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* From the Departments of Pulmonary Diseases (Dr. Kiljander) and Clinical Physiology (Dr. Laitinen), Tampere University Hospital, Tampere, Finland.
Correspondence to: Toni Kiljander, MD, PhD, Department of Pulmonary Diseases, Tampere University Hospital, PO Box 2000, FIN-33521 Tampere, Finland; e-mail: toni.kiljander{at}fimnet.fi
| Abstract |
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Study objective: To investigate the prevalence of GERD in adult patients with asthma.
Subjects and methods: The basic study population consisted of 2,225 asthmatic patients who were treated in six specialist-headed hospitals during 1 year. From the common computer-based discharge register, every 14th patient was randomly selected for the study. Ninety of the 149 contacted patients (60%) agreed to participate in the study. Twenty-fourhour esophageal pH monitoring was performed on all patients.
Results: GERD was found in 32 of the patients (36%). Eight of these patients (25%) were free from classical reflux symptoms. Forty-seven of the 90 patients (52%) presented with typical reflux symptoms. Twenty-four of these patients (51%) were found to have abnormal acidic reflux.
Conclusions: According to the current study, one third of adult patients with asthma have GERD. These patients often do not have typical reflux symptoms. However, the presence of typical reflux symptoms in an asthmatic patient does not seem to guarantee the presence of abnormal acidic reflux.
Key Words: asthma gastroesophageal reflux disease prevalence
| Introduction |
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| Materials and Methods |
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The definition for GERD is not unambiguous.17 For the current study, GERD was defined as abnormally high acid exposure time in the distal esophagus during 24-h esophageal pH monitoring. The study was approved by the Ethics Committee of the Tampere University Hospital, and every patient gave written informed consent.
Twenty-FourHour Esophageal pH Monitoring
After an overnight fast, the lower esophageal sphincter (LES) was located by manometry using a solid-state pressure transducer (Sentron 923001; Sentron Europe BV; Roden, Netherlands) connected to the LES identifier (Synectics Medical; Stockholm, Sweden). Esophageal pH recordings were made using dual monocrystant antimony pH catheters with 15 cm spacing the two pH electrodes (Synectics Medical), which were calibrated in buffer solutions of pH 1.0 and 7.0 before and at completion of each procedure. The pH catheter was passed transnasally into the esophagus, and the distal pH electrode was positioned 5 cm above the previously manometrically determined LES. An external reference electrode was attached to the skin of the chest wall. Esophageal pH was monitored 5 cm and 20 cm above the LES, and stored at 4-s intervals in a portable recorder (Digitrapper Mk II Gold; Synectics Medical) After the recording, the data were downloaded into a computer using appropriate analysis software (Esophogram 5.50; Gastrosoft; Irving, TX). Esophageal pH monitoring results were considered to be abnormal if total time pH < 4 in the distal esophagus was > 5.4%. During the pH monitoring, patients carried out their daily routines. All of the patients had been asked to stop possible histamine type-2 blocker or proton-pump inhibitor therapy for at least 1 week, and possible antacid therapy for at least 3 days before the pH monitoring.
Pulmonary Function Tests
Flow-volume spirometry (Medikro 101; Medikro; Kuopio, Finland) was performed on all patients, and at least two repeatable flow-volume curves were recorded. Finnish reference values were utilized.18 A methacholine bronchial challenge19 was then performed on all patients whose FEV1 was > 45% of predicted. During the challenge, methacholine chloride was nebulized in five cumulative doses of 18, 72, 270, 810, and 2,600 µg, and spirometry was repeated after each dose. The challenge was stopped when FEV1 fell
20% compared to baseline, or when 2,600 µg of methacholine had been administered. A patient was considered to have bronchial hyperresponsiveness if his/her FEV1 decreased
20% during the challenge. Prior to the pulmonary function tests, the patients were not allowed to use inhaled sympathomimetics for at least 8 h. Oral sympathomimetics and inhaled anticholinergics were withheld for at least 12 h, and theophylline was withheld for 48 h before pulmonary function tests.
Statistical Analysis
Descriptive analysis was used unless otherwise noted; p < 0.05 was interpreted as statistically significant.
| Results |
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2 test). Of the 90 patients participating in the study, 75 patients had FEV1 > 45% of predicted and were thus challenged with methacholine. Bronchial hyperresponsiveness was found in 52 of these patients (69%). Mean duration of the pH monitoring was 22.1 h (range, 19.5 to 23.5 h). Abnormal acidic reflux into the distal esophagus was documented in 32 of the patients (36%). Eight of these patients (25%) were free from typical GERD symptoms. As to demographic data, the patients with abnormal acidic reflux (n = 32) did not differ from those without (n = 58). Due to the small number of patients, the symptomatic (n = 24) and nonsymptomatic (n = 8) patients with GERD were not compared statistically. Detailed results of the pH monitoring are shown in Table 2 . Forty-seven of the patients (52%) presented with typical GERD symptoms. Twenty-four of these patients (51%) were found to have GERD in the pH monitoring.
