Autonomic Dysfunction Contributes to Impairment of Cerebral Autoregulation in Patients with Epilepsy

Breath-Hold-Triggered BOLD fMRI in Drug-Resistant Nonlesional Focal Epilepsy-A Pilot Study

PURPOSE

Individuals with drug-resistant epilepsy may benefit from epilepsy surgery. In nonlesional cases, where no epileptogenic lesion can be detected on structural magnetic resonance imaging, multimodal neuroimaging studies are required. Breath-hold-triggered BOLD fMRI (bh-fMRI) was developed to measure cerebrovascular reactivity in stroke or angiopathy and highlights regional network dysfunction by visualizing focal impaired flow increase after vasodilatory stimulus. This regional dysfunction may correlate with the epileptogenic zone. In this prospective single-center single-blind pilot study, we aimed to establish the feasibility and safety of bh-fMRI in individuals with drug-resistant non-lesional focal epilepsy undergoing presurgical evaluation.

METHODS

In this prospective study, 10 consecutive individuals undergoing presurgical evaluation for drug-resistant focal epilepsy were recruited after case review at a multidisciplinary patient management conference. Electroclinical findings and results of other neuroimaging were used to establish the epileptogenic zone hypothesis. To calculate significant differences in cerebrovascular reactivity in comparison to the normal population, bh-fMRIs of 16 healthy volunteers were analyzed. The relative flow change of each volume of interest (VOI) of the atlas was then calculated compared to the flow change of the whole brain resulting in an atlas of normal cerebral reactivity. Consequently, the mean flow change of every VOI of each patient was tested against the healthy volunteers group. Areas with significant impairment of cerebrovascular reactivity had decreased flow change and were compared to the epileptogenic zone localization hypothesis in a single-blind design.

RESULTS

Acquisition of bh-fMRI was feasible in 9/10 cases, with one patient excluded due to noncompliance with breathing maneuvers. No adverse events were observed, and breath-hold for intermittent hypercapnia was well tolerated. On blinded review, we observed full or partial concordance of the local network dysfunction seen on bh-fMRI with the electroclinical hypothesis in 6/9 cases, including cases with extratemporal lobe epilepsy and those with nonlocalizing 18F-fluorodeoxyglucose positron emission tomography (FDG-PET).

CONCLUSION

This represents the first report of bh-fMRI in individuals with epilepsy undergoing presurgical evaluation. We found bh-fMRI to be feasible and safe, with a promising agreement to electroclinical findings. Thus, bh-fMRI may represent a potential modality in the presurgical evaluation of epilepsy. Further studies are needed to establish clinical utility.

The Association of Nocturnal Seizures and Interictal Cardiac/Central Autonomic Function in Frontal Lobe Epilepsy: Heart Rate Variability and Central Autonomic Network Analysis

Purpose

Patients with epilepsy frequently experience autonomic dysfunction, closely related to sudden unexplained death in epilepsy (SUDEP). SUDEP occurs most often at night or during sleep, and frequent nocturnal seizures are an established risk factor. This study investigated the influence of nocturnal seizures on autonomic dysfunction in epilepsy.

Patients and Methods

This retrospective study enrolled frontal lobe epilepsy (FLE) patients who performed 24-hour EEG monitoring. All participants were divided into nocturnal FLE (NFLE, > 90% of seizures occurring during sleep) or diurnal FLE (DFLE) groups. EEG and ECG signals were simultaneously obtained during waking and sleep stages. EEG current density source and connectivity analysis of the autonomic network were performed. ECG was analyzed across time and frequency domains heart rate variability (HRV) analysis method was used. The obtained parameters were compared between the NFLE and DFLE groups.

Results

Fifteen NFLE and 16 DFLE patients were enrolled with no significant difference in age, sex, disease duration, seizure frequency, or the number of anti-seizure medications between the two groups. During sleep, a decrease in HRV parameters and an increase of the beta-1 (13-22 Hz) current source density power in the bilateral paracentral lobule (BA4,5,6), precuneus (BA7), and cingulate (BA31) were observed in the NFLE group compared to DFLE group. The NFLE group also showed hyperconnectivity in the central autonomic (12 edges distributed over 10 nodes), sympathetic (2 edges distributed over 3 nodes), and parasympathetic (4 edges distributed over 6 nodes) beta-1 frequency band networks during sleep. During wakefulness, central and cardiac autonomic variables were not significantly different between the NFLE and DFLE groups.

