Description of the condition
Asthma is a common chronic inflammatory disorder characterized by hypersensitivity of the airways and reversible, episodic airway obstruction (Miller 2001). Typical symptoms of asthma include wheezing, coughing, chest tightness and dyspnoea (i.e. shortness of breath). Many patients with asthma also have so-called 'somatopsychic imbalance' in such forms as suppressed emotion, anxiety and heightened self-consciousness together with muscle tension, both generalized and localized (Goyeche 1982). The asthma attacks and the panic or anxiety associated with the attacks can affect the lifestyle (e.g. social activities), wellbeing, and perceived health status of patients with asthma to varying degrees, making improving quality of life an important issue in asthma management. Over the past decade, the prevalence of asthma has dramatically increased. Globally, asthma affects about 300 million people, and this figure continues to rise (Masoli 2004; ISAAC 2006). Asthma represents a huge economic burden on society. In the United States of America (USA), the management of asthma costs more than US dollars (USD) 12.7 billion per year (Weiss 2001). In Germany, Switzerland and Singapore, national studies have estimated the annual total costs for asthma to be USD4.43 billion, USD1.41 billion and USD49 million respectively (Chew 1999; Stock 2005; Szucs 1999).
Current guidelines for asthma treatment recommend a severity-based, stepwise approach (Global Initiative for Asthma 2011). Common agents to treat people with asthma include inhaled corticosteroids and long-acting beta agonists (Becker 2003). For severe cases, additional controller medications such as anti-leukotrienes, oral corticosteroids and anti-IgE therapy are recommended (Global Initiative for Asthma 2011; Peters 2006). However, somatopsychic imbalance has been seldom addressed by traditional drug treatments, pointing to the need for a holistic, somatopsychic therapy for people with asthma (Goyeche 1982).
Description of the intervention
Yoga originated from ancient India and remains an important element of India's diverse culture. Common components of yoga include breathing exercises (pranayama), postures (asanas) and meditation (dhyana) (Riley 2004). As different combinations of and variations in components could represent a 'new' type of yoga, it is hard to tell exactly how many types of yoga are being practiced around the world. To our knowledge, types of yoga include but are not limited to the following: aerial yoga, Ananda yoga, Anusara yoga, Ashtanga (or Astanga) yoga, Bhakti yoga, Bikram yoga (hot yoga), Chair yoga, Forrest yoga, Hatha yoga, ISHTA (Integral Science of Hatha and Tantric Arts), Iyengar yoga, Jivamukti yoga, Jnana yoga, Kali Ray TriYoga, Karma yoga, Kripalu, Kriya yoga, Kundalini yoga, Mantra yoga, Moksha, Power yoga, prenatal yoga, Purna yoga (integral yoga), Raja yoga, Restorative yoga, Sahaja yoga, Satyananda yoga, Sivananda yoga, stand-up paddle yoga, Svaroopa yoga, Swara yoga, Tibetan yoga, Viniyoga yoga, Vinyasa yoga and White Lotus yoga (about.com; dailycupofyoga.com; iloveindia.com; matsmatsmats.com; mindbodygreen.com; spine-health.com; yogajournal.com; yogapoint.com). It appears that there has been no estimate of the proportion of each type of yoga taught by practitioners worldwide. According to the polls conducted by Yoga Journal, the most commonly-practiced yoga in the USA is Iyengar (43.6%), followed by Ashtanga (29.1%), Power yoga (15.9%), Bikram (7.3%), Kundalini (7.1%), Sivananda (6.4%), Viniyoga (5.7%) and other (Lamb 2006). The practice of yoga seeks to attain a perfect integration of body, mind and spirit (Anand 1991; Kappmeier 2006).
Yoga has been gaining in global popularity, partly due to its reputed physical and psychological benefits. Currently available data (which are not necessarily accurate) show that there were about 16 million yoga practitioners in the USA alone (Harris Interactive Service Bureau 2008), more than 3 million adult yoga practitioners in Germany in 2004, approximately 2 million (3% of the total population) in Great Britain in 2004, less than 1 million (around 8% of the total population) in Taiwan in 2005, 0.5 to 1 million (0.4% to 0.8% of the total population) in Japan in 2004, and 454,000 (2.8% of the total population) in Australia in 2007 (Lamb 2006; Penman 2008). The International Yoga Federation once estimated that there were about 300 million yoga practitioners worldwide (Lamb 2006).
