Airway Clearance in COPD: Need for a Breath of Fresh Air? A Systematic Review

Abstract

Background: Airway clearance is a key component of respiratory physiotherapy management for patients with excess secretions, including patients with chronic obstructive pulmonary disease (COPD). The aim of this review is to give an overview of the available evidence for the use of different airway clearance techniques (ACT) and their effects in patients with COPD. Methods: A systematic literature search was performed on CEBAM, PUBMED, Cochrane CT, Science Direct and Biomed central data bases. After screening, a total of 26 articles were included. Results: Studies that provide solid evidence of the effectiveness of different airway clearance techniques in patients with COPD are rather scarce. The available evidence indicates that active breathing techniques, such as active cycle of breathing techniques, autogenic drainage and forced expiration, can be effective in the treatment of COPD. The evidence for passive techniques such as postural drainage and percussion is low. Supporting techniques such as intrapulmonary percussive ventilation, positive expiratory pressure and non-invasive ventilation have little evidence because of the small number of studies. Little evidence is found for the combined use of active techniques and supporting techniques such as (oscillating) positive expiratory pressure, postural drainage and vibration in COPD patients. There is clearly a need for well-powered controlled clinical trials on the long-term effects of (combined) airway clearance techniques in COPD.

Keywords::

• Airway clearance
• Physiotherapy
• Physical therapy
• COPD

INTRODUCTION

Chronic obstructive pulmonary disease (COPD) is a preventable and treatable disease characterized by airflow limitation that is not fully reversible. The airflow limitation is usually progressive and is due to an abnormal inflammatory response of the lungs to noxious particles or gases, primarily caused by cigarette smoking. Although COPD affects the lungs, it also produces significant systemic consequences (1). COPD is currently the fourth-leading cause of death in the world, and both the worldwide prevalence and mortality associated with COPD are anticipated to increase in the coming decades (2–4). Reduction of total personal exposure to tobacco smoke and occupational and other indoor or outdoor dusts are important goals to prevent the onset and progression of COPD (5).

As exacerbations and hospitalizations represent an important drive of the cost and morbidity of COPD, high priority should be given to interventions aimed at delaying the progression of disease, preventing exacerbations and reducing the risk of co-morbidities to alleviate the clinical and economic burden of disease (6). Many authors summarized guidelines for the strategies for the diagnosis and treatment strategies of COPD patients (1, 7–11). These guidelines provide reasons for optimism. A considerable body of theoretical and practical knowledge has already been developed especially for pulmonary rehabilitation. There is still need for refining its process, improving its efficiency, optimizing its benefits and expanding its scope (9).

Physiotherapy has been utilized for a long time in the treatment of patients with respiratory problems. Since the 1950s respiratory physiotherapy has evolved from passive techniques to active techniques that can be enhanced by the use of devices to assist ventilation. Chest physiotherapy is routinely employed as a prophylactic measure prior to major surgery and postoperatively to prevent respiratory complications such as atelectasis and pneumonia (12). In his review Bohmwick summarised airway clearance performed by a physiotherapist as follows: techniques are best preceded by aerosol followed by the airway clearance techniques, divided in active and passive techniques.

These include Exercise, “Conventional Chest Physiotherapy”, Active Cycle of Breathing Techniques (ACBT), Autogenic Drainage (AD), Resistive Inspiratory Manoeuvres, Flutter, Positive Expiratory Pressure (PEP), High Frequency Chest Wall Oscillations (HFCWO), Non-Invasive Ventilation (NIV) and Pharmacological interventions (prescribed by medical doctors) (13). The role of respiratory physiotherapy in the management of COPD focuses on the care of these patients in both the primary and acute care settings. Although physiotherapy treatment enhances sputum evacuation (8), its long-term clinical benefit remains to be seen. In the absence of studies informing us of the long-term effects of bronchopulmonary hygiene techniques on morbidity and mortality, physiotherapists would do well to continue treatment of sputum hypersecretion using the evidence-based approaches (14).

Airway secretions are cleared by mucociliary clearance (MCC), in addition to other mechanisms such as cough, peristalsis, two-phase gas-liquid flow and alveolar clearance (13). Physical therapy and breathing training are designed to increase tidal volume, decrease respiratory rate, sense of dyspnoea and removal of secretions. Airway clearance techniques are techniques applied primarily with the aim of clearing secretions from the airways as described by Hill et al. (15).

