Nonintubated versus intubated thoracoscopic bullectomy for primary spontaneous pneumothorax: A multicenter propensity-matched analysis.

BACKGROUND: We aimed at comparing in a multicenter propensity-matched analysis, results of nonintubated versus intubated video-assisted thoracic surgery (VATS) bullectomy/blebectomy for primary spontaneous pneumothorax (PSP). METHODS: Eleven Institutions participated in the study. A total of 208 patients underwent VATS bullectomy by intubated (IVATS) (N = 138) or nonintubated (NIVATS) (N = 70) anesthesia during 60 months. After propensity matching, 70 pairs of patients were compared. Anesthesia in NIVATS included intercostal (N = 61), paravertebral (N = 5) or thoracic epidural (N = 4) block and sedation with (N = 24) or without (N = 46) laryngeal mask under spontaneous ventilation. In the IVATS group, all patients underwent double-lumen-intubation and mechanical ventilation. Primary outcomes were morbidity and recurrence rates. RESULTS: There was no difference in age (26.7 ± 8 vs 27.4 ± 9 years), body mass index (19.7 ± 2.6 vs 20.6 ± 2.5), and American Society of Anesthesiology score (2 vs 2). Main results show no difference both in morbidity (11.4% vs 12.8%; p = 0.79) and recurrence free rates (92.3% vs 91.4%; p = 0.49) between NIVATS and IVATS, respectively, whereas a difference favoring the NIVATS group was found in anesthesia time (p < 0.0001) and operative time (p < 0.0001), drainage time (p = 0.001), and hospital stay (p < 0.0001). There was no conversion to thoracotomy and no hospital mortality. One patient in the NIVATS group needed reoperation due to chest wall bleeding. CONCLUSION: Results of this multicenter propensity-matched study have shown no intergroup difference in morbidity and recurrence rates whereas shorter operation room time and hospital stay favored the NIVATS group, suggesting a potential increase in the role of NIVATS in surgical management of PSP. Further prospective studies are warranted.

Modulation of Hippocampal Activity by Vagus Nerve Stimulation in Freely Moving Rats.

BACKGROUND: Vagus Nerve Stimulation (VNS) has seizure-suppressing effects but the underlying mechanism is not fully understood. To further elucidate the mechanisms underlying VNS-induced seizure suppression at a neurophysiological level, the present study examined effects of VNS on hippocampal excitability using dentate gyrus evoked potentials (EPs) and hippocampal electroencephalography (EEG). METHODS: Male Sprague-Dawley rats were implanted with a VNS electrode around the left vagus nerve. A bipolar stimulation electrode was implanted in the left perforant path and a bipolar recording electrode was implanted in the left dentate gyrus for EEG and dentate field EP recording. Following recovery, VNS was applied in freely moving animals, using a duty cycle of 7 s on/18 s off, 30 Hz frequency, 250 µs pulse width, and an intensity of either 0 (SHAM), 25 µA or 1000 µA, while continuously monitoring EEG and dentate field EPs. RESULTS: VNS at 1000 µA modulated dentate field EPs by decreasing the field excitatory post-synaptic potential (fEPSP) slope and increasing the latency and amplitude of the population spike. It additionally influenced hippocampal EEG by slowing theta rhythm from 7 Hz to 5 Hz and reducing theta peak and gamma band power. No effects were observed in the SHAM or 25 µA VNS conditions. CONCLUSION: VNS modulated hippocampal excitability of freely moving rats in a complex way. It decreased synaptic efficacy, reflected by decreased fEPSP slope and EEG power, but it simultaneously facilitated dentate granule cell discharge indicating depolarization of dentate granule cells.

A Preclinical Study of Laryngeal Motor-Evoked Potentials as a Marker Vagus Nerve Activation.

Vagus nerve stimulation (VNS) is a treatment for refractory epilepsy and depression. Previous studies using invasive recording electrodes showed that VNS induces laryngeal motor-evoked potentials (LMEPs) through the co-activation of the recurrent laryngeal nerve and subsequent contractions of the laryngeal muscles. The present study investigates the feasibility of recording LMEPs in chronically VNS-implanted rats, using a minimally-invasive technique, to assess effective current delivery to the nerve and to determine optimal VNS output currents for vagal fiber activation. Three weeks after VNS electrode implantation, signals were recorded using an electromyography (EMG) electrode in the proximity of the laryngeal muscles and a reference electrode on the skull. The VNS output current was gradually ramped up from 0.1 to 1.0 mA in 0.1 mA steps. In 13/27 rats, typical LMEPs were recorded at low VNS output currents (median 0.3 mA, IQR 0.2-0.3 mA). In 11/27 rats, significantly higher output currents were required to evoke electrophysiological responses (median 0.7 mA, IQR 0.5-0.7 mA, p < 0.001). The latencies of these responses deviated significantly from LMEPs (p < 0.05). In 3/27 rats, no electrophysiological responses to simulation were recorded. Minimally invasive LMEP recordings are feasible to assess effective current delivery to the vagus nerve. Furthermore, our results suggest that low output currents are sufficient to activate vagal fibers.

