@article{70f25712b78e450a85d81f615b312728,
title = "Quantification of rat supraglottic laryngeal sensation threshold",
abstract = "Objective: Laryngeal adductor response (LAR) to air puff is used as a reliable method in evaluating sensation thresholds (ST) in human laryngeal sensory disorders. This method has been difficult to perform in small subjects such as rodents. The aims of this study were to 1) evaluate ST to air puff under binocular microlaryngoscopy in rats to evaluate laryngeal sensory disorders, 2) determine sensory thresholds at varying target locations, and 3) determine the ideal depth of anesthesia. Study Design: Animal study. Methods: Rats were induced with ketamine/xylazine. The level of anesthesia was monitored by spontaneous glottic closure and corneal reflex testing. Air puffs were delivered to the epiglottis, arytenoid, and piriform sinus at varied pressures with pulse time kept constant. Sensation thresholds were determined by direct visualization of the larynx using a binocular microscope. Topical lidocaine was then applied to the larynx and ST was determined. Trials were repeated in a small subset of animals. Results: Twenty-six trials were performed in 14 rats. Mean STs were 39 ± 9.7 mm Hg at the epiglottis, 48.8 ± 10.5 at the arytenoid, and not detectable at the pyriform sinus. Repeated trials demonstrated consistent results. Lidocaine effectively ablated the LAR in each trial. The LAR was difficult to induce while corneal reflex was absent and was difficult to distinguish from spontaneous glottic closures while under lighter sedation. Conclusion: Air pulse stimulation in rats is a simple, reliable, and effective way to determine laryngopharyngeal STs in rats and can be used as an efficient and affordable method for experimentation involving laryngeal sensory disorders. Level of Evidence: NA. Laryngoscope, 127:E265–E269, 2017.",
keywords = "Larynx, rat, sensory disorder, sensory testing, superior laryngeal nerve",
author = "Gale, {Derrick C.} and Bhatt, {Neel K.} and Paniello, {Randal C.}",
note = "Funding Information: The study was performed with accordance with the Policy Health Service policy on Humane Care and Use of Laboratory Animals, the National Institutes of Health Guide for the Care and Use of Laboratory Animals, and the Animal Welfare Act (7 U.S.C.et seq.); the animal use protocol was approved by the Institutional Animal Care and Use Committee at Washington University School of Medicine (St. Louis, MO). Adult male Sprague-Dawley rats were used with weight between 350 g and 650 g. The animals were housed in a limited access facility, with alternate 12-hour light/dark cycles. The animals were offered rat chow and water ad libitum. The facility staff was responsible for feeding, cleaning cages, and assessing animal wellbeing. The study was performed with accordance with the Policy Health Service policy on Humane Care and Use of Laboratory Animals, the National Institutes of Health Guide for the Care and Use of Laboratory Animals, and the Animal Welfare Act (7 U.S.C.et seq.); the animal use protocol was approved by the Institutional Animal Care and Use Committee at Washington University School of Medicine (St. Louis, MO). Adult male Sprague-Dawley rats were used with weight between 350 g and 650 g. The animals were housed in a limited access facility, with alternate 12-hour light/dark cycles. The animals were offered rat chow and water ad libitum. The facility staff was responsible for feeding, cleaning cages, and assessing animal wellbeing. To provide optimal positioning of the animals and secure the animal in position, a platform inclined to 35-degrees and with a wedged-out surface, was designed and created to be used as a procedure table. An operating room towel and towel clamp were used to secure the rats safely in position during the procedure. A fishhook weighted with a mosquito clamp was hung over the maxilla to gently extend the neck. A Carl Zeiss (Oberkochen, Germany) OPMI 1 FC binocular microscope was used for magnification (Fig.). A 1-liter air pressure chamber fitted with a Spacelabs Healthcare (Snoqualmie, WA) 511 calibrated pressure monitor was used to provide air puffs with known pressures and constant duration. The air puff delivery handpiece was a stainless steel cannula similar in shape to a Frazier suction with an inner lumen diameter of 0.57 mm, capable of delivering an air puff to a precise target on the larynx. An adult Farrior otologic speculum was modified to be used as a rat laryngoscope. This modification was done by cutting away about one-third of the speculum along its long axis, leaving intact 5 mm of the scope's diameter at the narrow end (Fig.). The space provided by cutting away part of the speculum created room for the maxillary incisors, allowing the speculum to be advanced into position without putting excessive force on the temporomandibular joint. The circumferentially intact portion at the small end of this laryngoscope retracted soft tissues of the hypopharynx, allowing an unobstructed view of the supraglottic larynx (Fig.). Rats' weights were recorded at the start of each trial. The animals were induced with a weight-based dose (see Results) of ketamine/xylazine, administered by intraperitoneal injection. Time of induction was recorded as the amount of time from injection to the time an animal was no longer making voluntary movements. Working time was recorded as the amount of time from induction until the animal was again making voluntary movements. Once the paw-pinch reflex was absent, the rat was placed supine in the platform, as described above. The laryngoscope was introduced transorally and gently advanced until there was full visualization of the larynx and surrounding hypopharynx. The epiglottis, arytenoids, and piriform sinuses were visible in a single view. The binocular microscope used to visualize the larynx was equipped with a video camera for recording and reviewing trials. The level of sedation was continually monitored throughout each trial by observing for spontaneous glottic closures and performing corneal reflex testing. Serial air puffs were delivered at varied pressures with pulse time kept constant. Sensation thresholds were recorded as the lowest pulse pressure that induced an LAR. After an ST was determined, three puffs were given at a pressure just lower than the proposed ST to confirm the value as the lowest pressure that induced glottic closure. LARs were determined by direct visualization of complete glottic closure and confirmed by a second observer watching through the microscope's teaching port (Fig.). Sensation thresholds were determined at three anatomic locations: the epiglottis, arytenoid, and piriform sinus. The order in which these locations were given air puffs was randomized for each trial. Tactile stimulation trials also were performed with a 1-mg monofilament polypropylene wire (similar to a Semmes-Weinstein monofilament used for proprioceptive testing in peripheral neuropathy) at each of the three locations, directly stimulating mucosa and eliminating other variables that air puffs may create, such as inadvertent air passage past the vocal cords and into the trachea. Following tactile stimulation trials, the larynx was anesthetized with 0.25 cc of topical 4% weight/volume lidocaine, and LARs to air-puff and tactile pressure were reassessed to validate the LAR as a response specific to laryngeal sensation. A total of 26 trials (4 preliminary and 22 experimental) were performed in 14 animals. Prior to starting data collection, preliminary trials (n = 4) were done to confirm proper equipment setup and make small adjustments to the equipment and protocol. Following these preliminary trials, STs for the first trials were calculated on the entire set of animals (n = 14). To confirm intra-animal reliability, a subset of the animals underwent repeat ST trials a second time (n = 5) and a third time (n = 3). Publisher Copyright: {\textcopyright} 2017 The American Laryngological, Rhinological and Otological Society, Inc.",
year = "2017",
month = aug,
doi = "10.1002/lary.26500",
language = "English",
volume = "127",
pages = "E265--E269",
journal = "Laryngoscope",
issn = "0023-852X",
number = "8",
}