The respiratory exercises include controlled breathing, diaphragmatic and pursed-lip breathing. Postural drainage has, in most parts of the world, been replaced by airway clearance regimens that include forced expiratory manoeuvres or technique of breathing at different airflow and lung volume (15). Percussions and external vibrations are seldom justified in adults (16). The evidence about instrumental chest physiotherapy with positive expiratory pressure support, seems to be indecisive except for intrapulmonary percussive ventilation (IPV) and non-invasive ventilation (NIV) in acute stages (16).

Which outcome parameters are the most sensitive to measure the effects of the used techniques? Van der Schans et al. concluded that lung function tests (LF) are not valid for evaluating the acute effects of airway clearance techniques. In the clinical practice, evaluation should be done by means of subjective experience of the patient and course of the disease (17). Assessment of patient-centered outcomes, such as symptoms, performance in daily activities, exercise capacity, and Health-related Quality of life (HRQoL), should be an integral component of the treatment (9). Recently developed techniques may give new insights in the assessment of the airway clearance techniques. One of the new promising techniques is computational fluid dynamics applied on the 3D images retrained by CT-scan. This technique allows for an evaluation of flow and resistance in each part of the lung up to the 8th bifurcation (18, 19).

OBJECTIVES

The aim of this review is to give an overview of the available evidence for the use of airway clearance techniques (ACT) and their effects in COPD patients

METHODS

We conducted a systematic literature search using CEBAM, PUBMED, Cochrane CT, Science Direct and Biomed central data bases. Selection criteria were set on clinical trials, physiotherapeutic techniques, COPD and drainage of the airways. Pharmaceutical studies were excluded. However, combinations of physiotherapeutic techniques and medication were allowed. The following keywords were used in the search: draining techniques, physical therapy (or Physiotherapy), Positive end expiratory Pressure, Clapping, vibration, Forced expiration techniques, Intrapulmonary percussive ventilation, cough, active cycle of breathing, airway clearance, inspiratory muscle training, flutter cornett, oral high frequency oscillation and COPD. Limits were set from 1980 until October 2008 in English, German and French articles. After the first selection we obtained 66 articles. A second screening reduced the number of relevant articles to 26. The flow chart of the literature search is shown in Figure 1.

Figure 1.  Flow chart of the systematic literature search. Flow of studies through the review. * Papers may have been excluded for failing to meet more than one inclusion criteria.

The selected articles were scored with the Pedro score by 2 (20) independent researchers. Conflicts were discussed and a consensus was made. The scores are shown in Figure 2. Fifteen of the 26 clinical trials (CTs) are from 2002 or earlier; 11 are less than 8 years old.

Figure 2.  Summarized number of CT's found for each technique. PEP: positive expiratory pressure;IMT: inspiratory muscle training; NIV: non-invasive ventilation; PD: postural drainage; Fet: forced expiration technique; IPV: intra pulmonary percussive ventilation; AD: autogenic drainage; ACBT: active cycle of breathing techniques. The numbers represent the number of studies found for each technique.

RESULTS

Techniques

An overview of studies and techniques are shown in Table 1. We divided the techniques into10 categories. The numbers of clinical trials for each category are shown in Figure 3. These figures demonstrate big differences in the quantity of research performed on respiratory physiotherapeutic techniques in COPD.

Table 1.  Overview of studies: Author, year, type of technique used, number of patients, diagnose and outcome parameters

