Airway clearance techniques and exercise in people with bronchiectasis: two different coins

For people with bronchiectasis, achieving long-term adherence to physiotherapy strategies is a major challenge. The regular use of airway clearance techniques (ACTs) reduces the burden of sputum-related symptoms (e.g. increased expectoration during ACT session and reduced need to expectorate/cough throughout the rest of the day), improves quality of life and may reduce exacerbations, according to a recent European Respiratory Society statement [1]; however, there are barriers to long-term implementation (figure 1). There are traditional (e.g. positioning, manual percussions and vibrations) and contemporary strategies (e.g. breathing techniques and devices providing vibrations and/or positive or negative pressures) for airway clearance [1]. The selection of the most appropriate ACT for an individual patient is usually determined by respiratory physiotherapists, with selection based on clinical judgement and the patient's characteristics, symptoms, understanding and preferences [2].

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FIGURE 1

Benefits, enablers and barriers for exercise and airway clearance techniques (ACTs) in bronchiectasis. Common features are highlighted in blue.

Data from international surveys, audits and registries reveal considerable differences around the world with respect to the use of specific ACTs in bronchiectasis [1–4]. Possible reasons for clinical practice variation include the lack of clear guidance regarding the most effective or appropriate technique in bronchiectasis [5, 6], challenges in accessing specialist treatment or ACT devices, and geographical differences in ACT education and training [7].

The efficacy of ACTs relies on individuals to perform the technique optimally and consistently. Receiving a tailored choice of airway clearance therapy and education by a physiotherapist facilitates adherence [8], while the main barriers related to low compliance to ACTs are lack of time, the need to coordinate techniques with specific timing for pharmacological treatments, and lack of motivation or access to reliable education pertinent to ACTs (figure 1) [8]. A potential strategy to facilitate adherence to ACTs is to improve efficiency of allocated time to reduce treatment burden [9]. Regular exercise is also recommended in bronchiectasis to improve functional and exercise capacity, improve quality of life and reduce exacerbations [10], as well as enhancing social interactions and being a more enjoyable treatment compared to ACTs. For this reason, it is not surprising that patients and clinicians are wondering whether exercise (i.e. brisk walking, cycling) is sufficient to enhance sputum expectoration and may be a suitable substitute for ACTs.

Exercise has already been suggested as a potential substitute for ACTs in people with COPD [11]. In cystic fibrosis (CF), surveys have suggested that 45–50% of patients might skip ACTs if they have been doing exercise [12, 13]. In fact, one of the top 10 research priorities in CF is to establish the efficacy of exercise as an ACT [14]. Patients with CF who are using exercise as an ACT are reported to have lower rates of lung function decline, lower daily sputum expectoration and reduced perception of disease severity [12, 13]. Importantly, these improvements enable a greater tolerance to higher exercise intensities, compared to those using ACTs but no exercise [12]. Likewise, clinical audits show that a considerable percentage of people with bronchiectasis (range 38–89%) use exercise as their main ACT [1, 2, 15]. However, these surveys fail to clarify the type of exercise (cardiovascular or resistance training), modality (e.g. interval or endurance training), intensity, whether the exercises are supervised (which could also impact intensity), and whether patients perform exercise alone or in combination with directed coughing or forced expiratory manoeuvres or other ACTs to improve expectoration.

Increased ventilation and expiratory airflow, and the resulting impact on shearing forces, are key physiological mechanisms that underpin the use of exercise as an ACT [9, 16]. Although less studied, the increased blood flow with exercise may also enhance airway clearance [17]. In addition, specific modalities of exercise (e.g. jogging) are postulated to transmit oscillations generated in the trunk to the airways [18]. Considering these physiological effects, exercise can generate mechanical stresses to the airways that stimulate the hydration of the mucus layer and potentially result in enhancing sputum expectoration [16, 19]. However, it is still unknown whether a minimum of exercise intensity is needed to achieve these physiological effects or even whether a specific exercise modality is superior in enhancing shearing forces in the airway surface layer.

Most evidence about the use of exercise as an ACT comes from short-term crossover trials in patients with CF, with two recent systematic reviews comparing the benefits of exercise and ACTs in this population [18, 20]. The majority of included studies used endurance training via treadmills and cycle ergometers, with the aim to achieve at least moderate exercise intensities to ensure greater ventilation and airflow [18, 20]. As a comparative arm to exercise, four studies used a combination of postural drainage, manual techniques (percussion, vibration, shakes) and the active cycle of breathing technique, a further four studies used positive expiratory pressure (PEP) devices and two studies used oscillatory PEP devices (Flutter and Bottle PEP). The conclusions were that exercise enhances the expectoration of sputum compared to no intervention and it may have similar effects to ACTs if coughing or forced expiratory manoeuvres are incorporated [18, 20]. Evaluating physiological outcomes, such as sputum properties, ventilatory parameters and mucociliary clearance rates, on airway clearance during or after exercise, has led to a better understanding about the role of exercise on airway clearance through the mucociliary escalator (e.g. exercise improves biophysical sputum properties and enhances more mucus clearance compared to no intervention in the intermediate and peripheral lung regions) [21–23].

