At two consecutive regular outpatient clinic visits, each participant will perform a session of the insufflation/exsufflation technique.~Participants will be randomised by a computer-generated code to one of the two sequences (CON-MOD or MOD-CON) using sealed envelopes. The randomisation list will be generated by a study nurse of the Department of Paediatrics who is not a member of the study group.~The randomisation envelope will be opened by the treating physiotherapist immediately before the first treatment session.~Standardised intervention~At randomisation, the measurement belt of the EIT system will be fitted around the chest of the participant. Once correct fit is confirmed, the baseline measurement (T0) will be taken. After the baseline assessment, the participants will perform the conventional (CON) or modified (MOD) insufflator/exsufflator therapy session under supervision of a physiotherapist. In teh investigator's institution a therapy session consists of 5 series of 5 insufflation/exsufflation manoeuvres each (Cough assist E70, Philips Respironics, Hamburg, Germany). Positive and negative pressures will be set at the individual level of each subject.~Measurements Changes in lung volume and ventilation distribution will be assessed by electrical impedance tomography (EIT). These parameters will be obtained five minutes before (T0) and five, ten, twenty, forty and sixty minutes after the treatment session (T1 - T5). Measurements of 3 minutes will be recorded at each time point. Additionally EIT measurements will be performed continuously during the treatment session.~Electrical Impedance Tomography (EIT) is a non-invasive, radiation-free technique for the assessment of spatial and temporal ventilation distribution based on the changes in electrical properties of the tissue during the respiratory cycle. EIT measurements will be performed using a commercially available setup (PulmoVista 500, Draeger, Germany). Image reconstruction will be performed with the GREIT-algorithm using the torso mesh function. [Adler, 2009] Relative change in end-expiratory lung impedance (EELI) and the global inhomogeneity (GI) index, a measure of ventilation inhomogeneity, will be calculated using customized software (Matlab® R2021b, The MathWorks Inc., Nattick, MA, USA).
In a randomized cross-over design, two different modes of a mechanical insufflator/exsufflator applied to pediatric subjects with neuromuscular disease will be compared with respect to their short term effect on lung function, i.e. lung volume.