Objective:To understand the function of diaphragm and analyze the clinical factors affecting the function of diaphragm by measuring twitch tracheal pressure (TwPtr) in patients with mechanical ventilation and in the weaning phase.Methods:Patients with more than 48 hours of invasive mechanical ventilation admitted to the department of critical care medicine of the First Affiliated Hospital of Guangzhou Medical University from December 2015 to March 2017 were enrolled. After the patient entered the weaning stage, TwPtr of patients was monitored by two-way non repetitive automatic respiratory trigger device, the effects of duration of mechanical ventilation, severe pulmonary infection, sedative application and chronic obstructive pulmonary disease (COPD) on weaning were analyzed.Results:A total of 62 patients were included, of which 45 were male and 17 were female. The average age was (66.8±11.7) years old. Twenty-three cases had severe pneumonia. The absolute value of TwPtr in severe pneumonia group was lower than that in non-severe pneumonia group [cmH 2O (1 cmH 2O = 0.098 kPa): 10.40±5.81 vs. 14.35±5.22, P = 0.021]. However, there was no significant difference in the duration of mechanical ventilation between the severe pneumonia group and non-severe pneumonia group [days: 26 (17, 43) vs. 15 (11, 36), P = 0.091]. In 62 patients with mechanical ventilation, there was a negative correlation between TwPtr and duration of mechanical ventilation ( r = 0.414, P = 0.002), there was also a negative correlation between the duration of mechanical ventilation and TwPtr after the assessment of diaphragm function ( r = 0.277, P = 0.039). There was a linear relationship between TwPtr and sedatives ( r = 0.220, P = 0.040), but there was no correlation between TwPtr and COPD ( r = -0.178, P = 0.166). Conclusions:For patients in the weaning stage of mechanical ventilation, severe pulmonary infection is one of the factors that affect the diaphragm dysfunction. There is a certain correlation between the diaphragm dysfunction and the use of sedatives.