Hyperventilation in asthma: A validation study of the Nijmegen Questionnaire - NQ

Introduction: The Nijmegen questionnaire (NQ) has previously been used for screening the hyperventilation syndrome (HVS) in asthmatics. However, no validity study has been reported so far. Objective: To examine the validity and reliability of the NQ in asthma patients and identify the prevalence of HVS. Methods: The NQ (n = 162) was examined for translation, construct, cross-sectional and discriminant validity as well as for internal consistency and test-retest reliability. Results: Principal component analysis and exploratory factor analysis revealed a single factor solution with 11 items and 58.6% of explained variability. These 11 NQ items showed high internal consistency (Cronbach's alpha = 0.92) and test-retest reliability (IR = 0.98). Higher NQ scores were found in the following subgroups: women versus men (p<0.01); participants with moderate versus mild asthma (p<0.001) or uncontrolled versus controlled asthma (p<0.001), and participants with breath-hold time (BHT) <30 versus >= 30 s (p<0.01) or end-tidal CO2 (ETCO2) <= 35 versus >35mmHg (p<0.001). A cut-off score of >17 discriminated the participants with regard to the presence of HVS. The NQ showed 92.73% sensitivity and 91.59% specificity. The total NQ score was found significantly correlated with ETCO2 (r = -0.68), RR (r = 0.66) and BHT (r = -0.65). The prevalence of HVS was found 34%. Conclusion: The NQ is a valid and reliable questionnaire for screening HVS in patients with stable mild-to-moderate asthma.