Background: The forced oscillation technique (FOT) is a noninvasive method that is used to measure respiratory mechanics, including respiratory resistance and reactance at multiple frequencies. The advantage of FOT over spirometry is that FOT does not require forced expiratory maneuvers. Moreover, a new FOT machine called MostGraph (Chest Co. Ltd., Tokyo, Japan), has been developed in Japan, and can be used clinically to diagnose and monitor asthma. The purpose of this study is to show the standard of FOT measured with MostGraph in adult Japanese asthmatics.
Methods: From our outpatient clinic, we recruited 151 stable asthmatics who were being treated with inhaled corticosteroids at the time of the study. For each subject, we measured the fraction of exhaled nitric oxide (FeNO) by using a chemiluminescent nitric oxide analyzer (Sievers280, GE, Boulder, Co); we determined the levels of forced expiratory volume in 1s (%FEV1) and maximum mid-expiratory flow rate (%MMF) by using spirometory; and we measured resistance at 5 Hz(R5), resistance at 20 Hz(R20), R5-R20, reactance at 5 Hz(X5), frequency of resonance (Fres), and low-frequency reactance area (ALX), by using a MostGraph FOT machine.
Results: Each of the FOT parameters measured by using the MostGraph machine was significantly correlated with %FEV1 and %MMF (p<0.001), with Fres showing the strongest association. Three of the FOT parameters, X5, Fres, and ALX, were significantly associated with the subject's age (p=0.01, p<0.001, p<0.001, respectively), and all FOT parameters were significantly associated with the subject's body mass index (BMI) (p<0.001 to p=0.018). The results of multiple regression analyses between FOT parameters and FEV1, age, BMI, and FeNO, showed that Fres was significantly associated with FEV1(p<0.001) and BMI (p<0.001). From the results of the simple linear regression between Fres and FEV1, we estimated that Fres values of 17.5 Hz corresponded to %FEV1 values of 60%; Fres values of 11.3 Hz corresponded to %FEV1 values of 80%; and Fres values of 4.94 Hz corresponded to %FEV1 values of 100%.
Conclusion: FOT parameters measured by using a MostGraph machine can be used successfully to assess the level of airflow limitation in adult stable asthmatics.