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Complexity Analysis of Respiratory Dynamics.

Letter to Editor We read with interest the article by Thamrin and colleagues (1), which discussed systems biology approaches to study respiratory system, as a complex system, within the context of diagnosis and monitoring of diseases. A section of the article described previous studies that characterized the complex behavior of the lung in respiratory diseases using nonlinear analysis of the fluctuations of physiologic variables over time. Chronic lung diseases have variable clinical symptoms and represent complex behavior which may be associated with a shift in dynamics of respiratory system toward either too regular or too irregular (2). Analyzing such nonlinear fluctuations may not only improve traditional assessments in diagnosing the onset of illness, its severity and prognosis (1), but also could provide new insights into the different pathophysiological characteristics of respiratory diseases (2). In addition to studies described by Thamrin and colleagues (1), our recent report (2) showed that both respiratory rhythm and volume fluctuate continuously under a delicate equilibrium to maintain adaptability to external or internal stimuli. These fluctuations showed decreased long-range correlation, increased regularity and reduced sensitivity to initial conditions in patients with asthma, particularly in uncontrolled state. More importantly, receiver operating characteristic (ROC) curve analysis showed that respiratory variability analysis can be useful not only to aid in asthma diagnosis and in differentiating uncontrolled from controlled asthma but also for discriminating between nonatopic and atopic asthma (2). We found decreased long range correlation, irregularity and chaotic nature of respiratory dynamic in non-atopic asthma as compared with atopic asthma, possibly reflecting different pathophysiological mechanisms and maybe justifying a higher degree of disease severity in patients with