Laryngoscopy Can Be a Valuable Tool for Unexpected Therapeutic Response in Noninvasive Respiratory Interventions

In reply:

We thank Antonio M. Esquinas and Giuseppe Fiorentino for their acknowledgments and for their summary of some of the findings from our investigation¹ on this understudied topic of laryngeal response patterns to mechanical insufflation-exsufflation.^2–4

We certainly agree that the larynx must not be seen merely as an opening at the top of the airway tree. As we have described in our work, the larynx is a highly complex valve that needs to adjust, adapt, and actively respond to a wide range of physiological situations and stressors. Basic features such as structure, function, and innervation are not fully understood in health or in disease. We know that the application of positive airway pressures can lead to laryngeal adduction, even in healthy individuals.² Moreover, laryngeal collapse due to high ventilatory volumes during ongoing exercise was recently defined and described as an independent disease entity labeled “exercise-induced laryngeal obstruction.^5,6 Thus, it should not come as a surprise that complex motor neuron diseases like amyotrophic lateral sclerosis (ALS) influence laryngeal function and can compromise the laryngeal ability to accommodate intermittent increases in air flow applied by mechanical insufflation-exsufflation. Whether high or abruptly applied positive pressures can lead to laryngeal collapse in a noninvasive ventilation setting is an issue that remains to be studied systematically.

Concerning the concern of “type of ALS” versus “laryngeal responses to mechanical insufflation-exsufflation,” these aspects were discussed in detail in our previous cross-sectional study.³ We agree that these issues are important to understand in order to expand on the utilization of noninvasive therapeutic alternatives in this vulnerable group of patients. We acknowledge and certainly encourage that our findings should be systematically tested in larger ALS populations treated and followed at institutions larger than ours. Our studies have so far demonstrated that the larynx in these patients plays the role of the bottleneck of the airways by its nature, and that it functions as an important valve that regulates pressure and air-flow access to the airway tree below. This has obvious consequences for the use of all types of mechanical respiratory support that utilize noninvasive positive airway pressures in these patients. Importantly, it seems reasonable to assume that these findings are relevant, not only in patients with bulbar innervated muscle dysfunction, but also in other and larger patient groups; however, this remains to be studied.

Obviously, as Esquinas and Fiorentino note, we could have randomized the order of the pressure settings while performing the intervention study instead of increasing the pressures gradually, as we chose to do. We chose this approach to provide the participants with the necessary time to familiarize themselves with the protocol, similar to the mechanical insufflation-exsufflation pressure titration typically used with patients in clinical settings.⁴ For obvious reasons, clinical research performed in ALS patients must be extraordinarily well designed and should include elements that aim to also improve the daily care of the included patients.⁷ Considering the explorative context in which this study was performed, we felt it important that the use of the patients “end-of-life time” should be perceived as meaningful, that the treatments had a clinical benefit, and that we could provide clinical advice to improve their care during their disease progression. In our opinion, the approach chosen did not influence our results significantly, but this should be tested in further studies.

To conclude, this research field is still in a very early phase, and there is a range of unanswered questions. Transnasal fiberoptic laryngoscopy has previously been seen as a specialized examination that should be performed in an otolaryngology clinic. At present, transnasal fiberoptic laryngoscopy is a technique that can be used in several functional contexts, such as during swallowing, inspiratory muscle training, or during an exercise test^8–11, and it can be performed by a trained doctor, by a speech therapist, and by other allied health professionals. We believe that transnasal fiberoptic laryngoscopy performed during ongoing noninvasive respiratory therapies will improve the understanding of laryngeal responses and will help clinicians optimize the treatment for patients who need noninvasively delivered pressures. We encourage others to use this method, both in clinical work and in research projects. We believe that transnasal fiberoptic laryngoscopy will be a valuable tool for a variety of respiratory therapeutic interventions in selected patients who do not respond as expected.

• Copyright © 2018 by Daedalus Enterprises