Intracranial CArtography of Cortical Contribution to Respiratory Load Compensation in Epilepsy

Condition(s) studied

Investigational drug(s) / intervention(s)

SEEG monitoring: Patients will be recruited among adult patients suffering from drug-resistant focal epilepsy who undergo SEEG monitoring at the Epilepsy Department of the Neurological Hospital. The study will be offered to patients during the hospitalization.

Comprehensive respiratory monitoring: In addition to SEEG monitoring, all participants will undergo comprehensive respiratory monitoring in order to collect respiratory data (tidal volume, VE, and respiratory rate) and gas exchange (PETO2 and PETCO2).

Cardio-respiratory monitoring: In addition to SEEG channels, cardio-respiratory monitoring consisting of pulse oximetry, respiratory efforts (thoracic and abdominal) and EKG recordings will be performed.

Expiratory load compensation: Expiratory load compensation will be assessed in the patient's room in the epilepsy monitoring unit. Patients will breathe through a facemask connected in series to a bidirectional pneumotach and a three-way T-shaped valve. The second port on the three-way valve will be open to room air, and third port will be connected to a CE-marked PEEP valve (PEEP 20 valve, Ambu A/S Denmark) allowing to adjust airflow resistance during expiration from 0.15-2.0 kPa (1.5-20 cmH2O). Respired air will be continuously sampled at the mouth and analyzed for fractional concentrations of O2 and CO2.

Hypercapnic challenge: The patient breathes through the mouth, using a mouthpiece and a nose clip, through a device fitted with a hermetically sealed bag that measures the various parameters of his/her breathing. At the start of the test, the patient breathes ambient air and his or her breathing is measured. Then, after a few minutes, the patient is connected to the bag, breathing in a closed circuit. This causes a gradual increase in carbon dioxide (CO2) in the inspired air. During this time, breathing parameters will be measured and gas exchanges studied with each breath. The test is stopped when the end-tidal carbon dioxide pressure (PetCO2) reaches 60 mm Hg, or in the event of intolerance.

Questionnaires: Caffeine intake Self-report the degree of "breathlessness" during Expiratory load compensation using a visual analogue scale Self-report the degree of "breathlessness

Study summary

30% of patients with epilepsy suffer from drug-resistant seizures and have a greater risk of premature mortality than the general population. Among all causes of death, the most frequent is SUDEP, for sudden and unexpected death in epilepsy patients. SUDEP typically occurs after a nocturnal seizure, and primarily results from a postictal central respiratory dysfunction in patients with generalized convulsive seizure (GCS), suggesting the critical role of seizure-related impairment of breathing control, and underscoring the importance of monitoring and preventive interventions during the post-ictal phase. Most of patients with drug-resistant seizures demonstrate transient peri-ictal apnea and hypoxemia especially in the aftermath of a GCS. Experimental and clinical data suggest that most SUDEP primarily result from a fatal seizure-related respiratory arrest 5. Apnea was the primary cause of death in several epilepsy models. In patients whose SUDEP had occurred during long-term video-EEG monitoring, we observed fatal postictal central apnea after a nocturnal GCS in all SUDEP. Accordingly, it is currently hypothesized that in a subgroup of patients, repetition of seizures may contribute to chronic alteration of respiratory regulation which may increase the risk of fatal postictal central respiratory arrest.

Central regulation of autonomic function is ensured by the so-called Central Autonomic Network (CAN), which anatomy in humans has primarily been investigated in neuroimaging studies or using intraEEG (iEEG) data in patients with drug-resistant focal epilepsy undergoing presurgical evaluation with intracerebral electrodes. Central regulation of breathing primarily rely on brainstem, especially the preBötzinger complex for rhythm generation and the retrotrapezoid nucleus and dorsal raphe for chemoreception, especially ventilatory response to hypercapnia. However, through an intricated structures connecting these regions, this respiratory signal projects to a network of cortical and subcortical regions mainly including the limbic and sensorimotor cortical areas. Studies in patients undergoing iEEG reinforced the role of limbic and paralimbic structures, with transient central apnea elicited by direct electrical stimulation of amygdala, hippocampus, anterior parahippocampal, and antero-mesial fusiform gyri. However, our group also reported transient hypoxemia could be elicited by cortical direct electrical stimulation outside the temporo-limbic structures, most commonly after stimulation of the perisylvian cortex. Importantly, our group recently showed that involvement of this perisylvian cortex in the epileptogenic zone is a strong risk factor of SUDEP, reinforcing the importance of further studying its integration in the cortical control of respiration.

The involvement of cortical control of ventilation is particularly important to ensure expiratory load compensation, a typical situation after GCS, which is associated with airway obstruction, especially when the face is positioned into the pillow. This cortical component of the physiological response to experimental expiratory loads was investigated in healthy subjects through the study of EEG activity during an expiratory load compensation protocol. Accordingly, EEGs were processed by ensemble averaging expiratory time-locked segments and examined for pre-expiratory EEG potentials, defined as a slow negative shift from the baseline signal preceding expiration, and suggestive of cortical preparation of expiration. Expiratory load compensation was associated with EEG premotor potential presumably involving the supplementary motor area. However, because of the limited spatial resolution of scalp EEG, the organization of cortical neural sources involved in this expiratory load compensation or during response to hypercapnia, especially the interaction between the premotor cortex, the sensorimotor cortical areas and the perisylvian cortex is unknown.

Eligibility

Primary outcome measure(s)

• Cortical localization of pre-expiratory potentials (via SEEG) during HETL (20 cmH₂O) in drug-resistant epilepsy — Through study completion, an average of 1 year
  Localization of SEEG contacts will use the anatomical MRI images performed in clinical routine. Pre-expiratory potentials are defined as a slow negative shift from the baseline signal starting between 2 and 0.5 s before the onset of expiration. Both visual and statistical analyses will be used to conclude on the presence of significant pre-expiratory potentials over each recording contact, using the same approach as the one our group used in the past in another physiological paradigm.

Trial sites (1)

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