Reversibility of the pulmonary function based on the partial flow-volume curve predicts the efficacy of bronchodilator therapy for treating chronic cough

Diagnostic Value of Fractional Exhaled Nitric Oxide and Small Airway Function in Differentiating Cough-Variant Asthma from Typical Asthma

Purpose

To explore the diagnostic value of fractional exhaled nitric oxide (FeNO), small airway function, and a combined of both in differentiating cough-variant asthma (CVA) from typical asthma (TA).

Methods

A total of 206 asthma subjects, including 104 CVA and 102 TA, were tested for pulmonary function, bronchial provocation test and FeNO. The correlation between FeNO, small airway function and other pulmonary indicators was analyzed by single correlation and multiple regression analysis. The receiver operating characteristic (ROC) curve was established to evaluate the diagnostic efficiency of FeNO, small airway function, and their combination and to predict the optimal cut-off point.

Results

All the respiratory function parameters and small airway function indicators in TA group were significantly different from those in CVA group, and FeNO value was significantly higher than that in CVA group. In addition, the area under the ROC curve (AUC) was estimated to be 0.660 for FeNO, 0.895 for MMEF_75%/25%, 0.873 for FEF_50%, 0.898 for FEF_25%, 0.695 for Fres, 0.650 for R5-R20, and 0.645 for X5. The optimal cut-off points of FeNO, MMEF_75%/25%, FEF_50%, FEF_25%, Fres, R5-R20 and X5, were 48.50 ppb, 60.02%, 63.46%, 45.26%, 16.63 Hz, 0.38 kPa·L⁻¹·s⁻¹, and −1.32, respectively. And the AUC of FeNO combined with small airway function indexes FEF_25%, Fres, R5-R20, and X5 were prior than single indicators.

Conclusion

FeNO and small airway function indexes might have great diagnostic value for differentiating CVA from TA. The combination of FeNO and FEF_25%, Fres, R5-R20, and X5 provided a significantly better prediction than either alone.

Validity of fractional exhaled nitric oxide and small airway function indices in diagnosis of cough-variant asthma

OBJECTIVE

Fractional exhaled nitric oxide (FeNO) is a non-invasive method used to reveal the eosinophilic inflammation of airway and to diagnose and manage asthma. The use of FeNO measurement or its combination with the small airway function in differentiating CVA patients from chronic cough patients is unexplored.

METHODS

From December 2012 to June 2016, patients with chronic non-productive cough for more than 8 weeks based on physician's opinion were subjected to FeNO, pulmonary function, and bronchial hyperresponsiveness (BHR) tests. Receiver operating characteristic (ROC) curves were obtained to evaluate the clinical value of FeNO and small airways indices in CVA diagnosis. The optimal cutoff point for the level of FeNO was also determined.

RESULTS

The FeNO value in the CVA group was significantly higher than that in the non-cough-variant asthma (NCVA) group [42(41) parts per billion (ppb) vs. (16(11) ppb), P < 0.05]. The area under the ROC curve was estimated to be 0.874 for FeNO. An optimal cutoff point of 25 ppb had respective sensitivity and specificity values of 81.3% and 84.0% in differentiating CVA patients from NCVA patients. The CVA group showed small airway dysfunction, and the small airway resistance was significantly higher than in the NCVA group. The area under the ROC curve of FeNO combined with maximal midexpiratory flow (MEF) (% predicted) was 0.883, and that combined with MEF50 (% predicted) was 0.886.

CONCLUSIONS

The measurement of FeNO is a non-invasive, reproducible, and sensitive method of differentiating CVA patients from NCVA patients. A combination of the level of FeNO (25 ppb) and the abnormal small airway function suggested higher CVA possibility, thereby resulting in a rapid diagnosis. Unnecessary treatments are avoided. This finding provides a new perspective for the management of patients with CVA.

Bronchodilator therapy for chronic cough

Experimental studies indicate that airway calibre increases the sensitivity of the afferents involved in the cough reflex but it has proved difficult to demonstrate that airway calibre increases the sensitivity of the afferents involved in the cough reflex. Therefore, bronchodilators might have a role, although rather minor, in the treatment of cough. However, although bronchodilators represent the standard of care in the treatment of airway obstruction associated with asthma or COPD, controversy persists regarding the mechanism(s) by which these agents alleviate cough. Furthermore, the available evidence indicates that the effects of bronchodilators on cough are rather inconsistent in humans and casts doubt on the appropriateness of the common practice of using bronchodilators in the treatment of patients with cough without any other evidence of airway obstruction. Regrettably, appropriate long-term trials specifically aimed at evaluating the clinical efficacy of bronchodilators in pathologic cough have not yet been performed. Therefore, properly executed clinical studies of bronchodilators in various types of acute and chronic pathologic cough are required.

Validity of Fractional Exhaled Nitric Oxide in Diagnosis of Corticosteroid-Responsive Cough

BACKGROUND

Whether fractional exhaled nitric oxide (FeNO) measurement alone or combined with sputum eosinophil and atopy is useful in predicting corticosteroid-responsive cough (CRC) and non-CRC (NCRC) is not clear.

METHODS

A total of 244 patients with chronic cough and 59 healthy subjects as control were enrolled. The causes of chronic cough were confirmed according to a well-established diagnostic algorithm. FeNO measurement and induced sputum for differential cell were performed in all subjects.

RESULTS

CRC occurred in 139 (57.0%) patients and NCRC occurred in 105. The FeNO level in CRC significantly correlated with sputum eosinophils (rs = 0.583, P < .01). The median (quarter) of FeNO level in CRC was significantly higher than NCRC (32.0 ppb [19.0-65.0 ppb] vs 15.0 ppb [11.0-22.0 ppb], P < .01). FeNO of 31.5 ppb had a sensitivity and specificity of 54.0% and 91.4%, respectively, in predicting CRC from chronic cough, with a positive predictive value of 89.3% and a negative predictive value of 60.0%. If the patients had a combination of low level of FeNO ( < 22.5 ppb), normal sputum eosinophil ( < 2.5%), and absence of atopy, the sensitivity and specificity would be 30.3% and 93.5% for predicting NCRC.

CONCLUSIONS

In our cohort, a high level (≥ 31.5 ppb) of FeNO indicates more likelihood of CRC, but the sensitivity is insufficient to rule out a diagnosis of CRC. A combination of low-level FeNO, normal sputum eosinophil, and absence of atopy suggests a lower likelihood of CRC.