Conclusion

Interictal cardiac and central autonomic dysfunction occurred simultaneously and can be attributed to the brain-heart autonomic axis. Our findings suggest that nocturnal seizures may contribute to interictal autonomic dysfunction during sleep in people with epilepsy.

Use of Hypoxic Respiratory Challenge for Differentiating Alzheimer's Disease and Wild-Type Mice Non-Invasively: A Diffuse Optical Spectroscopy Study

Alzheimer's disease is one of the most critical brain diseases. The prevalence of the disease keeps rising due to increasing life spans. This study aims to examine the use of hemodynamic signals during hypoxic respiratory challenge for the differentiation of Alzheimer's disease (AD) and wild-type (WT) mice. Diffuse optical spectroscopy, an optical system that can non-invasively monitor transient changes in deoxygenated (ΔRHb) and oxygenated (ΔOHb) hemoglobin concentrations, was used to monitor hemodynamic reactivity during hypoxic respiratory challenges in an animal model. From the acquired signals, 13 hemodynamic features were extracted from each of ΔRHb and -ΔOHb (26 features total) for more in-depth analyses of the differences between AD and WT. The hemodynamic features were statistically analyzed and tested to explore the possibility of using machine learning (ML) to differentiate AD and WT. Among the twenty-six features, two features of ΔRHb and one feature of -ΔOHb showed statistically significant differences between AD and WT. Among ML techniques, a naive Bayes algorithm achieved the best accuracy of 84.3% when whole hemodynamic features were used for differentiation. While further works are required to improve the approach, the suggested approach has the potential to be an alternative method for the differentiation of AD and WT.

Fitness, performance, and cardiac autonomic responses to exercise in people with epilepsy

People with epilepsy (PWE) are less fit and have an increased risk of sudden cardiac death. Imbalances within the autonomic nervous system (ANS) are believed to mediate some of those effects. However, results are mostly derived from patients whose seizures are refractory to medical therapy. In this study, an exhaustive bicycle ergometer test was delivered to 25 PWE (19 seizure free in the last 6 months) recruited in a community-based setting and 25 age-, sex-, and BMI-matched healthy controls. During the exercise test a 12-channel ECG was recorded and spirometry was carried out to determine the maximal oxygen uptake (VO₂peak) as the gold standard to assess fitness. Before and after exercise, heart rate variability (HRV) and electrodermal activity (EDA) were measured along with an electroencephalogram (EEG). Blood samples were collected to determine anti-seizure drug (ASD) serum levels and physical activity of daily living was evaluated via the International Physical Activity Questionnaire (IPAQ). People with epilepsy and healthy controls were similarly fit and physically active. However, PWE had a lower maximum heart rate, a lower heart rate reserve, and a lower chronotropic index. The ratio between low- to high-frequency HRV changes (LF/HF ratio) was lower in PWE. Two patients with idiopathic genetic epilepsies revealed generalized interictal epileptiform discharges only after, but not before exercise. However, post-exercise EEG measurement was three times longer than pre-exercise and those patients did not report exercise induced seizures in the history. Besides epileptogenesis, anti-seizure medications may also contribute to those autonomic differences.

Exploring factors associated with interictal heart rate variability in patients with medically controlled focal epilepsy

PURPOSE

Heart rate variability (HRV) reflects the balance between the functional outputs of the sympathetic and parasympathetic nervous systems. It is lower in patients with epilepsy than in the healthy controls. However, HRV has been inadequately studied in different patient subgroups with medically controlled epilepsy. Hence, this study aimed to investigate factors associated with interictal HRV in patients with medically controlled epilepsy.

METHODS

This retrospective cohort study included 54 patients (24 males and 30 females) with medically controlled focal epilepsy who only received monotherapy to eliminate the confounding effect of different antiseizure medications (ASMs). Patients with major systemic or psychiatric disorder comorbidities were excluded. For HRV analysis, electroencephalography and 5-minute well-qualified electrocardiogram segment recording were conducted during stage N1 or N2 sleep. In addition, the association between age, gender, seizure onset type, ASMs, and the time domain and frequency-domain HRV measures was analyzed.

RESULTS

HRV negatively correlated with advanced age. Patients with focal to bilateral tonic-clonic seizure (FBTCS) had a significantly lower HRV than focal impaired awareness seizures (FIAS). HRV was not associated with any gender and ASMs.

CONCLUSIONS

HRV negatively correlated with age, and patients with FBTCS had a decreased HRV. Thus, these patients may have a declining autonomic function. Therefore, different seizure types may carry different risks of autonomic dysfunction in patients with medically controlled focal epilepsy.