Cesare Braggion Director, Cystic Fibrosis Centre, Department of Paediatric Medicine, Anna Meyer Children’s Hospital, Florence , Giulia Placidi Physiotherapist, Intensive Care Unit, Department of Neurosurgery, Azienda Ospedaliero-Universitaria, Verona

Originally printed in:
» European Respiratory Disease 2007 - Issue II

Role of Airway Clearance Techniques in the Treatment of Lung Disease of Cystic Fibrosis

A striking and early feature of lung disease in cystic fibrosis (CF) is the plugging of airways with thick and sticky airway secretions.^1,2 At an early age, patients with CF develop bacterial infections such as Staphylococcus aureus and Pseudomonas aeruginosa that initially appear to clear with vigorous antibiotic therapy.^1,2 Later, however, permanent colonisation of the airways becomes established. It is likely that colonisation occurs because of reduced chloride secretion and increased sodium reabsorption in airway epithelium.^1–3 Both lead to reduced water content of secretions as well as reduced depth of periciliary fluid, which in turn lead to trapping of inhaled bacteria and slower mucociliary clearance.³ Infection induces an exuberant and persistent neutrophilic inflammatory response. The neutrophil and bacterial products ultimately destroy the airway wall and contribute to persistent and progressive airway obstruction.^1–3 Bronchiectasis is a typical lesion of the airways. With time, a modest degree of lung tissue fibrosis and emphysema develops.¹

Different airway clearance techniques (ACTs) are at present available to aid mucus clearance in patients with CF.^4–6 The aims of ACTs are to prevent or reduce the mechanical consequences of increased and viscous mucus. These include airway obstruction, atelectasis, ventilation/ perfusion mismatch (due to maldistribution of ventilation) and increased difficulty in breathing. Furthermore, the removal of infective mucus, inflammatory mediators and proteolytic and oxidative activity from the airways reduces or prevents host-mediated inflammatory tissue damage.

ACTs are mechanical interventions based on respiratory pathophysiology.⁶ Postural drainage (gravity-assisted drainage positions) combined with chest percussions, chest vibrations, forced expirations and coughing (the ‘ketchup-bottle method’) has for many years been considered the standard regimen. It remains an attractive option for younger patients and those too sick to co-operate with active clearance methods.^4,5 Active cycle of breathing technique (ACBT) is a combination of breathing control, thoracic expansion and the forced expiratory technique (FET).⁵ FET (huffing) produces a dynamic compression of the airways downstream from the point at which pressure outside the airway is similar to that inside the airway (flow-limiting segment): any mucus within this distance of compressed airways should be exhaled from the lung by increased air turbulence.⁵ When huffing and active expirations are prolonged, the compressing segment moves in the small airways. ACBT can be performed in gravity-assisted body positions.⁵ Autogenic drainage consists of breathing control, i.e. breathing at different lung volumes (below and above functional residual capacity) and with the highest possible airflow obtained in different airway generations with minimal airway compression.⁵ The positive expiratory pressure (PEP) device, as a face-mask with an expiratory resistor (PEPm), provides constant back pressure to the airways during expiration.⁷ PEP should increase gas pressure behind the mucus via collateral ventilation and may stabilise airways by keeping them open during expiration. Cycles of active breaths against an expiratory resistor may produce a dynamic hyperinflation with subsequent airway distension, but also an increase in respiratory work.

Devices have been brought into clinical use to assist in mucus clearance. A mechanical vest that inflates and deflates can rapidly vibrate the chest and does not require a partner.^5,8 Small hand-held pipelike devices (into which the patient blows) vibrate the airways to shake loose adherent mucus, provide back pressure to keep airways open and prevent collapse.⁵ Healthier patients can increase mucus clearance with aerobic exercise that stimulates deep breathing and coughing and activates collateral ventilation.⁵

A recent systematic review concludes that ACTs are recommended in patients with CF as effective techniques to increase mucus clearance. However, the effects of each treatment are relatively modest and the long-term benefits unproved.⁹

Airway Clearance Techniques and Severe Lung Disease

Severe lung disease (FEV₁ <40% of predicted) is associated with pulmonary complications such as recurrent haemoptysis and pneumothorax.¹⁰ Malnutrition, dyspnoea with reduced effort tolerance and respiratory failure are typical features of later stages of the illness.¹⁰ Respiratory failure still accounts for over 80% of deaths in patients with CF.¹⁰

An increase in resting energy expenditure and anorexia is associated with chronic pulmonary infection and may lead to an energy deficit.¹¹ Weight loss will result, initially causing a substantial loss of adipose tissue and, with time, a loss of lean tissue along with muscle wasting. The consequent weakness of respiratory and peripheral muscles adversely affects exercise tolerance.^12–14 A muscle-related abnormality in oxygen metabolism could contribute to limiting aerobic and anaerobic performance in patients with CF.^13,14 The impairment in ventilatory mechanics and hypoxaemia are the other main factors that decrease aerobic capacity.^15,16 Patients experience increasing shortness of breath, and habitual physical activity and daily activities decrease as the illness progresses.

Initially, patients are more likely to develop hypoxaemia with exercise or during sleep.¹⁰ As the disease progresses, alveolar hypoventilation and worsened ventilation perfusion mismatching result in chronic hypoxaemia and hypercapnia. Supplemental oxygen therapy has been shown to improve exercise tolerance and survival in patients with chronic obstructive pulmonary disease, and the prescription of long-term domiciliary oxygen therapy follows the global initiative for chronic obstructive lung disease (GOLD) guidelines for this disease.¹⁷ Lung transplantation became a viable option for CF patients about 20 years ago.¹⁸

Any given ACT may ideally suit the needs of patients with mild to moderate airway obstruction, but it may not be equally suitable or effective for patients with CF and severe airway obstruction. Radioaerosol studies showed that mucociliary and cough clearance were more impaired in patients with severe airway obstruction than in patients with mild or moderate lung disease.¹⁹ Moreover, unwanted effects could be associated with ACTs. Different studies showed that chest physiotherapy imposes additional respiratory work that produces a decrease in respiratory muscle strength, fatigue and oxyhaemoglobin desaturation^20–22. The combination of non-invasive positive pressure ventilation (NIPPV) with an ACT is proposed as a potential indication of NIPPV in patients with CF.^20–22 Preliminary experiences with NIPPV, using either continuous positive airway pressure (CPAP) generators or bi-level pressure support generators, showed improvement of gas exchange and decrease in respiratory work in CF patients.^23–25 Periodic CPAP therapy has been shown to aid in the mobilisation of retained secretions and to prevent or treat atelectasis after thoracic and abdominal surgery.²⁶