Fig. 1

(a) Respiratory impedance at 5 Hz (Zrs5) in the sitting and supine position. Comparison was made using one-way ANOVA test. Significant differences in Zrs5 in the sitting position were found between the snorers and OSAS patients (p < .001), inter-group multiple comparisons were made using bonferroni method. Significant differences in Zrs5 in the supine position appeared between snorers and mild-OSA and OSAS patients. (snorers vs. mild-OSA, p = .004; snorers vs. OSAS, p < .001; mild-OSA vs. OSAS, p = .013). (b) Respiratory conductance calculated as the reciprocal of Zrs5, expressed as Gz. Comparison was made using one-way ANOVA test. Significant differences in Gz in the sitting position were found between the snorers and OSAS patients (p < .001), inter-group multiple comparisons were made using bonferroni method. Significant differences in Gz in the supine position appeared between snorers and mild-OSA, and OSAS patients. (snorers vs. mild-OSA, p < .001; snorers vs. OSAS, p < .001). (c) Respiratory resistance at different oscillatory frequencies measured by IOS in the sitting position. Comparison was made using one-way ANOVA test. Significant differences were found only between the snorers and OSAS patients (all p < .005), inter-group multiple comparisons were made using bonferroni method. (d) Respiratory reactance at various oscillatory frequencies in the sitting position. Comparison was made using one-way ANOVA test. Significant differences in X5 were found between the snorers and mild-OSA and OSAS patients (p < .003), inter-group multiple comparisons were made using bonferroni method. Significant differences in X10, X15, X20, X25were found only between the snorers and OSAS patients. (all p < .005) There was no significant difference for respiratory reactance at the 35 Hz frequency between three groups. (p = 0.419). (e) Respiratory resistance at different oscillatory frequencies measured by IOS in the supine position. Comparison was made using one-way ANOVA test. Significant differences in all frequency resistance were found between the snorers and mild-OSA, and OSAS patients, (p < .003) inter-group multiple comparisons were made using bonferroni method. There were no significant differences were found between mild-OSA and OSAS patients in the resistance from 10 Hz to 35 Hz. (f) Respiratory reactance at various oscillatory frequencies in the supine position. Comparison was made using one-way ANOVA test. Significant differences were found for all frequency reactance between the OSAS patients and mild-OSA, and the snorers (all p < .001), inter-group multiple comparisons were made using bonferroni method. There were no significant differences were found between the snorers and mild-OSA in the reactance at all frequencies