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High-frequency chest wall oscillation: improving the lives of chronic lung disease patients

Jan Stephen Tecklin
1 July, 2006  

Jan Stephen Tecklin
MS, PT
Professor
Department of Physical Therapy
Arcadia University Glenside, US
E: Tecklin@arcadia.edu

Airway clearance (AC) describes a range of therapeutic activities with a common goal of clearing airways of retained secretions and debris in individuals with pulmonary disease or respiratory impairment. Common AC procedures include the application of physical manoeuvres using the hands, appropriate equipment and coordinated breathing techniques. Attempts to evacuate secretions via coughing, huff coughing, forced expiratory technique or aspiration should follow. The procedures are applied by healthcare professionals, a skilled family member or the educated patient. The ultimate clinical outcomes of AC include reducing airway obstruction, improving ventilation, enhancing physical function and diminishing the risk of continuing or new infections of the respiratory tract. The latter outcome is particularly important for individuals with chronic respiratory disease of a secretory nature, and for those with respiratory impairment secondary to a neuromuscular process.

AC developed throughout the 20th century, originating in England at the Brompton Hospital within the disciplines of nursing and physical therapy. Indeed, until the 1980s, AC techniques were known throughout the health professions as “chest physical therapy”, “chest PT”, “chest physiotherapy” or “physio”. In 1979, Murray stated: “… two generations of physicians have been taught that retention of excessive secretions in the respiratory tract is not only bad for pulmonary function but can also be lethal to the patient.”(1) Regardless of nomenclature, medical professionals have recognised the importance, time, burden and financial resources inherent in providing AC. Several major reviews have appeared in the literature over the past quarter century.(2,3) At least two professions – respiratory therapy and physical therapy – have promulgated standards of practice regarding skills required to achieve AC.(4,5) The following quote from The Guide for Physical Therapist Practice identifies AC as one of nine areas of procedural interventions within the physical therapy profession: “Airway clearance techniques are a group of therapeutic activities intended to manage or prevent the consequences of impaired mucociliary transport or the inability to protect the airway (eg, impaired cough). Techniques may include breathing strategies for airway clearance, manual/ mechanical techniques for airway clearance, positioning, and pulmonary postural drainage.”(5)

Airway clearance in cystic fibrosis
Of all the diseases and conditions for which AC offers therapeutic benefits, in no case are the various procedures more important than in cystic fibrosis (CF) and chronic bronchitis (CB). The very nature of the pathological process and the tenacious and voluminous bronchial secretions inherent in CF demands the use of AC techniques on a regular, ongoing basis. More than 250 published articles and a multitude of abstracts have described the effects of individual techniques in this disease. More recent studies have attempted to identify differences between and among those techniques. It can be said without disagreement that the vast majority of AC literature and research has focused upon patients with CF.

But what about evidence in CB? There is an exceptionally high incidence of COPD in the UK, the USA and throughout most of the world. In the UK alone, it is estimated that two percent of men aged 45–65 and seven percent of men over 75 have been diagnosed with COPD. This may represent as few as 25% of those who actually have the disorder throughout the UK. Not only is COPD common, medical care expenditures for patients with COPD are high and escalating quickly. Hospitalisations with this disease have increased by 50% between 1991 and 2000 and hospital costs due to COPD in 2001–2002 amounted to €869 million in the UK. More than five times the number of bed days are spent due to COPD compared with asthma. It is estimated that COPD causes at least 20.4 million lost working days among men and 3.5 million days among women every year in the UK – more than any other respiratory condition. (6)   
Many individuals diagnosed with COPD have a predominant pathophysiological pattern of CB that commonly results in significant mucus hypersecretion. This pattern is due to enlargement and hyperplasia of mucous secreting cells in the airway glands and epithelium. In addition to quantitative changes in mucus secretion, there is also qualitative difference in the secretions of individuals with CB. These changes arise from excess debris from inflamed cells, sloughed epithelial cells and the excessive mucus itself.(7) The excessive secretions lead to classic changes in pulmonary function tests including reduced FEV(1), reduced FEV(1)/FVC ratio, increased airways resistance and poor gas diffusion among others.(8) In addition, symptoms of cough, dyspnoea, decreased exercise tolerance and predilection to infection and hospitalisation are known to be associated with secretion retention. Despite these facts, there is a paucity of evidence to support the use of AC in these patients with CB though it is the primary expression of COPD.

