The human recurrent laryngeal nerve during the aging process

Dysphagia in patients with coronavirus disease undergoing orotracheal intubation

Objective

To assess the incidence and the risk factors for the development of dysphagia in patients with coronavirus disease 2019 (COVID-19) undergoing orotracheal intubation.

Study Design

Prospective cohort study.

Methods

In this prospective cohort study, we evaluated consecutive patients diagnosed with COVID-19 and underwent orotracheal intubation were evaluated. During hospitalization, extubated patients were classified as dysphagic and nondysphagic based on bedside functional assessment of swallowing. Patients discharged from hospital were asked to complete the Eating Assessment Tool-10 (EAT-10) questionnaire, followed by an endoscopic examination to identify laryngotracheal lesions, and a fiberoptic endoscopic evaluation of swallowing (FEES). The food consistencies used for FEES were moderately thick, extremely thick, thin, and regular.

Results

Based on the functional assessment of swallowing, performed a mean of 5.3 days and a median of 4 days after extubation, the incidence of dysphagia in patients with COVID-19 undergoing orotracheal intubation was 53.6%. In the late evaluation, performed a mean of 102 days after extubation, 12.8% of patients had an EAT-10 score >2. Orotracheal intubation (OTI) duration and tracheostomy were risk factors for the development of dysphagia. There was an association between EAT-10 > 2 and the presence of laryngotracheal lesion, with no difference between lesion type and EAT score >2.

Conclusions

The incidence of dysphagia varied according to the time of assessment, being higher the earlier the assessment after extubation. OTI duration and tracheostomy were risk factors for the development of dysphagia, and the presence of laryngotracheal lesions demonstrated an association with dysphagia.

Level of Evidence

3.

Correlation Between Presbylarynx and Laryngeal EMG

BACKGROUND

The normal aging process affects many human functions profoundly. The voice is no exception, and some aging effects on the voice are obvious including vocal fold atrophy, bowing, stiffness, more prominent vocal fold processes, and glottic insufficiency. The study's primary aim was to determine the correlation between presbylarynx and laryngeal electromyography (LEMG) results and to compare these electromyography (EMG) results with young and old voice patients without evidence of presbylarynx changes on strobovideolaryngoscopy.

METHODS

Medical records for voice patients seen in the senior author's (RTS) practice between 2015 and 2019 were reviewed retrospectively. Patients with presbylarynx confirmed by strobovideolaryngoscopy were identified and compared to two control groups. The first control group included patients with ages and American Society of Anesthesiologists scores similar to the experimental group but no presbylarynx. The second control group included younger patients (ages ranging between 18 and 35 years with mean age of 24.57 years) with vocal fold paresis. All groups had undergone LEMG because of suspected paresis clinically. Social and medical factors reviewed and compared between groups included smoking history, alcohol consumption, occupation (voice demanding versus not voice demanding occupation), Voice Handicap Index score at the initial office visit, medical comorbidities, medications, and LEMG results.

RESULTS

There was no significant difference in the recruitment results for three pairs of muscles (cricothyroid, thyroarytenoid and posterior cricoarytenoid) between the presbylarynx group and both control groups. Rate of asthma was higher in presbylarynx group compared with the first control group. Rates of corticosteroid inhaler use, thyroid medications, smoking, and Voice Handicap Index score were higher in presbylarynx group compared with the second control group. There was no significant difference in occupation type and alcohol consumption between groups.

CONCLUSION

There was no significant difference found in the neuromuscular function based on laryngeal EMG between presbylarynx patients and both old and young patients with vocal fold paresis but without presbylarynx. Corticosteroid inhaler is associated with atrophic changes seen in presbylarynx. There still could be differences in the neuromuscular function which weren't detected. More research is needed to confirm or refute these findings.

Age-Related Changes in Human Laryngeal Nerves

OBJECTIVES: We sought to perform a morphometric analysis of myelinated fibers from laryngeal nerves with the aim of verifying quantitative changes due to the aging process.

METHODS: A 1-cm fragment was collected from the superior laryngeal nerves and recurrent laryngeal nerves from 12 cadavers during autopsy. The sample was divided in two groups: an adult group (aged <60 years) and an elderly group (aged ≥60 years).

RESULTS: The total number of myelinated fibers from the superior laryngeal nerves was similar in both groups (adult group = 9017 ± 1692, elderly group = 7918 ± 1624; P = 0.79). The adult group had a higher total number of myelinated fibers in the recurrent laryngeal nerves than that of the elderly group (adult group = 3276 ± 383, elderly group = 2381 ± 669; P = 0.005), as well as a higher total number of fibers in the laryngeal nerves (both superior and recurrent) than the elderly group ( P = 0.02).

CONCLUSIONS: The adult group has a higher total number of myelinated fibers in the laryngeal nerves than the elderly group.