Passive techniques
	Year	Technique	n	Diagnosis	Outcome parameters
Postural drainage vibration and clapping
Singh [11]	2003	pulm rehabilitation (PLB; diaphrag, controlled cough, PD, drain position; limb excercises; ADL adjustments	40	stable COPD	spirometric, 6MWD, CRDQ
Bellone [21]	2000	PD and clapping, flutter and ELTGOL	10	Chron bronchitis	saturation; spirometry sputum weight
Olseni [22]	1994	FET and PD	14	COPD	Lungfunction; radio labelled particles
Moshenifar [23]	1985	clapping and PD	20	COPD	peakflow; lungfunction; saturation; ABG; sputumproduction
Active techniques
Coughing
Bellone [44]	2002	Pep mask and coughing vs coughing alone	30	COPD (hypersecretion and NIPPV)	sputum production; weaningtime; failing of the treatment; FEVI en VC; ABG
Van der Schans [26]	1990	Coughing, FET (on different lungvolumes)	8	emfisema/COPD/normal and decreased elastic recoil	spirometrics; radio active tracers
Forced expiration technique (FET)
Su Chien- Ling [25]	2007	PEP and FET	37	COPD	lungfunction; 6MWD; cough difficulty score; sputum production
Olseni [22]	1994	FET and PD	14	COPD	Lungfunction; radio labelled particles
Van der Schans [26]	1990	Coughing, FET (on different lungvolumes)	8	emfisema/COPD/normal and decreased elastic recoil	lung function radio active tracers
Active cycle of breathing techniques + Autogene drainge
Cesinsa [28]	1999	ACTB	19	COPD	VAS, Sputum collection, Lung function
Scavi [27]	2000	Autogenic drainage and ACBT	30	COPD	lungfunction, 6MWD, Saturation, ABG
Mechanical devices
PEP
Su Chien- Ling [25]	2007	PEP and FET	37	COPD	lungfunction, 6MWD; cough dificulty score; sputum production
Wolkove [29]	2004	flutter	17	COPD	6MWD, borg dyspnea, spirometric
Bellone [44]	2002	Pep mask and coughing vs coughing alone	30	COPD	sputum production; weaningtime; faling of the treatmetn; Lung function; ABG
Wolkove [32]	2002	Flutter and bronchodilatator	23	COPD	lungfucntion, 6MWD, HR
Haidl [30]	2002	cornett and particel deposition	14	COPD	radio isotopes
Cegla [31]	2002	Cornett	50	COPD	lungfunction, sticking to therapy
Bellone [21]	2000	PD and clapping, flutter and ELTGOL	10	Chron bronchitis	saturation, spirometric, sputum weight,
Intrapulmonal Percussive Ventilation
Vargas [35]	2006	IPV	25	COPD with expiratory flow limitation after extubation	mucus collect, gas exchange and RR
Nava [33]	2006	IPV	10	COPD minimal mucus hypersecretion	Saturation, flow, airway pressure, eusophag and gastric pressure, respiratory mechanics, dyn PEEPi, muscle strength
Vargas [34]	2005	IPV	33	COPD excacerbation on ICU	prevention of excacerbations, ABG, RR, Patient comfort, lung function
Non Invasive Ventilation
Vasiliki [37]	2008	non invasive ventilation	58	COPD	spirometeric MRC, dyspnea score, SF-36
Butcher [36]	2007	CPAP and HFCWO	11	COPD and CF and Healty	EELV Oscilating flow rate
Reuveny [39]	2005	excercise and BIPAP	19	COPD	lungfunction, ergo spirometry, expirated fraction O2 and CO2
Bellone [21]	2000	PD and tappotage, flutter and ELTGOL	10	Chron bronchitis	saturation, spirometric, is sputum weight,
Physical activity
Gimminez [43]	2000	aerobic program	7	COPD	Dyspnea, egrospirometric, ABG, Lactate,
Reuveny [39]	2005	inspanning en BIPAP	19	COPD	lungfunction, ergospirometrics, exp fraction O2 en CO2
Magadle R [41]	2007	IMT added to Pulmonary rehab	34	COPD	spirometrics 6MWD, Insp musc strenght, dyspnea,
Kamilla [42]	2008	Muscle reinforcement Lower/upper limbs bronchial Hygiene	22	COPD	atropometrics, spirometric, ergospirometric, dyspnea, distance

PEP, positive expiratory pressure; ACTB, active cycle of breathing; PD, postural drainage; FOT, forced expiration technique; ELTGOL, slow expiration with open glottis in lateral posture; IPV, intrapulmonary pressure ventilation; VC, vital capacity; RR, respiratory rate; CRDQ, Chronic Respiratory Disease Questionnaire; HR, heart rate; SF-36, Short Form (36) Health Survey; EELV, end-expiratory lung volume; Mip, maximal expiratory pressure; NIPPV, non-invasive positive pressure ventilation; VAS, visual analog scale; dyn PEEPi, dynamic intrinsic end-expiratory pressure; HFCWO, high frequency chestwall oscillations; IMT, inspiratory muscle training; Flutter and Cornett, oscillation PEP devices,

Figure 3.  Quality score of the articles using Pedro score; the X-axis represents the score, the Y-axis represents the number of studies for each score.

