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 over 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 spectrum center frequency of the diaphragm (CFdi) electrical activity. Six healthy subjects performed two 10-min periods targeting diaphragm electrical activation (EAdi) to 40% of maximum using (1) expulsive or Mueller maneuvers at 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 capacity (IC) generating a Pdi of 21.4 +/- 5.2 cm H2O. The Pdi did not decrease over time during either maneuver. During both periods RES increased (p < 0.001) and CFdi decreased (p < 0.001) over time with higher Pdi levels producing 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 obtained 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 level of diaphragm pressure generated.