Given these findings, the key question is: Is this the right time to examine the role of exercise as an ACT in people with bronchiectasis? In the planning to address this question, careful consideration of potential comparative ACTs to exercise is necessary. While existing literature does not demonstrate superiority of one technique over another, the slow expiration with glottis opened in lateral posture (ELTGOL) technique may be the optimal comparative treatment to exercise, as it is the sole ACT that has so far demonstrated long-term benefits compared to no treatment in people with bronchiectasis [24]. Another option could be autogenic drainage. Both techniques can be applied independently and are based on the same physiological mechanism; a reduction of the cross-sectional ratio of the airways to increase the linear air velocity in peripheral and medium airways, while maintaining the airway patency by modulating expiratory efforts [1]. This mechanism enhances the gas–liquid interaction, which facilitates the generation of mechanical stresses on the airways and results in the application of shearing forces on the mucus layer, thereby promoting sputum expectoration [19]. In addition, autogenic drainage fulfils one of the fundamental principles for improving mucus clearance “in vitro” (i.e. creating adequate peak expiratory to inspiratory flow ratio) [25]. Despite the differences in mechanisms of action between exercise and ELTGOL or autogenic drainage [26], both these techniques have the option of being performed independently, with minimal cost and the flexibility to be undertaken in a variety of settings or environments. In research studies, the inclusion of periodic or directed coughs or forced expiratory manoeuvres are frequently encouraged during or after exercise to maximise sputum expectoration [22, 27]. However, the lack of evidence and consensus in prescription of exercise as a substitute ACT (e.g. exercise modality, intensity, frequency, duration and when and how often it is optimal to include coughing and other forced expiratory manoeuvres to enhance expectoration) could promote patient hesitation about its real-life implementation, particularly during an acute exacerbation.

To date, there is insufficient evidence to support the long-term replacement of ACTs with exercise in any respiratory disease. Figure 1 outlines the range of benefits of exercise and ACTs in bronchiectasis, as well as general enablers and barriers reported for both treatments. Until the emergence of stronger findings, we should be cautious in recommending exercise for airway clearance [9]. Instead, we need to prioritise research studies that will answer this important and emerging question from patients and clinicians. In addressing this question, future studies should consider to clearly define the exercise characteristics (e.g. type, modality, intensity, frequency and supervision) and the characteristics of people with bronchiectasis best suited to using exercise as an ACT. Bronchiectasis is a more heterogeneous disease than CF, and individuals may present with characteristics which make it difficult to achieve high intensity or high duration exercise (e.g. older age, more cardiovascular comorbidities, other concurrent respiratory diseases). In CF, patients are encouraged to participate in sporting activities so as to engage with daily exercise [28]; people with bronchiectasis may face more barriers in incorporating exercise in their life [29]. These barriers can include breathlessness, fear of exacerbating their symptoms and a sense of loss, frustration and disappointment secondary to a reduced ability to exercise and remain physically active [29]. Moreover, the response intensity of the mucus layer to exercise in bronchiectasis may not be similar to CF, as has been observed with other treatments [30].

Our target population in bronchiectasis is likely to be people with daily expectoration, as this symptom negatively impacts on quality of life and social function. As the main goal of ACTs is to improve sputum-related symptoms, the primary or secondary endpoints in research studies of exercise as an ACT should be clinically relevant outcomes (e.g. exacerbations, hospital admissions, use of health resources) and patient experience [1]. These outcomes are more likely to capture the clinical effects on airway clearance compared to outcomes that are relevant to exercise capacity.

While there are still many questions to answer, based on the current evidence and as ACTs are essential in managing bronchiectasis, ACTs should not be replaced by exercise. Instead, exercise should be an adjunct to recognised airway clearance therapy. The selection of an optimal ACT comparative treatment and exercise prescription in future studies are essential. Conducting pragmatic trials that prioritise self-administered interventions and minimise treatment burden would facilitate clinical implementation. Although physiological studies evaluating the role of exercise as an ACT in bronchiectasis are desirable, if we want to answer the patients' question about the substitution of ACTs with exercise, it is important to use longitudinal studies with strategies that ensure optimal performance and facilitate long-term adherence for both treatments (e.g. telehealth for monitoring and motivation). For now, exercise and ACTs are two different coins rather than two sides of the same one, and using both of them can make those with bronchiectasis richer!

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