Degree of myelination (g-ratio) of the human recurrent laryngeal nerve

The g-ratio (estimated by dividing the axon diameter by the myelinated fiber diameter) can be useful to the evaluation of the relationship between nerve conduction velocity and fiber morphology during peripheral nerve regeneration. However, there is little detailed information about the g-ratio of the human recurrent laryngeal nerve (RLN), especially between men and women. The objective of this study was to investigate the g-ratio of the RLN by quantifying histomorphometric data (axon diameter and myelinated fiber diameter) in the RLN of men and women. The RLN was bilaterally studied in human specimens obtained from necropsies (seven men and seven women). The nerves were analyzed using histology, and the morphometric parameters were measured using Image Pro-Plus Software (Image Pro-Plus 6.0; Media Cybernetics, Silver Spring, MD, USA). When compared with the RLN of the women, the parameters of the RLN of the men are significantly larger, as shown by the axon diameter (19.0%) (P = 0.0001), myelinated fiber diameter (7.1%) (P = 0.0497), and g-ratio (12.5%) (P = 0.0005). Our findings demonstrated that there are morphological asymmetries between the g-ratio (degree of the myelination) of the masculine and feminine RLN. These morphological findings are probably related to physiological differences.

Challenges and opportunities in the management of the aging voice

Presbyphonia, or age-related dysphonia, is a diagnosis of exclusion, and other comorbidities must be considered in a complete evaluation of elderly patients with dysphonia. The aging voice can have a significant effect on the quality of life of the patient. In addition to the molecular effects of aging on the laryngeal tissues, the etiology of presbyphonia is often multifactorial because of comorbidities in the other organ systems involved in phonation. After a comprehensive evaluation, presbyphonia may be treated conservatively with voice therapy or with a range of interventions. Research into tissue engineering and electrical reanimation offers future options for treatment of presbyphonia. Currently, a multidisciplinary approach offers the most complete improvement in the vocal quality of life in this patient population.

Histological asymmetry of the human recurrent laryngeal nerve

Histological studies of the human recurrent laryngeal nerves (RLNs) have described differences in fiber length and thickness between the right and left RLNs. This asymmetry is probably involved in the different times of arrival of the stimuli to the laryngeal musculature controlled by each nerve. Histological and structural differences between the right and left RLNs could explain the synchronicity of laryngeal musculature contraction despite the differing nerve lengths. The purpose of this investigation was to shed some light on this paradigm by obtaining estimates of some morphometric parameters, such as intraperineural area, intraperineural perimeter, fiber area, fiber perimeter, fiber density (number of fibers/mm(2)), and total number of fibers in the right and left RLN of humans. Thus, the right and left RLNs were studied in a total sample of eight human specimens obtained from necropsies. The nerves were analyzed using histology, and the morphometric parameters were measured using Image Pro Plus Software 4.1 (Media Cybernetics, Silver Spring, MD, USA). No statistical differences between the two RLNs were observed in the intraperineural area, intraperineural perimeter, density (number of fibers/mm(2)), and total number of fibers. However, the area and perimeter of fibers of the right RLN were statistically larger when compared with those of the left RLN--21% and 11%, respectively. In conclusion, we show that in humans, the area and perimeter of the right RLN are larger than those of the left RLN. This morphological finding is probably related to the different time of arrival of the stimulus to the laryngeal musculature.

Análise quantitativa das fibras mielínicas dos nervos laríngeos em humanos de acordo com a idade

INTRODUÇÃO E OBJETIVO: Realizar análise morfométrica das fibras mielínicas dos nervos laríngeos com a finalidade de verificar modificações quantitativas decorrentes do processo de envelhecimento. FORMA DE ESTUDO: Clínico e experimental. Material e Método: Foi coletado fragmento de 1cm dos nervos laríngeos superiores e nervos laríngeos recorrentes de 12 cadáveres do sexo masculino. A amostra foi dividida em dois grupos: idade inferior a 60 anos (Adulto) e idade igual ou superior a 60 anos (Idoso). O material foi avaliado em microscópio de luz acoplado a sistema analisador de imagem. RESULTADOS: O número total de fibras mielínicas do nervo laríngeo superior foi semelhante nos dois grupos etários, mas com tendência para o maior número de fibras de 1µm no grupo adulto (p=0,0744). O grupo adulto apresentou maior número total de fibras mielínicas no nervo laríngeo recorrente (p=0,0006), e esta diferença ocorreu nas fibras com diâmetros de 1-3µm (p<0,007). O grupo adulto apresentou maior número total de fibras mielínicas nos nervos laríngeos (soma das fibras dos nervos laríngeos superiores e dos nervos laríngeos recorrentes) que o grupo idoso (p<0,0091). CONCLUSÃO: O número total de fibras mielínicas dos nervos laríngeos é maior no grupo com idade inferior a 60 anos.

