Figure 1.

The ZVV approach. Airway opening flow (A) and pressure (B) time series of two consecutive cycles with different V_T’s from a patient. Notice that the two breaths are different due to the statistically defined pattern of breaths in VV. The flow is used to detect breath cycles as shown in the 2^nd cycle flow data (red solid circles). The corresponding Discrete Fourier Transforms (DFTs) are shown in the insets. Using the transforms, R and E are computed from the complex ratio of pressure and flow, Z, as the real part and −2πF_R times the imaginary part, respectively. The pressure fit tracing is also plotted (red line). (C) F_R and (D) E for every breath as a function of time. (E) E plotted as a function of F_R can be divided into five equally-spaced frequency intervals separated by red dashed lines and (F) binned into histograms showing the mean and standard error at every bin center. Similarly, R is binned as a function of F_R. (D) shows a decrease in E with time, while (F) shows that E is mainly constant unlike R which decreases with frequency.