Laryngeal Adductor Reflex Movement Latency Following Tactile Stimulation

Laryngeal Hyposensitivity in Obstructive Sleep Apnea

INTRODUCTION

Impaired laryngopharyngeal sensation has been implicated in obstructive sleep apnea (OSA) and may play an important pathophysiological role. We evaluated sensory function in OSA by examining the laryngeal adductor reflex (LAR) response rate and temporal profile to tactile stimulation.

METHODS

Laryngeal sensation testing was performed in awake adults with and without diagnosed OSA by stimulating the medial aryepiglottic fold or arytenoid using 30-mm 5-0 and 4-0 nylon Cheung-Bearelly monofilaments. Video analysis by two independent reviewers evaluated for the presence of the LAR in response to satisfactory stimuli and LAR latency to vocal fold adduction.

RESULTS

Twenty-six OSA and 12 control subjects were tested with 270 satisfactory stimuli. The mean full LAR response rate to 4-0 stimulation was 38.3% in OSA vs 86.9% in control subjects (p <0.001) and to 5-0 stimulation was 27% in OSA vs 63.9% in control subjects (p  <0.001). The mean LAR latency to vocal fold closure in OSA was 123.7 ms (SD 35.8) vs 156.4 ms (SD 44.3) in control (p = 0.04) subjects. OSA LAR latency was positively correlated with the apnea-hypopnea index (r = 0.30; p = 0.008).

CONCLUSION

The OSA group exhibited reduced LAR response rates and shortened LAR latency, where latency was correlated with disease severity. Laryngeal hyposensitivity was affirmed and changes to LAR sensorimotor temporal dynamics were revealed. These pathophysiological alterations to the LAR may be accounted for by decreased somatosensory receptor sensitivity, increased sympathetic tone, and reorganized brain stem function in OSA.

LEVEL OF EVIDENCE

3 Laryngoscope, 134:3856-3861, 2024.

Understanding the variability of the electrophysiologic laryngeal adductor reflex

OBJECTIVE

The laryngeal adductor reflex (LAR) is vital for airway protection and can be electrophysiologically obtained under intravenous general anesthesia (IGA). This makes the electrophysiologic LAR (eLAR) an important tool for monitoring of the vagus nerves and relevant brainstem circuitry during high-risk surgeries. We investigated the intra-class variability of normal and expected abnormal eLAR.

METHODS

Repeated measures of contralateral R1 (cR1) were performed under IGA in 58 patients. Data on presence/absence of cR2 and potential confounders were also collected. Review of neuroimaging, pathology and clinical exam, allowed classification into normal and expected abnormal eLAR groups. Using univariate and multivariate analysis we studied the variability of cR1 parameters and their differences between the two groups.

RESULTS

In both groups, cR1 latencies had coefficients of variation of <2%. In the abnormal group, cR1 had longer latencies, required higher activation currents and was more frequently desynchronized and unsustained; cR2 was more frequently absent.

CONCLUSIONS

cR1 latencies show high analytical precision for measurements. Delayed onset, difficult to elicit, desynchronized and unsustained cR1, and absence of cR2 signal an abnormal eLAR.

SIGNIFICANCE

Understanding the variability and behavior of normal and abnormal eLAR under IGA can aid in the interpretation of its changes during monitoring.

Neurophysiology of the Superior Laryngeal Nerve in an In Vivo Rat Model

OBJECTIVE

The superior laryngeal nerve (SLN) is fundamental in laryngeal sensation, cough reflex, and pitch control. SLN injury has substantial consequences including altered sensation, aspiration, and dysphonia. To date, in vivo measurement of the SLN remains elusive. The purpose of this study was to assess the feasibility of recording motor and sensory evoked potentials in a rat SLN model.

METHODS

Twenty-two rat hemi-laryngeal preparations (n = 11) were obtained from 4-month-old Sprague-Dawley rats and included in this study. Compound motor action potentials (CMAPs) and motor unit number estimation (MUNE) were calculated by stimulating the SLN at the point of medial extension near the carotid artery and by placing a recording electrode on the cricothyroid muscle. Sensory response was determined through stimulation of the SLN and laryngoscopic visualization of a laryngeal adductor reflex (LAR). SLN and cricothyroid muscle cross-sections were stained and histologic morphometrics were quantified.

RESULTS

Laryngeal evoked potentials were successfully obtained in all trials. Mean CMAP latency and negative durations were 0.99 ± 0.57 ms and 1.49 ± 0.57 ms, respectively. The median MUNE was 2.06 (IQR 1.88, 3.51). LAR was induced with a mean intensity of 0.69 ± 0.20 mV. Mean axon count, myelin thickness, and g-ratio were 681 ± 192.2, 1.72 ± 0.26, and 0.45 ± 0.04, respectively.

