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Sniff nasal inspiratory pressure (SNIP) is used to assess respiratory muscle strength in neuromuscular diseases like amyotrophic lateral sclerosis (ALS). The effect of contralateral nostril occlusion and mouth sealing on SNIP measurement are unclear. 81 participants were included (16 healthy, 39 patients with limb-onset ALS and 26 patients with bulbar-onset ALS). SNIP was obtained with combinations of mouth open/sealed and contralateral nostril open/occluded. Occluding the contralateral nostril (with mouth closed) increased SNIP by 12 cmH 2 O (95% CI 4, 20; p=0.003) in the healthy participants, by 9 cmH 2 O (95% CI 5, 12; p<0.001) in the limb-onset cohort and by 10 cmH 2 O (95% CI 5, 14; p<0.001) in the bulbar-onset cohort. Opening the mouth decreased SNIP by 19 cmH 2 O (95% CI 5, 34; p<0.009) in healthy participants, by 8 cmH 2 O (95% CI 4, 13; p<0.001) in the limb-onset cohort and by 13 cmH 2 O (95% CI 7, 19; p<0.001) in the bulbar-onset cohort. With contralateral nostril occlusion, 11% fewer individuals would have qualified for non-invasive ventilation. In conclusion, contralateral nostril occlusion increased SNIP compared with standard technique, likely reflecting true strength. Opening the mouth reduced SNIP, emphasising the need for good mouth sealing. Documenting SNIP technique is important for longitudinal assessments and clinical decision-making., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2024. No commercial re-use. See rights and permissions. Published by BMJ.)

Background: Respiratory muscle weakness can impair cough function, leading to lower respiratory tract infections. These infections are an important contributor to morbidity and mortality in patients with neuromuscular disease. Mechanical insufflation-exsufflation (MIE) is used to augment cough function in these patients. Although MIE is widely used, there are few data to advise on the optimal technique. Since the introduction of MIE, the recommended pressures to be delivered have increased. There are concerns regarding the use of higher pressures and their potential to cause lung derecruitment and upper airway closure., Research Question: What is the impact of high-pressure MIE (HP-MIE) on lung recruitment, respiratory drive, upper airway flow, and patient comfort, compared with low-pressure MIE (LP-MIE), in patients with respiratory muscle weakness?, Study Design and Methods: Clinically stable patients using domiciliary MIE with respiratory muscle weakness secondary to Duchenne muscle dystrophy, spinal cord injury, or long-term tracheostomy ventilation received LP-MIE (30/-30 cm H 2 O) and HP-MIE (60/-60 cm H 2 O) in a random sequence. Lung recruitment, neural respiratory drive, and cough peak expiratory flow were measured throughout, and patients reported comfort and breathlessness following each intervention., Results: A total of 29 patients (10 with Duchenne muscle dystrophy, eight with spinal cord injury, and 11 with long-term tracheostomy ventilation) were included in this study. HP-MIE augmented cough peak expiratory flow compared with LP-MIE (mean cough peak expiratory flow HP-MIE 228 ± 81 L/min vs LP-MIE 179 ± 67 L/min; P = .0001) without any significant change in lung recruitment, neural respiratory drive, or patient-reported breathlessness. However, in patients with more pronounced respiratory muscle weakness, HP-MIE resulted in an increased rate of upper airway closure and patient discomfort that may have an impact on clinical efficacy., Interpretation: HP-MIE did not lead to lung derecruitment or breathlessness compared with LP-MIE. However, it was poorly tolerated in individuals with advanced respiratory muscle weakness. HP-MIE generates more upper airway closure than LP-MIE, which may be missed if cough peak expiratory flow is used as the sole titration target., Clinical Trial Registration: ClinicalTrials.gov; No.: NCT02753959; URL: www., Clinicaltrials: gov., Competing Interests: Financial/Nonfinancial Disclosures The authors have reported to CHEST the following: M. P. declares grants and consulting fees from Fisher & Paykel, Philips, and Resmed. None declared (N. M. S., C. A., G. K., S. M.-S., E.-S. S., R. F. D., G. A., E. L., N. H., P. B. M.)., (Copyright © 2023 American College of Chest Physicians. Published by Elsevier Inc. All rights reserved.)