Activation and PEP are the most studied techniques in this review, whereas studies investigating active techniques are limited: only 2 clinical trials in COPD patients investigated active cycle of breathing technique (ACBT). Only one looked at autogenic drainage (AD) with COPD patients. Many studies included more than 1 technique in their study design. Most of the drainage techniques have limited evidence due to relatively small sample sizes, poorly reported power analyses, small patient populations and a lower methodological quality score for clinical trials. A low score is defined as a score of 5/10 or lower on the Pedro scale for clinical trial (Figure 2). Nevertheless techniques can be effective but there evidence is poorly reported. We included NIV as this technique may be a promising aid for airway clearance techniques.

Postural drainage (PD)

Singh et al. looked at PD as part of a rehabilitation programme for outpatients with COPD. Duration and intensity of the PD was difficult to assess and underreported (11). The programme consisted of pursed lip breathing (PLB), diaphragmatic breathing. The removal of secretions was done by using controlled coughing, postural bronchial drainage and drainage positions. They also included lower extremity exercises and energy conservation and work simplification of activities of daily living. They found improvement in all outcome parameters except FEV₁. This indicates that PD could be part of a respiratory rehabilitation programme. However, the number of techniques used makes it difficult to draw any conclusions about the effectiveness of the separate elements of the treatment.

Bellone et al. looked at the effects of PD and compared them with an oscillation positive expiratory pressure device (Flutter) and slow expiration with open glottis in lateral posture (ELTGOL).(21). They found that more sputum was expectorated with ELTGOL and Flutter than by using PD alone. The other techniques seemed to prolong the sputum clearance compared to the PD. They concluded that all three techniques were effective in removing sputum. The active techniques had a more homogeneous drainage of the bronchial tree. Olseni et al. compared PD with positive expiratory pressure (PEP) (22). At the end of each session patients performed forced expiration technique (FET) manoeuvres. The results measured with the clearance of inhaled radio particles showed a significant greater clearance with PD and FET than with positive expiratory pressure, PEP and FET. These authors proposed that the choice of the technique should be considered in relation to the patient's preference.

Moshenifar et al. compared mechanical vibration with the conventional chest physiotherapy. They found no differences in the outcome parameters between both groups (23). In summary: The effectiveness of PD as standalone technique lacks evidence. However PD can be useful in addition to active airway clearance technique. The effect of gravity on the mucus in the airways and especially the small airways is questionable. PD can't be applied to all patients and should be used with caution.

Vibration

Vibration can be applied manually or mechanically. Toshihide et al. investigated in-phase chest wall vibration during exercise (24). They noted a significant reduction of dyspnoea during exercise. The decrease in dyspnoea was more pronounced as the severity of COPD increased. This technique is different from the other vibration techniques as it is given during exercise and was an in-phase percussion, which means mechanical vibration was given to the chest wall during inspiration. Therefore, the findings of this research group are to be interpreted with caution as this technique is rather different from the other techniques described in this review.

Moshenifar concluded that routine use of mechanical chest vibration and chest physiotherapy is not indicated in the treatment of stable outpatients with COPD and moderate amounts of sputum production (23). In their study they failed to demonstrate a beneficial effect of mechanical chest vibration on spirometry, gas exchange, or sputum production, although subjectively all patients felt better afterwards (23).

In summary: There is very little to no evidence that supports the effects of manual or mechanical shaking on mucus clearance in COPD patients. Although the technique was applied frequently in the past, more effective methods are available. Vibration alone is proven insufficient. Therefore it should be used as an additional technique for the patients’ subjective feeling of comfort. The goal of vibration may be mainly relaxation of the patient.

Clapping

Moshenifar compared chest clapping (also referred to as chest percussion or tappotage), mechanical vibration and postural drainage (23). As previously stated, he found no changes in the outcome parameters for any of the treatments and concluded that routine use of mechanical chest vibration and chest physiotherapy is not indicated in the treatment of stable outpatients with COPD and moderate amounts of sputum production. In summary: No study could show an effect of manual vibration or chest clapping on commonly used outcome parameters. It is possible that the effect of clapping does not reach the small airways and therefore has little effect on mucus expectoration. It seems clear that clapping alone is insufficient to evacuate excess mucus. Therapists should consider active mucus evacuation techniques instead.

Forced Expiration Technique (FET)

During FET, huffing is combined with breathing exercises and coughing to encourage mucus clearance from the small airway to the larger airways where they can be coughed up. Studies using FET alone are limited. Most trials combine FET with PEP (25) or other techniques (22, 26). Four-week PEP therapy as an adjunct to FET further enhanced diffusion capacity and 6MWD, and reduced cough difficulty compared to FET only in COPD patients with mucus hypersecretion (25). They concluded that PEP-FET combination is a non-invasive, inexpensive and non-time-consuming domiciliary intervention.

