Optimising insufflation parameters of mechanical insufflation-exsufflation to augment cough in patients with Duchenne muscular dystrophy (DMD).

Mechanical insufflation-exsufflation (MIE) augments cough in patiets with respiratory muscle weakness. Maximising inspiratory volume (V_i) should lead to improved cough augmentation. Increasing insufflation pressure can lead to upper airway closure (UAC). Therefore, this study sought to assess the effect of changing inspiratory time (Ti) and inspiratory rise time (IRT) as an alternative to increasing insufflation pressure, to increase V_i during MIE. Patients with DMD receiving domiciliary MIE via facemask were assessed. MIE was delivered with home pressures, at Ti 2 and 3s; and IRT 10%Ti, 50%Ti and 100%Ti. V_i, peak inspiratory (PIF) and cough flow (PCF) were measured with a pneumotachograph. Flow-volume curves were used to identify periods of absent flow (surrogate for UAC). 12 pts(31±6yrs) were included. Unassisted PCF 99±92L/min. Usual MIE pressures +38(5), -50(9) cmH2O. Increasing Ti from 2 to 3s resulted in an increase in V_i in 9/12 (75%), PIF in 6/12(50%), PCF in 8/12(66%) and PCF:PIF in 8/12(66%) participants. UAC was observed in 10/12(83%). Increasing IRT resulted in a decrease in V_i in 8/12(66%) and PIF in 6/12(50%) and increase in PCF in 7/12(58%) and PCF:PIF in 7/12(58%) participants. UAC was observed in 8/12(66%) at 10%Ti and 6/12(50%) at 100%Ti. Borg dyspnoea scale did not change throughout the protocol. Prolonging Ti from 2 to 3s resulted in a small increase in V_i, PCF and PCF:PIF in most individuals. Increasing the IRT from 10%Ti to 100%Ti resulted in a decrease in inspiratory volume and PIF but increase in PCF and PCF:PIF. T_i and IRT may be useful to augment cough, without increasing pressure, however UAC remains unaffected.