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- Material and methods
Background: Randomized controlled trials are needed to evaluate the effects of complementary treatments in asthma. This study assessed the effect of salt chamber treatment as an add-on therapy to low to moderate inhaled steroid therapy in asthma patients with bronchial hyperresponsiveness (BHR).
Methods: After a 2-week baseline period, 32 asthma patients who exhibited BHR in the histamine inhalation challenge were randomized: 17 to 2-week active treatment, during which salt was fed to the room by a salt generator, and 15 to placebo. The salt chamber treatment lasted 40 min and was administered five times a week.
Results: Median provocative dose causing a decrease of 15% in Fev1 (PD15FEV4) increased significantly in the active group (P = 0.047) but not in the placebo group. The difference in changes between the active and placebo groups was significant (P = 0.02). Nine patients (56%) in the active group and two patients (17%) in the placebo group exhibited at least one doubling dose decrease in BHR (P = 0.040). Six patients (38%) in the active group and none in the placebo group became non-hyperresponsive (P = 0.017). Neither the peak expiratory flow (PEF) values measured just before and after the treatment, nor FEV1 values measured before the histamine challenges, changed. The reduction in BHR was not caused by changes in the baseline lung function.
Conclusions: Salt chamber treatment reduced bronchial hyperresponsiveness as an add-on therapy in asthmatics with a low to moderate dose of inhaled steroids. The possibility that salt chamber treatment could serve as a complementary therapy to conventional medication cannot be excluded.
Complementary and alternative medicine is widely used in the treatment of asthma. However, data on the efficacy of these treatments are usually lacking. Randomized controlled trials are needed for exploring their possible effects (1, 2). They can also lead to undertreatment, and it is important to verify if they have any value in the treatment of asthma.
Bronchial hyperresponsiveness (BHR) gives valuable information on the patient's symptoms and airway inflammation (3). It has been used to assess the effect of some complementary treatments; e.g. Sahaga yoga has been shown to be beneficial (4) but short-term acupuncture therapy not so (5).
Subterranean environment therapy is called speleotherapy. Halotherapy is a form of speleotherapy, which makes use of the microclimatic conditions in a salt cave. Natural karst caves have been used for treating asthmatic patients in Germany, Switzerland, Hungary, Bulgaria, the former Yugoslavia and the former Soviet Union. The main therapeutic factors of speleotherapy in caves and mines are thought to be air quality, underground climate and radiation. Different combinations of temperature, relative humidity, pressure, radiation and aerosols are also vital elements.
The effects of salt mine treatment on health in the village of Solotvino, in the Carpathian Mountains have been investigated by Russian scientists. Natural dry sodium chloride dust which formed as a result of convection diffusion from salty walls was proposed to be the main microclimatic treatment factor. A ‘halochamber’ was constructed to simulate the microclimate of salt mines (6).
The Cochrane Database of Systematic Reviews evaluated the efficacy of speleotherapy in the treatment of asthma (7). It included controlled clinical trials that compared the clinical effects of speleotherapy with either another type of intervention or no intervention at all. Three trials on a total of 124 asthmatic children met the inclusion criteria, but only one trial had reasonable methodological quality (8). In the study by Novotny et al. (8), slight improvement of the lung function was observed at the end of the 3-week treatment period in the speleotherapy group compared with the control group. In two other trials, it has been reported that speleotherapy had a beneficial short-term effect on lung function as well. It was not possible to assess any other outcome. The conclusion was that the available evidence is insufficient to show speleotherapeutic interventions as an effective treatment measure for chronic asthma. Randomized controlled trials with long-term follow up are necessary (7).
We assessed the effect of the salt chamber treatment as an add-on therapy in patients with persistent asthma who exhibited BHR in the histamine challenge in spite of a low to moderate inhaled steroid dose.
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- Material and methods
This study is the first controlled trial investigating the effect of salt chamber treatment on BHR. A 2-week salt chamber treatment reduced BHR as an add-on therapy on a low to moderate dose of inhaled steroids.
