[RESPIRATORY IMPEDANCE MEASURING BY MostGraph-01 IS AFFECTED BY OBESITY].

Background: The forced oscillation technique (FOT) is a noninvasive method of measuring respiratory impedance, which includes respiratory system resistance (Rrs) and reactance (Xrs). The MostGraph-01 FOT device recently became clinically available in Japan, but standard impedance values for this device have not been determined in Japan.

Objective: To assess the correlation between spirometry parameters and respiratory impedance in obese (body mass index [BMI]>=25) and non-obese (BMI<25) subjects.

Methods: Clinical data were collected from 63 subjects without respiratory diseases who underwent spirometry and MostGraph-01 from January to October 2014. We investigated the correlation between spirometry parameters and respiratory impedance, and assessed the differing correlations among obese and non-obese subjects.

Results: The Rrs at 5 Hz (R5) was significantly correlated with vital capacity (VC), forced vital capacity (FVC), and forced expiratory volume in 1 second (FEV1). The Xrs at 5 Hz (X5), frequency of resonance (Fres), and low-frequency reactance area (ALX) were significantly correlated with the VC, FVC, and FEV1. Obese subjects showed a significantly lower X5 (median, -0.68 cmH2O/l/s vs. -0.35), higher Fres (median, 9.76 Hz vs. 7.46), and higher ALX (median, 2.65 cmH2O/l vs. 1.24) compared to non-obese subjects. Moreover, the VC, FVC, and FEV1 were more highly correlated with R5, X5, Fres, and ALX in nonobese subjects than in obese subjects. A p value of less than 0.05 was considered statistically significant.

Conclusion: For MostGraph-01, it is suggested that obesity may influence Xrs rather than Rrs.