The antidepressant-like effect of vagus nerve stimulation is mediated through the locus coeruleus.

It has been shown that vagus nerve stimulation (VNS) has an antidepressant-like effect in the forced swim test. The mechanism of action underlying this effect is incompletely understood, but there is evidence suggesting that the locus coeruleus (LC) may play an important role. In this study, noradrenergic LC neurons were selectively lesioned to test their involvement in the antidepressant-like effect of VNS in the forced swim test. Forced swim test behavior was assessed in rats that were subjected to VNS or sham treatment. In half of the VNS-treated animals, the noradrenergic neurons from the LC were lesioned using the selective neurotoxin DSP-4 [N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride], yielding three experimental arms: sham, VNS and DSP-4-VNS (n = 8 per group). Furthermore, the open field test was performed to evaluate locomotor activity. A dopamine-ß-hydroxylase immunostaining was performed to confirm lesioning of noradrenergic LC neurons. VNS significantly reduced the percentage of immobility time in the forced swim test compared to sham treatment (median: 56%, interquartile range: 41% vs. median: 75%, interquartile range: 12%). This antidepressant-like effect of VNS could not be demonstrated in the DSP-4-VNS group (median: 79%, interquartile range: 33%). Locomotor activity in the open field test was not different between the three treatment arms. The absence of hippocampal dopamine-ß-hydroxylase immunostaining in the DSP-4-treated rats confirmed the lesioning of noradrenergic neurons originating from the brainstem LC. The results of this study demonstrate that the noradrenergic neurons from the LC play an important role in the antidepressant-like effect of VNS.

The antidepressant mechanism of action of vagus nerve stimulation: Evidence from preclinical studies.

Vagus nerve stimulation (VNS) is a proposed neuromodulatory treatment for medically refractory major depression. Although VNS is already used in clinical practice, the underlying mechanism of action remains unknown. The present review provides an overview of the preclinical VNS studies in view of two major hypotheses in depression research: the monoaminergic and the neural plasticity hypothesis of depression.

Vagus nerve stimulation has antidepressant effects in the kainic acid model for temporal lobe epilepsy.

BACKGROUND: Depression is the most common psychiatric comorbidity in epilepsy patients. The lack of success with current pharmacological interventions for this patient population, highlights the importance of optimizing non-pharmacological neuromodulatory treatments such as vagus nerve stimulation (VNS). Studies on the antidepressant effect of VNS in epilepsy patients may be confounded by concurrent anti-epileptic drug therapy. To date, studies in epilepsy models overcoming this problem are lacking. OBJECTIVE: We investigated whether VNS affects anhedonia, a key symptom of major depression, in the kainic acid rat model for temporal lobe epilepsy. METHODS: Anhedonia was assessed in kainic acid (KA) and saline (SAL) injected rats using the saccharin preference test (SPT). To exclude differences in taste perception, the quinine aversion test (QAT) was performed. Both groups were randomly subdivided in a VNS and a SHAM group, yielding 4 experimental arms: KA-VNS, KA-SHAM, SAL-VNS and SAL-SHAM. Both VNS groups received 2 weeks of VNS, while the SHAM groups were not stimulated. Thereafter, the SPT and QAT were repeated. RESULTS: Saccharin preference was significantly reduced in the KA compared to the SAL rats (P < 0.05), without differences in quinine aversion. Two weeks of VNS significantly increased the saccharin preference in the KA-VNS group (P < 0.05), while it had no effect on quinine aversion. No effects of VNS or SHAM were found in the other groups. CONCLUSION: The KA rats displayed anhedonia which was significantly decreased by VNS, indicating that this neuromodulatory treatment could likewise diminish depressive symptoms in patients suffering from temporal lobe epilepsy and comorbid depression.

Electrophysiological responses from vagus nerve stimulation in rats.

The mechanism of action of vagus nerve stimulation (VNS) for pharmacoresistant epilepsy is unknown and the therapeutic outcome is highly variable. We investigated stimulation-induced vagus nerve electrophysiological responses in rats using various stimulation parameters. Conduction velocity, I(50), rheobase and chronaxie were calculated. We identified an early and late component corresponding to an afferent compound action potential (CAP) and a remote laryngeal motor-evoked potential (LMEP), respectively. The conduction velocity (CAP: 26.2 ± 1.4 m/s; LMEP: 32.4 ± 2.4 m/s) and I(50) (CAP: 2.4 ± 0.3 mA; LMEP: 1.8±0.2 mA) were significantly different for both components, the rheobase (CAP: 140±30 µA; LMEP: 110±26 µA) and chronaxie (CAP: 66±7 µs; LMEP: 73±9 µs) were not. Using a pulse of 10 µs, the CAP saturated between 4-5 mA. Our method can be used to record VNS-induced electrophysiological responses in rats and provides an objective biomarker for electrical stimulation with various parameters in an experimental set-up. Our findings are potentially useful for clinical purposes in the sense that combination of VNS and recording of vagal nerve CAPs may help clinicians to determine the individual optimal intensity required to fully activate fast-conducting afferent fibers.