Effects of Changes in Breathing Pattern on the Sensation of Dyspnea during Inspiratory Loaded Breathing

The ventilatory responses to external resistive and elastic loadings of the respiratory system have been extensively studied in a variety of experimental animals as well as also humans. It has been known that there are marked differences in the pattern of breathing during sustained inspiratory loadings between awake and anesthetized subjects (Margaria et al., 1973; Cherniack and Altose,1981; Milic-Emili and Zin,1986). In awake subjects sustained external elastic loading generally leads to increased breathing frequency and decreased tidal volume, whereas inspiratory resistive loading causes decreased frequency and increased tidal volume. By contrast in anesthetized subjects the changes in respiratory frequency are small or absent and independent of the type of external loading (Milic-Emili and Zin, 1986). Because the different responses between the awake and anesthetized subjects cannot be explained as a simple reflex (Cherniack and Altose,1981; Milic-Emili and Zin, 1986), it is assumed that conscious awareness of breathing or behavioral response may be responsible for the different breathing pattern observed during inspiratory resistive and elastic loadings. However, the nature of the behavioral control has not yet been evaluated. Thus, the aim of the present study was to examine the hypothesis that the breathing pattern during inspiratory loading might be optimized through cortical response so that the sensation of dyspnea would be minimized.