Use of the forced-oscillation technique to estimate spirometry values

Purpose: Spirometry is sometimes difficult to perform in elderly patients and in those with severe respiratory distress. The forced-oscillation technique (FOT) is a simple and noninvasive method of measuring respiratory impedance. The aim of this study was to determine if FOT data reflect spirometric indices. Patients and methods: Patients underwent both FOT and spirometry procedures prior to inclusion in development (n=1,089) and validation (n=552) studies. Multivariate linear regression analysis was performed to identify FOT parameters predictive of vital capacity (VC), forced VC (FVC), and forced expiratory volume in 1 second (FEV₁). A regression equation was used to calculate estimated VC, FVC, and FEV₁. We then determined whether the estimated data reflected spirometric indices. Agreement between actual and estimated spirometry data was assessed by Bland-Altman analysis. Results: Significant correlations were observed between actual and estimated VC, FVC, and FEV₁ values (all r>0.8 and P<0.001). These results were deemed robust by a separate validation study (all r>0.8 and P<0.001). Bias between the actual data and estimated data for VC, FVC, and FEV₁ in the development study was 0.007 L (95% limits of agreement [LOA] 0.907 and-0.893 L),-0.064 L (95% LOA 0.843 and-0.971 L), and-0.039 L (95% LOA 0.735 and-0.814 L), respectively. On the other hand, bias between the actual data and estimated data for VC, FVC, and FEV₁ in the validation study was-0.201 L (95% LOA 0.62 and-1.022 L),-0.262 L (95% LOA 0.582 and-1.106 L), and-0.174 L (95% LOA 0.576 and-0.923 L), respectively, suggesting that the estimated data in the validation study did not have high accuracy. Conclusion: Further studies are needed to generate more accurate regression equations for spirometric indices based on FOT measurements.