Glottal patency during experimental seizures in piglets

Imaging of focal seizures with Electrical Impedance Tomography and depth electrodes in real time

Intracranial EEG is the current gold standard technique for localizing seizures for surgery, but it can be insensitive to tangential dipole or distant sources. Electrical Impedance Tomography (EIT) offers a novel method to improve coverage and seizure onset localization. The feasibility of EIT has been previously assessed in a computer simulation, which revealed an improved accuracy of seizure detection with EIT compared to intracranial EEG. In this study, slow impedance changes, evoked by cell swelling occurring over seconds, were reconstructed in real time by frequency division multiplexing EIT using depth and subdural electrodes in a swine model of epilepsy. EIT allowed to generate repetitive images of ictal events at similar time course to fMRI but without its significant limitations. EIT was recorded with a system consisting of 32 parallel current sources and 64 voltage recorders. Seizures triggered with intracranial injection of benzylpenicillin (BPN) in five pigs caused a repetitive peak impedance increase of 3.4 ± 1.5 mV and 9.5 ± 3% (N =205 seizures); the impedance signal change was seen already after a single, first seizure. EIT enabled reconstruction of the seizure onset 9 ± 1.5 mm from the BPN cannula and 7.5 ± 1.1 mm from the closest SEEG contact (p<0.05, n =37 focal seizures in three pigs) and it could address problems with sampling error in intracranial EEG. The amplitude of the impedance change correlated with the spread of the seizure on the SEEG (p <<0.001, n =37). The results presented here suggest that combining a parallel EIT system with intracranial EEG monitoring has a potential to improve the diagnostic yield in epileptic patients and become a vital tool in improving our understanding of epilepsy.

Proposed Mechanism-Based Risk Stratification and Algorithm to Prevent Sudden Death in Epilepsy

Sudden Unexpected Death in Epilepsy (SUDEP) is the leading cause of death in young adults with uncontrolled seizures. First aid guidance to prevent SUDEP, though, has not been previously published because the rarity of monitored cases has made the underlying mechanism difficult to define. This starkly contrasts with the first aid guidelines for sudden cardiac arrest that have been developed based on retrospective studies and expert consensus and the discussion of resuscitation challenges in various American Heart Association certificate courses. However, an increasing amount of evidence from documented SUDEP cases and near misses and from animal models points to a consistent sequence of events that starts with sudden airway occlusion and suggests a mechanistic basis for enhancing seizure first aid. In monitored cases, this sudden airway occlusion associated with seizure activity can be accurately inferred from inductance plethysmography or (depending on recording bandwidth) from electromyographic (EMG) bursts that are associated with inspiratory attempts appearing on the electroencephalogram (EEG) or the electrocardiogram (ECG). In an emergency setting or outside a hospital, seizure first aid can be improved by (1) keeping a lookout for sudden changes in airway status during a seizure, (2) distinguishing thoracic and abdominal movements during attempts to inspire from effective breathing, (3) applying a simple maneuver, the laryngospasm notch maneuver, that may help with airway management when aggressive airway management is unavailable, (4) providing oxygen early as a preventative step to reduce the risk of death, and (5) performing cardiopulmonary resuscitation before the limited post-ictal window of opportunity closes. We propose that these additions to first aid protocols can limit progression of any potential SUDEP case and prevent death. Risk stratification can be improved by recognition of airway occlusion, attendant hypoxia, and need for resuscitation.

Laryngospasm, central and obstructive apnea during seizures: Defining pathophysiology for sudden death in a rat model

Seizure spread into the autonomic nervous system can result in life-threatening cardiovascular and respiratory dysfunction. Here we report on a less-studied consequence of such autonomic derangements-the possibility of laryngospasm and upper-airway occlusion. We used parenteral kainic acid to induce recurring seizures in urethane-anesthetized Sprague Dawley rats. EEG recordings and combinations of cardiopulmonary monitoring, including video laryngoscopy, were performed during multi-unit recordings of recurrent laryngeal nerve (RLN) activity or head-out plethysmography with or without endotracheal intubation. Controlled occlusions of a tracheal tube were used to study the kinetics of cardiac and respiratory changes after sudden obstruction. Seizure activity caused significant firing increases in the RLN that were associated with abnormal, high-frequency movements of the vocal folds. Partial airway obstruction from laryngospasm was evident in plethysmograms and was prevented by intubation. Complete glottic closure (confirmed by laryngoscopy) occurred in a subset of non-intubated animals in association with the largest increases in RLN activity, and cessation of airflow was followed in all obstructed animals within tens of seconds by ST-segment elevation, bradycardia, and death. Periods of central apnea occurred in both intubated and non-intubated rats during seizures for periods up to 33s and were associated with modestly increased RLN activity, minimal cardiac derangements, and an open airway on laryngoscopy. In controlled complete airway occlusions, respiratory effort to inspire progressively increased, then ceased, usually in less than 1min. Respiratory arrest was associated with left ventricular dilatation and eventual asystole, an elevation of systemic blood pressure, and complete glottic closure. Severe laryngospasm contributed to the seizure- and hypoxemia-induced conditions that resulted in sudden death in our rat model, and we suggest that this mechanism could contribute to sudden death in epilepsy.

