Introduction
Methods
Identification and Selection of Studies
PubMed (MeSH and free-text terms) |
(("Deglutition Disorders"[Mesh] OR "Deglutition"[Mesh]) OR (deglut* OR dysphag* OR swallow*)) AND (("Vagus Nerve Stimulation"[Mesh] OR "Electrodes, Implanted"[Mesh] OR "Implantable Neurostimulators"[Mesh]) OR (nerve stim* OR electr*)) |
("Deglutition Disorders"[Mesh]) OR "Deglutition"[Mesh]) OR deglut*) OR dysphag*) OR swallow*) AND (("Electrodes, Implanted"[Mesh]) OR "Implantable Neurostimulators"[Mesh]) AND "Cranial Nerves"[Mesh])) |
Embase (thesaurus and free-text terms) |
(((swallow* OR deglutition OR dysphagia) AND (cranial nerve OR trigeminal nerve OR facial nerve OR glossopharyngeal nerve OR vagus nerve OR accessory nerve OR hypoglossal nerve)) AND (electrode implant OR nerve stimulation OR vagus nerve stimulation) |
(Swallow* or dysphag*) AND (cranial nerve OR cranial nerve stimulation) |
(Swallow* or dysphag*) AND vagal nerve stimulation |
Cochrane (free-text terms) |
Cranial nerve stimulation OR trigeminal nerve stimulation OR facial nerve stimulation OR glossopharyngeal nerve stimulation OR vagal nerve stimulation OR accessory nerve stimulation OR hypoglossal nerve stimulation |
Inclusion criteria |
Studies describing swallowing function and/or OD associated with CNS |
Studies describing OD and/or aspiration even as an adverse reaction of CNS |
Studies on human subjects |
Exclusion criteria |
Studies including other forms of stimulation such as transcutaneous, intrapharyngeal, or deep brain stimulation |
Studies on CNS that did not report swallowing function or OD as outcome variable or adverse reaction |
Animal studies |
Data Analysis and Assessment of the Level of Evidence
Results
General Results and Level of Evidence
Refs | Number of subjects (N), gender (M:F), and indication for stimulation | Cranial nerve number, type of nerve stimulator | Stimulation parameters (stimulus duration; current intensity; pulse frequency; pulse width) | Measurement tool and outcome parameters on swallowing | Authors' conclusion |
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[29] | N = 7 Children with intractable epilepsy | VN (CI) NCP model 100, and electrodes | -Almost continuous stimulation (MAX): 120 s "on", 0.2 min "off" -Individual settings (IN USE): 7–30 s "on", 0.3–5.0 min "off" -Stimulator turned off (OFF) General settings: at the start intensity progressively increased from 0.25 mA to 1.25–2.0 mA; frequency 30 Hz; pulse width 500 µsec | -Videoradiography during barium swallow, using an aspiration scale 0–3 (normal passage of barium, penetration located on the epiglottis or supraglottic penetration, and glottic aspiration) -N = 2 showed an increased degree of aspiration during almost continuous stimulation (MAX) | Aspiration is a potentially serious AR of VNS. It could be prevented if the stimulator would have an electrical switch that the patient or caregiver could turn off, if necessary |
[30] | N = 8 Children with pharmacoresistant epilepsy | Left VN Type of nerve stimulator not specified | -Stimulator turned off -Customary settings: duration 3–4 min; current 1.0–2.0 mA -Maximum tolerated stimulation: duration 3–4 min; maximum current of 3.0 mA | -Videoradiography during barium swallow to determine laryngeal penetration/aspiration during electrical stimulation. No further information on the protocol was provided -N = 1 showed worsening of OD from “normal” to “laryngeal penetration” during VNS at customary settings N = 2 showed worsening of the OD from “normal” to “laryngeal penetration” at maximum tolerated stimulation | Stimulation of the left VN, under conditions used to treat epilepsy, does not cause aspiration, though one patient presented laryngeal penetration during stimulation in customized settings |
[31] | N = 4 (2:2) Patients with intractable epilepsy | Left VN (CI) Neurocybernetic Prosthesis (NCP) | Duration 7–30 s “on” 0.2–5 min “off”; current 0.5–3.25 mA; frequency 15–30 Hz; pulse width 130–500 µsec | -Fiberoptic endoscopic examination of the larynx (without a swallowing protocol) -All patients showed LVF paresis or dysfunction directly after implantation and during stimulation. After adjustment of the settings or during condition “off”, the LVF of two patients recovered. N = 1 showed mild aspiration and pyriform sinus pooling during VNS. N = 2 showed symptoms of OD (coughing while drinking, handling secretions or gagging), during VNS. N = 1 showed improvement of OD after adjustment of VNS | Attachment of the stimulator lead to the VN often results in usually transient vocal fold paresis. Furthermore, VNS itself can also cause vocal fold dysfunction. Clear communication between otolaryngologist and neurologist is essential in controlling potential ARs of the stimulation |
