Changes in respiratory effort sensation over time are linked to the frequency content of diaphragm electrical activity

This study evaluated whether respiratory effort sensation (RES) changes ove r time when breathing is performed with constant contraction pattern, fixed diaphragm activation, and maintained pressure generation. Another aim was to assess whether there was any association between RES and the power spect rum center frequency of the diaphragm (CFdi) electrical activity. Six healt hy subjects performed two 10-min periods targeting diaphragm electrical act ivation (EAdi) to 40% of maximum using (1) expulsive or Mueller maneuvers a t FRC generating a mean transdiaphragmatic (Pdi) pressure of 55.0 +/- 22.7 cm H2O (+/- SD) and (2) inspiration to 71.2 +/- 14.1% of inspiratory capaci ty (IC) generating a Pdi of 21.4 +/- 5.2 cm H2O. The Pdi did not decrease o ver time during either maneuver. During both periods RES increased (p < 0.0 01) and CFdi decreased (p < 0.001) over time with higher Pdi levels produci ng larger decreases in CFdi (p = 0.003) and greater increases in RES (p = 0 .008). Changes in CFdi and RES were related, and identical slopes were obta ined during the two maneuvers. In conclusion, while breathing with a fixed pattern, constant diaphragm activation, and maintained pressure generation, RES increases over time and is associated with CFdi independent of the lev el of diaphragm pressure generated.