Abstract
Background: Preoperative lung function tests are useful to evaluate the preoperative pulmonary condition and to detect a high risk of postoperative pulmonary complications. However, maximum expiratory effort by patients is necessary to determine lung function using spirometry, flow-volume curve and single breath N2 washout test. When patients are not able to expire completely during the measurement, incorrect data regarding their respiratory system is obtained. On the other hand, it is believed that respiratory system impedance using an impulse oscillatory system (IOS) can quickly evaluate total airway resistance (R5), large airway resistance (R20), small airway resistance (R5-R20) and capacitive reactance (X5) under breathing at rest. There are so few reports which indicate the standard values for IOS that the evaluation of IOS values is not clear. In this study we evaluate the relationship between parameters in ISO and non-ISO such as VC, FEV(1.0), PEFR, MMEF, V25, CV and FRC-CC.
Subjects and Methods: Six hundred twenty patients ranging from 20 to 89 years of age and scheduled for elective surgery were studied. IOS and non-IOS, such as spirometry [VC, FEV(1.0)], maximum expiratory flow-volume curve (PEFR, MMEF and V25) and single N2 washout curve (CV and FRC-CC) were preoperatively measured to investigate the relationship between parameters in IOS and non-IOS. We examined the relationship between IOS and non-IOS by calculating Pearson's product-moment correlation coefficient.
Results: Regression equations obtained between IOS and non-IOS parameters were statistically significant (p < 0.05). The highest correlation coefficient (R2) was 0.267 between X5 and FEV(1.0) (Table 2). The second highest R2 was 0.226 between X5 and VC. R2 was 0.189 between R5-R20 and MMEF, which is relatively high considering that those values indicate small airway conditions.
Conclusions: Although the relationship between IOS and non-IOS was statistically significant in this study, further study is necessary to obtain sufficiently high R2 to apply IOS clinically in place of non-IOS.