The number of patients was small, which increases the risk of error due to chance, and hence our results should be taken as preliminary only. BHR did not differ statistically between active and placebo groups in the baseline. There is, however, a more reactive group in the active treatment group and therefore any change could tend to favour the active group. Being in a trial environment may also have helped compliance and this would have again favoured the active treatment group. The 2-week baseline period may have been the factor leading to an apparent improvement, too. The duration of the effects on BHR and asthma control cannot be reliably estimated as the sample size became too small during the 2-month follow-up. As respiratory viral infections may increase BHR (11), these patients were excluded from the follow-up.
The mechanisms of the effect of salt chamber treatment are unclear and can only be speculated. BHR is a surrogate marker of bronchial inflammation. Sont et al. have stressed the value of a methacholine challenge in guiding treatment; reducing BHR leads to better control of asthma (12). Airway responsiveness to direct bronchoconstrictor stimulus as histamine or methacholine is, however, only loosely related to inflammation (13, 14). Further studies are needed to assess the effect of salt chamber treatment on more direct inflammatory parameters (e.g. exhaled NO or inflammatory markers in induced sputum).
Airway calibre depends on the balance between the force generated by airway smooth muscle (ASM) and a number of opposing factors, mainly autonomic nervous mechanisms tending to limit ASM tone and mechanical forces opposing ASM shortening (15). Salt chamber treatment did not cause any bronchodilation. Neither the PEF values measured just before and after the treatment, nor the FEV1 values measured before the histamine challenges changed. Therefore, the reduction in BHR was not caused by changes in baseline lung function as could have been one possible explanation (16, 17).
Bronchial hyperresponsiveness can be reduced by directly affecting airway smooth muscle contractility (18). Some cytokines may act directly or indirectly on ASM cells and alter myocyte function by modulating contractile agonist-induced calcium signalling in human ASM cells (18). There is also a strong positive correlation between bronchial reactivity and the level of intracellular magnesium: magnesium intervenes in the calcium transport mechanism and intracellular phosphorylation reactions (19). Whether these mechanisms are involved in the salt chamber treatment is unknown.
Inhalation of hypertonic saline can cause bronchoconstriction (20). Dry powder sodium chloride has even been used to assess BHR in asthmatics (21). As the resting ventilation is 6–10 l/min, the NaCl dose inhaled by the patients during a 40-min treatment period was about 18–30 mg. This is less than the provocative dose of NaCl causing the FEV1 to fall 20% from the baseline in an inhalation challenge test using dry NaCl (mean 103 mg) in the study by Andersson et al. (22). It is also far less than the daily sodium intake of female (2.36 g) and male (3.15 g) asthmatics in the study by Sausenthaler et al. (22). In that study, the sodium intake did not alter BHR assessed as PD20 to methacholine but might have increased mild BHR assessed as PD10 (22). In our study, no bronchoconstriction because of the salt chamber treatment was observed. It is, however, possible that increasing salt concentrations eventually cause bronchoconstriction in sensitive individuals. Salt inhalation may have a U-shaped effect, small and moderate doses being beneficial but higher doses causing adverse effects.
It is possible that the symptomatic relief the patients reported from salt chamber treatment is associated with the reduction in BHR. All patients used inhaled steroids but still showed a reduction in BHR to an extent which is not easy to attain by any drug treatment. The idea that salt chamber treatment could serve as a complementary therapy to conventional medication cannot be ruled out. No side-effects were observed.
Salt chamber treatment is, however, neither simple nor cost-free. The conditions in the individual salt chambers should be measured and standardized as we did in our study. The possible dose–response effect of salt concentrations should be studied in further trials. The optimum duration or regularity of treatments needed are not known. In practice, the length of individual salt treatments vary widely from 20 min to hours and last five to 25 sessions. The length and regime of our study mirrors the common practice in Estonia and in the salt chamber of Lappeenranta Spa. Health economic aspects should be evaluated. There might be benefits linked to the better control of asthma and reduced use of asthma medication. Expenses linked to the salt chamber treatment, as well as travel costs to the treatment centres, should be evaluated. In future studies, the cost benefit should be compared with other treatment modalities, including the improvement of existing drug treatment.