Yoga practice often involves a financial cost, such as the expense of attending classes, and purchasing props, clothing, books, magazines, DVDs and yoga mats. It has been reported that practitioners spend nearly USD6 billion on yoga classes and products each year in the USA (Harris Interactive Service Bureau 2008). An Australian national survey showed that 98.65 dollars were spent on yoga practice per participant per month on average, amounting to a total of 537.4 million dollars per year for all participants in Australia (Penman 2008). According to the 'conservative estimate' by a 2002 article in Yoga Journal, a yoga practitioner spends USD1,500 on yoga practice yearly (Lamb 2006).
How the intervention might work
As a holistic therapy, yoga practice contains no asthma-specific posture or breathing exercises (Goyeche 1982). The exact mechanism by which yoga may affect asthma symptoms is not fully understood (Vernpati 2009). However, several explanations have been proposed.
The first has to do with the breathing pattern in yoga practice. One trigger of asthma attacks is frictional stress in airways, which could damage the airway wall, affect the dynamics of airway smooth muscle and result in the mast cell degranulation (Singh 1990; Solway 1997; Chowdhary 1999). Some studies have shown that the tidal volume and breathing rate decrease during yoga practice (Kesterson 1989; Sudsuang 1991), which may interfere with the process that triggers asthma attacks. Empirically, randomised controlled trials conducted in patients with asthma have demonstrated that specific breathing exercises or techniques could help reduce acute exacerbations and rescue bronchodilator use as compared with no intervention, and could significantly improve quality of life as compared with asthma education (Fluge 1994; Bowler 1998; Opat 2000; Thomas 2003). However data were insufficient to draw conclusions to this effect in a Cochrane review comparing breathing exercises with usual care or asthma education control (Holloway 2004). Therefore, yoga practice involving breathing techniques may have some impact on asthma symptoms. Breathing exercises in yoga practice could help release suppressed emotion, reduce anxiety and self-consciousness, and relax tense muscles (Goyeche 1982).
Secondly, certain yoga postures may help expand the chest and increase breath-holding time as well as vital capacity (Goyeche 1982). This, logically, could have some effect on the lung function of patients with asthma.
Thirdly, by practicing yoga people with asthma may achieve a sense of relaxation and a positive mood, thus reducing the autonomic arousal factors like mast cell activation (Goyeche 1982; Manocha 2002; Vernpati 2009). Meditation, a common component of yoga, may even help yoga practitioners reach a state of complete mental silence ('Sahaja' in Sanskrit), which advocates of yoga consider to be an innately therapeutic process beneficial to people with chronic diseases, including asthma. Meditation may also help the control and feedback of respiratory muscles which would be adversely affected by asthma attacks (Nayak 2004).
Why it is important to do this review
Previous literature indicates that yoga might be applied for obstructive pulmonary disease (Donesky-Curenco 2009), pulmonary tuberculosis (Visweswaraiah 2004), hypertension (Patel 1975; Sundar 1984; van Montfrans 1990), myocardial infarction (Bulavin 1993), chronic back pain (Groessl 2008; Tekur 2008), osteoarthritis (Bukowski 2007) and other medical disorders (Jain 1993; Ramaratnam 2000; Culos-Reed 2006; DiStasio 2008). However, as the National Center for Complementary and Alternative Medicine stated, "there is not enough evidence to support the use of any complementary health practices for the relief of asthma" (NCCAM 2012). A number of clinical trials have been carried out to evaluate the efficacy of yoga for asthma. Some of them suggested that yoga may enhance pulmonary function and reduce airway hyper-responsiveness, emotional stress, and asthma attacks (Nagarathna 1985; Sodhi 2009; Vernpati 2009), while others showed that yoga conferred rather limited or even no benefit (Manocha 2002; Sabina 2005). Such information may confuse asthma patients when they are deciding whether or not to spend time and money on practicing yoga. To better understand current evidence and investigate potential sources of heterogeneity between studies, we propose to conduct the present Cochrane review.