Variability of Breathing Pattern
When studying the performance of any control system, it is important to know not only the mean response of the system but also the constancy with which that response is maintained. Research into the control of breathing, however, has been largely confined to analysis of the mean response to an experimental intervention, and little or no attention has been paid to the “tightness” of the response. In the recent edition of the Handbook of Physiology, Cherniack et al.  state that “the normal variability of breathing has been studied by only a few investigators”; moreover, studies of the variability of breathing pattern in patients with disease states are almost nonexistent. Investigation of the variability or constancy of the respiratory control system over prolonged periods is now feasible since breathing can be recorded in a nonobtrusive manner using devices that record motion of the rib cage and abdomen which, in turn, can be calibrated to provide a measure of tidal volume [2, 3], and by employing breathing pattern analysis [4–6]. Respiratory drive can be assessed on a breath-by-breath basis by calculating mean inspiratory flow (V T/T I) [4, 7]. In addition, the timing function of the control system can be assessed by measuring respiratory frequency and fractional inspiratory time (I I/TTOT). This is important since repiratory center timing differs from respiratory drive in its response to certain stimuli [8, 9].
KeywordsTidal Volume Breathing Pattern Inspiratory Flow Respiratory Frequency Respiratory Drive
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