Effects of positive inspiratory and expiratory pressure on diaphragmatic mobility in asymptomatic individuals: Randomised, crossover clinical trial.

Nothing was measured about how much air the participants were moving (tidal volume, minute volume) while the pressures were applied, so the study cannot show that the extra diaphragm movement came from better ventilation rather than from the pressure itself. No lung function test was done to confirm that everyone's lungs were normal, and the participants were a healthy, young, mostly active group, so the findings say nothing about people with respiratory disease, weakness or an ICU stay. The ultrasound images of 14 people could not be used and those participants were dropped from the analysis, and the study ended up far larger than the 38 people it had calculated it needed because healthy young volunteers were easy to recruit, so it was not powered for the comparisons between pressure levels. Each pressure was applied for only five minutes in a single session, so nothing is known about what happens over hours or days of ventilation, which is the situation where diaphragm weakness and atrophy matter. Inspiratory muscle strength was not related to diaphragm movement in this group, which goes against what other studies have reported, and the authors cannot explain why.

The authors declare no conflict of interest relevant to the paper and state that they received no financial or material support of any kind for the work.

Do not read this as evidence that non-invasive ventilation protects or strengthens the diaphragm in patients. The participants were healthy young adults with no lung disease, each pressure setting was applied for only five minutes, and lung volumes were not measured, so what was seen is a short-term change on an ultrasound scan. The authors themselves state that these physiological findings should be extrapolated to patient groups with caution.