[32] | N = 3 (3:0) Dysphagic patients with MS and PCT | VN Type of nerve stimulator not specified | Duration 62 s “on”, 60 s “off”; current was eventually 1.25 mA (progression: 0.25 mA increase/week); frequency 10 Hz, pulse width 250 µsec | -50 mL water swallowing speed test -Before start VNS: mean time of 18 s with nine pauses or ‘piecemeal’ deglutition periods (normally 1–2/50 mL of ingested liquid). During the follow-up of 2–3 months, water intake and ‘piecemeal’ deglutition improved by 65% and 78%, respectively, referring to an improved swallowing duration and lower number of piecemeal deglutition | VNS is an alternative in the treatment of advanced MS in which OD is a potentially life threating complication of this disease |
[33] | N = 9 (4:5) Healthy subjects | ISLN DISA 15E07 stimulator | The pulse generator triggered the DISA stimulator at 0; 500 ms; 1 s; 2 s; 5 s delays after the swallow command. Resulting in four phases: phase A (500 ms): just before onset of the swallow; phase B (1 s): occurring during the swallow; phase C (2 s): occurring within the first 3 s postswallow; phase D (5 s): occurring between 3 and 5 s postswallow | -Signals recorded from the bilateral TA muscles were used to measure laryngeal muscle reflex responses (for airway protection) to electrical stimulation of the ISLN -The more rapid and shorter unilateral responses of TA muscles (R1) to stimulation continued to provide some, albeit reduced, laryngeal protective functions after swallowing, whereas the later contralateral responses (R2) to stimulation were suppressed both in occurrence and amplitude for up to 3 s after swallow (phase C) | The results suggest that the later laryngeal adductor responses are suppressed up to 3 s after the swallow during ISLNS. Residue in the laryngeal vestibule after a swallow, increased the risk for the entry of foreign substances into the airway, when receiving ISLNS |
[34] | N = 2 (1:1) Hemispheric stroke patients with chronic aspiration | Left RLN Neurocontrol Implantable Receiver-Stimulator | Patient 1: current 1 mA, frequency 42 Hz, pulse width 72–176 µsec Patient 2: current 1.5 mA, frequency 42 Hz, pulse width 20 µsec | -Videofluoroscopy -A significant reduction in aspiration during swallows of thin and thick liquids | The authors concluded that vocal fold pacing via the left RLN is a potentially effective method for the control of aspiration in these two stroke patients |
[35] | N = 5 (3:2) Patients with various neurologic conditions (MS, CP, stroke) and chronic aspiration pneumonia | RLN Modified Vocare stimulator, Finetech Medical Ltd. Welwyn Garden City, England | Current 1.2 mA; frequency 42 Hz; pulse width, 188–560 μsec | -Videofluoroscopy; chest x-ray; health-related quality of life obtained via patient interview -N = 4 showed an overall decrease in aspiration during stimulation, if vocal fold adduction and glottic closure were achieved with RLNS. All patients reported improved health-related quality of life. There was a decrease in the frequency of chronic aspiration pneumonia | Vocal fold pacing via the RLN seems appropriate as treatment for chronic aspiration pneumonia as long as there was glottic seal during the stimulation |
[36] | N = 14 (9:5) Patients with OSA | HN Type of nerve stimulator not specified | No information on settings | -EAT-10 questionnaire -Only during the first week following the implantation a temporary increase of patient reported dysphagia symptoms was observed | The implantation and use of HNS over five months did not demonstrate any sustained, patient reported changes in OD symptoms |
Refs | Type of nerve stimulator; stimulus duration, current intensity, pulse frequency, pulse width | Indication for stimulation | OD as AR (N) |
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[37] | VNS (VNS Therapy; CI); ON for 30 s and OFF for 5 min, 20 Hz, LOW (0.25 mA, 130 µsec), MEDIUM (0.5–1.0 mA, 250 µsec), HIGH (1.25–1.5 mA, 250 µsec) | TRD | N = 10 (9%) patients in low dose stimulation group, N = 17 (15.9%) patients in medium dose stimulation group, N = 18 (15.9%) patients in high-dose stimulation group OD was reported as an AR. No further information was provided |
[38] | VNS (CI); ON for 30 s and OFF for 5 min, 0.25–3.5 mA, 20 Hz, 500 µsec | TRD | N = 25 (21%) patients of the VNS group and N = 13 (11%) patients in the Sham group OD was coded using COSTART |