Olseni used lung clearance index and sinctography for the evaluation of the FET technique. He compared PD with FET using PEP to end both sessions (22). Improvements were more significant in the PD+FET group but PD and PEP were both effective.

In the study of Van der Schans COPD patients with normal and decreased elastic recoil were observed (26). Three protocols were performed in random order: spontaneous mucus clearance, the effect of forced expirations with an open glottis at different lung volumes (ELTGOL), and the effect of coughing in patients with sputum production.

They evaluated the techniques by using radioactive tracers and a gamma camera for the effects on the movements of mucus. This study showed that physiotherapy that includes forced expirations and coughing can enhance mucus clearance in patients with lower elastic recoil when elastic recoil pressure is normal. But this is unlikely to be effective when elastic recoil pressure is decreased (26). In summary: The number of long-term studies using FET in COPD patients is very limited. It is usually combined with other techniques especially with the PEP technique. FET is an inexpensive mean of airway clearance but patients need a good elastic recoil to benefit from this technique. An appropriate education of the technique is a necessity to avoid airway collapse. FET is also seen as part of the active cycle of breathing technique.

Autogenic drainage (AD) and the active cycle of breathing techniques (ACBT)

Scavi compared the ACBT with the autogenic drainage as developed and introduced by Jean Chevalier. Both techniques where applied for 20 min a day, and patients 20 sessions were carried out. Autogenic drainage improved forced vital capacity, FEV₁ and peak expiratory flow (PEF) rate. The ACBT increased FVC, PEF, arterial oxygenation and exercise performance. PEF increased more in AD than in ACBT. In AD treatment, the increase in oxygen saturation was significantly higher than in ACBT treatment. Chronic hypercapnia improved more significantly in AD treatment than in ACBT. No differences were found in other lung function parameters.

The ACBT was performed in four positions: supine, prone, left, and right lateral decubitus positions, for 5 min each. Autogenic drainage was performed in an upright sitting position in a chair. Six-minute walking distance improved significantly after both treatments in our study. The results of this study revealed that both AD and the ACBT are effective techniques in the clearance of mucus, which is one of the causes of airway obstruction in patients with COPD. This was shown by improvement in pulmonary function tests, arterial blood gases, physical performance and the sensation of dyspnoea during exercise.

Although the AD technique was more difficult for patients to learn, once patients used the technique correctly it was found to be as effective. The ACBT application was a lot simpler than AD. However, no single technique can be the best for every patient. Each patient should be assessed to determine the most appropriate and effective technique (27). Cesina et al. found that ACBT in the horizontal position is a simple airway clearance regimen suitable for individuals who produce more than 20 g of sputum per day. Subjects were less breathless and preferred the ACBT in the horizontal position compared to the prone, left and right lateral position, thus providing a treatment alternative that may improve adherence in individuals who are required to carry out daily airway clearance treatments (28).

In summary: Techniques based on breathing control and achieving the highest flow in different lung volumes, have the advantage that they can be independently used by the patients, after they have been instructed. The results of AD and ACBT on mucus clearance are similar. There are very few studies on the effect of these techniques in a COPD population. Therefore results should be interpreted with caution. More studies are needed as these techniques look promising for airway clearance in COPD patients and are widely used among respiratory physical therapists.

Positive expiratory pressure (PEP)

PEP, when combined with Forced Expiration Technique (FET), seems to improve the lung's ability to transfer gases (diffusion capacity), when compared to the effect of FET alone (25). In this study a PEP device which can generate a pressure for 10 to 20 cmH₂O was used. Although no significant differences were found in forced vital capacity (FVC) or other lung function parameters, the 6MWD improved significantly in the PEP+FET group compared to FET alone. FET+PEP facilitated sputum expectoration significantly, making PEP a useful addition to FET (25).

Wolckove et al. investigated the efficiency of an oscillating PEP device (flutter) and its additional effect to inhalation medication (29). They found that the use of the device gave an enhanced response to the inhaled medication. The effect persisted after one week of use and was associated with a better score on the 6MWD and a lower dyspnoea score. It also significantly improved the forced expiratory volume in 1 second FEV₁ for the PEP group, immediately after the use of the device. Pursed lip breathing (PLB) is a form of PEP and can be used without restrictions. It is the cheapest way of PEP because of its simplicity and lack of devices.

