Primary ciliary dyskinesia (PCD) is characterized by impaired airway clearance and mucus stagnation. This results in recurrent upper and lower respiratory tract infections often leading to chronic inflammation and, if not treated early and properly, to irreversible functional and structural changes of the respiratory tract. As there is no causal treatment of PCD yet, airway clearance techniques (ACT) provide fundamental care for these patients.

Simeox is a new airway clearance device, recently developed by the French company PhysioAssist. This technology is based on pneumatic vibrations generated by the device itself. Vibrations are induced by rapidly alternating between atmospheric and negative pressure as the patient exhales, providing the most effective clearance of mucus from the lungs. Vibrations of different intensity and frequency are known to alter the rheological properties of mucus in the airways, whilst the negative pressure during exhalation helps to mobilise and drain the mucus to the central bronchi.

Although there have not yet been any evidence based papers published clarifying the effect of Simeox specifically in patients with PCD, using up-to-date information, experience, and positive feedback from our patients, we assume that there could be a significant benefit for the effectiveness of ACT.

In this study the effectiveness of ACT will be evaluated based on the short-term effect(s) of respiratory physiotherapy with Simeox on changes in lung function and thoracic expansibility paediatric patients with PCD.

An interventional randomised non-inferiority crossover trial will be conducted in Motol University Hospital; the project was developed by the multidisciplinary team (MDT) of the Division of Paediatric Pulmonology of the Department of Paediatrics, 2nd Faculty of Medicine, Charles University in Prague and Motol University Hospital; and the Department of Rehabilitation and Sports Medicine, 2nd Faculty of Medicine, Charles University in Prague and Motol University Hospital.

Eligible patients will be randomly assigned into 2 arms - "Simeox-first group" and "Pari-O-PEP first" group. Randomisation will be done using computer generated code for each patient. The protocol will include 3 study visits - K0, K1 and K2 planned 3 months apart. After 6 months (second visit - K1), each patient will be switched to the other interventional group (crossed over). The first session (K0) includes an initial lung function assessment using spirometry, nitrogen-Multiple Breath Washout test (N2-MBW), Electrical Impedance Tomography (EIT), 6 Minute Walk Test (6 MWT), respiratory amplitudes (RA), and a theoretical introduction to therapy with the Simeox device. The second (K1) and third (K2) sessions will be interventional, including a respiratory physiotherapy session in between each measurement, excluding 6 MWT, which will be measured just once per session.

According to randomisation criteria, participants will initially undergo either physiotherapist-administered 20-minute ACT session using the Simeox device or 30-minute therapy with PARI O-PEP. In accordance with the rules for crossover study design, each patient will undergo therapy with both ACT devices, ideally within six-month duration of the study. These interventions will take place in between each measurement (spirometry, MBW, EIT, RA) during the second (K1) and the third (K2) session.

Inclusion Criteria:

• diagnosis of PCD confirmed by Transmission Electron Microscopy (TEM) analysis of ciliary ultrastructure showing clear structural axonemal defect and/or positive genetic testing for one (autosomal dominant) or two (autosomal recesive) PCD-causing mutations;
• age range 4 - 18 years;
• established chest physiotherapy with PARI O PEP

Exclusion Criteria:

• inability to undergo the assessment and intervention
• noncompliance and/or nonadherence