Peak Cough Flow Fails to Detect Upper Airway Collapse During Negative Pressure Titration for Cough-Assist

Upper Airway Assessment and Responses During Mechanically Assisted Cough

“…52,88 The dogma that upper airway collapse during exsufflation causes MI-E treatment failure, highly influenced former evaluation methods, assessing the exsufflation phase alone. Sancho et al's CT-scannings 25 and Lacombe's flow-curve shapes 84 confirmed Bach's postulate that exsufflation caused upper airway collapse in subjects with bulbar dysfunction. 6 Later studies indicate that this exsufflation-related hypopharyngeal narrowing occurs also in the healthy.…”

“…82,83 As lung insufflation and exsufflation require an adequately sized laryngeal inlet, 37 one may assume that visually observed laryngeal adduction causes airflow obstruction, influencing treatment efficacy. 9,10,56,84 Elaborating on Bach's postulation of exsufflation being the main challenge, Lacombe et al 84 analyzed exsufflation airflow curves to subjects with NMDs. Following PCF, they described an abrupt flattening, or a flow decrease during exsufflation, assumed to indicate upper airway collapse.…”

“…It was suggested that using CPF alone failed to detect upper airway collapse during negative pressure titration in MI-E, and that studying the complete exsufflation airflow curve, not just the peak value, could reveal laryngeal opening or closure. 84 When comparing flow curves and visualized laryngeal events during MI-E, preliminary findings from Andersen et al 85 indicate that efforts to cough or exhale during exsufflation affect flow curve geometry (shape). The authors were unable to link visualized laryngeal response characteristics to unique airflow geometry patterns, but recognized several MI-E airflow geometry patterns ( Figure 6).…”

“…23,80 A certain narrowing is beneficial, increasing linear airflow velocity and shear forces that move secretions proximally. 1,2 However, the studies of Bach, 6 Sancho et al 25 and Lacombe et al 56,84 have been essential, introducing the vital understanding that MI-E airflows and pressures delivered via the upper airways may cause structural responses. In studies where the larynx was visualized during the whole MI-E cycle, adduction of laryngeal structures during insufflation was revealed in subjects with bulbar ALS, the opposite of the findings in nonbulbar subjects and healthy controls.…”

“…105,106 The CPF phase accounts for only 25% of the cough shearing force, and the sustained flow rate which occurs after this is probably of great significance. 107 Lacombe's group suggested there is a volume dependent factor of ECV that may detect upper airway obstruction, 84 and they also suggested a time-dependent efficacy factor during exsufflation, defined as effective cough time (ECT); the time spent above CPF >180 L/min. 56 To conclude, judging MI-E efficacy is complex.…”