaining sleep, is one of the most common sleep disorders. To study underlying mechanisms for insomnia, we studied autonomic activity changes around sleep onset in participants without clinical insomnia but with varying problems with initiating or maintaining sleep quantified as increased sleep onset latency (SOL) and wake after sleep onset (WASO), respectively. Polysomnography and electrocardiography were simultaneously recorded in 176 participants during a single night. Cardiac autonomic activity was assessed using frequency domain analysis of RR intervals and results show that the normalized spectral power in the low frequency band (LFnu) after sleep onset was significantly higher in participants with long SOL compared to participants with short SOL. Furthermore, the normalized spectral power in the high frequency band (HFnu) was significantly lower in participants with long SOL as compared to participants with short SOL over 3 time periods (first 10 min in bed intending to sleep, 10 min before, and 10 min after sleep onset). These results suggest that participants with long SOL are more aroused in all three examined time periods when compared to participants with short SOL, especially for young adults (20–40 years). As there is no clear consensus on the cutoff for an increased WASO, we used a data-driven approach to explore different cutoffs to define short WASO and long WASO groups. LFnu, HFnu, and LF/HF differed between the long and the short WASO groups. A higher LFnu and LF/HF and a lower HFnu was observed in participants with long WASO for most cutoffs. The highest effect size was found using the cutoff of 66 min. Our findings suggest that autonomic cardiac activity has predictive value with respect to sleep characteristics pertaining to sleep onset and maintenance.

Effects of the Trier Social Stress Test on the distributions of IL-6 and MAP levels

Trier Social Stress Test (TSST) is an experimental psychological test that induces changes in autonomic, endocrinological and immunological activity. Two measures used to evaluate the inflammatory activity induced by this test are the interleukin 6 (IL-6), a cytokine sensitive to changes in sympathetic nervous activity, and the mean arterial pressure (MAP), a measure sensitive to changes in autonomic activity. This study had two goals: first, the study examined whether TSST increases IL-6 and MAP levels; second, pre- and post-TSST IL-6 levels were compared for participants whose IL-6 levels increased or decreased due to the TSST. Saliva samples of IL-6 and MAP were taken from 42 participants clinically healthy, without psychiatric history, and data were analysed via quantile comparisons. The results showed that TSST did not lead to an increase in sympathetic activity as indexed by IL-6. Instead, TSST led to increases in MAP. Also, there were significant differences between the IL-6 distributions of people whose IL-6 levels changed from low to high (63%) and from high to low (37%) before and after the TSST. These findings suggest that the TSST will not have the same effect on all participants; that is, individual differences can be assessed using a biomarker to identify people with specialized psychological care needs.

Parasympathetic nervous system changes after the menopause: A comparative study

Background: Autonomic nervous system control is a major determinant in various cardiovascular diseases. Onset of menopause in women results in increased risk of cardiovascular mortality. Early assessment of the changes in autonomic activity after menopause can help reduce the prevalence of cardiovascular mortality in women. Aims and Objectives: The aim of the study is to compare the parasympathetic autonomic nervous system activity in age-matched pre- and postmenopausal women. Materials and Methods: The study was conducted in the physiology department of Government Medical College, Amritsar. Two groups of 40 women each were enrolled in the study. We enrolled pre-menopausal women in Group I and post-menopausal women in Group II. Parasympathetic nervous system assessment was done using 30:15 ratio, standing: lying ratio (S: L ratio), Valsalva ratio, and deep breathing test (DBT). Statistical analysis of the collected data was done using student t-test. Results: Parasympathetic functions tests did not reveal any significant change in the mean 30:15 ratio, S: L ratio, Valsalva ratio, and the mean value for DBT (P > 0.05). Conclusion: No significant variation in parasympathetic activity between the pre-menopausal and post-menopausal groups was observed.

Autonomic dysfunction in programmed hypertension

Hypertension is an important modifiable risk factor for cardiovascular diseases. Its high prevalence, combined with the significant morbidity and mortality associated with secondary complications, make it a major public health concern. Despite decades of research, over 95% of all cases of hypertension remain of unknown etiology, necessitating that treatments target the established symptoms and not the cause. One of the important recent advances in hypertension research is an understanding that hypertension often may have a developmental origin. A substantial body of evidence indicates that exposure to an adverse intrauterine environment during critical periods of development may predispose an individual to develop hypertension later in life. A causative mechanism has yet to be identified, but may include epigenetic modifications, and/or alterations in renal, vascular or autonomic cardiovascular functions. This review will present evidence regarding changes in autonomic activity as a possible causative pathophysiological mechanism underlying the development of programmed hypertension. In man, low birth weight is the best-known risk factor for hypertension of developmental origins, although this is a broad surrogate measure for intrauterine adversity. This review will include clinical studies across the lifespan that have investigated autonomic function in individuals with fetal growth restriction and those born preterm. A determination of whether altered autonomic function is seen in these individuals in early life is imperative, as hypertensive disorders that have their origins in utero, and that can be identified early, will open the door to risk stratification, and the development of new strategies that prevent or specifically target these mechanisms.

Tracking autonomic balance using an open-loop model of the arterial baroreflex.

Blood pressure control is vital for maintaining adequate perfusion of the brain and other organs in the body across varying physiological demands, and the arterial baroreceptor reflex (baroreflex) is the major short-term blood pressure control loop mediated by the autonomic nervous system (ANS). Accurate quantitative models of the baroreflex would provide physiological insight and could allow for real-time tracking of ANS activity in clinical settings. In this work, we formulate a causal, parametric beat-to-beat model, relating systolic blood pressure (input) to heart rate (output). Model structure and parameterization are explicitly based on prior physiological insights of the response dynamics of the sympathetic and parasympathetic branches of the ANS. We analyze the model's ability to track changes in autonomic balance using data from 14 nonsmoking adult males, without any history of cardiopulmonary disease, subject to both pharmacological blockade and postural changes. Our results show that the model parameters faithfully track expected changes in autonomic balance resulting from changing posture ( P < 0.01) and sympathetic blockade ( P < 0.05), and in many cases, the model parameters are more sensitive to changes in autonomic activity and balance than autonomic indices derived from the power spectral density of heart rate variability. Overall, the contributions of this work further the goal of obtaining real-time quantitative assessment of the ANS.