Isaac Naggar

Neurogenic pathway mediated remote preconditioning protects the brain from transient focal ischemic injury.

Attenuation of ischemic injury can be achieved by priming the brain with a sub-lethal ischemic insult, a phenomenon known as ischemic preconditioning (IP). We sought to determine if subjecting a distant organ, such as the lower limb, to a similar priming ischemic insult would result in protection of the brain from a subsequent severe ischemic injury, as induced by middle cerebral artery occlusion (MCAo) and if this protection is mediated via a neurogenic pathway. Adult Wistar male rats were subjected to either remote preconditioning (RPC) or sham surgery and then subsequently underwent 2 h MCAo 24, 48 or 72 h after the RPC/sham RPC stimulus. Of the animals undergoing RPC, only those that sustained MCAo 24 h later showed significantly smaller cerebral infarct volumes (150.34±30.91 mm(3)) and better clinical neurological outcomes (1.15±0.69) as compared to the sham RPC group (infarct volume 250.25±26.98mm(3); neurological score 1.80±0.87) (P<0.05). RPC animals sustaining MCAo at 48 and 72 h later did not show significant differences in cerebral infarct volumes or clinical neurological outcomes as compared to the sham RPC group. Furthermore, attenuation of the neuroprotective effect by the ganglion blocker hexamethonium suggested a neurogenically mediated pathway responsible for this phenomenon. Remote sub-lethal ischemic injury to both lower limbs results in cerebral protection from subsequent ischemia within 24 h of initiation of the RPC stimulus and this protection in part may be mediated via a neurogenic pathway.

Relation of autonomic and cardiac abnormalities to ventricular fibrillation in a rat model of epilepsy.

Cardiac autonomic, conduction, and structural changes may occur in epilepsy and may contribute to sudden unexpected death in epilepsy (SUDEP), e.g. by increasing the risk for ventricular fibrillation (VF). In a model of chronic seizures in rats, we sought to study (1) cardiac and autonomic derangements that accompany the epileptic state, (2) whether chronically seizing rats experienced more significant cardiac effects after severe acute seizures, and (3) the susceptibility of chronically seizing rats to VF arising from autonomic and hypoxemic changes, which commonly occur during seizures. Sprague-Dawely rats were injected with saline or kainic acid to induce chronic seizures. At 2-3 months or 7-11 months after injection, these rats were studied with both 12-lead electrocardiography (to assess heart rate variability and QT dispersion) and echocardiography under ketamine/xylazine or urethane anesthesia. Hearts were subsequently excised, weighed, and examined histologically. Epileptic rats exhibited decreased vagal tone, increased QT dispersion, and eccentric cardiac hypertrophy without significant cardiac fibrosis, especially at 7-11 months post-injection. Of these three findings, vagal tone was inversely correlated with heart weights. Epileptic rats exhibited diminished systolic function compared to controls after severe acute seizures. However, animals with long-standing chronic seizures were less susceptible to autonomic/hypoxemia-driven VF, and their susceptibility inversely correlated with mean left ventricular wall thickness on histology. On the basis of this model, we conclude that cardiac changes accompany epilepsy and these can lead to significant seizure-associated cardiac performance decreases, but these cardiac changes actually lower the probability of VF.

Quantitative video laryngoscopy to monitor recovery from recurrent laryngeal nerve injury in the rat.

Recovery from unilateral vocal-fold paralysis is lengthy, unpredictable, and often incomplete, highlighting the need for better treatments of the injured recurrent laryngeal nerve. To be able to monitor recovery of vocal-fold motion in studies with rats, we developed a procedure for quantitative video laryngoscopy. An asymmetry index was defined as a continuous and robust measure of unequal vocal-fold motion and calculated from spectral-density plots of vocal-fold displacements. In a cohort of 8 animals, unilateral vocal-fold paralysis was observed within seconds after clamping of the right recurrent laryngeal nerve and was accompanied by a markedly negative asymmetry index. Over the next month, the asymmetry index gradually returned to zero, concomitant with a visible recovery of vocal-fold motion. Our results suggest that quantitative video laryngoscopy is a sensitive and discriminating method for monitoring recovery from recurrent laryngeal nerve injury and set the stage for testing novel surgical and pharmacological treatments of unilateral vocal-fold paralysis.

Vagal control of cardiac electrical activity and wall motion during ventricular fibrillation in large animals.