Quantitative analysis of myelinic fibers in human laryngeal nerves according to age

INTRODUCTION AND AIM

To carry out a morphometric analysis of myelinic fibers in laryngeal nerves aiming to identify quantitative changes as a result of aging.

STUDY DESIGN

Clinical and experimental.

MATERIAL AND METHOD

A 1cm fragment was collected from the superior laryngeal nerves and recurrent laryngeal nerves taken from twelve male cadavers. The sample was divided into two groups: those aged below 60 years (Adult) and those aged 60 years or more (Elderly). The material was evaluated under light microscopy coupled with an image analysis system.

RESULTS

The total number of myelinic fibers from the superior laryngeal nerve was similar in both age groups; there was, however, a trend for a higher number of 1 microm fibers in the adult group (p=0.0744). The adult group had a higher total number of myelinic fibers in the recurrent laryngeal nerve (p=0.0006), and this difference was seen in fibers with diameters between 1-3 microm (p<0.007). The adult group had a higher total number of myelinic fibers in the laryngeal nerves (sum of superior laryngeal nerves and recurrent laryngeal nerves fibers) compared to the elderly group (p<0.0091).

CONCLUSION

The total number of myelinic fibers in laryngeal nerves is higher for the group aged below 60 years.

Morphometric analysis of the inferior alveolar nerve fails to demonstrate sexual dimorphism

PURPOSE

With regard to the incidence of inferior alveolar nerve (IAN) damage after an IAN block or following oral and maxillofacial surgical procedures, there are reports of sexual dimorphism, no sexual dimorphism, and little sexual dimorphism. However, details of the morphology and sexual dimorphism in the characteristics of the IAN have not been available in textbooks. We morphometrically analyzed the human IAN and clarified these issues.

MATERIALS AND METHODS

The materials were obtained from 22 cadavers (11 female and 11 male), aged 59 to 84 years (average age: 74.1 yr), and dentulous. The causes of death did not influence the nervous system, so the IANs were considered to be normal. Human IANs were resected at the mandibular foramen. We counted the myelinated axons and measured the transverse area, perimeter, and circularity ratio of the myelinated axons.

RESULTS

We estimated the average total number of myelinated axons in the female IAN to be 25,230, with an average transverse area of 34.1 microm(2), an average perimeter of 21.8 microm, and an average circularity ratio of 0.86, with the same measurements in the male IAN being 20,278, 31.7 microm(2), 20.7 microm, and 0.87, respectively. Our data showed no significant difference between the female and male specimens in any measured item (P < .05).

CONCLUSIONS

We assumed that the sex difference in the incidence of IAN damage was not affected by the morphometric findings. Our findings might partly explain why there is no significant sex difference in the incidence of IAN damage.

Morphometric evaluations of the human nervous system

It is very important to evaluate and accurately understand the various conditions of the human nervous system. In this review article, we introduce several morphometric reports that are proven to be accurate from the view point of various errors (range of tissue shrinkage ratios, microscopic multiple counting, artifacts of microscopic structures, etc.). We review the following aspects of the selected reports: methodology, developmental research, neuronal differences, gender differences, aging process and miscellaneous (nerve fibers, unmyelinated fibers, in relation to neuropathology, clinical image-analysis and immunohistochemistry).

Morphometric aspects of the human hypoglossal nerve in adults and the elderly

AIM

Perform a morphometric analysis of the myelinic fibers of the right hypoglossal nerve, in two age groups; to verify quantitative changes as a result of the aging process.

STUDY DESIGN

Anatomic.

MATERIAL AND METHOD

A 1 cm fragment of the right hypoglossal nerve was collected from 12 male corpses without any medical history of diseases such as: diabetes, alcoholism, and malignant neoplasia. The sample was divided in two groups: group with six corpses under sixty years old (adult), and another group with six corpses sixty years old or above (elderly). The material was fixed at 2.5% glutaldehyde and 2% paraformaldehyde solution; post-fixed at 2% osmium tetroxide; dehydrated with increasing ethanol concentrations, and included in epoxy resin. Semi-thin sections of 0.3 microm were obtaining, colored in 1% toluidine blue, and evaluated with light microscope combined with image analyzing system. The following morphometric data were quantified: intraperineural transversal section area, number, and diameter of the myelinic fibers.

RESULTS

The intraperineural area of the hypoglossal nerve was similar in both age groups (p=0.8691). The average area in the adult group was 1.697 mm2 and in the elderly group it was 1.649 mm2. The total number of myelinic fibers of the hypoglossal nerve was similar in both age groups (p=0.9018). The adult group presented an average of 10,286 +/- 2,308 myelinic fibers, and the elderly group presented an average of 10,141 +/- 1,590 myelinic fibers. A bimodal distribution of the myelinic fibers was observed, with a significant peak on the 9 microm fibers, and another smaller peak on the 2 microm fibers.

CONCLUSION

The intraperineural area and the total number of myelinic fibers of the right hypoglossal nerve are similar in both age groups.