Date Published: September 19, 2011
Publisher: BioMed Central
Author(s): Tamotsu Ishizuka, Shinichi Matsuzaki, Haruka Aoki, Masakiyo Yatomi, Yosuke Kamide, Takeshi Hisada, Takahiro Tsuburai, Kunio Dobashi, Kihachi Ohshima, Kazuo Akiyama, Masatomo Mori.
The fractional concentration of nitric oxide in exhaled air (FENO) is used as a biomarker of eosinophilic airway inflammation. FENO is increased in patients with asthma. The relationship between subjective asthma symptoms and airway inflammation is an important issue. We expected that the subjective asthma symptoms in women might be different from those in men. Therefore, we investigated the gender differences of asthma symptoms and FENO in a survey of asthma prevalence in university students.
The information about asthma symptoms was obtained from answers to the European Community Respiratory Health Survey (ECRHS) questionnaire, and FENO was measured by an offline method in 640 students who were informed of this study and consented to participate.
The prevalence of asthma symptoms on the basis of data obtained from 584 students (266 men and 318 women), ranging in age from 18 to 24 years, was analyzed. Wheeze, chest tightness, an attack of shortness of breath, or an attack of cough within the last year was observed in 13.2% of 584 students. When 38.0 ppb was used as the cut-off value of FENO to make the diagnosis of asthma, the sensitivity was 86.8% and the specificity was 74.0%. FENO was ≥ 38.0 ppb in 32.7% of students. FENO was higher in men than in women. The prevalence of asthma symptoms estimated by considering FENO was 7.2%; the prevalence was greater in men (9.4%) than women (5.3%). A FENO ≥ 38.0 ppb was common in students who reported wheeze, but not in students, especially women, who reported cough attacks.
The prevalence of asthma symptoms in university students age 18 to 24 years in Japan was estimated to be 7.2% on the basis of FENO levels as well as subjective symptoms. Gender differences were observed in both FENO levels and asthma symptoms reflecting the presence of eosinophilic airway inflammation.
Bronchial asthma is a chronic inflammatory disease characterized by reversible airway limitation and airway hyper-reactivity. Clinically, patients with asthma have repeated symptoms, such as wheeze, shortness of breath, or cough, especially at night or early morning. When we make a diagnosis of asthma, it is helpful to expect that the patients have eosinophilic airway inflammation although asthma is not always associated with eosinophilic inflammation. In recent years, the fractional concentration of nitric oxide in exhaled air (the fraction of exhaled nitric oxide, FENO) has been used as a biomarker of eosinophilic inflammation in the airway [1-3]. In fact, FENO is increased in asthmatic patients compared to healthy subjects . Measurements of FENO are useful for making the diagnosis of asthma, and its sensitivity and specificity as a marker for the diagnosis are relatively high [5-8]. There are two procedures for FENO measurements: online and offline. Exhaled gas is collected in a reservoir and subsequently analyzed for nitric oxide (NO) concentrations in offline measurements . Particularly in epidemiologic studies, offline measurement might be superior to online measurement because it is economical and makes it easy to measure a number of samples in a short time [10,11].
The gold standard of asthma diagnosis is obstructive lung disease with airway reversibility, or airway reactivity confirmed by challenge testing, not history or symptoms. Information obtained from the questionnaire which only asks asthmatic symptoms and history of asthma is not enough to make diagnosis of asthma, because clinical suspicion of asthma should be confirmed by objective measures of pulmonary function . Strictly, current asthma symptoms on the ECRHS questionnaire are not equal to clinically current symptoms because this questionnaire is designed to detect asthma symptoms over 1 year. Although we must also emphasize that the ROC curve was constructed only to classify subjects of this study and that it was not constructed to help diagnose asthma, a previous study using the same offline method proposed that the optimal cut-off value of FENO was 38.0 ppb for detecting allergic airway inflammation in an adult population . This cut-off value was equal to that we used in this study.
The prevalence of asthma symptoms in university students in Japan in a single year was 7.2%, estimated on the basis of FENO levels as well as subjective asthmatic symptoms. The prevalence, based on both of these factors, was higher in men than in women. Gender differences were observed in both FENO levels and asthma symptoms.
ECRHS: European Community Respiratory Health Survey; FENO: The fractional concentration of nitric oxide in exhaled air.
The authors declare that they have no competing interests.
Intellectual planning of the project was mainly done by TI. TH, KO, KD, TT, KA, and MM participated in the design of the study. Actual experimental works were performed by TI, SM, HA, MY, and YK. TH, TT, and KA were involved in the development of methods for FENO measurements. All authors read and approved the final manuscript.
All authors are Doctor of Medicine. TI, TH, KD, and KA are representatives of the Japanese Society of Allergology. TI, SM, TH, TT, KD, and KA are medical specialists approved by the Japanese Society of Allergology. TI is an associate professor of Gunma University Graduate School of Medicine and a clinical professor of Gunma University Hospital. SM, HA, MY and YK are research fellows in Gunma University Graduate School of Medicine. TH is an assistant professor of Gunma University Graduate School of Medicine. TT is on the faculty of Sagamihara National Hospital. KD is a professor of Gunma University Graduate School of Health Sciences. KO is a professor of Health and Medical Center, Gunma University. KA is the chief executive officer of the Japanese Society of Allergology and the director of Sagamihara National Hospital. MM is a professor of Gunma University Graduate School of Medicine.