Accuracy of Peak Cough Flow Measurements Using a Mechanical Insufflator-exsufflator

Patients with a neuromuscular disease (NMD) lose strength in their breathing muscles which leads to an inability to generate an effective cough. Peak Cough Flow (PCF) is a simple objective measure of cough and is the recommended measure in patients with NMD. Critical peak cough flow values are used to evaluate cough, these include PCF less than 160 L/min to indicate an ineffective cough, PCF between 161- 270 to indicate an impaired cough and PCF greater than 270 L/min to indicate an effective cough. Mechanical insufflator- exsufflator (MIE) devices more commonly known as 'cough assist' devices have an inbuilt measure of PCF however they aren't currently recommended for use to due to limited information available regarding their accuracy. This will be a single centre prospective observational study. Once patients have consented to participate in the study, they will be visited once on the unit during their admission by the researcher with the visit lasting approximately an hour.

During the visit they will receive their usual care MIE with a pneumotachograph fitted into the circuit. The primary outcome is the agreement of MIE assisted PCF measures between the MIE device and pneumotachograph. Before and after the intervention the patient will be asked to rate the presence of mucous in their lungs using a visual analogue scale.

The following data will be recorded

• Neuromuscular diagnosis
• Age, height, weight,
• Comorbidities
• Hospital length of stay (Days)
• Ventilation dependency(hours/Day)
• Bronchodilator and/or mucolytic medications
• Vital observations (heart rate, blood pressure, oxygen saturations)
• Method of MIE delivery (mask or tracheostomy)
• Tracheostomy size, type and brand
• Bulbar function if available (Laryngoscope)
• Spirometry - Forced Expired Volume in 1 second (FEV1), Forced Vital Capacity (FVC), (from clinical notes)
• Voluntary PCF (collected from patient by researcher)
• MIE Mode (collected from device by researcher)
• MIE Total number cycle repeats (collected from device by researcher)
• MIE device Inspiratory pressure (collected from device by researcher)
• MIE inspiratory pressure at interface (Pressure transducer)
• MIE inspiratory time (collected from device by researcher)
• MIE peak inspiratory Flow (from device by researcher)
• MIE device expiratory pressure (collected from device by researcher)
• MIE expiratory pressure at interface (Pressure transducer)
• MIE Expiratory time (collected from device by researcher)
• MIE Assisted PCF Pneumotachograph (From patient by researcher)
• MIE Assisted PCF MIE (From patient by researcher)
• Visual Analogue Scale regarding secretion presence pre and post MIE (from patient by researcher)

Inclusion criteria

• Patients with neuromuscular disease-related respiratory failure and are receiving MIE as part of their usual care
• Patients who are clinical stable and documented as such by the supervising clinician
• Patients who are cognitively intact and have the capacity able to provide informed consent

Exclusion criteria

• Pregnancy
• Aged <18
• Significant physical or psychiatric co-morbidity that would prevent compliance with trial protocol