[39] | VNS (CI); ON for 7–60 s and OFF for 0.3–180 min, 0.0–2.25 mA, 2–30 Hz, 130–750 µsec | TRD | N = 31 (13%) patients during the first quarter of a year; N = 19 (8%) patients in the second quarter; N = 15 (7%) patients in the third quarter; N = 9 (4%) patients during the fourth quarter OD was coded using COSTART |
[40] | VNS (CI); ON for 30 s, OFF for 5 min, 0.25–2.0 mA, 10–30 Hz, 250–500 µsec | TRD | Population European (D03) study; after 3 months N = 6 (8.5%) patients, 6 months N = 0 (0%) patients, 9 months N = 0 (0%) patients, 12 months N = 2 (3.3%) patients Population USA study; after 3 months N = 13 (5.6%) patients, 6 months N = 8 (3.6%) patients, 9 months N = 7 (3.2%) patients, 12 months N = 4 (1.9%) patients OD was coded using COSTART |
[41] | VNS (CI); ON for 30 s, OFF for 3–5 min, 0.25–3.0 mA, 20–30 Hz, 250–500 µsec | TRD | N = 3 (10%) patients OD was coded using COSTART |
[42] | VNS (CI); ON for 30 s, OFF for 3–5 min, 0.25–3.0 mA, 20-30 Hz, 250–500 µsec | TRD | N = 8 (13%) patients. Onset of OD after a mean duration of 11.3 days. OD spontaneously resolved in N = 7 (87.5%) patients OD was coded using COSTART |
[50] | VNS; mean values (ON for 21.6 s and OFF for 1.1 min, 1.3 mA, 25 Hz, 220 µsec) | TRD and bipolar disorder | N = 1 (6.7%) OD was reported as AR. No further information was provided |
[43] | VNS (CI); ON for 7 s or 30 s, OFF for 12–30 s or 3–5 min, 0.25–2.0 mA, 30 Hz, 500 µsec | Intractable epilepsy | N = 2 (12.5%) patients showed repeated coughing, swallowing difficulties, and significant increase of aspiration when stimulator was turned ON OD reported via patient interview and videoradiography during barium swallow |
[44] | VNS (CI) | Partial-onset seizures refractory to medical therapy | N = 4 (8.7%) patients OD was reported using an AR questionnaire comprising six questions aimed to determine the effect of VNS on swallowing function. Reprogramming the device seemed to have little effect on swallowing |
[45] | VNS; ON for 7–30 s, OFF for 18 s-5 min, 0.25–2.0 mA, 20 Hz | Intractable focal epilepsy | N = 12 (80%) patients reported cough, hoarseness, and mild OD OD was reported as AR. No further information was provided |
[46] | VNS | Intractable pediatric epilepsy | N = 3 (4.8%) patients OD was reported as AR. OD was managed by reprogramming the device or a temporary switch-off of the device using a magnet. No further information was provided |
[48] | VNS; ON for 7–30 s, OFF for 30 s-5 min, 0.25–3.0 mA, 20–30 Hz 250–500 µsec | Drug-resistant seizures | N = 3 (4%) patients OD was reported as AR. No further information was provided |
[49] | VNS (CI); ON for 30 s, OFF for 5 min, 0.25–2.0 mA, 30 Hz, 500 µsec | Intractable Epilepsy | N = 2 (7.4%) patients OD was reported as AR during VNS. No further information was provided |
[51] | VNS (CI); ON for 30 s and OFF for 5 min, 0.25 mA, 20 Hz, 250 µsec | Medically refractory multifocal or generalized epilepsy | N = 2 (2.8%) patients reported intermittent OD OD was reported as AR. OD resolved by adjusting the stimulation parameters. No further information was provided |
[52] | VNS (CI); mean values (ON for 29 s and OFF for 4 min, 2.04 mA, 25 Hz, 307 µsec) | Intractable epilepsy | N = 1 (1%) patient suffered from transient OD OD was reported as AR. No further information was provided |
[53] | VNS (CI); ON for 14–30 s and OFF for 1.1–5 min, 0.75–2.5 mA, 20–30 Hz, 500 µsec | Drug-resistant epilepsy | N = 1 (1.8%) patient reported OD and vomiting OD was reported as AR. No further information was provided |
[16] | VNS | Medically intractable epilepsy | N = 1 (1.4%) patient OD was reported as AR. Reprogramming the device did not improve OD. No further information was provided |
[54] | VNS; ON for 7–30 s and OFF for 30 s-5 min, 0.25–2.25 mA, 20–30 Hz, 250–500 µsec | Refractory epilepsy | N = unknown. OD is, among hoarseness and coughing, the most common AR No further information was provided |
[47] | VNS (CI); ON for 30 s, OFF for 5 min, 0.5–2.5 mA, 20 Hz, 250 µsec | Treatment-resistant fibromyalgia | N = 2 (14%) patients OD was reported as AR. No further information was provided |
[36] | VNS (Model 304; CI; 500 ms, 0.8 mA, 30 Hz, 100 µsec | Chronic ischemic stroke | N = 1 (11%) patient showed transient OD and left vocal fold palsy after device implantation. N = 1 (11%) patient reported mild OD in the evening after therapy sessions OD was reported via patient interview. Other causes for vocal fold palsy than stimulation were excluded by a computed tomographic scan |