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| Discussion |
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In a previous study14 by our group, 24-h esophageal pH monitoring was performed on 107 patients with asthma, and GERD was found in 53% of the patients investigated. However, since we were not able to investigate consecutive patients, it is possible that the result is biased. After excluding patients who were referred because of typical GERD symptoms, Sontag et al12 performed 24-h esophageal pH monitoring on 104 consecutive asthmatic patients. GERD was found in 82% of the patients. Unfortunately, they did not report how many patients refused and how many patients had to be excluded. Although selection bias was attempted to be avoided in that study,12 it is highly possible that the result may be upwardly biased. In addition to possible selection bias, the high GERD prevalence found in that study might also partly be due to the fact that Sontag et al12 defined abnormal reflux separately for upright and supine positions, not for total esophageal acid exposure time as the other studies111314 did. More recently, Avidan et al20 performed ambulatory esophageal pH monitoring on 128 consecutive asthmatic patients. Unfortunately, that study20 was focused only on the temporal association between reflux episodes and pulmonary symptoms, and no GERD prevalence was reported.
Nagel et al11 performed esophageal pH monitoring on 44 patients with asthma, of whom 15 patients (34%) were found to have GERD. Vincent et al13 investigated 105 consecutive asthmatic patients with ambulatory esophageal pH monitoring. In their study,13 the prevalence of GERD was found to be 32%. In accordance with these two studies,1113 the current study, using a random sample of asthmatics, found GERD in one third of the patients. It is of interest that a great number of the patients who were found to have GERD were free from typical reflux symptoms. This is substantiated by other studies.51314 For example, Harding et al5 performed 24-h esophageal pH monitoring on 26 patients with stable asthma without typical reflux symptoms. In that study,5 abnormal esophageal acidic reflux was found in 62% of the patients. In the present study, or in the study by Harding et al,5 no endoscopies were performed, and one could therefore speculate that perhaps the presence of esophagitis might be important for the presence of classical reflux symptoms. However, there appears to be only a poor correlation between esophagitis and classical reflux symptoms.21
The authors accept that there are some limitations in the current study. Firstly, GERD was defined as pH < 4 in the distal esophagus > 5.4% of the total registration time. Most of the studies mentioned above used the reference values described by Johnson and DeMeester,22 using a 4.2% cutoff point to determine abnormal esophageal acid exposure time. However, other reference values use a 5.8% cutoff point to determine abnormal esophageal acid exposure,23 and for example the study by Harding et al5 used these reference values. In general, there are several different reference values for 24-h esophageal pH monitoring, and these differ only slightly.222324 Thus, using our definition for GERD is not believed to be a major source of error in the present study. Secondly, 40% of the original study population refused to participate in the study. Thus, although using a random sample of asthmatic patients, the possibility of selection bias is present also in the current study. However, 60% of the patients participated, which can be interpreted as an excellent result when such a semi-invasive technique as 24-h esophageal pH monitoring is used. Moreover, those participating in the study and those refusing were not found to differ, except for the age. Thirdly, prior to the pulmonary function tests, and at the same time prior to the pH monitoring, a washout period in certain antiasthmatic drugs was held, and this prevented us to investigate the possible effects of these drugs on esophageal acid contact times. Finally, almost one third of the patients challenged with methacholine did not present with bronchial hyperresponsiveness. This might get one to question whether these patients actually had asthma. However, it must be kept in mind that 70% of the patients were receiving inhaled, and 6% were using oral corticosteroids, which are known to reduce bronchial responsiveness.25 Moreover, the medical records of the patients were reviewed in order to ensure that the diagnosis of asthma was made according to the ATS criteria.16
It has been suggested that airway obstruction may increase the negative pleural pressure, thereby increasing the pressure gradient across the diaphragm favoring gastroesophageal reflux, and that air trapping leads to flattening of the diaphragm and possibly weakens the antireflux barrier.26 Therefore, one could have expected to see a negative correlation between the severity of GERD and pulmonary function in the current study. We found no such correlation. On the contrary, there was a weak positive association between FEV1 and two pH variables in the proximal esophagus. However, because these associations were very weak, and no other correlations could be found, they are concluded to be due to coincidence. The lack of correlation between asthma severity and the severity of GERD in our study may be due to the fact that the pathophysiology of GERD is very complex, and several other factors than transdiaphragmatic pressure influence the esophageal reflux. Nevertheless, on the basis of the previous studies, it is apparent that increased airway obstruction increases gastroesophageal reflux in asthmatics.7
The role of nonacidic reflux in the pathogenesis of reflux-associated respiratory conditions is yet to be solved. Combined multichannel intraluminal impedance and pH measurement is a promising new technique that hopefully will clarify this issue in the future.27 However, possible nonacidic reflux might, at least partly, explain why in the current study only 51% of the patients who presented with classical reflux symptoms were found to have GERD in the esophageal pH monitoring. Other explanations might include possible alterations in normal eating and activity patterns during the pH monitoring, and possible day-to-day variation of reflux.
It is well documented that airway obstruction and some medicines commonly used for asthma treatment can induce esophageal reflux.78910 There is also evidence that in asthmatic patients with GERD, more severe reflux disease predicts favorable asthma outcome after acid suppressive therapy.2829 This tempts one to speculate that mild GERD often found in asthmatic patients could be caused by asthma medication or by asthma itself, whereas only more severe GERD is capable of aggravating asthma. The above hypothesis explains the high prevalence of GERD found in asthmatic patients, but could also explain the inconsistent results of the intervention studies.4263031 Namely, patients with relatively mild GERD (which could be caused by asthma rather than be a trigger for asthma) have also been included in most of the treatment studies.142832333435
To conclude, according to the current data, one third of adult asthmatic patients have GERD. These patients do not often have typical reflux symptoms such as heartburn or regurgitation. However, the presence of typical reflux symptoms in an asthmatic patient does not seem to guarantee the presence of pathologic acidic esophageal reflux.
| Footnotes |
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Received for publication September 30, 2003. Accepted for publication June 1, 2004.
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