Vagal inputs control pacemaking and conduction systems in the heart. Anatomical evidence suggests a direct ventricular action, but functional evidence that separates direct and indirect (via the conduction system) vagal actions is less well established. We studied vagus nerve stimulation (VNS) during sinus rhythm and ventricular fibrillation (VF) in pigs and sheep to determine: 1) the range of unilateral and bilateral actions (inotropic and chronotropic) and 2) whether VNS alters left ventricular motion and/or electrical activity during VF, a model of abnormal electrical conduction of the left ventricle that excludes sinus and atrioventricular nodal function. Adult pigs (N=8) and sheep (N=10) were anesthetized with urethane and mechanically ventilated. VNS was performed in animals at 1, 2, 5, 10, 20, 50, and 100Hz for 20s. VF was induced with direct current to the ventricles or occlusion of the left anterior descending coronary artery. In 4 pigs and 3 sheep, left ventricular wall motion was assessed from endocardial excursion in epicardial echocardiography. In sheep and pigs, the best frequency among those tested for VNS during sinus rhythm to produce sustained electrical and mechanical ventricular standstill was 50Hz for unilateral or bilateral stimulation. When applied during VF, bilateral VNS increased the variability of the dominant VF frequency, indicating a direct impact on the excitability of ventricular myocytes, and decreased endocardial excursion by more than 50% during VF. We conclude that the vagus nerve directly modulates left ventricular function independently from its effects on the conduction system.

Assessment of arterial stiffness from pedal artery Korotkoff sound recordings: feasibility and potential utility

Brachial artery (BA) Korotkoff sound (KS) timing reflects arterial stiffness. We recorded pedal artery (PA) KS in 68 healthy subjects using an electronic stethoscope and electrocardiography. Intervals between QRS complex of the electrocardiogram and KS waveform peaks (termed the QKD interval) were measured for 60 seconds, averaged, and QKD velocity (v) calculated. Carotid-BA and carotid-PA pulse wave velocities (PWVs) were measured by applanation tonometry. Analyzable KS recordings were obtained from BA and PA in 100% and 92% subjects. PA QKDv decreased less than BA QKDv with progressive cuff inflation. At diastolic blood pressure + 20 mm Hg (maximal yield), BA QKDv was independently associated with weight and pulse pressure, whereas PA QKDv was related to weight and age. PA QKDv correlated with its corresponding PWV stronger than BA QKDv. In conclusion, PA KS is optimally recorded at diastolic blood pressure + 20 mm Hg; PA QKDv is correlated with age and better correlates with PWV than does BA QKDv. This technique may provide a simple arterial stiffness measure.

Restoration of Recurrent-Laryngeal-Nerve Function after Injury in a Rat Model

Objectives: Recurrent laryngeal nerve (RLN) injury occurs in 4-10% of thyroid surgeries. Spontaneous RLN regeneration takes months and is often incomplete. Lithium promotes neuronal growth in vitro. We developed methods to objectively detect vocal-fold impairment in the rat and tested whether systemic lithium enhances recovery after RLN injury. Methods: The right RLN was crushed in eight adult rats, and osmotic pumps releasing either lithium or water were implanted. Eight sham-operated animals were also implanted with either lithium or water pumps. Vocal-fold motion was captured by microsuspension laryngoscopy and was measured quantitatively by image analysis at the time of surgery and at one and four weeks. Vocalizations, breathing patterns, and laryngeal electromyography were assessed at four weeks. Results: Cessation of unilateral vocal-fold motion was observed simultaneously with every RLN crush. One week after surgery, 50% of “Crush/Water” animals exhibited full vocal-fold motion, compared to 75% of “Crush/Lithium” and 100% of the sham-operated animals. In animals with unilateral vocal-fold immobility, the quantitative analysis also revealed a subtle decrease of vocal-fold movement on the non-operated side. At four weeks after surgery, vocalizations, breathing patterns, vocal-fold motion, and electromyograms were indistinguishable among all groups. Lithium-treated animals weighed 5% less than water-treated controls. Conclusions: Quantitative endoscopy is a sensitive and efficient tool for detecting vocal-fold impairment in rats. While our results might suggest enhanced recovery in lithium treated animals, all animals showed a rapid return of vocal-fold motion. Perhaps more severe nerve injury is necessary to uncover an effect of lithium on nerve regeneration.