Sigh et al. looked at PLB as part of a physical activity program and concluded that a physical activity programme that included PLB had a positive effect on the 6MWD an dyspnoea score (11). Haidle et al. investigated the additional effect of the oscillating positive pressure device (Cornett) on the inhaled particle deposition (30). The device was integrated in the jet-nebulizer aerosol circuit. The control group had a normal valve on the circuit. Sinctographic scans were taken. They found no significant effects between groups for the deposition. Celga et al studied the combinational use of the Cornett device with medicine treatment over a 2-year period (31).

They found significant improvements in airway resistance and percentage of predicted vital capacity (%VC). They also found that with the use of the PEP device, patients needed less antibiotics and hospitalization compared to the group who only received drug therapy. These results underline the potential value of adding oscillating PEP to a physical activity programme in COPD patients (32).

Bellone et al. compared the Flutter with 2 other airway clearance techniques: slow expiration with open glottis in lateral posture (ETGOL) and PD. They used FEV1 and oxygen saturation (SaO₂) as outcome parameters and found no significant changes in these parameters between the techniques. The sputum production in the first 30 min after treatment was assessed with a sputum-weight-collection technique. The Flutter, ELTGOL and PD were all effective and a significant increase in sputum production was noted. However, there were no significant differences between the groups. After 1 h the amount of sputum produced was significantly bigger in the Flutter and ETGOL group compared to the PD group. All 3 methods were effective in removing the secretions, but Flutter and ETGOL are more effective than PD (21). In summary: PEP breathing allows the airways to stay open longer during expiration which enables patients to ventilate better. This is beneficial for evacuating mucus from the airways and optimizing gas exchange.

Intrapulmonary Percussive Ventilation (IPV)

IPV is a method that consists of small bursts of high-flow respirator gas given upon a normal breathing pattern using a sliding Venturi principle. The system used in this technique is an open system which allows a normal breathing pattern and no mixture of in and exhaled air. The technique can be described as a high frequency vibration of the airways instead of vibrations of the chest (33).

Nava and colleagues assessed the physiological effects of IPV in stable COPD patients. They tested several frequencies and compared the IPV with PSV (pressure support ventilation). No differences were found during the various trials in lung compliance and resistance.

A homogenisation of the breathing pattern occurred after 10 min of IPV. In addition, a significant reduction of the energy expenditure of the diaphragm was found. It was concluded that the technique is safe and overall well tolerated, especially when using low frequencies (33). IPV can decrease respiratory rate, as described by Vargas et al. (34). In this study the use of IPV led to a significant increase in PaO₂ and a decrease of PaCO₂ which indicates that patients’ ventilation improved. In the experimental group there was no worsening of exacerbations. This led to a significant reduction in the hospitalisation of patients with an acute exacerbation.

The authors concluded that the technique was safe for COPD patients with a mild respiratory acidosis. (35). In summary: There are few studies that describe the use of IPV in COPD patients. The device seems to be safe to use in patients with acute exacerbations and patients admitted to an intensive care unit. The effects are mainly subjective and changes in lung function parameters are limited. Diffusion however seems to be influenced positively. Still more research is needed to look at the applications and long-term effects of IPV in COPD patients.

Non-Invasive Ventilation (NIV)

Non-invasive ventilation is starting to make an entrance in the techniques used for draining of secretions (36). NIV was given additionally to a standard rehabilitation programme in the study of Vasiliki (37). In this study no changes were found in spirometric parameters. Participants of the NIV group however scored better on Health related quality of life questionnaire (HRQoL). Improvement of dyspnoea, arterial blood gasses and daytime sleepiness were found to be the major determinants for the difference in HRQoL.

Butcher et al. found that the combination of continuous positive airway pressure (CPAP) and high-frequency chest-wall oscillations may have a positive effect on the treatment (36).

Pressure support may prolong the duration of exercise induced lactataemia and results in lower PCO₂ levels, which results in better exsufflation of PCO₂ (38). This is supported by the findings of Reuveny et al., who could demonstrate that training with ventilator support has beneficial effects on VO₂max and anaerobic threshold (39). In this randomized clinical trial patients were randomized in 2 groups: 1 group received BIPAP during treadmill training while the other group received unsupported treadmill training. Lung-function parameters did not change while exercise tolerance increased in the BIPAP group but not in the unsupported group (39). The effects of breathing support during exercise are described by Petrof et al. They found that CPAP reduces inspiratory muscle effort during exercise in COPD patients. The expected improvements in dyspnea did not show in all patients. This may be explained by difference in increase of expiratory muscle strength (40).

