[Dyspnea sensation during resistive loading].

To examine the relationship among the sensation of dyspnea, the respiratory muscle oxygen consumption (VO2 resp), minute ventilation and occlusion pressure, seven normal volunteers were studied during incremental dead space loading induced hyperventilation with and without inspiratory resistive load. Although the sensation of dyspnea and VO2 resp at the same level of minute ventilation increased with an increase in resistance, there appeared to be a unique relationship among the sensation of dyspnea, VO2 resp and occlusion pressure, which was not affected by inspiratory resistive loading from 0 to 20 cmH2O/l/sec. These results show that the ventilatory command signal is closely related to the dyspnea sensation. We also found that during incremental dead space loading the quality of the sensation changed relatively quickly at some point, where tidal volume was maximum with each resistive loading and the breathing pattern changed. In the other experiment, the functional residual capacity (FRC) decreased during inspiratory resistive and elastic loading. Because the decreased FRC was associated with the decrease in the dyspnea sensation, it was speculated that the subject decreased his FRC through a cortical response so that the sensation of dyspnea during loading decreased.