Emergence of high-frequency chest wall oscillation
During the last 10–15 years, there has been a marked increase in clinical popularity in the US of an AC device that produces high-frequency chest wall oscillation (HFCWO). HFCWO therapy has been shown for those with CF to be effective, safe and very importantly cost-effective.(9-15) Moreover, HFCWO has increased AC treatment adherence (typically very low), acceptance and the quality of life for individuals and their families who use the device regularly.(16,17)   

HFCWO is very different from traditional chest physical therapy that includes manual percussion, or “clapping” therapy, as well as other technique-dependent approaches, such as positive expiratory pressure, active cycle of breathing and autogenic drainage, all of which are standard methods of AC practised around the world. HFCWO therapy utilises air pulses delivered through a flexible hose to an inflatable garment worn by the patient. As the garment is inflated, the pulses cyclically compress and release the chest wall. Each cycle begins with an air pulse to more fully inflate the garment causing chest wall compression. This rapid compression creates a burst of air through the patient’s airways that results in a brief cough-like response – a “staccato cough”. These rapidly recurring bursts of air provide a shear force that cleaves secretions from airways walls.(18)  

In addition to the shear forces, air pulses reduce secretion viscosity and move secretions in the cephalad direction (towards the head) to a point from which they may be removed by coughing, huff coughing, or via suctioning.(19-21) All lung lobes and segments are treated concurrently and the patient sits upright throughout treatment without assuming the 10–12 different positions required for traditional postural drainage with percussion and vibration (PDPV).(22)

A HFCWO treatment typically requires 10–30 minutes, depending on the physician’s prescription. The air pulses are delivered at a frequency of 5–20Hz, although frequencies around 13Hz appear to provide the best results for secretion clearance.(23) It is accurate to say that HFCWO has become the most widely accepted and adhered to method of AC in the CF population in the US. More recently, it is being employed by those with respiratory disorders due to neuromuscular disorders and those with CB. Reimbursement by government and insurance companies has become common place.

There is, nevertheless, limited evidence at present for HFCWO application in CB. Most studies of patients with COPD fail to categorise subjects “with secretions” versus “those without secretions”. Nonetheless, a poster presented at the American College of Chest Physicians meeting in 2001 studied 59 patients with COPD who were >40 years old, had an FEV(1) <70%, showed evidence of retained secretions and dyspnoea or decreased functional ability. The investigators studied baseline medical history, PFTs, six minute walk distance, dyspnoea, symptoms and SF-36 quality of life scores. Patients then received in-home training on HFCWO and were instructed to do two 15–30 minute treatments per day during a 90-day period after which testing was repeated. Each patient served as his/her own control. At retesting, all patients using HFCWO had a reduction in symptom scores compared to baseline. A subgroup of 38 of the 59 subjects chose to continue HFCWO after the formal study. By the time of final assessment, those who continued HFCWO had shown a 175 foot increase in six minute walk test, reduction in perceived breathlessness during exercise, improved quality of life in the physical domain and general health domain (SF-36), and reported higher treatment satisfaction and adherence when compared with those who reverted to their prior AC techniques. The authors concluded that patients with COPD may improve their symptoms, function and quality of life with regular AC provided by HFCWO.(24) Furthermore, there are few, if any, negative aspects to its use, and it usually finds great acceptance from those requiring its assistance.

The future for HFCWO
Given the research cited above regarding efficacy, acceptance and improvement in patient adherence for individuals in the US who have CF, there are many good reasons that support HFCWO for broader use throughout the world. One of the areas of further impact will likely be seen in patients with many types of neuromuscular disorders that impair AC. These include amyotrophic lateral sclerosis, various myopathies, infectious polyneuropathy and spinal cord injury among others.
 
A strong likelihood is that, with increased learning, hundreds of thousands of individuals with CB in Europe will ultimately experience the physiological, symptomatic, and functional benefits associated with HFCWO. Given its ease of use, rapid acceptance by patients and families, adherence, portability and cost-effectiveness, HFCWO therapy is likely to become a standard method of long-term AC care for the large portion of the COPD population. By evacuating excess secretions, patients should realise a reduction in the incidence of lung infections and slower rate of decreasing lung function.

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References  

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