In summary: NIV is a relatively new technique to most physiotherapists; it seems to be useful for the treatment of acute exacerbations and may support airway clearance techniques or exercise programmes. An identification of which patients may benefit of this technique is needed. Most studies are relatively short-term, therefore well-empowered long-term studies are necessary.

Physical activity

Physical activity (PA) has an influence on the respiratory system (41). How PA can help in draining excess mucus in COPD patients is less known. Exercise programmes are commonly used in COPD patients. They are part of most physical activity programmes aimed to reduce dyspnoea and decrease ventilatory limitations (39, 41, 42). PA causes a change in breathing pattern. The ERV and IRV are used for breathing during PA.

Four clinical trials on activation in COPD patients were included. Kamilla et al. looked at training both upper as well as lower limbs and compared those with bronchial hygiene therapy over a 6-week period (42). The bronchial hygiene therapy is described as chest percussion and vibration whenever necessary. They found that lower limb training resulted in a lower ventilation/maximal voluntary ventilating ratio (Ve/MVV) or dyspnea index during resting and walking situations. The bronchial hygiene group did not change in any outcome parameter. Moreover, they decreased in maximal number of stairs taken compared to the upper limb training group (ULTG) who increased their capacity to take stairs. The ULTG remained the same in both groups. Both training programmes reduced the dyspnoea scores during the activities.

The effect of intensity of an exercise programme was studied by Gimenez et al. A maximally intense anaerobic exercise program can be created for most COPD patients that can significantly improve both skeletal and respiratory muscle strength and endurance as well as dyspnea and physiological parameters (43). In summary: Physical activity programmes are generally accepted and activation has a beneficial effect on exercise tolerance and ADL activities. Activation as an aid for mucus evacuation is far less studied. Combinations of airway clearance aids and exercise programs might have more beneficial effects than the techniques performed stand alone.

GENERAL DISCUSSION

Airway clearance techniques are considered to be an important part of the treatment of COPD patients, especially for patients with hypersecretion or acute exacerbations (13). Studies that provide solid evidence for the effectiveness of different airway clearance techniques in COPD patients are rather limited. As previously mentioned, in most studies sample sizes are rather small. There seems to be a lack of well-empowered, long-term studies in particular with a long-term follow-up.

Usually different techniques are compared and results are used to indicate which techniques are superimposed on other techniques (11, 21–23, 25, 27, 36, 44). Techniques may mobilize mucus, but the effects of the movement are not always picked up by conventional outcome parameters. Evidence on the effects of airway clearance techniques such as PEP, oscillating PEP, PD and vibration in COPD patients is poor. This is possibly due to a lack of appropriate trials rather than any evidence for lack of benefit. Clinical guidelines for the use of mechanical and supporting techniques seem to be lacking.

As these techniques are frequently used in physiotherapy treatments there is a need for evidence-based guidelines. Objective parameters do not always support these subjective findings. Although long-term effects are not well studied, physiotherapy remains an important part of the treatment program in COPD patients. There seems to be insufficient evidence to support exercise as sole method for airway clearance, but an adjunctive benefit may be achieved.

There are still many questions regarding ACTs for patients with COPD. A main concern remains how clinicians should chose the appropriate technique for their patients? What is the ideal method and time to perform ACTs? No studies have been published about the optimal duration of the methods or number of treatments a day or education of ACTs for patients with COPD.

CONCLUSION

This systematic review summarizes the available evidence for airway clearance in COPD patients. To the best of our knowledge the effects of combining physical activity with conventional airway clearance techniques on mucus clearance in COPD patients have not been studied. Based on the evidence presented here, we conclude that it is recommended to use active airway clearance techniques (ACBT and autogenic drainage) to remove secretions in COPD patients, although more high-quality evidence is needed. These techniques can be supplemented with the use of (oscillating) PEP devices. Relatively new techniques such as IPV and NIV look promising and should be available for acute hospital COPD care. Future studies should aim to specify which techniques are best applied in different COPD subgroups with special attention to age subgroups and treatment time.

Declaration of Interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.