Process trends episodes

Section II introduces the formal framework for the definition anc description of process trends at all levels of detail qualitative, order-of magnitude, and analytic. A detour through the basic concepts of scale-spact filtering is necessary in order to see the connection between the concept o process trends and the classical material on signal analysis. Within th( framework of scale-space filtering we can then elucidate the notions o episode, scale, local filtering, structure of scale, distinguishec features, and others. 

Once the stable reconstruction of a signal has been accomplished, its subsequent representation can be made at any level of detail, i.e. qualitative, semi-quantitative, or fully real-valued quantitative. The triangular episodes (described in Section I, A) can be constructed to offer an explicit, declarative description of process trends. 

Apnea of prematurity generally resolves as the neonate matures and approaches typical term age. Therefore, the PK/PD model must account for this trend with respect to time. Figure 27.2 showed the time course of apneic episode frequency. The number of daily episodes increased after birth with a peak between 1 and 2 weeks on average. A gradual decline was observed thereafter. A number of functional forms were considered to describe this profile, but two of the models evaluated are presented here. The first model, TCI (Eq. (27.15)), included a zero-order progression rate of episode frequency and a first-order resolution rate of episode frequency. In the second model, TC2 (Eq. (27.16)), the progression and resolution rates were both treated as first-order processes. Note that the use of resolution is meant to imply lessening of disease severity with maturity, not resolution of a specific apneic episode. 

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