CONCLUSIONS

This study demonstrates the feasibility of recording evoked response potentials following SLN stimulation. We hypothesize that this work will provide a tractable animal model to study changes in laryngeal sensation and cricothyroid motor function with aging, neurodegenerative disease, aspiration, or nerve injury.

LEVEL OF EVIDENCE

NA Laryngoscope, 134:1778-1784, 2024.

Abnormal Laryngopharyngeal Sensation in Adductor Laryngeal Dystonia Compared to Healthy Controls

BACKGROUND/OBJECTIVES

Laryngeal sensory abnormality has been implicated as a component of adductor laryngeal dystonia (AdLD). The study objective was to assess laryngopharyngeal sensation in AdLD utilizing a calibrated, tactile aesthesiometer to deliver differential stimuli to lateral pyriform sinus (LPS), aryepiglottic fold (AEF), and false vocal fold (FVF).

METHODS

Patients with known Botox-responsive AdLD underwent sensory testing using a previously-validated methodology involving calibrated tactile stimuli (6-0, 5-0, 4.5-0, 4-0 nylon monofilaments). Laryngeal adductor reflex (LAR) and participant-rated perceptual strength of stimulI were evaluated. Responses were compared to normative controls (n = 33). Two-samples, Mann-Whitney and Fisher exact tests compared mean strength ratings and LAR between AdLD and control groups. Mixed-effects logistic regression and linear models assessed association of filament size, stimulus site, age, sex, and LD status on LAR and perceptual strength rating respectively.

RESULTS

Thirteen AdLD patients (nine women, mean age 60+/-15 years) completed testing. Average LAR response rates were higher amongst all filament sizes in AdLD versus controls at LPS (56.3% vs. 35.7%) and AEF (96.1% vs. 70.2%) with comparable rates at FVF (90.2% vs. 91.7%). AdLD had 3.3 times the odds of observed LAR compared to controls (p = 0.005), but differences in subjective detection of stimuli, perceptual strength ratings, and cough/gag rates were insignificant on multivariate modeling (p > 0.05).

CONCLUSIONS

This is the first study to objectively assess laryngopharyngeal sensation in AdLD. Findings demonstrated increased laryngopharyngeal sensation in AdLD compared to controls. The identification of increased laryngeal hypersensitivity in these patients may improve understanding of AdLD pathophysiology and identify future targets for intervention.

LEVEL OF EVIDENCE

2 Laryngoscope, 133:2271-2278, 2023.

An Ex Vivo Investigation of Tactile Aesthesiometer Force in Laryngopharyngeal Sensory Testing

BACKGROUND/OBJECTIVE

Cheung-Bearelly aesthesiometers can deliver buckling-force stimuli to the laryngopharynx and objectively evaluate sensation. Ambiguity surrounds the transformation of stimuli in the laryngopharyngeal environment. This study aims to evaluate the effect of aesthesiometer size, saliva, successive compressions, and angles of tissue contact on stimulus force delivered.

METHODS

An ex vivo stimulus delivery device was constructed to measure the buckling force of aesthesiometers. Dry and saliva-saturated aesthesiometers (6-0, 5-0, 4.5-0, and 4-0) were each compressed six times on cadaveric buccal mucosa on an electronic balance. The force for each compression was recorded at 0, 15, 30, 45, and 60° from the vertical plane. 240 compressions were analyzed utilizing a mixed-effects statistical model.

RESULTS

The mean force delivered by the 6-0, 5-0, 4.5-0, and 4-0 aesthesiometers were 0.017, 0.082, 0.120, and 0.268 g respectively (p < 0.001). Mean force significantly reduced for the 4-0 aesthesiometer at 30° (p = 0.003) and 60° (p = 0.001). Force decreased by the 4th compression for the 5-0 aesthesiometer (p = 0.004) and after one compression for the 4.5-0 (p = 0.004) and 4-0 (p < 0.001) aesthesiometer. By the 4th compression, the 4.5-0 aesthesiometer was indistinguishable (p > 0.05) from the 5-0 aesthesiometer. The effect of saliva was insignificant (p = 0.83).

CONCLUSION

Aesthesiometers can deliver discrete buckling-force stimuli to evaluate laryngopharynx sensory function. Up to 60° (15° for 4-0 aesthesiometer) deviation from orthogonal tissue contact and salivary forces do not significantly alter force delivered. 4.5-0 aesthesiometers should be exchanged after three compressions. For all other aesthesiometers, force reduction after six compressions is likely clinically insignificant given current laryngopharyngeal sensory testing protocols.

LEVEL OF EVIDENCE

N/A Ex Vivo Laboratory Design Laryngoscope, 2022.