LAUSR

which makes the interpretation of Figure 5 challenging in the context of increasing or decreasing diaphragm function. The response of a muscle to a summation of twitches can be influenced by many factors, including twitch duration (pulse width), amplitude, and time between stimuli. With similar pulse intensity (charge = amplitude3 pulse width), a generated force after a twitch stimulation is always lower than the force generated with a pulse train. This was also demonstrated for the diaphragm muscle, for example, in rabbits (2) and in vivo using magnetic stimulation (3). We noticed differences in pulse width between the single twitch and stimulations for the F/F response curve (0.015 vs. 0.0015 s, respectively). Therefore, single twitches may have resulted in higher force output. What was the reason for this difference, and why were twitch measurements not presented within the F/F response analysis? It would ease the interpretation of the measured diaphragm force if the authors could comment on this, potentially by presenting Pdi waveforms of a representative case per group. Last, animals were divided into groups based on the tertiles of measured levels of breathing effort and not by defining limits for effort a priori. It is suggested that a certain level of breathing effort can be protective for the diaphragm; however, it appears that some subjects in the RTmiddle-effort and RT low-effort groups have very similar levels of breathing effort (Figure 3 of the original work [1]). We therefore suggest that the emphasis on group-related outcomes should be attenuated. A sensitivity analysis on the impact of grouping animals on the basis of different breathing effort limits could be considered. Undoubtedly, unraveling the effects of RT on diaphragm function is crucial to understanding the impact of RT on clinical outcomes. Developing animal models may be of great help to study the impact of patient-ventilator interaction, especially RT, on the diaphragm. However, results should be interpreted with care in light of the physiology of diaphragm function and breathing effort.