Swine model for translational research of invasive intracranial monitoring

Focal cortical epilepsy is currently studied most effectively in humans. However, improvement in cortical monitoring and investigational device development is limited by lack of an animal model that mimics human acute focal cortical epileptiform activity under epilepsy surgery conditions. Therefore, we assessed the swine model for translational epilepsy research. Swine were used due to their cost-effectiveness, convoluted cortex, and comparative anatomy. The anatomy has all the same brain structures as the human, and in similar locations. Focal subcortical injection of benzyl-penicillin produced clinical seizures correlating with epileptiform activity demonstrating temporal and spatial progression. Swine were evaluated under five different anesthesia regimens. Of the five regimens, conditions similar to human intraoperative anesthesia, including continuous fentanyl with low dose isoflorane, was the most effective for eliciting complex, epileptiform activity after benzyl-penicillin injection. The most complex epileptiform activity (spikes, and high frequency activity) was then repeated reliably in nine animals, utilizing 14 swine total. There were 20.1 ± 10.8 [95% confidence interval (CI) 11.8-28.4] epileptiform events with > 3.5 Hz activity occurring per animal. Average duration of each event was 46.3 ± 15.6 (95% CI 44.0-48.6) s, ranging from 20-100 s. In conclusion, the acute swine model of focal cortical epilepsy surgery provides an animal model that mimics human surgical conditions with a large brain and gyrated cortex, and is relatively inexpensive among animal models. Therefore, we feel this model provides a valuable, reliable, and novel platform for translational studies of implantable hardware for intracranial monitoring.

Swine models in the design of more effective medical countermeasures against organophosphorus poisoning

Although the three most commonly used large mammal species in the safety assessment of drugs remain the dog, the macaque and the marmoset, swine, especially minipigs, have also been widely used over the years in many toxicological studies. Swine present a number of interesting biological and physiological characteristics. Similarities in skin properties with humans have led to extensive in vitro and in vivo studies. There is a specific interest in cardiovascular research, as well as in anaesthesiology and critical care medicine due to common features of swine and human physiology. Although knowledge of swine brain structure and functions remains incomplete, data does exist. The multiple blood sampling that is necessary in pharmacokinetic and toxicokinetic studies are possible, as well as multiparametric monitoring and interventions with equipment used in human clinical settings. Practicality (handling), scientific (stress reduction) and ethical (invasive monitoring) reasons have led research teams to incorporate anaesthesia into their paradigms which makes the analysis of data increasingly difficult. Although not substantiated by scientific data, the swine appears to have an intermediate position in the scale of public perception between non-human primates and animals commonly referred to as pets (i.e. dogs and cats) and rodents. The benefits of the swine model justify the use of these animals in the design of more effective medical countermeasures against known chemical warfare agents (nerve agents, vesicants and lung damaging agents). Exposure to organophosphorus (OP) pesticides represents a severe health issue in developing countries, while OP intoxication with the more lethal military nerve agents is not only of military concern but also a terrorist threat. Tailoring therapeutic regimens to the reality of OP poisoning is of the utmost importance when little experimental data and sparse human clinical data are available in the decision making process. We will present some of the advantages and disadvantages of the swine model in OP countermeasures elaborating on two examples. First, we will present the issues related to the use of anaesthesia during experimental OP poisoning and second we will show how results from experiments with swine can be integrated into a kinetic-based dynamic model to evaluate oxime efficacy. A better knowledge of OP poisoning in swine (comparative toxicokinetics, pharmacokinetics and biochemistry) is definitely necessary before accepting it as a first choice non-rodent model. However, there exists a large amount of data in the model on anaesthesia and different types of shock favouring their use for evaluation of complex situations such as the anaesthesia of OP poisoned patients and combined injuries.

Intrinsic muscles and distribution of the recurrent laryngeal nerve in the pig larynx

To use the pig larynx in studies of laryngeal reinnervation, it is essential to have a clear understanding of its anatomy. We aimed to define the macroscopic anatomy of the intrinsic muscles and the course of the recurrent laryngeal nerve (RLN) in the pig larynx. Twelve large white pig larynges were used. Five larynges were preserved in formalin, then dissected to study the anatomy of the intrinsic muscles. Seven larynges were stained using the modified Sihler's staining technique, which results in nerves being stained dark purple while the remainder of the larynx is rendered translucent. The intrinsic muscles of the pig larynx were similar to those in the human. The RLN gives off a branch that enters the posterior cricoarytenoid muscle (PCA) on its deep surface and supplies the entire muscle, although the branching pattern of the nerve within the muscle varies considerably. These results facilitate detailed reinnervation studies in the pig laryngeal transplant model.

Glottal patency during experimental cortical seizures in piglets

OBJECTIVE

Systemically-induced seizures produce glottal airflow obstruction in anesthetized pigs, resulting in hypercapnia and respiratory acidosis. Cortically-induced seizures may be more representative of human seizure disorders. The purpose of this study was to describe glottal area patency (GAP) in piglets during cortically-induced seizures.

METHODS

Nineteen spontaneously breathing, lightly anesthetized (alphaxalone-alphadolone IV) piglets (aged 10 +/- 2 days) were instrumented for recording nasal airflow, subglottic pressure, and electrocorticogram. Glottal visualization was achieved supraglottically using a 1.2-mm fiberoptic scope inserted through the thyrohyoid membrane. Following baseline-control, hypoxic-rebreathing, and new baseline recordings, seizures were induced using subcortical injections of crystalline penicillin G (100,000 units/ injection). Five consecutive-breath representative epochs were digitized from baseline-control, hypoxic-rebreathing, and seizure conditions. For each breath, GAP was measured at the onset of inspiratory pressure, peak of inspiratory effort (Ip), and onset of expiration.

RESULTS

The piglets were physiologic at baseline-control and new baseline conditions, and showed expected increases in ventilation and GAP during rebreathing experiments. GAP was maximum at Ip under baseline and rebreathing conditions, but was significantly decreased and airway resistances were increased during seizure conditions (p < 0.05, ANOVA).

CONCLUSIONS

Generalized seizure activity results in reduced GAP at the peak of inspiratory effort. Increased work of breathing during seizures is created by direct mechanical obstruction at the level of the larynx.